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Transport,
6 Ion
Osmoregulation, and
Acid–Base Balance
W.S. Marshall and M. Grosell
CONTENTS
I. Introduction ........................................................................................................................179
A. Major Osmoregulatory Strategies..............................................................................179
1. Hyper-/Hypo-osmoregulation and Osmoconformity...........................................179
B. Major Osmoregulatory Organs..................................................................................180
1. Gills......................................................................................................................180
2. Kidney..................................................................................................................181
3. Gastrointestinal Tract...........................................................................................181
4. Rectal Gland (Elasmobranchs) ............................................................................182
5. Skin and Opercular Membrane ...........................................................................182
6. Urinary Bladder ...................................................................................................183
II. Marine Teleost Hypo-Osmoregulation...............................................................................183
A. Gill Microanatomy and Chloride Cells.....................................................................183
1. Cell Morphology..................................................................................................183
2. Sea-Water Transport Mode — Na+,K+-ATPase and Na+,K+,
2Cl– Co-transport .................................................................................................184
3. Anion Channels ...................................................................................................185
4. Potassium Recycling and Secretion ....................................................................185
5. Is Na+ Secretion Passive? ...................................................................................186
B. Gastrointestinal Tract.................................................................................................187
1. Drinking Reflex and Regulation..........................................................................187
2. The Role of the Esophagus .................................................................................188
3. Role of the Intestine ............................................................................................189
4. NaCl Absorption ..................................................................................................190
5. HCO3– Secretion and Anion Exchange................................................................191
6. Divalent Ions........................................................................................................191
7. Alkaline Precipitation ..........................................................................................191
C. Kidney........................................................................................................................192
1. Tubule Anatomy...................................................................................................192
2. Aglomerular and Glomerular Kidney Function ..................................................192
3. Renal Tubular Secretion ......................................................................................192
4. Renal Tubular Reabsorption ................................................................................194
5. Urinary Bladder ...................................................................................................195
6. Integrative Perspective.........................................................................................195
III. Freshwater Teleost Hyperosmoregulation .........................................................................196
177
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The Physiology of Fishes
A.
Gill .............................................................................................................................196
1. Gill Mitochondria-Rich (MR) Cells....................................................................196
2. Role of Pavement Cells .......................................................................................197
3. Ion Uptake Models ..............................................................................................197
4. Vacuolar-Type ATPase and Na+ Transport .........................................................197
5. Na Channel and Na Uptake.................................................................................199
6. NKCC and Na Uptake.........................................................................................201
7. Cl– Uptake: Exchanger or Co-transporter? .........................................................201
8. Ammonia Handling .............................................................................................202
9. Cultured Epithelia and Fresh-Water Opercular Membranes...............................202
B. Intestinal Salt (RE)Absorption ..................................................................................203
C. Kidney and Urinary Bladder .....................................................................................203
1. Tubule Anatomy...................................................................................................203
2. Glomerular Filtration ...........................................................................................204
3. Tubular Reabsorption...........................................................................................204
4. Role of the Urinary Bladder................................................................................204
IV. Marine Osmoconformation and Hypo-Ionoregulation ......................................................205
A. Elasmobranchs and Coelacanths ...............................................................................205
B. Gill Function..............................................................................................................205
1. Impermeability to Urea .......................................................................................205
2. Ion Transport........................................................................................................205
C. Rectal Gland ..............................................................................................................206
1. Ion Secretion........................................................................................................206
2. Regulation of Secretion .......................................................................................206
C. Kidney........................................................................................................................207
1. Tubule Anatomy...................................................................................................207
2. Glomerular Filtration ...........................................................................................207
3. Tubular Reabsorption...........................................................................................207
V. Freshwater and Euryhaline Elasmobranch
Hyperosmoregulation .........................................................................................................208
A. Ion Absorption at The Gill ........................................................................................209
B. Rectal Gland ..............................................................................................................209
C. Kidney........................................................................................................................209
VI. ACID–Base Balance ..........................................................................................................210
A. Where Fish are Different...........................................................................................210
B. General Model ...........................................................................................................211
C. Extreme Environments ..............................................................................................212
1. Alkaline Lakes .....................................................................................................212
2. Acid Lakes ...........................................................................................................212
3. Estivation Pouches and Burrows .........................................................................213
VII. Conclusion..........................................................................................................................213
A. Intertwining of Acid–Base and Ion Regulation ........................................................213
B. Euryhalinity, Complexities of Regulation .................................................................213
C. Metamorphosis for Migration, Complexities of Heterochrony ................................213
D. Freshwater Transport Diversity, Multiple Evolutionary Events ...............................213
E. Feeding and Osmoregulation.....................................................................................214
Acknowledgments ..........................................................................................................................214
References ......................................................................................................................................214
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Ion Transport, Osmoregulation, and Acid–Base Balance
I.
179
INTRODUCTION
A. MAJOR OSMOREGULATORY STRATEGIES
1. Hyper-/Hypo-osmoregulation and Osmoconformity
Fishes have evolved three fundamental strategies in handling the composition of the extracellular
fluid (plasma, lymph, and interstitial fluid): osmoconformity, where fish plasma osmolality matches
the marine environment; hyperosmoregulation, where fish plasma is regulated at a level higher than
the (dilute) environment; and hypo-osmoregulation, where fishes regulate body fluid composition
below that of sea water (Figure 6.1). A minority of species have a broad capacity to maintain body
fluid composition in both dilute and concentrated environments. These euryhaline animals vary in
their ability to adapt to salinity changes, with the hardiest generally being estuarine animals that
frequently experience large salinity changes. Still other species such as salmon (Atlantic and pacific
species),235 shad (Alosa sapidissima),388 gaspereau (Alosa pseudoharengus), eel (Anguilla spp.) and
lamprey (Petromyzon marinus) undergo metamorphic changes a few times in their lives for anadromous (upstream) and catadromous (downstream) reproductive migrations into and out of freshwater streams. Excellent reviews exist of smolting (metamorphosis prior to downstream migration)
in salmonids and the hormonal control of smolting by Hoar161 and McCormick235 and of recent
molecular advances in eel osmoregulation.59
a. Hyperosmoregulation.
For osmoregulation in dilute environments, where there is diffusive ion loss and osmotic water
gain across the large surface area of the gill epithelium, the animal produces large volumes of
extremely dilute urine in a kidney specialized for electrolyte absorption and gains ions by food and
by active ion uptake. For detailed and quantitative approaches to general fresh-water animal
2.0
Osmoidentity
Blood Osmolality (Osm/kg)
Osmoconformer (marine)
1.5
Stenohaline marine
Hyperosmoregulation
Stenohaline freshwater
Euryhaline teleost
(freshwater type)
(Oreochromis mossambicus)
1.0
Hypoosmoregulation
0.5
Euryhaline teleost (marine
type) (Fundulus heteroclitus)
Euryhaline elasmobranch
(Dasyatis sabina)
0.0
0.00 0.25
DW HFW
0.50
0.75
1.00 1.25 1.50
SW
Environment (Osm/kg)
1.75
2.00
FIGURE 6.1 Graphic overview of osmoregulatory capabilities of major fish groups. Abscissa: environmental
osmolarity (Osm/kg) — DW, distilled or soft fresh water, HFW, hard fresh water; Ordinate: blood osmolality
with isotonicity being 0.3 Osm/kg. Osmoconformers live strictly in sea water (hagfish), while marine elasmobranchs osmoconform in sea water but can actually survive by hyperregulating to varying extents in salinities
down to one third sea water. Most marine “stenohaline” teleosts can also survive in sea water and in dilute
salinities down to isotonic conditions. Stenohaline fresh-water forms typically can survive in DW, HFW, and
in salinities up to one third sea water. Euryhaline marine (e.g., the goby Gillicthys mirabilis, the mudskipper
Periopthalmus schlosseri and the killifish Fundulus heteroclitus) and euryhaline fresh-water teleosts (e.g.,the
tilapia, Oreochromis mossambicus) survive in sea water and lower salinities down to hard fresh water. In
addition, the freshwater type euryhaline teleosts can typically survive in soft fresh water (“DW”).
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The Physiology of Fishes
osmoregulation, see Kirschner.187,188,190 In fresh water, most teleosts have a small positive transgill
electrical potential that favors anion (Cl–) uptake, but because the concentration gradients are so
large, both Na+ and Cl– must be actively pumped into the blood across the gill epithelium.188,287
b. Hypo-osmoregulation.
In contrast, sea-water teleosts osmotically lose water across the gills and must drink to maintain
osmotic balance through absorption of the salts and water across the gastrointestinal tract. This
strategy loads the blood with NaCl that is secreted actively across the gill and skin epithelia, where
the osmotic permeability is very low. In sea water, the transgill electrical potential is large and
positive, favoring cation (Na+) secretion; thus, Cl– is the major actively transported ion, whereas
Na+ secretion is passive.188,287,289 In marine teleosts, the kidney exhibits very low glomerular filtration
or even lacks glomeruli and produces a minimal volume of isotonic urine that is rich in divalent
cation salts.
c. Osmoconformity.
True osmoconformers benefit from not having to spend metabolic resources on osmoregulation,
but even the hagfish (Eptatretus stouti) regulates plasma ions to some extent.245 Connected with
the osmoconforming strategy, hagfish stand out in that they have very high osmotic permeability
1.28 cm.s—1 × 10–4 compared with marine teleosts 0.074 to 0.29 cm.s—1 × 10—4.188 Marine elasmobranchs have plasma osmolality that is actually slightly hyperosmotic to sea water, typically 944
to 1,095 mOsm·kg–1 compared with sea water from various sources at 925 to 1,074163 such that
they can gain water without drinking any. Homer Smith328 found that urea is the principal osmolyte
retained, typically at 350 mM, which, in turn, allows these animals to osmoconform while hyporegulating Na+, Cl–, Ca2+, Mg2+, SO42– and other ions.
This chapter includes hormonal regulation only peripherally, focusing instead on osmoregulatory strategies by various fish groups. Readers interested in hormonal regulation of ion transport
and osmoregulation are directed to recent reviews by Evans et al.,82 who deal with cell level
signaling; McCormick,236who emphasizes hormonal regulation of euryhaline animals; WendelaarBonga,365 who examines stress; and Shepherd et al.,313 who focus on functions of prolactin and
growth hormone.
B. MAJOR OSMOREGULATORY ORGANS
1. Gills
Teleost, sarcopterygian, agnathan, and elasmobranch gills have 8 to 10 paired holobranchs or gill
arches. On each arch, there are numerous gill filaments that support thousands of platelike lamellae
that are primarily for gas exchange (Figure 6.2). The epithelium of the gill filament itself is instead
specialized for ion transport. The gills are the major site for not only gas exchange but also ion
transport, acid–base regulation, and nitrogenous waste excretion. These multiple functions of the
gills were reviewed in detail by Evans et al.87 There is a dual blood supply to the filaments such
that branches of the afferent arteriole serving the posterior side of each filament supply the lamellae
and the oxygenated blood is recollected in the efferent arteriole on the anterior side, the arterioarterial vasculature.197 Branches of the efferent arterioles (oxygenated blood) supply the filament
proper through anastomoses that drain into a central venous sinus in the core of the filament.197,361
Blood from the venous sinus then drains into filamental veins. This is the blood supplying the iontransporting cells that include flattened pavement cells and cuboidal to columnar mitochondria-rich
cells. This dual gill vasculature is shared among all fish groups, except the Dipnoi, in which the
nutrient circulation lacks the venous sinus.197 In their review of perfusion methods, Perry et al.,276
evaluated in vitro perfusion of single gill arches and the perfused head preparation, among others.
The latter system provided the main evidence supporting the functional separation between the
arterioarterial and the arteriovenous gill circulation, typified by the ion transport of the arteriovenous
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181
Ef.E
A
C
is this a
Greek mu?
ditto
au/PE:
please check
Ef.E
Ef.E
*
.E
*
Ef
*
B
L
*
Af.E
arch
Ef
.E
Ion Transport, Osmoregulation, and Acid–Base Balance
*
D
FIGURE 6.2 Scanning electronmicrographs of gills from various fish groups. A: Gill arch from a Gulf toadfish
(Opsanus beta) with radiating gill filaments. One part (boxed) includes a gill filament and lamellae. Bar 100 mm.
B: Higher magnification of gill filaments from an agnathan (pouched lamprey Geotria australis) with the
blood efferent edge (Ef.E) on the upper surface. The asterisk indicates one lamella. Bar 100 mm. C: Profile ditto
of a gill filament from an elasmobranch (ocellated river stingray Potamotygon motoro) with the blood afferent
edge (Af.E) and blood efferent edge (Ef.E) and lamella (L) labeled. Bar = 100 mm. D: Gill filament from
Atlantic stingray (Dasyatis sabina) cut lengthwise to expose the interior of the lamellae with numerous pillar
cells (arrows) that separate the lamellar epithelia and lamellar blood spaces (asterisk). Bar = 50 mm. From ditto
Evans et al., 2004, without permission (thus far).
system and the gas exchange of the arterioarterial system. Whereas the gills of teleosts and
elasmobranchs are clearly the major source for ion uptake from fresh water,87 the role for marine
elasmobranch gills is less clear.87,371
2. Kidney
The teleost kidney is mesonephric and contains renal tubules (nephrons) that may possess glomeruli
(fresh-water and euryhaline species), possess greatly reduced glomeruli, or completely lack glomeruli and thus be aglomerular nephrons (the latter two forms are found mostly in marine species).151
Elasmobranchs and lampreys, marine and fresh water, all have glomerular nephrons. Blood supply
to the kidney is twofold, the renal arteries as branches of the dorsal aorta supply the glomeruli (if
present) and the renal portal system that drains from the posterior portion of the animal anterior
to the tubules.151 Drainage is into the cardinal sinus and from there anterior to the heart. No fish
kidney has loops of Henle, and thus, none can produce urine that is hypertonic to the blood.
In fresh water, glomerular filtration rate is rapid, and urine flow rates are high. The urine
produced is strongly hypotonic, to minimize ion loss, as shown in the pioneering work by Marshall
and Smith.214 In marine aglomerular species, small volumes of urine are produced by secretion,
and secretion is important even in glomerular species.18 In both cases, the isotonic product excreted
is rich in divalent ions (Ca2+, Mg2+, SO42–), very often to the point of super saturation and precipitation.18 In marine forms, the main purpose of the kidney appears to be excretion of excess
multivalent elements that the animal gains likely from intestinal diffusive reabsorption.
3. Gastrointestinal Tract
The morphololgy of the gastrointestinal tract of fishes varies greatly among species depending, in
part, on feeding strategies.30,303,329 In fishes, the stomach is usually guarded by a cardiac sphincter
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The Physiology of Fishes
regulating entry from the esophagus and a pyloric sphincter regulating transfer from the stomach
to the intestine; but in contrast to higher vertebrates, there are no obvious charateristics to indicate
the presence of a large intestine. A minority of teleosts possess pyloric ceca which vary greatly in
size, shape, and number (from one to thousands).175 These ceca are located in the anterior part of
the intestine immediately distal to the pyloric sphincter.
In marine teleosts, the gastrointestinal tract plays a direct critical role in osmoregulation by
taking up water to compensate for osmotic water loss to the hyperosmotic environment. Esophageal
desalinization and drinking reflex (regulation of the cardiac sphincter) form the first two steps,
while intestinal absorption (and secretion) processes as well as rectal fluid output complete this
process (see Marine Teleost Hypo-osmoregulation below). Retention time of fluid within the
gastrointestinal tract is controlled by the drinking reflex, fluid absorption rates, and, finally, rectal
fluid flow rates. The latter most likely is regulated by rectal and anal sphincters that separate the
posterior intestine from the rectum and the rectum from the surrounding sea water, respectively.
In addition to this direct role of the gastrointestinal tract in marine teleost osmoregulation, the
digestive functions of the gastrointestinal tract also have implications for osmoregulation in all
fishes. Digestion is achieved by a combination of secretions and absorption, which in all cases
involves electrolyte transport,175 and ingested meals contain different concentrations of electrolytes,
depending on food type. In addition, feeding events have implications for water balance because
swallowing is associated with direct water intake191 and ingested natural food has high water content.
Further, drinking rates are clearly altered postprandially.356,357 Currently, very little is known about
the interactions between osmoregulation and feeding.
4. Rectal Gland (Elasmobranchs)
The rectal gland secretes NaCl in aid of marine elasmobranch ionoregulation, but gland extirpation
does not produce ionic imbalance.371 Many branched secretory tubules draining into a central canal
form this simple, tubular rectal gland. Secretion from the rectal gland drains via the central canal
through a duct into the intestine, distal to the spiral valve. Blood is supplied to the gland from a
single rectal gland artery and drains from the gland via a large intestinal vein,182 with blood supply
being highly regulated (see below). The artery branches into arterioles that feed the capillaries
surrounding the secretory tubules and appear to be arranged in a countercurrent direction to tubular
flow.256 The latter arrangement suggests postsecretory modification of fluid within the tubules, but
this remains to be documented. The secretory tubules are composed of cells possessing numerous
mitochondria and greatly expanded basolateral membrane regions and are similar (at least in
appearance) to the salt-secreting cells of marine birds and reptiles.31,74,315
5. Skin and Opercular Membrane
au: symbol
missing?
In most fish species, the gills are virtually the only transporting portion of the body surface, but in
animals with well-vascularized skin containing mitochondria-rich (MR) ion-transporting cells, the
skin can contribute significantly not only to gas exchange but also to ion transport, particularly in
gobies (Gillichthys mirabilis 215,216,230) mudskippers (Periophthalmus modestus385), and blennies
(Blennius pholis 259). For Gillichthys that have MR cells covering all exposed skin except the lenticule
over the eye, there is potentially 10 to 25% ion transport and an equivalent amount of gas exchange
across that surface. For blennies, it is even larger, about 60%.259 In the killifish and goby, the skin
lining the opercular bone is rich in MR cells.69,230 This is a smaller total surface area, but transport
rates are very high, more than 10 mEq Cl– cm–2 · h–1. The opercular epithelium of tilapia and killifish
and the goby skin have been used extensively as model preparations of MR cells in the study of ion
transport and its regulation.69,70,98,215,222 In addition, the yolk sac epithelium of fish larvae, before the
development of gills, has MR cells that serve as the ion transport organ for the embryo in fresh
water and sea water.135,157,159 Not only is the skin an important accessory osmoregulatory organ, it
is also a valuable model system for ion transport that has helped us understand gill function.
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Ion Transport, Osmoregulation, and Acid–Base Balance
183
6. Urinary Bladder
The urinary bladder of teleosts in fresh water acts as a final location for ion uptake, guaranteeing
that the urine released is as hypotonic as possible, thus minimizing renal salt loss. In rainbow trout,
ureteral urine collected via a catheter has a much higher NaCl content (10 to 15 mM) compared
with the approximately 1 mM NaCl in urine collected directly from the bladder post mortem 219
or that spontaneously released by free-swimming fishes.57 In the euryhaline goby, the urinary bladder
has zones that are more active in ion transport and are affected by prolactin.206 In sea-water teleosts,
the reabsorption of NaCl occurs in the urinary bladder as well, but the epithelium has a higher
osmotic permeability, thus causing reabsorption of more water167,206 and often producing bladder
stones containing Ca2+and Mg2+ salts.
II.
MARINE TELEOST HYPO-OSMOREGULATION
A. GILL MICROANATOMY
AND
CHLORIDE CELLS
1. Cell Morphology
The ultrastructure of sea-water mitochondria-rich (MR) cells is shown in Figure 6.3. These cells,
first observed by Keys and Willmer,185 have an elaboration of the basolateral membrane, of branching
and anastomosing tubules similar in appearance to smooth endoplasmic reticulum. Sardet et al.,305
who analyzed the tubular system, saw that it was continuous with the basal fluid and showed that
lanthanum could penetrate the system as well as the leaky junction between chloride cells and
B
A
ac
v
P
MR
C
D
rer
MR
mv
acc
FC
FIGURE 6.3 Electronmicrographs of mitochondria-rich (MR) cells from the jaw skin of the seawater goby
Gillichthys mirabilis. A: The MR cell has a typical invagination or crypt at the apical surface (ac) and below
the apical membrane are numerous vesicles (v), possibly involved in apical membrane turnover. The pavement
(P) cells attach tightly to the MR cell and have microridges on their apical surfaces (r). B: Higher magnification
highlights the tubular system (arrows) that ramifies among the mitochondria and is continuous with the
basolateral membrane of the cell. C: Near the nucleus (labeled MR) are well-developed Golgi bodies (arrows
in C and D), and surrounding the MR cell are actin-rich filament containing cells (FC). D: The Golgi bodies,
rough endoplasmic retulum (rer), and multivescicular bodies (mv) indicate rapid protein and organelle turnover
au: symbol?
in the MR cell, while an accessory cell (acc) has fewer mitochondria. Lines in all figures are 2 mm.
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The Physiology of Fishes
accessory cells. In sea water, the apical membrane is cup shaped, and the main MR cell is juxtaposed
and interwoven with an accessory cell with fewer mitochondria.165,305 The two cells form an operative
NaCl secretory unit, a microscopic marine salt secreting “gland.” The surrounding pavement cells
join with each other and with MR cells and accessory cells with elaborate, well-developed junctions
that have low permeability. Foskett and Scheffey 98 showed that current from active chloride secretion
flows only in localized micro-zones through chloride cell complexes. Hence, the secondary active
transcellular transport of anions and the paracellular leak for cations are effectively at the same locus.
The apical surface of the MR cell is highly plastic, typically with an apical crypt in sea water279
and changes with salinity from “deep-hole” openings in sea water to “shallow-hole” openings in
ion-rich fresh water; in ion-poor fresh water, the apical surface usually is thrown into microvilli,
likely to increase surface area for transport.40
2. Sea-Water Transport Mode — Na+,K+-ATPase
and Na+,K+, 2Cl– Co-transport
NaCl secretion by teleost gills is accomplished by secondary active transport of Cl– and passive
transport of Na+ (Figure 6.4) and the mechanism has been recently reviewed in detail.87,160 The
driving force for the active transport is Na+,K+-ATPase, which maintains intracellular Na+ at low
Seawater MR Cell Complex
(NaCl secretion; Ca2+ uptake)
Seawater
500 mM NaCl
0 mV
Blood
150 mM NaCl
P
+35–40 mV
AC
Na+
Na,K,2Cl−
Cl−
K+
Na+
Cl−
Na+
Cl−
~
MR
Na+
K+
Ca2+
Ca2+
P
Na+
~
Ca2+
~
Channel
Symport
Exchanger Active pump
FIGURE 6.4 This model of mitochondria-rich salt-secreting cell complexes typical of marine teleost gills
and opercular epithelium includes a mitochondria-rich (MR) cell and an accessory cell (AC). The MR and
AC cells form a leaky paracellular shunt that is cation selective and allows Na+ to be secreted passively, while
pavement (P) cells form a diffusive barrier. Symbols for channels, co-transporters, exchangers, and pumps are
below the figure; approximate NaCl concentrations and electrical potentials are included. In a membrane with
low osmotic permeability, Cl– enters via the Na+,K+,2Cl co-transporter driven by the Na+ gradient, which is
maintained by Na+,K+-ATPase. Cl– accumulates above its electrochemical equilibrium intracellularly, sufficient
to allow exit at the apical membrane through CFTR type anion channels. Shown also is an independent Ca2+
absorptive pathway that is essentially the same in sea water as well as fresh water and involves Ca2+ entry
apically via channels and basolateral exit via Na+–Ca2+ exchange and Ca2+ ATPase pump. Not shown is the
au: symbol? tubular system that folds the basolateral membrane to within 2 to 5 mm of the apical membrane, thus the
ditto?
complex functions as a very thin (ca 5 mm) NaCl secretory pump.
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Ion Transport, Osmoregulation, and Acid–Base Balance
au: should
this be
expanded at
first occurrence?
185
levels and intracellular K+ at high levels. The enzyme has been shown to be localized by tritiated
ouabain binding to the basal part of the cells.176 By biochemical precipitate and TEM,164 and more
recently by immunogold studies and TEM,63 Na+,K+-ATPase is shown to be localized specifically
to the tubular system. Cl– secretion by the opercular membrane and goby skin is inhibited by
ouabain only from the basal side,69,215 consistent with the basolateral enzyme-powering transmural
NaCl transport. Most recently, transfer of rainbow trout from fresh water to sea water evokes a
switch from expression of one catalytic (a) subunit of Na+,K+-ATPase to another, presumably marine
form in the gills,302 thus underscoring potential differences in operation and regulation of the pump
with salinity. Meanwhile, there is differential regulation of H+-ATPase and Na+,K+-ATPase when
rainbow trout acclimate to sea water. H+-ATPase activity, typical of ion uptake cells (see below) is
greatly reduced, while Na+,K+-ATPase activity rises in the peanut lectin–negative subtype but falls
in the peanut lectin–positive subtype.142 From these two elegant studies, it is now apparent that the
Na+,K+-ATPase isoform switching observed at the molecular level302 results from the differential
responses of two subtypes of the MR cell.142
Also on the basolateral membrane is the epithelial Na+:K+:2Cl– cotransporter sodium, potassium, 2 chloride co-transporter 1 (NKCC1, the secretory isoform of this family of co-transporters).137
The NKCC1 was originally cloned out of shark rectal gland and expressed in HEK-293 cells, where
it imparts bumetanide-sensitive uptake that is activated by depletion of the cells of Cl–.384 Two
closely related isoforms of NKCC1 have been cloned from European yellow eel (Anguilla anguilla)
expressed heavily in fresh-water and sea-water gills and in sea-water esophagus and stomach.58
Sea-water adaptation evokes increased NKCC1 abundance in the gills starting one day after
transfer.58 NKCC protein abundance increases up to 30-fold after smolting of Atlantic salmon
(Salmo salar), in accord with its role in sea-water osmoregulation.352 Secretion of Cl– by the isolated
goby skin and killifish opercular membrane is dependent on Na+217and is blocked by furosemide
and bumetanide.69 The NaCl secretion is also dependent on K+ and, as K+-free solutions inhibit
much more rapidly than does ouabain,224 the NaCl entry step apparently requires K+. Hence, Cl–
secretion clearly involves basolateral Na+:K+:2Cl– co-transport.
3.
Anion Channels
The NKCC co-transporter accumulates Cl intracellularly above its electrochemical equilibrium
such that Cl– exits passively via anion channels in the apical membrane. These anion channels are
low conductance (7 pS), 4,4’-diisothiocyanostilbene-2,2’-disulfonic acid (DIDS) insensitive, 5nitro-2-(3-phenylpropylamino) bezoic acid (NPPB) inhibited, and cyclic adenosine monophosphate
(cAMP) activated and have linear I/V relations that are indistinguishable from cystic fibrosis
transmembrane conductance regulator (CFTR) ion channels.76,226 CFTR has been cloned and
sequenced from Fundulus gill tissue,32 expressed in amphibian oocytes, and imparts cAMP-stimulated anion conductance to that system. Also, CFTR has been localized immunocytochemically
to the apical membranes of sea-water chloride cells of several species: (Fundulus heteroclitus 179,229;
mudskipper Periophthalmus schlosser 370; and Hawaiian Goby Stenogobius hawaiiensis).238 In
cultured pavement cells from fish gills, there appears a CFTR-like channel76 and a maxi Cl–
channel.260 Further, gill CFTR expression is evoked by transfer to sea water coincident, from 24
hours after transfer, with augmented transepithelial Cl– secretion by chloride cells in the opercular
epithelium.228,320
4. Potassium Recycling and Secretion
NaCl secretion in opercular membranes is blocked by barium,68 suggesting dependence on K+
channels. Because NKCC and Na+,K+-ATPase both carry K+ into the cell, it is thermodynamically
necessary to recycle K+ out via conductive pathways. One candidate K+ channel, identified in
cultured epithelial cells from sea bass gills,75 is a large conductance-stretch-sensitive channel that
may be a contributor to cell volume regulation. However, cultured epithelia from teleost gills have
au: please
provide
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The Physiology of Fishes
few actual MR cells, and so it is not clear that this channel is present in chloride cells. A very
promising candidate is the hypertonicity induced, inward-rectifying K+ channel expressed richly
in gills of sea-water-acclimated Japanese eel but weakly in fresh-water eel gills.339 Further, immunoelectronmicroscopy has localized this K+ channel to the tubular system of chloride cells,339 and
because the inward rectification is not complete, with in vivo K+ gradients, the channel will conduct
K+ out of the cell. This channel activates with the same stimulus (hypertonicity) that activates Cl–
secretion in the opercular epithelium, consistent with chloride cell transport regulation.386 Because
sea-water fish gills also secrete small amounts of K+, seen in vivo304 and in vitro in the sea-water
opercular membrane,216 one can predict that there may be several regulated K+ channels involved
in chloride cell operation.
5.
Is Na+ Secretion Passive?
The cation selectivity of the sea-water-adapted trout gill189 and that of membranes containing large
numbers of chloride cells70,217 led to the conclusion that Na+ is secreted passively down its electrochemical gradient through the lateral intercellular spaces and leaky junctions between chloride
cells and accessory cells. With NaCl gradients mimicking sea-water conditions, both the Gillichthys
mirabilis skin217 and the Fundulus opercular epithelium272 secrete Cl– against the approximately
3.4:1 concentration gradient and +37 to 40 mV electrical potential. The magnitude of that electrical
potential in vivo has been measured by transgill potentials of sea-water teleosts (Table 6.1), and
they range from +17 to +40 mV (see Figure 6.4). This voltage, which includes large diffusive and
smaller electrogenic components,287,289 is in the right direction but, in most cases, is too small to
drive Na+ across the gill epithelium out of the animal into sea water. The fact that the huge surface
TABLE 6.1
Transgill Electrical Potentials (with respect to ground outside animal) for Freshwater and Marine Teleosts, Measured in vivo in Various Environmental Media
Name
Species (acclimation salinity)
Freshwater Teleosts
Rainbow trout
Oncorhynchus mykiss (FW)
Brown trout
Salmo trutta (FW)
Goldfish
Carassius auratus (FW)
Rainbow trout
Seawater Teleosts
Oncorhynchus mykiss (SW)
Eel
Anguilla anguilla (SW)
Fat sleeper
Dormitator maculatus (SW)
European flounder
Platichthys flesus (SW)
Bermuda killifish
Fundulus bermudae
(SW embryos)
Opsanus beta (SW)
Toadfish
* Ca2+ content of 1.0 mM or greater.
Medium
FW
FW
FW
FW
FW
FW
(Hard)*
(soft)
(Hard)
(Soft)
(Hard)
(Soft)
SW
FW
SW
FW
SW
FW
SW
10% SW
FW
SW
5% SW
SW
Transgill PD (mV)
References
+8
–14.8
+5
–18
+10
–20
184
183
286
+10
–40
+22
–35
+17
–36
+19, +34, +27
–28
–78
+40
–11
–8
189
78
212
166
86
72,288,289
135
81
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Ion Transport, Osmoregulation, and Acid–Base Balance
187
area of pavement cells in the gill adds a passive shunt in parallel to the chloride cell complexes
likely reduces the voltage measured in vivo from that localized at the chloride cell. In three
experimental Cl– secreting systems without the lamellae — notably the Fundulus yolk sac embryos
in vivo,135 the isolated Gillichthys skin,217 and the isolated Fundulus opercular membrane,272 — the
voltage measured in sea water is +37 to +40 mV, which is several mV greater than the calculated
Nernst equilibrium potential of +29 mV. Thus, there is ample voltage, generated by the Cl– active
secretion, to drive Na+ through the cation selective shunt, out of the fish, and into sea water.
In a few species, notably sygnathids and toadfish (Opsanus sp.), the transgill potential in
seawater instead is slightly negative (see Table 6.1). For these species, the ion permeability of the
gill must be different (less selective for cations), and the Na+ secretion pathway may not be passive,
as it appears to be for most marine species.
B. GASTROINTESTINAL TRACT
au: expand?
It was first recognized in 1905 by Dekhuyzen71 that formation of isotonic or hypotonic urine by
marine teleosts requires osmotic work. Subsequently, Smith326 demonstrated that renal and extrarenal fluid loss to the concentrated marine environment was compensated for by ingestion of sea
water. In these early studies, drinking rates of 2.8 and 4.8 ml kg–1 h–1 were determined in eel and
sculpin, respectively, using phenol red. Since then, drinking rates have been determined, mainly
using esophageal cannulation, 51Cr-EDTA and 14C-polyethylene glycol (PEG) techniques in a large
number of marine teleosts to be in the order of 1 to 5 ml kg–1 h–.1 38,103,125,129,203,273,312,343,373 Regulation
of drinking and alimentary fluid and electrolyte transport in marine teleosts have been discussed
in detail in recent excellent reviews.4,208,344
1. Drinking Reflex and Regulation
Ambient salinity greatly influences drinking rate such that euryhaline fishes exhibit 10- to 50-fold
higher drinking rates in sea water than they do in fresh water.38,104,203,213,273 The many additional
individual factors which influence drinking in stenohaline and euryhaline teleosts (Table 6.2).
Although some controversies exist, the renin–angiotensin system (RAS) also is clearly involved in
the regulation of drinking in teleosts. 38,105,106,273,343
In fishes, angiotensin II (ANGII), the terminal biologically active part of RAS, stimulates
reflex swallowing centers in the medulla oblongata and thereby initiates water ingestion.342,343,345
TABLE 6.2
Summary of the Influence of Various Stimuli on Drinking Rates in Teleosts
Stimulus
Ambient [Cl–]
[Cl–] in the intestinal lumen
Distension of stomach
Distension of intestine
Hemorrage/hypovolemia
Plasma hypertonicity
Plasma hypertonicity
Nitric oxide
Atrial natriuretic peptide
Bradykinins
Cortisol
Growth hormone
Drinking
Species
Environment
Reference
Anguilla japonica
Anguilla japonica
Anguilla japonica
Anguilla japonica
Anguilla japonica
Anguilla japonica
Anguilla japonica
Salmo salar
Anguilla japonica
Anguilla japonica
Salmo salar, Oncorhynchus mykiss,
Oreochromis mossambicus
Salmo salar
Marine
Marine
Marine
Marine
Marine
Marine
Freshwater
Freshwater
Freshwater & Marine
Marine
Marine & Freshwater
154
5
154
154
154,346
154,346
154
106
354
347
102,204
Marine
103
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188
The Physiology of Fishes
The concentration of ANGII or plasma renin activity is generally higher in sea-water-adapted than in
fresh-water-adapted euryhaline fishes, and there is a transient increase in both following abrupt sea water
transfer.330,351,354 This may, at least in part, explain the higher drinking rates in marine fishes. However,
the constant drinking rates seen in the Japanese eel, despite suppression of plasma ANGII levels,343
suggest that factors in addition to RAS are involved in the regulation of marine teleost drinking rate.
Elevated ambient Cl– concentration but not that of Na+, immediately stimulates the drinking
reflex. The onset of drinking occurs within minutes, prior to any changes in plasma osmolality and
is regarded as an anticipatory response to elevated salinity.9,154 A negative gastrointestinal feedback
system also seems to be in place to downregulate drinking when the stomach or the intestine is
distended154 and when intestinal Cl– concentrations are increased.5 These negative feedback loops
appear beneficial because they act to reduce drinking when the gastrointestinal tract is distended
from fluids already ingested and when high intestinal Cl– concentrations provide substrate for
intestinal fluid absorption (see below). The potential links between these negative feedback loops
and RAS remain to be investigated.
Reduced blood volume154 and reduced blood pressure caused by vasodilation106 potently stimulate the drinking reflex, while elevated plasma osmolality alone has an inhibitory effect.154,346 The
combined action of reduced blood volume and elevated plasma tonicity caused by esophageal
cannulation, however, is to stimulate drinking.38 Because the increased drinking response during
vasodilation can be inhibited by angiotensin-converting enzyme (ACE) inhibitors, it seem likely
that increased drinking during hypovolemia and hypotension is mediated through the RAS system.106 Perhaps surprisingly, hypertonicity induced by NaCl infusion failed to induced drinking in
sea-water-adapted eels but, rather, transiently reduced drinking.154 This seems counter intuitive, and
it is possible that the decreased drinking was instead a response to hypervolemia caused by the
rapid infusion. The effect of hypervolemia on the drinking reflex in marine fishes remains to be
characterized (see Iwama et al., elsewhere in this volume).
Bradykinins (BK) form an active component of the kallikrein–kinin (KK) system which, in
mammals, influence vascular permeability. BK is present in fishes and inhibits the drinking reflex
in sea-water eels.55,347 Interestingly, both the KK and the RAS systems utilize the ANGI-converting
enzyme, which is responsible for the production of ANGII and at the same time the degradation
of BK.110. The complexity of the drinking response regulation is further illustrated by findings of
reduced drinking rates during BK infusion despite a simultaneous increase in plasma ANGII.347
Also interacting with the drinking reflex and RAS is the atrial natriuretic peptide (ANP), which
inhibits drinking while lowering plasma ANGII levels.354 At present, it is unknown whether ANP
acts directly on the drinking reflex or if the ANP effect is mediated through RAS. The catadromous
eel, the anadromous salmon, and the euryhaline flounder have evolved highly sensitive drinking
reflexes, presumably to cope with salinity change during migration. Drinking control in stenohaline
marine forms is similar to the migratory type, but stenohaline fresh-water fishes clearly have reduced
sensitivity12 and may have secondarily lost the reflex.
In euryhaline fishes, experimentally elevated cortisol stimulates a more immediate and pronounced drinking response, compared with control fishes after transfer from fresh water to sea
water.102,204 However, cortisol seems to have no effect on drinking rate in fresh-water fishes204 and
may inhibit drinking rate in euryhaline fishes fully acclimated to sea water.102 Similarly, growth
hormone, which has no effect on drinking rate in fresh-water salmon, stimulates drinking in fish
upon transfer to sea water.103 Whether cortisol and growth hormone are involved in regulation of
drinking rate in stenohaline marine fishes awaits clarification.
2. The Role of the Esophagus
The ionic composition of the ingested sea water medium changes dramatically along the gastrointestinal tract as illustrated in Figure 6.5. Processing of imbibed sea water begins in the esophagus,
and esophageal NaCl absorption reduces Cl– and Na+ concentrations as well as osmolality so that
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Ion Transport, Osmoregulation, and Acid–Base Balance
189
300
100
30
Cl−
Na+
Mg2+
SO42−
14
10
3
K+
HCO3−
12
10
1
pH
8
Ca2+
6
4
[K+], [Ca2+], (mM) & pH
[Na+], [Cl], [Mg2+], [SO42−], [HCO3−] (mM) & mOsm
Osmolality
Esophagus
um
ct
r
io
er
st
Re
id
Po
er
nt
A
M
io
r
h
ac
om
St
SW
2
Intestine
FIGURE 6.5 The progressive change in the composition of imbibed sea water along the gastrointestinal tract
in an unfed typical marine teleost fish (note logarithmic Y-axis). Data are derived from a total of 24 different
marine or sea-water acclimated euryhaline teleosts. Some species are represented by more than one measurement, and no single species contributed data to all parameters reported for all five segments of the gastrointestinal tract.36,128,186,263,312,324,326,373
the stomach fluid is much less concentrated than sea water.186,263,326,373 The absorption of NaCl in
the esophagus consists of both passive and active components and is the main reason for the reduced
concentration of these ions, although some dilution via fluid secretion may occur in the stomach.263
The esophageal epithelium is largely impermeable to other ions and exhibits low water permeability.155,263 From the few studies of esophageal transport, it is clear that the active uptake of Na+ is
driven by the basolateral Na+,K+-ATPase and depends on the presence of Cl–. However, in the
winter, flounder Na+ uptake is insensitive to furosamide, ruling out the involvement of Na+:Cl–
(NC) and Na+:K+:2Cl– (NKCC) co-transporters. NaCl uptake is sensitive to amiloride in the luminal
saline, suggesting the presence of Na+–H+ exchangers (NHE) and/or Na+ channels.263
3. Role of the Intestine
The osmolality of intestinal fluids is further reduced to approximately 400 mOsm in the anterior
intestine and as low as 300 to 360 mOsm in the rectal fluids (see Figure 6.5). The main osmolytes
of intestinal fluids are not Na+ and Cl–, as in sea water but, rather, Mg2+, SO42,– and HCO3– (see
Figure 6.1). The unique chemistry of the intestinal fluids is the product of combined absorptive
and secretory processes (summarized in Figure 6.2) as well as the differential permeability of the
intestinal epithelium. It should be noted that although the overall function of the marine teleost
intestine clearly is to absorb Cl– and fluids, this epithelium switches, if strongly stimulated, to Cl–
and fluid secretion.233 The intestinal epithelium exhibits higher osmotic permeability than does the
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The Physiology of Fishes
esophagus,77,155 and in marine teleosts, the majority of water absorption, which is critically linked
to Na+ and Cl– absorption, occurs in the intestine. The exact mechanism of water absorption remains
unknown and may involve both transcellular and paracellular pathways. Although aquaporins are
present in the intestinal tissue, there is no direct evidence that they are involved in water absorption.2,61,199 However, several co-transporters, including K+:Cl– and Na+:glucose transporters, have
been demonstrated to transport water205 and may contribute to transcellular water movement in the
marine teleost intestine.
4. NaCl Absorption
Regardless of the mechanism, water transport is tightly linked to the active absorption of Na+ and
Cl– .210,321,358 Na+ absorption is fueled by the basolateral Na+,K+-ATPase extruding 3Na+ across the
basolateral membrane in exchange for 2K+.322,323 The activity of this enzyme thus maintains low
intracellular Na+ concentration207 and sustains a substantial cytosol-negative membrane potential
(Figure 6.6). The importance of Na+,K+-ATPase for successful sea water osmoregulation is illustrated by increased Na+,K+-ATPase messenger ribonucleic acid (mRNA) expression and Na+,K+ATPase enzymatic activity in the intestinal epithelium of euryhaline fishes following sea water
transfer.60,174,210,310
The apical electrochemical Na+ gradient energizes the absorption of both Cl– and K+ by
two parallel co-transport systems: Na+:Cl– (NC) and Na+:K+:2Cl– (NKCC) co-transporters (see
Figure 6.6).93,101,140,253 Removal of Cl– from the intestinal lumen blocks Na+ absorption (consistent
with NKCC operation), whereas limited Cl– absorption persists even in the absence of Na+,128,211
demonstrating an alternative Cl– uptake pathway. The involvement of NKCC in sea water osmoregulation is evident also from increased NKCC mRNA expression in the intestinal epithelium of
Lumen
Extracellular fluid
Na+,
K+,
2Cl−
K+
Na+
~
Cl−
K+
Cl−
Na+, Cl−
HCO3−
HCO3−
Cl−
CO2 + H2O
CA
H+
K+
~
H+
H2O
Na+
Cl−
−20 mV
−100 mV
0 mV
Apical membrane
Basolateral membrane
FIGURE 6.6 Schematic cellular model of transport processes in the intestinal epithelium of marine teleosts.
Transcellular and/or paracellular fluid absorption is driven by the active NaCl transport fueled primarily by
the basolateral Na+:K+-ATPase which provides the electrochemical gradient for Na+, Cl– and K+ import
across the apical membrane. Two parallel symporters, the Na+:Cl– and the Na+:K+:2 Cl– co-transporters, account
for Na+ and some Cl– uptake, with the remaining Cl– uptake occurring in exchange for HCO3–. The apical
anion exchange accounts for 30 to 70% of the net Cl– absorption and produces highly elevated luminal HCO3–
concentrations. The source of HCO3– for the exchange process appears to be endogenous CO2. Carbonic
anhydrase facilitates CO2 hydration to sustain the high HCO3– secretion rates. Cl– exits the epithelial cells
across the basolateral membrane via Cl– channels and K+:Cl– co-transporters.
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Ion Transport, Osmoregulation, and Acid–Base Balance
191
European eel after transfer from fresh water to sea water.58 A large number of studies show much
higher net absorption rates for Cl– than for Na+ both in situ and in vitro,92,93,113,211,234,252 which may,
in part, be explained by the stoichiometry of NKCC. However, considering the relatively low K+
concentration in sea water and intestinal fluids, NKCC by itself cannot explain the often substantial
excess net Cl– absorption.
5. HCO3– Secretion and Anion Exchange
Recently, apical Cl–/HCO3– exchange (AE) has been demonstrated to play a role in Cl– absorption
and accounts for 30 to 70% of net Cl– uptake under in vivo–like conditions.125,127,128,133 The apical
AE secretes copious amounts of HCO3– and produces luminal HCO3– concentrations — in some
cases, higher than 100 mM372,375 — which may be associated with highly alkaline intestinal fluids
reaching pH values of 9 or more. The source of HCO3– for luminal secretion appears to be
endogenous epithelial CO2,374 with hydration being catalyzed, in part, by carbonic anhydrase373
(see Figure 6.6). The H+ arising from this hydration reaction is extruded across the basolateral
membrane through a mechanism yet unidentified. Species-specific differences in the mechanism
of luminal HCO3– secretion likely occur because Na+-dependent, transepithelial HCO3– transport
has been demonstrated in the Japanese eel.6
Regardless of the route of apical Cl– entry into the epithelial cells, Cl– transport across the
basolateral membrane appears to occur via Cl– channels209 and K+:Cl– co-transporters.139
6. Divalent Ions
By far the dominant divalent ions in the intestinal fluids are Mg2+ and SO42–, reaching concentrations,
in some cases, higher than 100 mM128,130,326 (see Figure 6.5). Thus, Mg2+ and SO42– are concentrated
well above seawater levels of approximately 50 and 30 mM, respectively, as a function of water
absorption. Marine fishes continuously void small volumes of rectal fluid. The rate of rectal fluid
excretion accounts for 15 to 40% of the corresponding drinking rate with the remaining 60 to 85%
of the imbibed water being absorbed along the intestine.312,324,326,373 Assuming 75% fluid absorption
in the intestine and no net absorption of Mg2+ and SO42-, the predicted concentration of these ions
in the rectal fluids would be 200 and 120 mM, respectively. The predicted concentration of SO42–
is thus very similar to the average rectal fluid SO42– concentration displayed in Figure 6.5. This
suggests that no, or very little, SO42– is absorbed by the intestinal epithelium in vivo, despite a
substantial transepithelial gradient that favors uptake. Part of the explanation for this could be the
active extrusion of SO42– in exchange for Cl– , as observed in the winter flounder.270 This exchange
mechanism may not only explain the apparent lack of net SO42– uptake but may also assist Cl–
absorption.
In contrast to SO42–, the predicted concentration of Mg2+ exceeds the average rectal fluid Mg2+
concentration in marine teleosts (see Figure 6.5) by approximately 80 mM, which suggests substantial intestinal Mg2+ uptake. However, a recent study on the European flounder, with control of
both Mg2+ ingestion and rectal excretion, revealed that >90% of Mg2+ entering the intestine can be
recovered in the rectal fluids showing only very modest net intestinal Mg2+ uptake.374 These
observations are in agreement with findings from those of the Southern flounder.150
7. Alkaline Precipitation
The Ca2+ concentrations in intestinal and rectal fluids are substantially lower than sea-water Ca2+
concentrations. This led to numerous suggestions of a substantial intestinal net Ca2+ uptake in
marine teleosts.83,150,177 However, recent findings have revealed that intestinal absorption of Ca2+ is
modest and that the low Ca2+ concentrations in the intestinal fluids are the result of alkaline
precipitation, rather than intestinal absorption. The high luminal HCO3– concentrations and the
alkaline conditions result in CaCO3 precipitation, evident as white mucus-coated precipitates within
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The Physiology of Fishes
the intestinal lumen. These precipitates are excreted with the rectal fluids and can be easily observed
in the water of aquaria housing marine teleosts. The precipitation can account for 30 to 65% of
the ingested Ca2+312,374 but only a minor fraction (<5%) of the ingested Mg2+,374 as the precipitates
consists largely of CaCO2 and MgCO2.362 The precipitates reduce the concentration of Ca2+ and
CO32– substantially, resulting in a reduced osmolality of the intestinal fluids by as much as 73
mOsm.374 Although the intestinal epithelium is capable of absorbing water against an osmotic
gradient,321 such a reduction in luminal osmolality undoubtedly is advantageous for marine teleosts
combating dehydration.
C. KIDNEY
Marine teleosts with glomerular or aglomerular kidneys produce low urine flow rates of 0.03 to
0.89 or 0.03 to 0.45 ml kg–1 h–1, respectively.18,96,151,241,242,244,326 The tonicity of urine in marine
teleosts (with glomerular or aglomerular kidneys) is similar to the extracellular fluids; however,
the major electrolytes are Mg2+ , SO4 2– , and Cl– , rather than the Na+ and Cl– of blood
plasma.18,28,151,241,242,312
1. Tubule Anatomy
With few exceptions, both glomerular and aglomerular stenohaline marine fishes lack a distal
nephron,64 which is responsible for NaCl reabsorption in fresh-water fishes and other vertebrates.151
The typical marine glomerular nephron consists of a renal corpuscle containing the glomerulus and
a neck segment followed by two or three proximal segments (which make up the major portion of
the nephron). The proximal segments connect directly to the collecting duct via the collecting
tubule. In contrast, the nephrons of the aglomerular kidney, which have been reported from approximately 30 teleost species (mostly marine but a few fresh-water),18,22 lack a renal corpuscle; the
aglomerular nephron consists entirely of a proximal tubule segment connecting directly to a
collecting tubule and duct.
2. Aglomerular and Glomerular Kidney Function
Although fishes with aglomerular kidneys are rare, it seems that the loss of glomeruli has occurred
on three separate occasions during evolution.18 These multiple evolutionary events combined with
reports of aglomerular teleost fishes present in brackish water and even fresh water18 suggest that
tubular secretion is an intrinsic part of renal function in fishes and perhaps all vertebrates.18 Multiple
species of the toadfish family, Batrachoididae inhabit fresh water,52,53 indicating that true aglomerular
fresh-water species are perhaps more numerous than previously thought. Importantly, tubular secretion is not restricted to fluids and electrolytes but also include secretion of creatinine231 and a number
of organic cations and anions.28,64 Glomerular filtration rates in marine teleosts are generally much
lower than in fresh-water teleosts,10,28,151 while obviously no filtration takes place in aglomerular
nephrons. Despite glomerular filtration rates of ~0.5 ml kg–1 h–1 in glomerular marine teleosts, urine
flow rates of aglomerular and glomerular marine fish are similar to each other (see above). Further,
urine composition from glomerular and aglomerular fishes is indistinguishable.19,22 These observations strongly suggest that the renal contribution to marine teleost osmoregulation, regardless of the
presence or absence of glomeruli, is dominated by tubular secretion; subsequently, this preurine is
modified by absorption.
3. Renal Tubular Secretion
Fluid secretion rates and composition are very similar in isolated tubules from aglomerular and
glomerular kidneys with Na+ and Cl– being the dominant electrolytes. Figure 6.7 presents a
schematic overview of tubule anatomy and principal transport characteristics. Although Mg2+ and
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Ion Transport, Osmoregulation, and Acid–Base Balance
193
GFR ~ 0.3 ml kg−1h−1
Na+
Cl−+2
Mg
SO42−
H2O
Early proximal tubule
Glucose
and other organic solutes
Na+
Cl− Late proximal tubule
H2O
A
Collecting tubule
Na+
Cl−
Mg2+
SO42−
H2O
Bladder
Na+
Cl−
H2O
Early proximal tubule
+
Na
Cl−
H2O
UFR ~ 0.3 ml kg−1h−1
Late proximal tubule
B
Collecting tubule
Bladder
Na+
Cl−
H2O
UFR ~ 0.3 ml kg−1h−1
FIGURE 6.7 Overview of ion and water movement in glomerular (A) and aglomerular (B) tubules of marine
teleosts. Urine flow rate and composition in aglomerular and glomerula fishes are generally indistinguishable,
thus pointing to the importance of tubular secretion. Inspired by schematic illustrations by Nishimura & Imai.257
SO42– concentrations in tubular secretions are elevated far above plasma concentrations and thus
may contribute to fluid secretion, it appears that the majority of proximal tubule fluid secretion is
driven by Na+ and Cl– transport in the early proximal tubule. Insight into the mechanisms of tubular
fluid secretion come from studies performed on the dogfish Squalus acanthias16,20 and has since
been confirmed for marine teleosts using sea-water-acclimated killifish.48,49
Tubular secretion of Na+ and Cl– occurs as secondary active transcellular Cl– transport with
electrically coupled paracellular Na+ transport (Figure 6.8). Electrochemical gradients for K+ and
Na+ allow Cl– entry across the basolateral membrane presumably via NKCC and results in cytosolic
Cl– concentrations above equilibrium. Apical Cl– secretion is via a cAMP-stimulated conductive
pathway, presumably via anion channels.20,50
Although Mg2+ concentrations in tubular secretions are lower (~20 mM17,21,51,297) than in bladder
urine (~140 mM11,151,248), tubular fluid Mg2+ concentrations must be the product of active transport.
Passive entry of Mg2+ across the basolateral membrane is thought to occur via Mg2+ channels,18
whereas the active exit of Mg2+ across the apical membrane occurs either via Mg2+:Na+
exchange254,301 ultimately driven by Na+,K+-ATPase or via Mg2+:H+ exchange driven by H+ pumps
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The Physiology of Fishes
A Early proximal tubule
Lumen
Extracellular fluid
Na+
Na+
Cl−
Na+
Mg2+
K+
+
+
Na , K , 2Cl−
Mg2+
H+
H+
~
CA
Cl−/HCO3−
CO2 + H2O
~
SO42−
Na+
2−
H+
SO4
K+
OH−
H2O
B Late proximal tubule
Lumen
H2O
Extracellular fluid
Na+
Na+
Glucose, aa
Na+
H+
HCO3−
K+
~
Na+, 2HCO3−
Cl−
Cl−
FIGURE 6.8 Schematic cellular model of secretory and absorptive processes in the early (A) and late (B)
proximal tubule of glomerular and aglomerular marine teleosts. A: Secretory processes include secondary
active Cl– secretion driven by the activity of the basolateral Na+:K+-ATPase providing the electrochemical
gradient for Cl– entry via the basolateral Na+:K+:2Cl– co-transporter. Cl– exits across the apical membrane
down its electrochemical gradient to the lumen via Cl– channels (presumably CFTR type), while Na+ is excreted
via electrically coupled paracellular pathways. Mg2+ secretion involves carrier-mediated entry of Mg2+ across
the basolateral membrane down its electrochemical gradient that provides cellular Mg2+ for Na+/Mg2+ exchange
and H+–Mg2+ exchange across the apical membrane. The H+–Mg2+ exchange process may be driven by apical
H+-pump activity, while the Na+–Mg2+ exchange process is fueled by the Na+ gradient established by the
basolateral Na+/K+-ATPase. Secretion of SO42– involves anion exchange processes in both the basolateral and
the apical membranes and is dependent on carbonic anhydrase (CA). (See excellent recent reviews by
Beyenbach18 and Pelis & Renfro271 for more detail).
present in the apical membrane18 (see Figure 6.8). Tubular SO42– secretion is evident from concentrations of approximately 10 mM in tubular secretions in marine fishes.17,51 Even in teleosts with
glomerular renal tubules, the majority of renal SO42– excretion is the result of active tubular
secretion.23,73,299 Tubular SO42– secretion is facilitated by DIDS-sensitive electroneutral anion
exchange mechanisms in both the basolateral and the apical membrane and by intracellular carbonic
anhydrase269,298,300 (see Figure 6.8). Basolateral import of SO42– occurs via exchange with OH–,
while apical extrusion into the tubular lumen occurs in exchange for uptake of HCO3– or Cl–.271
4. Renal Tubular Reabsorption
The high bladder urine concentrations of Mg2+ and SO42– (~140 and 80 mM, respectively151,248) is
the product of not only tubular secretion (see above) of these divalent ions but also of Na+, Cl– and
water reabsorption. The NaCl reabsorption occurs in the late proximal tubule and in the urinary
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Ion Transport, Osmoregulation, and Acid–Base Balance
195
bladder (see below) and results in a low-average urine flow rate in marine teleosts of ~0.3 ml kg–1
h–1. The discrepancy between average glomerular filtration rates and urine flow rates in marine
teleosts is not large, but fluid secretion rates are substantial and may exceed glomerular filtration
rates by several times. In his recent and thorough evaluation of aglomerular urine formation,
Beyenbach18 demonstrates, from measurements of tubular fluid secretion rates and composition of
tubular fluid, that tubular secretion may exceed glomerular filtration by as much as three- to fourfold.
In his example, even a glomerular marine teleost exhibits tubular fluid reabsorption in the order of
2 ml kg–1 h–1. This substantial reabsorption of largely secreted, rather than filtered, fluid explains
the high concentrations of Mg2+ and SO42– in bladder urine. The reabsorption of Na+ and Cl– in the
proximal tubule is reviewed in detail by Dantzler64 and Braun and Dantzler.28 The driving force for
solute and fluid reabsorption is provided indirectly by the basolateral Na+, K+-ATPase, that creates
a favorable gradient for Na+ entry from the tubular lumen across the apical membrane and drives
Na+-glucose, Na+-amino acid co-transport and Na+/H+ exchange. Tubular reabsorption of Cl– occurs
via an electroneutral process also driven by the electrochemical Na+-gradient and is suggested to
occur via Cl–/HCO3– exchange coupled with the Na+/H+ exchange process (see Figure 6.8).
5. Urinary Bladder
The urinary bladder of sea-water fish contributes to NaCl and water absorption, thereby concentrating divalent ions in the urine and minimizing water loss. The NaCl uptake by isolated flounder
(Pseudopleuronectes americanus) urinary bladder is interdependent,295 is ouabain and furosemide
sensitive, and is accompanied by fluid reabsorption, with a calculated absorbate concentration of
about 145 mM.294 Na+,K+-ATPase is localized to the basolateral surfaces of urinary epithelial cells.296
In the toadfish (Opsanus tau), the in vivo bladder reabsorbs 60% of the urine volume.167 In seawater
gobies (Gillichthys mirabilis), there is both electroneutral and electrogenic, ouabain-sensitive NaCl
reabsorption in mitochondria-rich columnar cell portions of the urinary bladder.206 A unique thiazidesensitive NaCl co-transporter is expressed only by flounder urinary bladder, while other tissues
express a different NaCl transporter.109 The caudal neurosecretory system (urophysis) and its
peptides (urotensin I and I) may control transport and contractility of the urinary bladder.15 Whereas
freshwater rainbow trout urinary bladder is urea permeable, that of the toadfish (Opsanus beta) is
not, an interesting association of intermittent urination (by toadfish) and low urea permeability.240
6. Integrative Perspective
Table 6.3 summarizes exchange of water and major electrolytes with the marine environment for
nonfed marine fishes in steady state. Typical drinking rates and urine flow rates as well as seawater
chemical composition have been assumed for the following considerations. The majority of the
fluid loss occurs across nonrenal and nonintestinal surfaces and is assumed to take place mainly
across the gill epithelium, with renal fluid loss contributing only about 15% of whole body fluid
loss. Of the NaCl ingested with sea water >95% is absorbed along the gastrointestinal tract, and
very little of this absorbed NaCl is ultimately eliminated through the urine. Consequently, the vast
majority, a net extrusion of 800 to 900 µmol kg–1 h–1 Na+ and Cl–, must occur at the gills. While
these extrusion rates may seem high, they are only one tenth the corresponding unidirectional efflux
rates of Na+ and Cl– reported for marine teleosts.132,383 As for Mg2+ and Ca2+ balance, an individual
study used carefully controlled intestinal infusion rates and measurement of rectal loss of these
cations.374 These considerations reveal that only 10 to 20 % of the ingested divalent cations are
absorbed by the intestine and that renal excretion of divalent cations easily accounts for the observed
uptake by the gastrointestinal tract. The same is not true for SO42– because gastrointestinal absorption
appears to exceed renal excretion. It should be noted, however, that the apparent need for branchial
SO42– secretion is based on average values of urine flow, drinking rate, and SO42– concentration in
rectal fluid and urine. Gastrointestinal SO42– intake and rectal output have yet to be measured
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The Physiology of Fishes
TABLE 6.3
Summary of Mass Balance of Fluid and Major Electrolytes in a Typical Nonfed Marine Teleost
Component
Gastrointestinal Tract
Gills*
Water (µl kg–1 h–1)
Na+ (µmol kg–1 h–1)
Cl– (µmol kg–1 h–1)
Mg2+ (µmol kg–1 h–1)
SO42– (µmol kg–1 h–1)
Ca2+ (µmol kg–1 h–1)
K+ (µmol kg–1 h–1)
–1,300
–814
–905
19
–16 (?)
2
–15
Renal System
Ingestion
Rectal Fluid
Net GI
2,000
840a
980a
100a
60a
20a
20a
–400
–20a
–39a
–80d
–20a
–16g
–5a
1,600
820
941
20
40
4
15
–300
–6b
–36c
–39e
–24f
–6h
<1i
[Average urine flow rate of 0.3 and drinking rate of 2 ml kg–1 h–1 and typical seawater composition has been assumed for
these calculations. The net contribution of the gastrointestinal tract (“Net GI”) is simply the difference between ingested
water and ions and volume and composition of voided rectal fluids.]
* or nongastrointestinal and nonrenal surfaces
au: correct?
a
values obtained from Figure 6.1.
b
assumed urine [Na+] of 20 mM18,151
c
assumed urine [Cl–] of 120 mM18,151
d
fractional values for rectal Mg2+ loss obtained from Wilson & Grosell374
e
assumed urine [Mg2+] of 180 mM18,151
f
assumed urine [SO42–] of 80 mM18,151
g
values of rectal fluid Ca2+ loss make up 80% of ingested Ca2+ and include Ca2+ in voided precipitates374
h
assumed urine [Ca2+] of 20 mM151
i
assumed urine [K+] of 1.4 mM151
simultaneously in a marine teleost; they should be determined together to assess whether renal
SO42– elimination is sufficient to maintain homeostasis. Further, it seems clear that the majority of
the K+ absorbed along the gastrointestinal tract must be eliminated across the gills because renal
output is minimal. Finally, it should be noted that almost everything we know about gastrointestinal
contributions to osmoregulation is derived from studies performed on nonfed animals and that
feeding undoubtedly will influence osmoregulatory processes. A large meal for a piscivorous fish,
for example, will provide a substantial K+ and Ca2+ load (from prey intracellular K+ and bone,
respectively), although this remains to be documented, and will, at the same time, influence bile
and pancreatic secretion rates as well as intestinal re-absorptive processes.175
III.
FRESHWATER TELEOST HYPEROSMOREGULATION
A. GILL
1. Gill Mitochondria-Rich (MR) Cells
The debate continues as to whether mitochondria-rich (MR) cells are the only ion-transporting
cells of the gill and whether there are subtypes of MR cells. The function and morphology of MR
cells have been reviewed.87,276 The morphological changes in MR cells with salinity, particularly
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ditto
197
in the elaboration of the apical membrane in fresh water,40,285 imply changes in apical membrane
components as well. Morphologically, the electron dense b cells and less dense a cells are distinct,
but the a cell is involved in fresh water as well as sea water transport, while the role for the b
cells is not clear.285 Lungfish have MR cells in the gill and skin epithelia337 that are physiologically
similar to fresh-water teleosts. The recent findings of lectin binding to one subpopulation of MR
cells but not another in rainbow trout gill120 may have resolved the issue. There are two functional
subtypes (at least) that are very similar ultrastructurally. The peanut lectin–insensitive (peanut
agglutinin, PNA–) cells have higher levels of H+ -ATPase activity. Furthermore, the PNA– cells
have high levels of acid-stimulated, phenamil- and bafilomycin- sensitive Na+ uptake,293 demonstrating co-localization of the putative Na+ channel and V-type H+-ATPase pump in one cell type.
The peanut lectin–sensitive (PNA+) cells, on the other hand, have as high levels of Na+,K+ATPase, about half the V-type H+-ATPase level compared with the PNA+ cells and no phenamilsensitive Na transport.108,293
2. Role of Pavement Cells
au: could
you please
simplify this
sentence?
Partitioning of fluxes across the gills of teleosts into two portions — the lamellar circulation and
the filamental circulation — not only produced strong evidence for major involvement of the
filament MR cells in ion transport but also revealed a minor contribution by lamellae to ion
exchanges in both marine and fresh-water fishes (reviewed by84,267,276). Pavement cells form a
continuous epithelial sheet of the lamellae and interlamellar regions and are joined to each other
and to MR cells by well-developed, tight intercellular junctions. Because of the tight junctions
and the paucity of mitochondria, they were thought not to contribute significantly to either the
passive ion loss or to active ion uptake. Pavement cells grow vigorously in culture and easily
form confluent epithelial sheets.8,378,380 With fresh water on the outside, these sheets prove to be
a significant passive barrier, with electrical resistances and low permeability to radiolabelled
polyethylene glycol.378 The findings that ion transport proteins are detected by immunocytochemistry in the pavement cells of fresh-water-adapted rainbow trout, including H+-ATPase and an
epithelial sodium channel,369 and, by basolateral CFTR immunofluorescence in killifish229 suggest
that some small amount of transport may occur across pavement cells. However, without substantial metabolic potential to drive transport, the contribution of these cells to ion uptake is
likely minor.
3. Ion Uptake Models
Summary models for ion uptake abound87,160,221,275 and have changed substantially, since the previous
edition of this book, based on new molecular and immunocytochemical discoveries. Goss and coworkers108,120 have successfully separated from fresh-water teleost gills acid and base secreting
cells, based on their affinity for peanut agglutinin (PNA). Hence PNA+ and PNA– mitochondria
rich (MR) cells have different components (Figure 6.9). Pivotal to the model is the V-type H+ATPase that serves as the core driving force for both Na+ and Cl– uptake.
4. Vacuolar-Type ATPase and Na+ Transport
The vacuolar-type (V-type) proton ATPase is a ubiquitous enzyme of organelles and of the plasma
membrane.255 Until recently, it was thought that the H+-ATPase was immunolocalized only to the
apical membrane of (some) MR cells, especially in rainbow trout.200 This was the logical location,
parallel with a phenamil-sensitive Na+ channel, to drive Na+ uptake across the gill epithelium. This
model clearly explains the ability of rainbow trout to excrete acid equivalents in acidic environments
(down to about pH 5.5.201,202
Evidence for the proton ATPase is strong. Bafilomycin is a specific inhibitor of the H+-ATPase
and, when added to fresh water, strongly inhibits Na+ uptake in whole animal flux experiments
au: please
provide
ditto
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The Physiology of Fishes
PNA+ MR Cell
(Cl− uptake; base secretion)
Ca2+
Freshwater
1 mM NaCl
0 mV
~
Na+
Na+
Ca2+
Cl−
HCO3−
HCO3−
Blood
150 mM NaCl
+10 mV
~
K+
CA
CO2
Cl−
~
H+
PNA− MR Cell
(Na+ uptake; acid secretion)
Na+
Na+
H+
~
~
K+
Cl−
CA
HCO3−−
CO2
FIGURE 6.9 Fresh-water teleost gills have morphologically similar cell types that are functionally distinct,
separable with peanut agglutinin (PNA). The PNA+ cells secrete base and take up Cl– by an apical Cl––HCO3–
exchange driven indirectly by a proton pump that is situated on the basolateral membrane (V-type ATPase).
Cl– exit basally is via CFTR-like anaion channels. Shown in this cell type only (but probably present in both)
is the Ca2+ uptake involving apical Ca2+ channels and basolateral Na–Ca exchange and Ca-ATPase. By contrast,
PNA– cells are specialized for acid secretion and Na+ uptake, where the V-type ATPase is in the apical membrane
along with an epithelial type Na+ channel. Electrical gradient established by the H+-ATPase drives Na+ into
the cell, and it exits via the Na+,K+-ATPase pump. Here, HCO3– exits the basolateral membrane in exchange
for Cl– which, in turn, recycles through CFTR-like anion channels.
au: minus
hundred
okay?
with tilapia, carp,90 rainbow trout,37,124 and zebrafish.25 Estimates of the metabolic cost of ion
pumping by freshwater cutthroat trout using bafilomycin and phenamil demonstrate that only about
4% of total oxygen consumption is expended on gill ion transport.249 Immunocytochemical localization places the proton ATPase on the apical membranes of the MR cells of rainbow trout
gills.200,369 Immunostaining in the apical membrane of the pavement cells of trout gills also occurs
(using an antibody to the carboxy terminus), and there is upregulation of expression of H+-ATPase
by the gill when the animals are exposed to respiratory acidosis.338 The gene for H+-ATPase has
been cloned and its expression characterized in rainbow trout gills.277 In this work, the beta subunit
is shown to be 85% identical to other vertebrate H+-ATPases, is highly expressed in ion transporting
tissues (kidney and gill) with low expression in muscle and liver. Further, gill and kidney expression
of H+-ATPase is enhanced by respiratory acidosis.277 In the operation to take up Na+, it is proposed
that the H+-ATPase generates a high apical membrane potential in the order of –100 mV that can
drive Na+ down its electrochemical gradient into the cell even from low Na+ (<1 mM) environments.
No direct transmembrane voltage measurements exist, and the channel has not been isolated, but
there is growing evidence of an Na+ channel.
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Ion Transport, Osmoregulation, and Acid–Base Balance
199
GFR ~4 ml kg−1 h−1
Glucose and other organic solutes
+
Na
Proximal tubule
Cl−
H2O
Na+
Cl−
Distal tubule
Na+
Cl−
Collecting tubule
Bladder
Na+
Cl−
UFR ~3 ml kg−1 h−1
Note to
author/PE:
Figures 6.10
through 6.12
have not
been called
out in text.
FIGURE 6.10 Overview of water and ion movement in the freshwater teleost nephron. Glomerular filtration
is an important component of urine formation in fresh-water glomerular fishes, with the ultrafiltrate being
modified by reabsorptive processes in the proximal, distal and collecting tubules, as well as in the urinary
bladder. While the proximal tubules exhibit some water re-absorption, the distal and collecting tubules are
highly water impermeable allowing for the production of very dolute urine.
5. Na Channel and Na Uptake
Evidence for the sodium uptake pathway points to an epithelial sodium channel (ENaC) in the
apical membrane. Phenamil, a potent inhibitor of epithelial Na+ channels, inhibits Na+ uptake by
rainbow trout in vivo37,124 and by isolated MR cells from rainbow trout gills.293 An ENaC-like
protein has been immunologically localized to apical surfaces of the MR cells and possibly
pavement cells in the tilapia (Oreochromis mossambicus) and rainbow trout gills.369 There is good
evidence that the environmental toxin silver and the essential micronutrient copper transits the same
pathway as does Na+.37,124 There are still some questions, however, because (1) the genetic model
teleost zebrafish (Danio rerio) is an excellent survivor in extremely low Na+ , low Ca2+ environments
and exhibits limited response to amiloride derivate,25 and (2) searches of the zebrafish genome have
failed to locate the ENaC gene. Also, attempts to clone ENaC from teleosts have not been fruitful.275
For some species, there may be alternative cation channels that could conduct Na+ (such as epithelial
Ca2+ channels) or relatively nonselective channels275 (such as those of larval amphibians153) that
may serve as substitutes for the ENaC.
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The Physiology of Fishes
Early distal tubule
Extracellular fluid
Lumen
Na+
Na+
Na+
~
K+
H+
Na+,K+, 2Cl−
Cl−
K+, Cl−
K+
FIGURE 6.11 Schematic presentation of major ion transport mechanisms in the water impermeable distal
tubule. The tubular lumen exhibits a positive potential and the active absorption of Cl– is driven by the
basolateral Na+/K+-ATPase which creates gradients favoring apical import of Na+, K+ and Cl– via NKCC.
Apical K+ channels allow for recycling of K+ across the apical membrane. Cl– exits the tubular cells across
the basolateral membrane via K+:Cl– co-transport and conductive pathways. Both apical Na+:H+ exchange and
paracellular pathways may, in some cases, contribute significantly to Na+ absorption.
UFR ~ 1 ml kg−1h−1
Dorsal
Na+
Cl−
H2O
Urea
Intermediate segment
Na+
Cl−
H2O
Urea
Mg2+
SO42−
Na+
Cl−
H2O
Urea
Distal tubule
Na+
Cl−
H2O
Urea
Intermediate segment
Na+
Cl−
H2O
Proximal tubule
Neck
GFR ~ 3.5 ml kg−1 h−1
Proximal tubule
Collecting tubule
Glucose and
other macro
molecules
Ventral
FIGURE 6.12 Schematic presentation of the marine elasmobranch nephron consisting of four loops forming
five closely adjacent tubular segments, which make up the tubular countercurrent system. Urine formation in
marine elasmobranchs is the product of high glomerular fitration rates, highly efficient urea reabsorption
mechanisms as well as Na+, Cl–, and water reabsorption. Transport processes in the early proximal tubules is
dominated by absorption of Na+,Cl–, water, glucose, and other macromolecules, while the majority of the urea
reabsorption occur in the intermediate and distal segments. As in marine teleosts, secretion of divalent ions
takes place in the proximal tubules.
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Ion Transport, Osmoregulation, and Acid–Base Balance
201
6. NKCC and Na Uptake
With regard to energy, the Na+,K+,2Cl– co-transporter (NKCC2) may perhaps be able to contribute
to Na+ uptake in some dilute media (see).190 To take up Na+ by this means requires a source of
extracellular K+ and sufficient NaCl in the boundary layer to allow Na+ uptake down its concentration gradient (NKCC2 operates neutrally, unaffected by the voltage). It is unlikely to operate for
NaCl uptake in extremely dilute solutions (<2 mM NaCl). Hiroi158 reported NKCC2 immunofluorescence in the apical region of the MR cells of tilapia gill membranes when the animals were
adapted to a high sodium fresh water; Preest et al.,290 reported bumetanide-sensitive Na and Cl
uptake across goldfish gills, suggesting that NKCC may, in some way, contribute to salt uptake in
some freshwater species.
au: change
okay?
7. Cl– Uptake: Exchanger or Co-transporter?
au: okay to
put this in
parentheses?
au to expand
While Na+ uptake can occur through cation channels in the apical membranes of freshwater fish
gills, the same cannot be true for Cl– because of the approximately 60-mV electrical potential
operating against anion uptake. Therefore, the greatest focus in chloride uptake is on neutral anion
exchangers, such as the band III protein of erythrocytes. Immunocytochemical evidence places the
anion exchanger in the apical region of the MR cells of the gill epithelium of freshwater tilapia
(Oreochromis mossambicus), and in the red blood cells in the capillaries of the same sections.
However, trout gill epithelium was negative for the anion exchanger, while the erythrocytes were
still positive,369 and so not all animals apparently use this anion exchanger. This might explain the
inconsistent results with band III protein blockers, DIDS, and 4-acetamino-4'-isothiocyantostilbene2,2'-disulphonic acid (SITS). While proton excretion by trout gills is insensitive to SITS,201 trout
in unbuffered alkaline water (0.1 mM SITS) produced increased plasma HCO3– and lowered plasma
Cl– concentrations; this indicates the role of branchial Cl–/HCO3– exchange in regaining the lost
Cl– and eliminating the HCO3– accumulated during exposure to alkaline water.246 Expression of
trout anion exchanger AE1 in cell lines operates in Cl–/HCO3– exchange but is insensitive to DIDS.65
NaHCO3 infusion (metabolic alkalosis) causes an increase in bicarbonate secretion and Cl– uptake
as well as an increase in the surface area of MR cell exposure in the gill epithelium of rainbow
trout;122,274 thus, physiologically, the exchanger exists. Addition of SITS to the water significantly
inhibits Cl– uptake by freshwater rainbow trout and results in retention of HCO3– and the development of metabolic acidosis.276 The Osorezan dace instead has an Na+/HCO3– co-transporter (sodium
bicarbonate co-transporter 1, NBC1) that is DIDS sensitive when expressed in PSA120 cells; it is
expressed specifically in the gills and upregulated by acidification of the environment.156 NBC1
co-localizes with Na+,K+-ATPase, apparently on the basolateral membrane, where its presumed
function is to accumulate HCO3– intracellularly. The fresh-water elasmobranch Potamotrygon has
saturable Cl– uptake (Km 300 to 500 mM) that is insensitive to (low concentrations of) DIDS and
SITS but is blocked by diphenylamine-2-carboxylate (DPC).379 Whereas Cl– uptake and HCO3–
secretion in most fishes are tightly linked to each other and have dual acid–base and ionoregulatory
functions, the mechanisms used are not universally an apical-membrane-located band III–type
exchanger. However, in support of anion exchange mediating Cl– uptake include observations of
reduced Cl– uptake in zebrafish and rainbow trout treated with lipophilic carbonic anhydrase
inhibitors which presumably depletes the apical anion exchange for cytosolic HCO3– substrate.25,278
Extrusion of H+ across the apical membrane via H+-ATPase appears to fuel Cl– uptake by allowing
for cytosolic accumulation of HCO3– from CO2 hydration. This occurs because inhibition of
H+-ATPase activity by bafilomycin A1 results in reduced Cl– uptake in tilapia and zebrafish, at least
at low ambient Cl– concentrations.25,90 Notably, these observations are in agreement with studies
of active Cl– uptake by amphibian skin driven by H+-ATPase activity.172,173,196
Recently, an additional link between H+ extrusion and Cl– uptake has been proposed. According
to this suggestion, proton extrusion, which acidifies the unstirred boundary layer at the gill surface,
au: please
expand
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The Physiology of Fishes
may effectively titrate HCO3– in this microenvironment.221 Such removal of external HCO3– would
aid HCO3– extrusion and would thus favor Cl– uptake via Cl–/ HCO3– exchange.
At the basolateral membrane, Cl– uptake can continue passively, if afforded anion channels in
the basolateral membrane to exit into the interstitial fluid. There are two candidate channels, the
first being the CFTR-like channel of the fish gill, which is, however, expressed in the basolateral
membranes instead of the apical membrane, as in sea water. Evidence for the CFTR channel, by
immunocytochemistry, is that it appears in the basal portions of MR cells in fresh-water Fundulus
heteroclitus.229 This distribution has not been universally observed,179 and this channel is DIDS
insensitive but blocked by DPC. The second candidate is the maxi-Cl channel observed in cultured
gill epithelia.260 This channel has single-channel conductance in excess of 370 pS and has permeability ratios (P) of Cl– to other anions of P(HCO3)/P(Cl) = 0.81, P(SO4)/P(Cl) = 0.31, and
P(isethionate)/P(Cl) = 0.53. This maxi-channel is blocked by Zn2+, SITS, DIDS, and DPC.
Finally, there are fishes that seem to lack high affinity Cl– uptake mechanisms. To date, the
killifish Fundulus heteroclitus,265,266 the American eel (Anguilla rostrata),121 the European eel
(Anguilla anguilla),126 and the bluegill (Lepomis macrochirus)353 have been shown not to have high
affinity Cl– uptake. The American eel has a different way of handling metabolic alkalosis (HCO3–
infusion) from that of trout — it manipulates Cl– efflux. In these animals, presumably Cl– would
be maintained through the diet rather than by transgill uptake.
8. Ammonia Handling
In examining ion exchanges in fresh-water aquatic animals, Krogh192 came to the conclusion that
Na+ influx balanced ammonium ion efflux, an Na+/NH4+ exchange. This idea — a combined
excretion of nitrogenous waste in exchange for a needed ion — was appealing, but subsequent
experiments found some inconsistencies. The situation is examined in detail by Wilkie366 and
Kirshner.190 Avella and Bornancin7 showed that influx of Na+ was a better match for H+ ion excretion
than it was for ammonia movement. In accord, Wilson et al.,376 found that the Na+ influx rate was
reduced by amiloride and low Na+ and the ammonia efflux rate was altered by buffering of the
boundary layer, but the corresponding changes in the flux of the other substance failed to follow
in a tight one-for-one exchange. Ammonia excretion occurs mostly by direct excretion of dissolved
NH3 passing across the gill lamellae (completely uncoupled from Na+ efflux, with a smaller portion
opportunistically occupying the Na+–H+ exchanger.366 However, important to the smooth operation
of NH3 excretion is the acidification of the boundary layer of water next the gill, where NH3 is
converted to NH4+ to maintain the gradient for NH3 diffusion. This may, in part, explain the apparent
link between Na+ and NH4+ excretion, as originally pointed out by Krogh.192 Because ammonia
protonization is pH sensitive and high pH reduces the rate at which NH3 can be protonized in the
boundary layer near the gills, alkaline waters present special problems for ammonia excretion. As
a case study in the adaptation, the Lake Magadi tilapia (Oreochromis alkalicus grahami), lives in
extreme high pH (and temperature) and survives by switching to urea excretion.368 Wilkie367 also
has reviewed urea transport and urea-facilitated diffusion mechanisms in teleosts.
9. Cultured Epithelia and Fresh-Water Opercular Membranes
au: okay or
leak pathways?
Several attempts have been made to devise a freshwater gill model that is geometrically simple,
that is, a flat membrane preparation that can be studied in detail as an isolated system. Freshwater
teleosts do not have high densities of MR cells in opercular epithelia or related skins, and these
epithelia in vitro lack active Na+ and Cl– uptake.227,237 Mounted with fresh water on the mucosal
side, opercular epithelia from fresh-water-adapted euryhaline teleosts show Cl– uptake by the
Ussing flux ratio criterion; however, because of proportionately large leaks pathways (likely the
result of shunt pathways opening during tissue dissection), the net fluxes are negative.225 Another
approach has been to culture gill epithelia from dispersed gills of fresh-water fishes. These cultured
au: please
correct
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Ion Transport, Osmoregulation, and Acid–Base Balance
203
epithelia, comprising pavement cells, have extremely low permeability but also have little, if any,
NaCl uptake.380 Lately, double seeding of MR cells into prepared pavement cell epithelia have
provided evidence for NaCl uptake. With fresh water on the mucosal side, there is a negative
transepithelial potential and detectable Na+ uptake from fresh water but, disappointingly, still net
negative ion balance overall.378,387 The in vitro membranes in asymmetrical conditions all have
negative transepithelial potentials,225,378,380,387 while the whole animals (i.e., intact fresh-water fish
gills) have a positive electrical potential, if the fresh water has sufficient Ca2+ (see Table 6.1). This
polarity difference points to possible differences in ionic conductance. Clearly, there remain some
problems in managing shunt permeability or missing factors that maintain/augment ion uptake
systems in these isolated preparations that will turn these “losers” into “gainers.”
B. INTESTINAL SALT (RE) ABSORPTION
While osmotic dehydration presents a physiological challenge to marine teleosts, freshwater species
instead experience osmotic water gain. In addition to the diffusive water gain across the gills, water
ingested with food191 must be compensated by renal elimination (see below). Secretion of ions is
associated with the production of digestive fluids in the stomach and intestine and will thus present
a potential disruption of salt balance. However, while some of the secreted ions are recovered by
salt reabsorption, ingested food may provide a substantial contribution to ion uptake.331 For example,
an ingested meal of 3% body mass containing 50 mM Na+ kg–1 (typical whole body Na+ concentration in fishes)126 represents a potential Na+ gain of 150 µmol kg–1. To put this in perspective,
assuming a urine flow rate of 3 ml kg–1 h–1 and a urinary Na+ concentration of 1 mM, renal Na+
loss in a typical fresh-water fish would be 3 µmol kg–1 h–1. Thus, a single feeding event, assuming
complete salt absorption in the intestine, would offset urine Na+ loss for a 48-hour period. In unfed
fresh-water fishes, typical branchial Na+ uptake rates131 are ~200 µmol kg–1 h–1, and so the potential
intestinal salt absorption may not appear to be quantitatively important. However, it should be noted
that especially in environments where branchial Na+ uptake may be limited, such as ion-poor waters
and acid waters, dietary salt intake may be of significance.62,382 In the fresh-water stingray (Potamotrygon sp.) the ambient Na+ concentration at which the gill Na+ uptake is sufficient to counterbalance the Na+ diffusive loss is about twice as high as Na+ concentrations in the waters of its
natural habitat.379 The obvious conclusion from these observations is that dietary Na+ (and Cl–)
uptake contributes significantly to ionoregulation in these freshwater elasmobranchs.
C. KIDNEY
AND
URINARY BLADDER
Urine flow and composition in fresh-water teleosts differs greatly from that of sea-water fishes.
Urine flow rates are highly variable among freshwater species but typically range between 2 and
10 ml kg–1 h–1.28,57,130,134,151,243 These high urine flow rates reflect the need to eliminate excess water
gained from the dilute fresh-water environment presumably via the gills, and the high urine flow
also serves to rid the animal of many metabolic waste products such as creatine and creatinine.151
Unlike terrestrial vertebrates, which excrete nitrogenous waste products renally as urea or uric acid,
nitrogenous waste is excreted by teleosts mainly across the gills, primarily as ammonia (for
mechanisms of ammonia excretion, see above).381 The dominant electrolytes in fresh-water teleost
urethral urine is Na+ and Cl– with concentrations typically being less than 5 to 10 mM151 and other
electrolytes being in the submillimolar range.
1. Tubule Anatomy
In contrast to the marine teleost kidney, the kidneys of fresh-water species have distal renal tubules
connecting the proximal segments (via a narrow, short intermediate segment) to the collecting duct
(via collecting tubules).151 With very few exceptions (aglomerular fresh-water fishes, see above)
fresh-water teleosts have glomeruli contained in renal corpsules.
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2. Glomerular Filtration
Urine formation in fresh-water teleosts consists of glomerular ultrafiltration and substantial reabsorption of especially monovalent ions across tubular epithelia. In contrast to the tubular epithelium
of marine fishes, that of fresh-water fishes exhibits much lower water permeability, with the lowest
permeability seen in the distal regions.151 However, some water is absorbed (presumably mostly in
the proximal tubules) with the reabsorption of electrolytes and organic solutes such that urine flow
rates are lower than glomerular filtration rates. Interestingly, a linear relationship exists, within
species, between glomerular filtration rate and urine flow rate, with a fixed proportion of the filtered
fluids being reabsorbed by the tubules, regardless of glomerular filtration rates and metabolic
rates.149,151,162 Urine flow rates in fresh-water teleosts are thus directly controlled by glomerular
filtration, which is in contrast to the regulated tubular water reabsorption seen in terrestrial vertebrates.28 Whole kidney glomerular filtration is the result of the regulation of filtration by individual
nephrons. Perhaps, with the exception of cyclostomes,247,292 nonmammalian vertebrates regulate
filtration by individual nephrons in an all-or-none manner, rather than by the graded regulation of
individual nephron filtration rates in mammals.28,151 This glomerular intermittency was illustrated
by Brown et al.,29 in studies on rainbow trout; they found that the percentage of all glomeruli that
were perfused and filtering was 45% in fresh water but only 5% in sea water. Perfused but
nonfiltering nephrons appear to be common in trout acclimated to both fresh water and sea water,
particularly when the hydrostatic pressure falls below the colloid osmotic pressure. Further, nonfiltering and nonperfused nephrons appear to be abundant in sea-water-acclimated trout.29 This is
not equivalent to renal failure, as would be the case in mammals, but rather reflects a water
conservation strategy.18
3. Tubular Reabsorption
While some reabsorption of electrolytes may occur in the late proximal tubules, as outlined for
marine teleosts above, the majority of the monovalent ions are reabsorbed in the water-impermeable
distal tubules of nonmammalian vertebrates.28 In addition, the urinary bladder contributes to conservation of monovalent ions, as discussed below. The mechanisms of reabsorption of monovalent
ions in the distal tubules differ from those seen in the late proximal tubules (see section on marine
teleosts) and appear to be common for vertebrates in general (with the exception of fresh-water
lampreys).28,64 In the early distal tubule, there is a lumen positive potential that is dependent on the
presence of both Na+ and Cl– in the lumen, sensitive to luminal loop diuretics, and inhibited by
serosal ouabain; together, this indicates the involvement of basolateral Na+,K+-ATPase and apical
NKCC in NaCl reabsorption.28,64,258 The apical NKCC co-transporter allows for cellular Cl– accumulation above the thermodynamic equilibrium and Cl– exit across the basolateral membrane via
K+:Cl– co-transporters or conductive Cl– channels. The Na+ and Cl– absorption via NKCC may rely
partly on cycling of K+ across the apical membrane via apical K+-channels.28,64 Apical Na+:H+
exchange occurs across the apical membrane and may contribute to Na+ absorption in amphibian,
mammalian, and possibly teleost nephrons,119,261 and paracellular Na+ transport driven by the lumen
positive potential may also contribute to Na+ reabsorption. Nothing is known about the transport
mechanism in the late distal tubules, collecting tubules, and collecting ducts of teleosts.
4. Role of the Urinary Bladder
au: please
check word,
unable to
verify
(counterion?)
The urinary bladder of fresh-water teleosts is the final “diluting segment”. The urinary bladder
is a high-resistance, tight epithelium with very low water permeability that actively absorbs NaCl
and is capable of net absorption from dilute urine down to about 2 mM NaCl. In brook trout
(Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss), Na+ and Cl– active uptake is
electrically silent and largely independent of the counterion.35,219 NaCl uptake is partially inhibited
by amiloride,219 suggesting Na+/H+ exchange, but is insensitive to thiazide and bumetanide,35,219
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inhibitors of NaCl-coupled transport. In Cl–-free media, Na+ uptake is accompanied by acidification
of the urine,219 that is blocked by 1 mM amiloride,223 indicating Na+/H+ exchange. Osmotic permeability and mannitol permeability are exceedingly low, yielding a calculated absorbate concentration of 1.56 M NaCl.220 The trout urinary bladder is urea permeable and has a urea transporter.240
In hard fresh water, the rainbow trout urinary bladder takes on a different profile and seems to be
leakier and have coupled NaCl uptake,99 more like the sea water condition. The mechanism also
involves a basolateral anion channel that is sensitive to diphenylamine-2-carboxylate.41
IV.
A. ELASMOBRANCHS
AND
MARINE OSMOCONFORMATION
AND HYPO-IONOREGULATION
COELACANTHS
Very little is known of osmoregulation in the coelacanth Latimeria chalumnae, but its blood
composition seems to be isosmotic with sea water through hypo-ionoregulation and retention of
urea,123 very similar to the blood composition of elasmobranchs. The coelacanth also has a postanal
gland, structurally and ultrastructurally similar to the rectal gland of sharks,198 that likely secretes
NaCl. For these reasons, this section on elasmobranchs covers what likely occurs also in lobefinned fishes.
B. GILL FUNCTION
1. Impermeability to Urea
The large surface area of the gill epithelium in marine elasmobranchs must have very low permeability to urea to maintain the 350 mM urea that they retain for osmoregulation, but as it turns out,
urea transport may also be needed. Pärt et al.,264 measured urea permeability of perfused gills to
be 3.2 × 10–8 cm s–1, the same as in vivo values. Because the competitive inhibitor of urea transport,
phloretin, increases urea efflux, they concluded that a urea transporter in the basolateral membrane
keeps cytosolic urea low in gill cells, thus reducing the apical urea gradient and the passive urea
loss. More recently, urea transport across the basolateral gill membrane of spiny dogfish Squalus
acanthias, in the direction from cell to extracellular fluid, has been implicated in urea retention by
the branchial epithelium.94 In addition, Fines and co-workers reported an unusual phospholipid
membrane bilayer composition, presumably with low urea permeability. In accord with this model,
Hill et al.,152 found low urea and water permeability in elasmobranch apical membrane vesicle
preparations from gill epithelium. However, because the permeability is not low enough to explain
the large concentration gradient in urea, it seems that specific and apparently active urea transport
systems, as described by Fines et al.,94 are involved.
2. Ion Transport
Unlike the marine teleost gill which excretes Na+ and Cl– and thereby forms an active component
of salt homeostasis, the marine elasmobranch gill does not appear to contribute to net NaCl
secretion.315 Rather, the rectal gland appears to be the primary NaCl homeostatic organ (see below).
Marine elasmobranchs contain branchial mitochondria-rich (MR) cells, but these cells lack the
extensive tubular system seen in teleosts.371 The marine elasmobranch MR cells appear to comprise
two distinct types, with one type containing relatively high levels of basolateral H+-ATPase and
another containing relatively high levels of basolateral Na+/K+ ATPase.281,371 Rather than being
involved in ion extrusion, these cells appear to be involved in the regulation of acid–base balance
(see Section VI below). Consistent with this, the anion exchanger pendrin is expressed in the MR
cells containing the basolateral H+ pump,283 while the Na+–H+ exchanger expressed in the gill cells
of elasmobranchs79 is hypothesized to be co-localized with Na+/K+-ATPase.283 While these apical
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The Physiology of Fishes
exchange processes are most likely involved in the regulation of acid–base balance by being able
to extrude HCO3– and H+, they provide uptake of Cl– and Na+ rather than excretion and thus do
not contribute to salt balance in marine elasmobranchs. That these systems are not involved primarily
in salt homeostasis is illustrated by decreased abundance of H+-ATPase and Na+/K+-ATPase in
euryhaline elasmobranchs following sea water acclimation280,281 and the failure of the gills to
upregulate MR cells after rectal gland extirpation.371
C. RECTAL GLAND
Burger and Hess34 were the first to demonstrate the function of the rectal gland in salt homeostasis
in marine elasmobranchs. Since then, this organ has become an extensively used model for studies
of epithelial Cl– secretion, not only in elasmobranchs but also in vertebrates in general. In their
early studies, Burger and Hess demonstrated that the rectal gland secretes a fluid iso-osmotic to
the extracellular fluid with Na+ and Cl– being by far the principal solutes. The concentrations of
Na+ and Cl– in rectal fluid secretions are approximately twice those found in the extracellular fluids,
and the gland secretions therefore amount to substantial Na+ and Cl– elimination. Although the
spiny dogfish is able to compensate for rectal gland removal371 by increasing urinary salt excretion,
with diuresis as a consequence, the lack of a rectal gland impairs the ability to effectively clear
injected NaCl loads from the plasma.32 Similar findings have since been reported for other marine
elasmobranchs, illustrating the importance of the rectal gland for NaCl homeostasis.39,145
1. Ion Secretion
Mechanisms of NaCl secretion by the rectal gland is, in principle, similar to those seen in the
marine teleost fish gill (see Figure 6.4) and the secretory segments of renal tubules (see Figure 6.8).
The activity of the basolateral Na+,K+-ATPase maintains Na+ well below equilibrium within the
cell; this allows for entry of not only Na+ but also Cl– and K+ via the secretory isoform of NKCC
which is as well located in the basolateral membrane.95,141 K+ recycles across the basolateral
membrane via K+ channels,317 while Cl– exits the cell across the apical membrane via CFTR-type
channels down the electrochemical Cl– gradient.232 Na+ is extruded across the basolateral membrane
by Na+,K+-ATPase, follows its electrochemical gradient, and is secreted via paracellular pathway
to accompany the secondary active transcellular Cl– secretion.
2. Regulation of Secretion
Regulation of rectal gland secretion appears to be complex, involving several types of neural and
hormonal receptors and second messengers. Chiasson43 made the interesting initial observation that
stingray spinal cord destruction impaired salt balance, and he concluded that the control mechanism
for elasmobranch ion regulation resided in the posterior of the animal, long before the association
of the rectal gland with ion balance.144 Excellent recent publications summarize the current knowledge about regulation of rectal gland secretion.85,146,316,318 Hypervolemia stimulates secretion of
cardiac natriuretic peptide (CNP)309,334 that, in turn, stimulates rectal gland secretion.333 Approximately half the NaCl secretion resulting from CNP release is an indirect response caused by local
release of vasoactive intestinal peptide (VIP) from rectal gland nerves.319 This VIP release initiates
a cAMP-mediated Cl– secretion, at least in some species.146 In addition, CNP directly stimulates
secretion by the rectal gland because isolated tubules and cultured cells without neural components
respond by increasing Cl– secretion. The direct action of CNP is not via cAMP pathways but rather
via guanylate cyclase and protein kinase to stimulate NaCl secretion.136,318
In addition to direct regulation of transport activity, rectal gland secretion rates appear to be
correlated with the gland blood perfusion rate.315 It appears that the vasculature within the gland is
partly constricted under normal physiological conditions caused by circulating levels of
catecholamines314 and that stimulation of the gland must be associated with local vasodilation. As such,
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adenosine and VIP abolish norepinephrine-mediated vasoconstriction in spiny dogfish, perhaps indicating that some of the stimulatory effects of of these secretagogues may be related to increased blood
perfusion and not caused by direct effects on tubular cells.314
More recently, stimulation of an extracellular Ca2+-sensing receptor (CaR) has been demonstrated to cause rectal gland artery constriction. This type of receptor is inhibited by increased ionic
strength, which suggests that CaR may cause vasodilation and thus increased gland secretion when
extracellular fluid NaCl concentrations are elevated.88,89 Finally, the rectal gland itself contains a
peripheral smooth muscle ring that may be involved in the regulation of secretory function by
changing whole gland dimensions.85
C. KIDNEY
With extracellular fluids of slightly higher osmolality than the surrounding sea water, marine
elasmobranchs gain “free” water osmotically. Drinking rates in marine stenohaline elasmobranchs
are thus very low (but measurable)66 compared with those in marine teleosts, but glomerular filtration
rates are of the same magnitude as in fresh-water teleosts. In agreement with these observations,
urine flow rates tend to be lower than in fresh-water teleosts.151 The marine elasmobranch urine is
generally hypo-osmotic by 50 to 250 mOsm compared with the extracellular fluids,33,327 with Na+
and Cl– being the dominant electrolytes at concentrations similar to those of the blood plasma.
1. Tubule Anatomy
au: should
this be corpuscle?
The marine elasmobranch nephron is very long and has large glomeruli. The nephrons consist
of a long neck segment connecting the corpsule to the proximal segments, followed by an
intermediate segment leading to the distal segments and the collecting tubules and ducts. The
proximal, the intermediate, and the distal tubules all contain numerous specialized segments,
presumably with unique transport properties, which, by and large, remain to be fully characterized
(see Lacy & Reale193 for a detailed review of functional elasmobranch nephron morphology).
The marine elasmobranch nephron displays a complicated three-dimentional structure with a
total of four loops arranged such that tubular fluids travel in opposite directions in five closely
adjacent tubular segments from the same nephron. This arrangement forms the renal countercurrent system,27,195 which likely serves to enhance retention of urea and trimethylamine oxide
(TMAO) (see below).
2. Glomerular Filtration
Whole animal glomerular filtration rates average 4 ml kg–1 h–1 in marine elasmobranchs151 and
appear to be regulated by the number of filtering individual nephrons (glomerular intermittency)181,311,332 as is the case for euryhaline teleosts.29
3. Tubular Reabsorption
The fraction of filtered fluid being reabsorbed varies greatly with average reabsorption being in the
order of 60 to 85%151,181,307 and is closely associated with the reabsorption of urea and TMAO, the
most abundant solutes in the absorbed fluid. Although secretion can occur in the proximal tubules
of elasmobranchs,20 filtration and tubular reabsorption are the important renal functions for marine
elasmobranch osmoregulation.18,20 The proposed mechanisms of salt and fluid secretion in the
proximal tubules appear to be similar in elasmobranchs and teleosts and are summarized in
Figure 6.8A. Consistent with fluid reabsorption, 60 to 70 % of the filtered Na+ and Cl– are reabsorbed
by active Na+ and passive Cl– transport, as outlined in Figure 6.8B.
The most efficient reabsorption in the marine elasmobranch nephron is that of urea and TMAO,
with more than 90% of the filtered load being reabsorbed.97 The majority of this reabsorption could
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The Physiology of Fishes
perhaps be accounted for by simple solvent drag because ~70% of the filtered fluids are being
reabsorbed. However, because urine urea concentrations are much lower than plasma urea concentrations, excess urea (and TMAO) transport must occur. The tubular reabsorption of urea has
received much attention for nearly a century, but the mechanisms involved are far from being
resolved. It is clear that the majority of the urea reabsorption takes place between the end of the
proximal tubule and the beginning of the collecting ducts306 or even within the collecting ducts.336
Furthermore, urea reabsorption has long been recognized to be linked to Na+ reabsorption in a fixed
ratio over a wide range of urine flow rates.308 The complex countercurrent arrangement of the
nephron has led to suggestions of passive rather than directly active movement of urea along
favorable concentration gradients created by the absorption of Na+, Cl–, and water.27 According to
this suggestion, the absorption of water results in low urea concentrations in the environment
surrounding the distal segments of the nephron, thus providing a gradient for urea diffusion. Along
similar lines of thinking, selective permeability for water and urea, together with the countercurrent
arrangement of the nephron, could concentrate urea within the tubules to encourage passive diffusion
out of the terminal nephron segments.100 Interestingly, both these proposed mechanisms for passive
urea reabsorption would rely on Na+, Cl–, and water absorption and thus are in accord with the
original observations of correlated Na+ and urea reabsorption.
Carrier-mediated urea transport in elasmobranch kidneys has long been assumed143,181,195,307,308,327
but is now conclusively demonstrated. A facilitated urea transporter (shark urea transporter,
ShUT) cloned from the spiny dogfish shark exhibits high expression in the kidney and in
phloretin-sensitive urea transport when expressed in oocytes.325 Even more recently, two
separate apical urea transport pathways have been characterized from elasmobranch kidneys.
A phloretin-sensitive, nonsaturatable uniporter is found primarily in the dorsal section, whereas
a saturatable, phloretin-sensitive Na+-urea co-transporter is dominant in the ventral section.250
While ShUT is a diffusion carrier that may facilitate urea diffusion along local gradients, as
discussed above, the Na+-urea co-transporter may perform secondary active urea transport
driven by Na+,K+-ATPase activity in the basolateral membrane. Since the discovery of the
ShUT, facilitative urea carriers have also been identified from the dogfish168 and the Atlantic
stingray.169 Findings of UT expression exclusively in the final segments of the nephron168 agree
with the proposed role of this region in urea reabsorption. Although the recent identification
of at least two urea carrier systems have added to our understanding of renal urea handling in
elasmobranchs, this area and the that of tubular TMAO handling remain challenging topics
for further research.
Finally, like marine teleost urine, marine elasmobranch urine also contains high concentrations
of divalent ions, especially Mg2+ and SO42–,151,336,377 which, considering plasma concentrations of
these ions and even the high glomerular filtration rates, must be secreted by the proximal tubule
as in teleosts (see above).151,336
V.
FRESHWATER AND EURYHALINE ELASMOBRANCH
HYPEROSMOREGULATION
Of an estimated 1,100 species of cartilaginous fishes, approximately 43 species in four families
tolerate fresh water for extended periods of time.54 Several elasmobranches are truly euryhaline,
such as the bull shark Carcharhinus leucas and the Atlantic stingray Dasyatis sabina, but only very
few are stenohaline fresh-water residents, such as the members of the Potamotrygonidae family,
the stingrays of Rio Negro and tributaries. Early work by Chiasson43 found that skates in dilute
media maintain blood osmolality higher than the environment. Smith327 found that freshwater
elasmobranchs slowly lose urea by diffusion across the gills and that the kidney actively conserves
urea (see section on kidney below). The degree of euryhalinity in representatives of the group has
been reviewed and assessed by Hazon et al.,146 and they concluded that even marine elasmobranchs
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have the ability to independently regulate Na, Cl, and urea in brackish water. In all cases, adaptation
to dilute environments results in the animals losing urea and yet maintaining blood osmolality
much higher than the environment. Freshwater elasmobranchs, such as the Atlantic stingray67 and
Amazonian stingray Potamotrygon,379 do not retain urea in their tissues, nor are they ureotelic;
instead, they have low urea levels more typical of freshwater teleosts and are ammoniotelic. The
Atlantic stingray (Dasyatis sabina) has a landlocked fresh water population that is physiologically
euryhaline; if challenged by transfer to sea water, it increases NaCl and urea concentrations in
plasma and osmolality to almost seawater levels.282 Increased salinity also induces a transient
drinking response in euryhaline elasmobranchs following the increase in ambient salinity, which
does not occur in their marine equivalentso.3
A. ION ABSORPTION
au: please
provide symbol
AT
THE GILL
Piermarini and Evans282 put forward a novel model for ion uptake by the freshwater Atlantic stingray
Dasyatis sabina, in which V-type H+ ATPase is localized to the basolateral membrane of one subtype
of MR cells, while Na+,K+-ATPase is more prevalent in another subtype. This points to division of
transport of Na+ and of Cl– by different cell types. For Na+, the driving force from the vacuolar
type H+-ATPase (V-ATPase) is on the basolateral membrane, which explains the relatively high Km
of Na+ uptake. In Potamotrygon, NaCl uptake is saturable and has a relatively high Km of 300 to
500mM and Na+ uptake was inhibited by amiloride and its analogs. However, Cl– fluxes were
insensitive to DIDS and SITS but were strongly inhibited by the anion channel blocker DPC,379
consistent with the Piermarini model.
B. RECTAL GLAND
Rectal gland secretion is predicted to be of little importance in elasmobranchs residing in lowsalinity environments, since compensation for diffusive salt loading is not required. Therefore, it
is not surprising that freshwater acclimated euryhaline elasmobranchs have smaller rectal glands
than do marine elasmobranchs112,262,282,284 and that these glands have fewer glandular tubules. In
the only true fresh-water elasmobranchs (Potamotrygonidae), the rectal gland is reduced in size
and severely atrophied.111
C. KIDNEY
Although the rectal gland of marine elasmobranchs is obviously involved in regulating extracellular
Na+ and Cl– levels (see above), it is clear that the kidney plays an important role in the regulation
of Na+, Cl–, urea, and water in euryhaline species exposed to reduced salinity. Renal tubule
morphology of euryhaline elasmobranchs does not differ from that of marine elasmobranchs
(described briefly above), but the stenohaline fresh-water stingray (Potamotrygonidae) exhibits a
different tubular anatomy.193 Unlike the four loops found in marine and euryhaline renal tubules,
freshwater stingrays have only two loops and lack the tubular bundles (i.e., the countercurrent
system).194
Euryhaline elasmobranchs respond to reduced salinity by increasing glomerular filtration and
urine flow rate, while reducing retention of major plasma electrolytes, urea, and presumably
TMAO.44,117,118,171,268,327,377 Although marine elasmobranchs adjust extracellular fluid osmolality to
be lower when they are held in low-salinity environments, these fishes still maintain high levels of
urea, Na+ and Cl–. The changes in osmolyte concentrations are not proportional to the change in
external salinity; this results in an increased osmotic gradient282,284 that favors increased osmotic
water gain, which, in turn, explains the need for increased urine flow rate. Even though Na+ and
Cl– concentrations in the urine of euryhaline elasmobranchs are greatly reduced in response to
reduced ambient salinity, a substantial renal loss of these electrolytes still occurs because of the
high urine flow rates. Presumably, the ion loss must be compensated for by the gills. The increase
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The Physiology of Fishes
in urea excretion appears to exceed the excretion of electrolytes and becomes the dominant urinary
solute.170,268,327,377 Interestingly, as pointed out by Janech et al.,170 overall renal urea reabsorption is
increased during exposure to dilute environments, even though the fractional tubular retention is
reduced. This phenomenon relates to the increased glomerular filtration rates and clearly demonstrates the importance of the kidney in osmoregulation in euryhaline elasmobranchs at lower
salinities.
In the only truly fresh-water elasmobranchs (Potamotrygonidae), however, ureotely has apparently been lost, and plasma levels of urea and electrolytes are similar to those of fresh-water
teleosts.24 In these animals, even elevated salinity fails to markedly increase urea levels.111,348,349,350
Thus, renal handling of urea is of little importance to osmoregulation in these fresh-water elasmobranchs because nitrogenous waste is excreted as ammonia rather than urea.379 Renal function in
this unique group of elasmobranchs offers an exciting area for investigation.
VI.
ACID–BASE BALANCE
This brief section only supplements the excellent reviews of the topic by Claiborne et al., 45,47 Perry
et al., 275,276 and Heisler 147,148 and a biographical treatment of the remarkable work of T. Maren.340
We also include some recently revealed adaptations of fishes to extreme environments.
A. WHERE FISH
ARE
DIFFERENT
The gills of fishes are ventilated by huge volumes of water with relatively low oxygen content so
that the animals can maintain sufficient oxygen uptake for normal activity. Dissolved CO2 is freely
permeable across biological membranes and has high solubility in aqueous liquids. The result is
that metabolic CO2 is cleared from the blood very efficiently, and the blood PCO2 is very low,
compared with that of animals with lungs. In turn, the low PCO2 results in high blood pH levels
of 7.7 to 7.9 and low HCO3– concentrations ~2 to 7 mM.45,47,147,148 A consequence of low blood
PCO2 is that fishes have little scope or need for reduction in PCO2 by hyperventilation in compensating for acid–base perturbations.
Another large difference in acid–base reality for fishes is that normal behavioral activity is very
likely to produce massive metabolic acidosis from the operation of large white muscle mass.
Whereas cruising muscles are typically oxidative and “red,” burst swimming that is typical during
pursuit of prey or escape from predators uses the much larger mass of “white” glycolytic muscle.
This is a practical issue in the treatment of fishes in catch-and-release sports fisheries. Even short
duration (30 s) aerial exposure at critical times after extreme exercise of rainbow trout results in
80% mortality in the released fish91; and for small- and largemouth bass, there are species differences
in hypoxia tolerance and acidosis.107
Aquatic species also have no choice but to be exposed to changes in environmental pH and
thus are stressed in highly acidic or basic lakes. Sea water, on the other hand, is well buffered,
and its pH varies very little. Fresh water chemistry in this area is multifaceted because of variable
amounts of organic acids, ammonia, carbonate, phosphate, and bicarbonate, all contributors to
the buffer capacity of the water. Furthermore, as one of many water chemistry variables that can
affect heavy metal availability,364 slight reductions in water pH changes the speciation of heavy
metals in the water and can increase the effective toxicity of the metal180 (important for the
fishes) and the rate of metal accumulation by the fishes (important for the people who eat those
fishes).138,364
Given these possible perturbations of acid–base status, fishes (elasmobranchs and teleosts)
regulate blood pH to within 0.15 pH units across species,147 and all respond similarly to temperature
change, with plasma pH falling as temperature rises. Typical plasma pH is 7.95 at 10°C, decreasing
to 7.80 at 20°C and 7.70 at 30°C.148
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B. GENERAL MODEL
au: please
expand
In general, metabolic CO2, buffered by intracellular proteins, passes, by diffusion, to extracellular
fluid. CO2 is then carried in the blood mostly as HCO3– in the plasma compartment because red
cells contain carbonic anhydrase and band III anion exchanger that allows HCO3– out of the cells
into the plasma.45,47 The vast majority of CO2 released, primarily across the gill epithelium, is as
dissolved CO2. In small fishes and larvae, there is larger contribution by skin and yolk sac
epithelia.147 The balance of CO2 may be secreted as HCO3– in effective secretion of alkaline
equivalents; this is envisioned to occur at the PNA+ cells (see Figure 6.9). In acidic environments
and with metabolic acidosis from strenuous exercise, there is acid secretion, powered in trout by
the H+-ATPase201 or in some other species by more indirectly using Na+-H+ exchange.47 From this
brief overview, we will proceed to deal with the major components, starting with carbonic
anhydrase.
Carbonic anhydrase (CA) catalyzes the bicarbonate buffer system that has a lower buffer
capacity than in lunged animals but still is the predominant buffer system. Teleost CA, cloned from
trout, gar, and zebrafish, is similar to human CAI, CAII, and CAVII isoforms and is primarily
cytosolic in its distribution in red blood cells and gill epithelial cells.80 In Antarctic fishes with red
blood cells and in those lacking hemoglobin, 97% of blood CA is localized to the cytosol of blood
cells, while the remaining 3% is membrane associated, anchored by phosphatidylinositol–glycan
linkage.355 In the Pacific spiny dogfish (Squalas acanthias), unlike in a representative teleost
(rainbow trout), there is evidence from membrane-impermeant CA inhibitors suggesting that extracellular branchial CA exists and is sufficient to contribute to CO2 excretion115 and to compensate
for severe anemia.114 Extracellular CA has been shown to extend to ratfish (i.e., all condrichthians)
and is membrane bound.116 Thus, these buffer reactions are well catalyzed and should be in
equilibrium both in the red blood cells and in the gill epithelium. In the mudskipper, CA is localized
to the apical portions of MR cells along with the Na+–H+ exchanger.370 Thus, transport of CO2 and
bicarbonate should be very sensitive to local pH. There is good evidence for the acidification of
the boundary water next to the gill lamellae,367,370 which at once contributes to acid secretion and
enhances ammonia excretion.
Whether CA is membrane bound is an important issue. Mammalian carbonic anhydrase II is
ionically linked to the cytosolic side of the anion exchanger AE1 via a negatively charged tetrad
of amino acids with a lead leucine (LDADD) near the carboxy terminus of AE1360 and via a binding
site on extracellular loop 4 of AE1 to a second CA (IV) on the extracellular side,335 thus forming
an efficient Cl–/HCO3– transport “metabolon.” BLAST searches reveal that the mammalian LDADD
sequence is exactly the same in fugu and zebrafish genomic AE1, while the corresponding elasmobranch sequence has one amino acid substitution with the same charge (LDGDE). For rainbow
trout, the sequence is LDASD (less negatively charged but still capable of binding carbonic
anhydrase.360 The complementary binding site on mammalian CAII has four basic amino acids in
the first 17 residues of the amino terminus that bind to AE1.359 Elsamobranchs are the fish group
that has membrane bound CAII 341 and presumably this group has the CAII/AE1/CAIV metabolon
intact. In the elasmobranchs, there are basic residues near the amino terminus of CAII (... RQ ...
NQ..., tiger shark, Galeocerdo cuvier), even though in a sequence unrelated to the mammal. This
is not so in the case of teleosts, where the CAII amino terminus lacks the requisite basic residues.
Thus, the inability of CAII to bind to membrane resident AE1 in teleosts apparently resides in
fewer basic and more acidic amino acids in the first 17 residues at the amino terminus of CAII
(true for zebrafish, flounder, rainbow trout and fugu CAII). This explains how most CAII in teleosts
is instead cytosolic and coupling of anion exchange with CO2 hydration is less efficient.
The H+-ATPase, as discussed in the section on hyperosmoregulation, is present and creates a
pH gradient, along with a voltage gradient across the apical membrane of at least some MR cells
in the gill epithelium of some fresh-water teleosts. For these animals, acid secretion is straightforward. However, in fresh-water elasmobranchs and fresh-water killifish, the H+-ATPase is instead
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located on the basolateral membrane.178,281 Furthermore, the acid-tolerant Osorezan dace (see acid
lakes, below) secretes acid equivalents very effectively, apparently without involving H+-ATPase
but rather by a combination of apical Na+–H+ exchange and basolateral Na+-HCO3– co-transport
linked to the Na+,K+-ATPase pump.156 Clearly, there is a diversity of mechanisms for acid–base
balance in fishes.
The Na+–H+ exchanger was cloned from fresh-water rainbow trout (Oncorhynchus mykiss) red
blood cells, euryhaline killifish (Fundulus heteroclitus), marine sculpin (Myoxocephalus octodecimspinosus), and the gills of the dogfish shark.26,46,251 Whereas the rainbow trout uses H+-ATPase
to drive acid secretion and Na+ uptake, the Osorezan dace156 and the brackish and marine fishes
apparently use the Na+–H+ exchanger for acid secretion. For brackish and marine forms, where
environmental Na+ is above cytosolic Na+, the Na+–H+ exchanger would not have to be linked to
an active pump46. Cl––HCO3– exchanger is present in the plasma membrane of red cells but also
apparently in the gill epithelium of some species. Its location and operation are dealt with in the
section on Cl– uptake (above).
C. EXTREME ENVIRONMENTS
1. Alkaline Lakes
As we have seen with ammonia handling by the Lake Magadi tilapia (they have become ureotelic),
acid–base balance by these animals is highly specialized for life in an alkaline environment.291,368
The Lake Magadi tilapia, living in 32°C water at pH 9.9, has blood pHe, pHi, and [HCO3–] of
approximately 8.1, 7.6, and 15 mM, respectively — slightly alkalotic when compared with rainbow
trout. The Lake Magadi tilapia becomes severely acidotic in neutral pH water, evidence of its
apparent obligatory secretion of alkaline equivalents. This fish drinks large volumes of the alkaline
medium and, by anatomical side pocketing of the stomach, protects the stomach contents from
alkalinization. More than 80% of the imbibed water and NaCl goes on to be absorbed,14 which is
necessary apparently because the animal is rather leaky to NaCl. How these fishes secrete base is
still unknown. Teleosts in alkaline saline lakes, such as the scale-less carp (Gymnocypris przewaslskii), instead of resorting to ureotelism, seems to be ammonia tolerant.363
2. Acid Lakes
Many teleosts cannot tolerate low pH (<5.0) and die because of decreased plasma ions and
osmoregulatory failure.180,239 The cause of this is an increase in paracellular diffusive leak
pathways218 that apparently open as a result of titration of Ca2+ out of intercellular tight junctions
in the gill epithelium. Those few animals that survive at low pH must have more acid-stable
intercellular tight junctions first, as well as other adaptations.
Some teleost species survive in extremely acidic conditions, such as the dace (Tribolodon
hakonensis) that normally inhabits Lake Osorean at pH of 3.5 but returns to neutral pH streams to
spawn.156 The MR cells of the gills concentrate CA (isoform II), Na+–H+ exchanger type 3, Na+,K+ATPase, Na–HCO3– co-transporter, and aquaporin III, all upregulated by the adaptation of the dace
to acid waters. In the Osorezan dace, H+-ATPase is expressed at a low level and is not upregulated
by acid exposure. While the electrogenic Na+–2HCO3– co-transporter and Na+,K+-ATPase are
basolateral in location, and CA is cytosolic, the Na+–H+ exchanger is apparently in the apical
membrane. In the gill, there are multicellular follicles with two distinct cell types, one expressing
NBC and the other not, suggesting a balanced cooperation in NaCl uptake and acid secretion in a
controlled microenvironment of the follicle lumen.156 If the apical N+–H+ exchanger were to be
exposed to the low pH bulk solution, it would almost certainly operate in reverse, gaining acid and
losing Na+ to the detriment of the animal. The composition of the crypt fluid and placement of
Cl––HCO3– exchangers and H+-ATPase are essential to understanding how this complex system
works.
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213
3. Estivation Pouches and Burrows
au: is this a
reference?
Estivation in lungfish invoves the animals remaining completely inactive in a dried mucus coccoon
for more than 40 days. Lungfish do this in air, and so oxygen supply is plentiful, but oxygen uptake
continues at a vastly diminished rate. These animals avoid acid–base imbalance by shifting from
ammonia to urea as the nitrogenous waste product, and blood ammonia levels actually fall during
estivation.42
Tropical burrowing fishes, such as the Gobiid mudskipper Periopthalmodon schlosseri, have
hypoxic, hypercapneic water in the burrow that is partly filled with air pockets supplied by the
animal gulping air from the surface and transporting it to the brood chamber. They maintain oxygen
uptake mostly by buccopharyngeal ventilation, a process stimulated by hypercapnia1; the acid–base
consequences are unknown. Gulf toadfish, which are intertidal burrowers, exhibit pulsatile urea
excretion by activation of recently cloned and sequenced gill urea transporter(Walsh, P.J., 2000
2399 /id).
VII.
CONCLUSION
In the multivariate field of ion transport and acid–base balance, there are still some complexities
to be resolved.
A. INTERTWINING
OF
ACID–BASE
AND ION
REGULATION
There is a tendency for researchers to measure either acid–base variables or ion transport aspects,
but rarely the entire suite of variables in one study. In spite of the difficulty, it may be beneficial
to repeat classic experiments and monitor transport and acid–base variables together. In this way,
the integrated response by the animal may be revealed.
B. EURYHALINITY, COMPLEXITIES
OF
REGULATION
The way in which fishes adapt to salinity change is multifaceted and develops in stages. Some
immediate responses involve changes in cell exposure and phosphorylation states of existing
transporters. Later developments revolve around de novo sysnthesis of new transporters and their
regulatory proteins. In the final stages, new ion transporting cells replace the reorganized cells.
Meanwhile, real euryhaline fishes make sojourns, often of short duration, into different salinities
thus “coping” and avoiding metabolically expensive larger adaptations.222
C. METAMORPHOSIS
FOR
MIGRATION, COMPLEXITIES
OF
HETEROCHRONY
Preparation for upstream or downstream migration involves, for salmon, eel, shad, and gaspereau,
a whole suite of different characters and a complex of hormones in tight chronological order.235,236
There are frequent failures (stunted and “desmolt” salmon) that, having missed the critical time or
stage, will render the fishes unable to migrate or even survive. It will be exciting to uncover the
suite of genes involved and their regulators and to compare the well-studied commercial species
and other anadromous and catadromous fish.
D. FRESHWATER TRANSPORT DIVERSITY, MULTIPLE EVOLUTIONARY EVENTS
The apparent diversity of fresh-water ionoregulatory mechanisms arises from the diversity of freshwater species and the fact that fresh water geologically is a “temporary” environment, which is
ultimately destroyed by inundation or desiccation. Each time a new body of fresh water is formed,
there is the opportunity for yet another genetic adaptation to the fresh water habitat. For instance,
three spine stickleback (Gasterosteus aculeatus) have a suite of characters, including reduced body
au: is this
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armor and reduced pelvic girdle, that allows them to evolve to a fresh-water form; they do so within
a few generations13 and have done so repeatedly in geological history of fresh-water lakes in North
America.56 In addition, the presence of relatively small amounts of NaCl and CaCl2 in some bodies
of fresh water can allow an entirely different suite of transporters, more typical of brackish water,
to operate to the benefit of the animal, adding to the diversity of mechanisms operating. For these
reasons, and from emerging differences already observed, it is clear that one model involving a
single set of transporters cannot explain ionoregulation in all fresh-water fishes. Instead, we should
organize the diversity we see.
E. FEEDING
AND
OSMOREGULATION
The impact of feeding on osmoregulation is a topic that has been almost universally avoided by
physiologists, who routinely deny food to experimental animals or who use in vitro models. Some
fishes, notably sharks, are intermittent feeders, and thus, feeding is among the largest of impacts
on their physiology. Because the free-living animal has recourse to diet and diet changes when
migrating or facing salinity challenge, it will be necessary to include these variables in the study
to understand the whole phenomenon.
ACKNOWLEDGMENTS
Supported by NSERC discovery grant to W.S.M. and by NSF-IBN 0416440 to M.G. Thanks to
R.S. Nishioka for TEMs in Figure 6.2.
REFERENCES
1. Aguilar, N. M., Ishimatsu, A., Ogawa, K. and Huat, K. K.: Aerial ventilatory responses of the
mudskipper, Periophthalmodon schlosseri, to altered aerial and aquatic respiratory gas concentrations., Comp.Biochem.Physiol., 127A, 285–292, 2000.
2. Alves, P., Soveral, G., Macey, R. I., and Moura, T. F.: Kinetics of water transport in eel intestinal
vesicles., J.Membr.Biol., 171, 177–182, 1999.
3. Anderson, W. G., Takei, Y., and Hazon, N.: Osmotic and volaemic effects on drinking rate in
elasmobranch fish., J.Exp.Biol., 205, 1115–1122, 2002.
4. Ando, M., Mukuda, T., and Kozaka, T.: Water metabolism in the eel acclimated to seawater: from
mouth to intestine., Comp.Biochem.Physiol.B, 136, 621–633, 2003.
5. Ando, M. and Nagashima, K.: Intestinal Na+ and Cl– levels control drinking behavior in the seawateradapted eel Anguilla japonica, J.Exp.Biol., 199, 711–716, 1996.
6. Ando, M. and Subramanyam, M. V. V.: Bicarbonate transport systems in the intestine of the seawater
eel., J.Exp.Biol, 150, 381–394, 1990.
7. Avella, M. and Bornancin, M.: A new analysis of ammonia and sodium transport through the gills of
the freshwater rainbow trout (Salmo gairdneri)., J.Exp.Biol., 142, 155–175, 1989.
8. Avella, M., Part, P. and Ehrenfeld, J.: Regulation of Cl– secretion in seawater fish (Dicentrarchus
labrax) gill respiratory cells in primary culture., J.Physiol.Lond., 15, 353–363, 1999.
9. Balment, R. J., Warne, J. M. and Takei, Y.: Isolation, synthesis, and biological activity of flounder
[Asn(1), Ile(5), Thr(9)] angiotensin I., Gen.Comp.Endocrin., 130, 92–98, 2003.
10. Baustian, M. D. and Beyenbach, K. W.: Natriuretic peptides and the acclimation of aglomerular
toadfish to hypo-osmotic media., J.Comp.Physiol. B., 169, 507–514, 1999.
11. Baustian, M. D., Wang, S. Q., and Beyenbach, K. W.: Adaptive responses of aglomerular toadfish to
dilute sea water., J.Comp.Phys. B. 167, 61–70, 1997.
12. Beasley, D., Shier, D. N., Malvin, R. L., and Smith, G.: Angiotensin-stimulated drinking in marine
fish., Amer.J.Physiol., 250, 1034–1038, 1986.
2022_C006.fm Page 215 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
215
13. Bell, M. A., Aguirre, W. E. and Buck, N. J.: Twelve years of contemporary armor evolution in a
threespine stickleback population., Evolution, 58, 814–824, 2004.
14. Bergman, A. N., Laurent, P., Otiang’a-Owiti, G., Bergman, H. L., Walsh, P. J., Wilson, P. and Wood,
C. M.: Physiological adaptations of the gut in the Lake Magadi tilapia, Alcolapia grahami, an alkalineand saline-adapted teleost fish., Comp.Biochem.Physiol., 136A, 701–715, 2003.
15. Bern, H. A., Pearson, D., Larson, B. A. and Nishioka RS: Neurohormones from fish tails: the caudal
neurosecretory system. I. “Urophysiology” and the caudal neurosecretory system of fishes.,
Recent.Prog.Horm.Res., 41, 533–552, 1985.
16. Beyenbach, K. W.: Secretory NaCl and volume flow in renal tubules., Amer.J.Physiol., 250,
R753–R763, 1986.
17. Beyenbach, K. W.: Secretory electrolyte transport in renal proximal tubules of fish., Cellular and
Molecular Approaches to Fish Ionic Regulation, Fish Physiology, C.M.Wood and T.J.Shuttleworth,
(Eds.), San Diego, California: Academic Press, 85–105, 1995.
18. Beyenbach, K. W.: Kidneys sans glomeruli., Amer.J.Physiol., 286, F811–F827, 2004.
19. Beyenbach, K. W. and Baustian, M. D.: Comparative physiology of the proximal tubule., Comparative
Physiology, Structure and Function of the Kidney, Kinne RKH, Kinne-Saffran, E., Beyenbach, K.W.
(Eds), Basel: Krager., 104–142, 1989.
20. Beyenbach, K. W. and Fromter, E.: Electrophysiological evidence for Cl secretion in shark renal
proximal tubules., Amer.J.Physiol., 248, F282–F295, 1985.
21. Beyenbach, K. W. and Kirschner, L. B.: Kidney and urinary bladder functions of the rainbow trout
in Mg and Na excretion., Amer.J.Physiol., 229, 389–393, 1975.
22. Beyenbach, K. W. and Liu, P. L. F.: Mechanism of fluid secretion common to aglomerular and
glomerular kidneys., Kidney Int., 49, 1543–1548, 1996.
23. Beyenbach, K. W., Petzel, D. H., and Cliff, W. H.: Renal proximal tubule of flounder .1. Physiological
properties., Amer.J.Physiol., 250, R608–R615, 1986.
24. Bittner, A. and Lang, S.: Some aspects of the osmoregulation of amazonian freshwater stingrays
(Potamotrygon hystrix). I. Serum osmolality, sodium and chloride content, water content, hematocrite,
and urea level., Comp.Biochem.Physiol., 67A, 9–13, 1980.
25. Boisen AMZ, Amstrup J, Novak I, and Grosell M: Sodium and chloride transport in soft water and
hard water acclimated zebrafish (Danio rerio)., Biochim.Biophys.Acta., 1618, 207–218, 2003.
26. Borgese, F., Sardet, C., Cappadoro, M., Pouyssegur, J. and Motais, R.: Cloning and expression of a
cAMP-activated Na+/H+ exchanger: evidence that the cytoplasmic domain mediates hormonal regulation., Proc Natl Acad Sci U S A., 89, 6765–6769, 1992.
27. Boylan, J. W.: A model for passive urea reabsorption in the elasmobranch kidney., Comp.Biochem.Physiol., A 42, 27-30, 1972.
28. Braun, E. J. and Dantzler, W. H.: Vertebrate renal system., Handbook of Physiology — Comparative
Physiology, 1, 481–576, 1997.
29. Brown, J. A., Oliver J. A., Henderson, I. W., and Jackson, B. A.: Angiotensin and single nephron
glomerular function in the trout Salmo gairdneri., Amer.J.Physiol., 239, R509–R514, 1980.
30. Buddington, R. K., Kroghdal, A., and Bakke-McKellep, A. M.: The intestine of carnivorous fishes:
structure and functions and relations with diet., Acta Physiol.Scand., 161 (Suppl. 638), 67–80, 1997.
31. Bulger, R. E.: Fine structure of the rectal (salt-secreting) gland of the spiny dogfish., Squalus acanthias,
Anat.Rec., 147, 95–127, 1963.
32. Burger, J. W.: Roles of the rectal gland and the kidneys in salt and water excretion in the spiny dogfish,
Physiol.Zool., 38, 191–196, 1965.
33. Burger, J. W.: Problems in the electrolyte economy of the spiny dogfish, Squalus acanthias., In Sharks,
Skates and Rays P. W. Gilbert, R. F. Mathewson, and D. P. Rall (Eds) Baltimore, Maryland: John
Hopkins Press, 1967.
34. Burger, J. W. and Hess, W. N.: Function of the rectal gland in the spiny dogfish., Science, 131,
670–671, 1960.
35. Burgess, D. W., Miarczynski, M. D., O’Donnell, M. J. and Wood, C. M.: Na+ and Cl– transport by
the urinary bladder of the freshwater rainbow trout (Oncorhynchus mykiss )., J.Exp.Zool., 287, 1–14,
2000.
36. Bury, N. R., Grosell, M., Wood, C. M., Hogstrand, C., Wilson, R. W., Rankin, J. C., Busk, M., Lecklin,
T., and Jensen, F. B.: Intestinal iron uptake in the European flounder (Platichthys flesus)., J.Exp.Biol.,
204, 3779–3787, 2001.
2022_C006.fm Page 216 Tuesday, June 7, 2005 5:27 PM
216
au: name of
journal?
au: is this a
book chapter or a journal article?
The Physiology of Fishes
37. Bury, N. R. and Wood, C. M.: Mechanisms of branchial apical silver uptake by rainbow trout is via
the proton coupled Na+ channel., Amer.J.Physiol., 277, R1385–R1391, 1999.
38. Carrick, S. and Balment, R. J.: The renin-angiotensin system and drinking in the Euryhaline flounder,
Platichthys flesus. , Gen.Comp.Endocrinol., 51, 423–433, 1983.
39. Chan, D. K. O., Phillips, J. G., and Chester Jones, I.: Studies of electrolyte changes in the lip-shark,
Hemiscyllium plagiosum (Bennett), with special reference to hormonal influence on the rectal gland.,
Comp.Biochem.Physiol., 23, 185–198, 1967.
40. Chang, I. C., Wei, Y. Y., Chou, F. I. and Hwang, P. P.: Stimulation of Cl– uptake and morphological
changes in gill mitochondria-rich cells in freshwater tilapia (Oreochromis mossambicus )., Physiol.Biochem.Zool., 76, 544–552, 2003.
41. Chang, W. and Loretz, C. A.: DPC blockade of transepithelial chloride absorption and single anion
channels in teleost urinary bladder., Amer.J.Physiol., 265, R66–R75, 1993.
42. Chew, S. F., Chan, N. K., Loong, A. M., Hiong, K. C., Tam, W. L. and Ip, Y. K.: Nitrogen metabolism
in the African lungfish (Protopterus dolloi) aestivating in a mucus cocoon on land., J.Exp.Biol., 207,
777–786, 2004.
43. Chiasson, A. F.: The changes in blood concentration of Raja erinacea produced by modification of
the salinity of the external medium., Contrib.Can.Biol.Fisheries, 5, 475–485, 1930.
44. Choe, K. P. and Evans, D. H.: Compensation for hypercapnia by a euryhaline elasmobranch: Effect
of salinity and roles of gills and kidneys in fresh water., J.Exp.Zool. A., 297A, 52–63, 2003.
45. Claiborne, J. B.: Acid-base regulation, 2, 177–198, 1997.
46. Claiborne, J. B., Blackston, C. R., Choe, K. P., Dawson, D. C., Harris, S. P., Mackenzie, L. A. and
Morrison-Shetlar, A.: A mechanism for branchial acid excretion in marine fish: identification of
multiple Na+/H+ antiporter (NHE) isoforms in gills of two seawater teleosts., J.Exp.Biol, 202, 315–324,
1999.
47. Claiborne, J. B., Edwards, S. and Morrison-Shetlar, A. I.: Acid-base regulation in fishes: Cellular and
molecular mechanisms., J.Exp.Zool., 293, 302–319, 2002.
48. Cliff, W. H. and Beyenbach, K. W.: Fluid secretion in glomerular renal proximal tubules of freshwateradapted fish., Amer.J.Physiol., 254, R154–R158, 1988.
49. Cliff, W. H. and Beyenbach, K. W.: Secretory renal proximal tubules in seawater-adapted and freshwater-adapted killifish., Amer.J.Physiol., 262, F108–F116, 1992.
50. Cliff, W. H. and Beyenbach, K. W.: Secretory renal proximal tubules in seawater-adapted and freshau: same as
water-adapted Killifish., Am.J.Physiol., 262, F108-F116, 1992.
51. Cliff, W. H., Sawyer, D. B., and Beyenbach, K. W.: Renal proximal tubule of flounder.2. Trans- above.
epithelial Mg secretion, Amer.J.Physiol., 250, R616–R624, 1986.
52. Collette, B. B.: A review of the venomous toadfishes, subfamily Thalassophryninae, Copeia, 4,
846–864, 1966.
53. Collette, B. B.: Potamobatrachus trispinosus, a new freshwater toadfish (Batrachoididae) from the
Rio Tocantins, Brazil., Ichthyol.Explor.Freshwaters, 6, 333–336, 1995.
54. Compagno, L. J. V. and Cook, S. F.: The exploitation and conservation of freshwater elasmbranchs:
status of taxa and prospects for the future., In: The Biology of Freshwater Elasmobranchs, Oetinger,
M. I., Zorzi, G. D. (Eds.), J.Aquaric.Aquat.Sci., Vol VII, 62–90, 1995.
55. Conlon, J. M.: Bradykinin and its receptors in non-mammalian vertebrates., Regulatory Peptides, 79,
71–81, 1999.
56. Cresko, W. A., Amores, A., Wilson, C., Murphy, J., Currey, M., Phillips, P., Bell, M. A., Kimmel,
C. B. and Postlethwait, J. H.: Parallel genetic basis for repeated evolution of armor loss in Alaskan
threespine stickleback populations., Proc.Natl.Acad.Sci. USA., 101, 6050–6055, 2004.
57. Curtis, B. J. and Wood, C. M.: The function of the urinary-bladder in vivo in the fresh-water rainbowtrout., J.Exp.Biol., 155, 567–583, 1991.
58. Cutler, C. P. and Cramb, G.: Two isoforms of the Na+/K+/2Cl– cotransporter are expressed in the
European eel (Anguilla anguilla), Biochim.Biophys.Acta., 1566, 92–103, 2002.
59. Cutler, C. P. and Cramb, G.: Molecular physiology of osmoregulation in eels and other teleosts:
the role of transporter isoforms and gene duplication., Comp.Biochem.Physiol. A., 130, 551–564,
2001.
60. Cutler, C. P., Brezillon, S., Bekir, S., Sanders, I. L., Hazon, N., and Cramb, G.: Expression of a
duplicate Na,K-ATPase beta(1)-isoform in the European eel (Anguilla anguilla)., Amer.J.Physiol., 279,
R222–R229, 2000.
2022_C006.fm Page 217 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
au: please
provide
217
61. Cutler, C. P. and Cramb, G.: Branchial expression of an aquaporin 3 (AQP-3) homologue is downregulated in the European eel Anguilla anguilla following seawater acclimation., J.Exp.Biol, 205,
2643–2651, 2002.
62. D’Cruz, L. M. and Wood, C. M.: The influence of dietary salt and energy on the response to low pH
in juvenile rainbow trout., Physiol.Zool., 71, 642–657, 1998.
63. Dang, Z., Balm, P. H., Flik, G., Wendelaar Bonga, S. E. and Lock, R. A.: Cortisol increases Na+/K+ATPase density in plasma membranes of gill chloride cells in the freshwater tilapia Oreochromis
mossambicus ., J.Exp.Biol, 203, 2349–2355, 2004.
64. Dantzler, W. H.: Regulation of renal proximal and distal tubule transport: sodium, chloride and organic
anions, Comp.Biochem.Physiol. A., 136, 453–478, 2003.
65. Davis, E. M., Musch, M. W. and Goldstein, L.: Transfection of an inducible trout anion exchanger
(AE1) into HEK-EcR cells, J.Exp.Zool., 293, 46–57, 2002.
66. De Boeck, G., Grosell, M., and Wood, C.: Sensitivity of the spiny dogfish (Squalus acanthias) to
waterborne silver exposure, Aqua.Tox., 54, 261–275, 2001.
67. De Vlaming, V. L. and Sage, M.: Osmoregulation in the euryhaline elasmobranch, Dasyatis sabina.,
Comp.Biochem.Physiol. A., 45, 31–44, 1973.
68. Degnan, K. J.: The role of K+ and Cl– conductances in chloride secretion by the opercular epithelium.,
J.Exp.Zool., 236, 19–25, 1985.
69. Degnan, K. J., Karnaky, K. J. Jr. and Zadunaisky, J. A.: Active chloride transport in the in vitro
opercular skin of a teleost (Fundulus heteroclitus), a gill-like epithelium rich in chloride cells., J
Physiol.Lond., 271, 191–1977.
70. Degnan, K. J. and Zadunaisky, J. A.: Passive sodium movements across the opercular epithelium: the
paracellular shunt pathway and ionic conductance., J Membr Biol., 55, 175–185, 1980.
71. Dekhuyzen, M. C.: Sur la pression osmotique dans le sans et dans L’urine des poissons.,
Arch.Néerl.Sci., 2, 121,1905.
72. Dharmamba, M., Bornancin, M. and Maetz, J.: Environmental salinity and sodium chloride exchanges
across the gill of Tilapia mossambica ., J.Physiol.(Paris), 70, 627–636, 1975.
73. Dickman, K. G. and Renfro, J. L.: Primary culture of flounder renal tubule cells - transepithelial
transport., Amer.J.Physiol., 251, F424–F432, 1986.
74. Doyle, W. L.: Tubular cells of the rectal salt-gland of urolophus., Amer.J.Anat., 111, 223–237, 1962.
75. Duranton, C., Mikulovic, E., Tauc, M., Avella, M. and Poujeol, P.: Potassium channels in primary
cultures of seawater fish gill cells. I. Stretch-activated K(+) channels., Amer.J.Physiol., 279,
R1647–R1658, 2000.
76. Duranton, C., Tauc, M., Avella, M. and Poujeol, P.: Chloride channels in primary cultures of seawater
fish (Dicentrarchus labrax) gill., Amer.J.Physiol., 273, C874–C882, 1997.
77. Eckert, S. M., Yada, T., Shepherd, B. S., Stetson, M. H., Hirano, T., and Grau, E. G.: Hormonal control
of osmoregulation in the channel catfish Ictalurus punctatus., Gen.Comp.Endocrinol., 122, 270–286, 2001.
78. Eddy, F. B.: The effect of calcium on gill potentials and on sodium and chloride fluxes in the goldfish
Carassius auratus l., J.Comp.Physiol, 96, 131–142, 1975.
79. Edwards, S. L., Donald, J. A., Toop, T., Donowitz, M., and Tse, C.-M.: Immunolocalization of sodium/
proton exchanger-like proteins in the gills of elasmobranchs., Comp.Biochem.Physiol. A, 131,
257–265, 2002.
80. Esbaugh, A. J., Lund, S. G. and Tufts, B. L.: Comparative physiology and molecular analysis of
carbonic anhydrase from the red blood cells of teleost fish., J.Comp.Physiol., 174B, 429–438-2004.
81. Evans, D. H.: Kinetic studies of ion transport by fish gill epithelium., Amer.J.Physiol., 238,
R224–R230, 1980.
82. Evans, D. H.: Cell signalling and ion transport across the fish gill epithelium., J.Exp.Zool., 293,
336–347, 2002.
83. Evans, D. H.: Osmotic and ionic regulation, The Physiology of Fishes. Evans D. H. (Ed), Boca Raton:
CRC Press, 315–341, 1993.
84. Evans, D. H., Piermarini, P. M., and Choe, K. P.: The physiology of the fish gill, Physiol.Zool., xx,
xxx-xxx, 2004.
85. Evans, D. H. and Piermarini, P. M.: Contractile properties of the elasmobranch rectal gland.,
J.Exp.Biol., 204, 59–67, 2001.
86. Evans, D., Carrier JC, and Bogan M.: The effect of external potassium on the electrical potential
measured across the gills of the teleost Dormitator maculatus J.Exp.Biol, 70, 213–220, 1974.
2022_C006.fm Page 218 Tuesday, June 7, 2005 5:27 PM
218
au: please
provide
The Physiology of Fishes
87. Evans, D., Piermarini PM, and Choe, KP.: The physiology of the fish gill., Physiol Zool, xx, xxx-xxx,
2004.
88. Fellner, S. K. and Parker, L.: A Ca2+-sensing receptor modulates shark rectal gland function.,
J.Exp.Biol, 205, 1889–1897, 2002.
89. Fellner, S. K. and Parker, L.: Ionic strength and the polyvalent cation receptor of shark rectal gland
and artery, J.Exp.Zool., 301A, 235–239, 2004.
90. Fenwick, J. C., Wendelaar Bonga, and Gert, F.: In vivo bafilomycin-sensitive Na+ uptake in young
freshwater fish., J.Exp.Biol., 202, 3659–3666, 1999.
91. Fergusson, R. A. and Tufts, B. L.: Physiological effects of brief air exposure in exhastively exercised
rainbow trout (Oncorhynchus mykiss ) — Implications for catch and release fisheries.,
Can.J.Fish.Aquat.Sci., 49, 1157–1162, 1992.
92. Field, M., Smith, P. L., and Bolton, J. E.: Ion transport across the isolated intestinal mucosa of the
winter flounder Pseudopleuronectes americanus: II. Effects of cyclic AMP., J.Membr.Biol., 53,
157–163, 1980.
93. Field, M., Karnaky, K. J., Kinter, W. B., Bolton, J. E., and Smith, P. L.: Ion transport scross the
isolated intestinal mucosa of the winter flounder, Pseudopleuronectes Americanus. , J.Membr.Biol.,
41, 265–293, 1978.
94. Fines, G. A., Ballantyne, J. S. and Wright, P. A.: Active urea transport and an unusual basolateral
membrane composition in the gills of a marine elasmobranch., Amer.J.Physiol., 280, R16–R24,
2001.
95. Forrest, J. N.: Cellular and molecular biology of chloride secretion in the shark rectal gland: Regulation
by adenosine receptors., Kidn.Int., 49, 1557–1562, 1996.
96. Forster, R. P.: A comparative study of renal function in marine teleosts., J.Cell.Comp.Physiol., 42,
487–509, 1953.
97. Forster, R. P.: Osmoregulatory role of the kidney in cartilaginous fishes (Chondrichthys)., In: Sharks,
Skates and Rays P. W. Gilbert, R. F. Mathewson, and D. P. Rall (Eds) Baltimore, Maryland: John
Hopkins Press, 187–195, 1967.
98. Foskett, J. K. and Scheffey, C.: The chloride cell: definitive identification as the salt-secretory cell in
teleosts., Science, 215, 164–166, 1982.
99. Fossat, B. and Lahlou, B.: The mechanism of coupled transport of sodium and chloride in isolated
urinary bladder of the trout., J.Physiol.Lond., 294, 211–222, 1979.
100. Friedman, P. A. and Hebert, S. C.: Diluting segment in the kidney of dogfish shark. I. Localization
and characterizaiton of chloride absorption., Amer.J.Physiol., 258, R398–R408, 1990.
101. Frizzell, R. A., Smith, P. L., Field, M., and Vosburgh, E.: Coupled sodium-chloride influx across brush
border of flounder intestine., J.Membr.Biol., 46, 27–39, 1979.
102. Fuentes, J., Bury, N. R., Carroll, S., and Eddy, F. B.: Drinking in atlantic salmon presmolts (Salmo
salar L.) and juvenile rainbow trout (Oncorhynchus mykiss Walbaum) in response to cortisol and sea
water challenge., Aquaculture, 141, 129–137, 1996.
103. Fuentes, J. and Eddy, F. B.: Drinking in atlantic salmon presmolts and smolts in response to growth
hormone and salinity., Comp.Biochem.Physiol., 117A, 487–491, 1997.
104. Fuentes, J. and Eddy, F. B.: Effect of manipulation of the renin-angiotensin system in control of
drinking in juvenile Atlantic salmon (Salmo salar L) in fresh water and after transfer to sea water.,
J.Comp.Physiol. B., 167, 438–443, 1997.
105. Fuentes, J. and Eddy, F. B.: Cardiovascular responses in vivo to angiotensin II and the peptide
antagonist saralasin in rainbow trout Oncorhynchus mykiss ., J.Exp.Biol., 201, 267–272, 1998.
106. Fuentes, J., McGeer, J. C., and Eddy, F. B.: Drinking rate in juvenile Atlantic salmon, Salmo salar L
fry in response to a nitric oxide donor, sodium nitroprusside and an inhibitor of angiotensin converting
enzyme, enalapril, Fish Physiol.Biochem., 15, 65–69, 1996.
107. Furimsky, M. Suski, C. D., Cooke , S. J., Wang, Y. X. and Tufts, B. L.: Respiratory and circulatory
responses to hypoxia in largemouth bass and smallmouth bass: Implications for “live-release” angling
tournaments., Trans.Amer.Fisheries.Soc., 132, 1065–1075, 2003.
108. Galvez, F., Reid, S. D., Hawkings, G. and Goss, G. G.: Isolation and characterization of mitochondriarich cell types from the gill of freshwater rainbow trout., Amer.J.Physiol., 282, R658–R668, 2002.
109. Gamba, G., Saltzberg, S. N., Lombardi, M., Miyanoshita, A., Lytton, J., Hediger, M. A., Brenner, B. M.
and Hebert, S. C.: Primary structure and functional expression of a cDNA encoding the thiazide-sensitive,
electroneutral sodium-chloride cotransporter., Proc.Natl.Acad.Sci. U.S.A., 90, 2749–2753, 1993.
2022_C006.fm Page 219 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
219
110. Gardiner, S. M., Kemp, P. A., and Bennett, T.: Differential-effects of captopril on regional hemodynamic responses to angiotensin-I and bradykinin in conscious rats., Brit.J.Pharm., 108, 769–775,
1993.
111. Gerst, J. W. and Thorson, T. B.: Effects of saline acclimation on plasma electrolytes, urea excretion,
and hepatic urea biosynthesis in a freshwater stingray, Potamotrygon sp. Garman, 1877., Comp.Biochem.Physiol., 56A, 87–93, 1977.
112. Gerzeli, G., De Stefano, G. F., Bolognani, L., Koenig, K. W., Gervaso, M. V., and Omodeo-Sale,
M. F.: The rectal gland in relation to the osmoregulatory mechanisms of marine and freshwater
elasmobranchs., In: Investigations of the Ichthyofauna of Nicaraguan Lakes. Thorson, T.B.(Ed.),
University of Nebraska-Lincoln, Lincoln, Nebraska: School of Life Sciences, 619–627, 1976.
113. Gibson, J. S., Ellory, J. C., and Lahlau, B.: Salinity acclimatiom and intestinal salt transport in the
flounder: The role of the basolateral cell membrane., J.Exp.Biol., 128, 371–382, 1987.
114. Gilmour, K. M. and Perry, S. F.: Branchial membrane-associated carbonic anhydrase activity maintains
CO2 excretion in severely anemic dogfish., Amer.J.Physiol., 286, R1138–R1148, 2004.
115. Gilmour, K. M., Perry, S. F., Bernier, N. J., Henry, R. P. and Wood, C. M.: Extracellular carbonic
anhydrase in the dogfish, Squalus acanthias: a role in CO2 excretion., Physiol.Biochem.Zool., 74,
477–492, 2001.
116. Gilmour, K. M., Shah, B. and Szebedinszky, C.: An investigation of carbonic anhydrase activity in
the gills and blood plasma of brown bullhead (Ameiurus nebulosus), longnose skate (Raja rhina),
and spotted raffish (Hydrolagus colliei)., J.Comp.Physiol., 172B, 77–86, 2002.
117. Goldstein, L. and Forster, R. P.: Osmoregulation and urea metabolism in the littel skate Raja erinacea.,
Amer.J.Physiol., 220, 742–746, 1971.
118. Goldstein, L., Oppelt, W. W., and Maren, T. H.: Osmotic regulation and urea metabolism in the lemon
shark Negaprion brevirostris., Amer.J.Physiol., 215, 1497, 1968.
119. Good, D. A., Knepper, M. A., and Burg, M. B.: Ammonia and bicarbonate transport by thick ascending
limb of rat kidney., Amer.J.Physiol., 247, F35–F44, 1984.
120. Goss, G. G., Adamia, S. and Galvez, F.: Peanut lectin binds to a subpopulation of mitochondria-rich
cells in the rainbow trout gill epithelium., Amer.J.Physiol., 281, R1718–R1725, 2001.
121. Goss, G. G. and Perry, S. F.: Different mechanisms of acid-base regulation in rainbow trout (Oncorhynchus mykiss) and americal eel (Anguilla rostrata) during NaHCO3 infusion, Physiol Zool, 67,
381–406, 1994.
122. Goss, G. G., Perry, S. F., Fryer, J. N. and Laurent, P.: Gill morphology and acid-base regulation in
freshwater fishes., Comp.Biochem.Physiol., 119A, 107–115, 1998.
123. Griffith, R. W., Umminger, B. L., Grant, B. F., Pang, P. K. T. and Pickford, G. E.: Serum composition
of the coelacanth, Latimeria chalumnae Smith., J Exp Zool., 187, 87–102, 1974.
124. Grosell, M. and Wood, C. M.: Copper uptake across rainbow trout gills: mechanisms of apical entry.,
J.Exp.Biol., 205, 1179–1188, 2002.
125. Grosell, M., De Boeck, G., Johannsson, O., and Wood, C. M.: The effects of silver on intestinal ion
and acid-base regulation in the marine teleost fish., Papophrys vetulus., Comp.Biochem.Physiol.C.,
124, 259–270, 1999.
126. Grosell, M., Hogstrand, C., Wood, C. M., and Hansen, H. J. M.: A nose-to-nose comparison of the
physiological effects of exposure to ionic silver versus silver chloride in the European eel (Anguilla
anguilla) and the rainbow trout (Oncorhynchus mykiss )., Aqua.Tox., 48, 327–342, 2000.
127. Grosell, M. and Jensen, F. B.: NO2- uptake and HCO3– excretion in the intestine of the European
flounder (Platichthys flesus)., J.Exp.Biol., 202, 2103–2110, 1999.
128. Grosell, M., Laliberte, C. N., Wood, S., Jensen, F. B., and Wood, C. M.: Intestinal HCO3– secretion
in marine teleost fish: Evidence for an apical rather than a basolateral Cl–/HCO3– exchanger., Fish
Physiol.Biochem., 24, 81–95, 2001.
129. Grosell, M., McDonald, M. D., Walsh, P. J., and Wood, C. M.: Effects of prolonged copper exposure
in the marine gulf toadfish (Opsanus beta). II. Drinking rate, copper accumulation and Na+/K+-ATPase
activity in osmoregulatory tissues., Aqua.Tox., 68, 263–275, 2004.
130. Grosell, M., McDonald, M. D., Wood, C. M., and Walsh, P. J.: Effects of prolonged copper exposure
in the marine gulf toadfish (Opsanus beta). I. Hydromineral balance and plasma nitrogenous waste
products., Aqua.Tox., 68, 249–262, 2004.
131. Grosell, M., Nielsen, C., and Bianchini, A.: Sodium turnover rate determines sensitivity to acute
copper and silver exposure in freshwater animals., Comp.Biochem.Physiol. C., 133, 287–303, 2002.
2022_C006.fm Page 220 Tuesday, June 7, 2005 5:27 PM
220
au: update?
The Physiology of Fishes
132. Grosell, M. and Wood, C. M.: Branchial versus intestinal silver toxicity and uptake in the marine
teleost Parophrys vetulus., J.Comp.Physiol. B., 171, 585–594, 2001.
133. Grosell, M., Wood, C. M., Wilson, R. W., Bury, N. R., Hogstrand, C., Rankin, J. C., and Jensen, F. B.:
Active bicarbonate secretion plays a role in chloride and water absorption of the European flounder
intestine, Amer.J.Physiol., Under review — manuscript number R-00684-2003, 2004.
134. Grosell, M. H., Hogstrand, C., and Wood, C. M.: Renal Cu and Na excretion and hepatic Cu metabolism
in both Cu acclimated and non acclimated rainbow trout (Oncorhynchus mykiss )., Aqua.Tox., 40,
275–291, 1998.
135. Guggino, W. B.: Salt balance in embryos of Fundulus heteroclitus and F. bermudae adapted to
seawater., Amer.J.Physiol., 238, R42–R49, 1980.
136. Gunning, M., Solomon, R. J., Epstein, F. H., and Silva, P.: Role of guanylyl cyclase receptors for
CNP in salt secretion by shark rectal gland., Amer.J.Physiol., 42, R1400–R1406, 1997.
137. Haas, M. and Forbush, B. 3rd: The Na-K-Cl cotransporter of secretory epithelia., Annu.Rev.Physiol.,
62, 515–534, 2000.
138. Haines, T. A., Komov, V. and Jagoe, C. H.: Lake acidity and mercury content of fish in Darwin
National Reserve, Russia., Environ Pollut., 78, 107–112, 1992.
139. Halm, D. R., Krasny, E. J., and Frizzell, R. A.: Electrophysiology of flounder intestinal mucosa.I.
Conductance of cellular and paracellular pathways., J.Gen.Physiol., 85, 843–864, 1985.
140. Halm, D. R., Krasny, E. J. and Frizzell, R. A.: Electrophysiology of flounder intestinal mucosa.II.
Relation of the electrical potential profile to coupled NaCl absorption., J.Gen.Physiol., 85, 865–883,
1985.
141. Hannafin, J. E., Kinne-Saffran, D., Friedman, D., and Kinne, R.: Presence of sodium-potassium
chloride cotransport system in the rectal gland of Squalus acanthias., J.Membr.Biol., 75, 73–83, 1983.
142. Hawkings, G. S., Galvez, F. and Goss, G. G.: Seawater acclimation causes independent alterations in
Na+/K+- and H+-ATPase activity in isolated mitochonndria-rich cell subtypes of the rainbow trout gill,
J.Exp.Biol., 207, 905–912, 2004.
143. Hays, R. M., Levine, S. D., Myers, J. D., Heinemann, H. O., Kaplan, M. A., Frank, N. and Berliner,
H.: Urea transport in the dogfish kidney, J.Exp.Zool., 199, 309–316, 1977.
144. Hayslett, J. P., Schon, D. A., Epstein, M. and Hogben, C. A.: In vitro perfusion of the dogfish rectal
gland., Amer.J.Physiol., 226, 1188–1192, 1974.
145. Haywood, G. P.: A preliminary investigation into the roles played by the rectal gland and kidneys in
the osmoregulation of the striped dogfish Poroderma africanum , J.Exp.Zool., 193, 167–176, 1975.
146. Hazon N, Wells A, Pillans RD, Good JP, Anderson WG, and Franklin CE: Urea based osmoregulation
and endocrine control in elasmobranch fish with special reference to euryhalinity., Comp.Biochem.Physiol., 136B, 685–700, 2003.
147. Heisler, N.: Acid-base regulation in fishes. In: Fish Physiology, Vol XA: Gill. anatomy, gas tranfer
and acid-base regulation. W. S. Hoar and D. J. Randall, (Eds.), New York: Academic Press,, 315–401,
1984.
148. Heisler, N.: Acid-base regulation., In: The Physiology of Fishes., H. D. Evans (Ed.), Boca Raton,
Florida: CRC press,, 343–378, 1993.
149. Hickman, C. P.: Studies on renal function in freshwater teleost fish, Trans.R.Soc.Can., 3, 213–236,
1965.
150. Hickman, C. P.: Ingestion, intestinal absorption, and elimination of seawater and salts in the southern
flounder, Paralichthys lethostigma. , Can.J.Zool., 46, 457–466, 1968.
151. Hickman, C. P. and Trump, B. F.: The kidney., In: Fish Physiology, Hoar, W. S. and Randall, D. J.
(Eds.), New York: Academic Press, 91–239, 1969.
152. Hill, W. G., Mathai, J. C., Gensure, R. H., Zeidel, J. D., Apodaca, G., Saenz, J. P., Kinne-Saffran, E.,
Kinne, R. and Zeidel, M. L.: Permeabilities of the teleost and elasmobranch gill apical membrane:
evidence that lipid bilayers alone do not account for barrier function., Amer.J.Physiol., 287,
C235–C242, 2004.
153. Hillyard, S. D. and Van Driessche, W.: Effect of amiloride on the poorly selective cation channel of
larval bullfrog skin., Amer.J.Physiol., 256, C168–C174, 1989.
154. Hirano, T.: Some factors regulating water intake by the eel, Anguilla japonica, J.Exp.Biol, 61, 737–747,
1974.
155. Hirano, T. and Mayer-Gostan, N.: Eel esophagus as an osmoregulatory organ, Proc.Nat.Ac.Sci. U.S.A.,
73, 1348–1350, 1976.
2022_C006.fm Page 221 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
221
156. Hirata, T., Kaneko, T., Ono, T., Nakazato, T., Furukawa, N., Hasegawa, S., Wakabayashi, S.,
Shigekawa, M., Chang, M. H., Romero, M. F. and Hirose, S.: Mechanism of acid adaptation of a fish
living in a pH 3.5 lake., Amer.J.Physiol., 284, R1199–R1212, 2003.
157. Hiroi. J., Kaneko, T. and Tanaka, M.: In vivo sequential changes in chloride cell morphology in the
yolk-sac membrane of mozambique tilapia (Oreochromis mossambicus ) embryos and larvae during
seawater adaptation., J.Exp.Biol., 202, 3485–3495, 1999.
158. Hiroi, J.: Does absorptive type of Na+/K+/Cl- cotransporter (NKCC2) exist and function in the gills
of freshwater tilapia?, Symp.Environ.Adapt. Fish: Rev.New Insights, 2004.
159. Hiroi, J., Kaneko, T., Seikai, T. and Tanaka, M.: Developmental sequence of chloride cells in the body
skin and gills of Japanese flounder (Paralichthys olivaceus) larvae., Zool.Sci., 15, 455–460, 1998.
160. Hirose, S., Kaneko, T., Naito, N. and Takei, Y.: Molecular biology of major components of chloride
cells., Comp.Biochem.Physiol., 136B, 593–620, 2003.
161. Hoar, W. S.: The Physiology of Smolting Salmonid , 275–344, 1988.
162. Hofmann, E. L. and Butler, D. G.: The effect of increased metabolic rate on renal function inthe
rainbow trout, Salmo gairdneri, J.Exp.Biol, 82, 11–23, 1979.
163. Holmes, W. N. and Donaldson, E. M.: The Body Compartments and the Distribution of Electrolytes ,
1–90, 1969.
164. Hootman, S. R. and Philpott, C. W.: Ultracytochemical localization of Na+,K+-ATPase in chloride
cells from the gills of a euryhaline teleost., Anat.Rec., 193, 99–130., 1979.
165. Hootman, S. R. and Philpott, C. W.: Accessory cells in teleost branchial epithelium, Amer.J.Physiol.,
238, R199–R206, 1980.
166. House, C. R. and Maetz, J.: On the electrical gradient across the gill of the seawater adapted eel.,
Comp.Biochem.Physiol. A., 47A, 917–924, 1974.
167. Howe, D. and Gutknecht, J.: Role of urinary bladder in osmoregulation in marine teleost, Opsanus
tau., Amer.J.Physiol., 235, R48–R54, 1978.
168. Hyodo, S., Katoh, F., Kaneko, T., and Takei, Y.: A facilitative urea transporter is localized in the renal
collecting tubule of the dogfish Triakis scyllia., J.Exp.Biol., 207, 347–356, 2004.
169. Janech, M. G., Fitzgibbon, W. R., Chen, R. H., Nowak, M. W., Miller, D. H., Paul, R. V. and Ploth,
D. W.: Molecular and functional characterization of a urea transporter from the kidney of the Atlantic
stingray., Amer.J.Physiol., 284, F996–F1005, 2003.
170. Janech, M. G., Fitzgibbon, W. R., Miller, D. H., Lacy, E. R. and Ploth, D. W.: Effect of dilution on
renal excretory function of the Atlantic stingray, Dasyatis sabina, FASEB J. 12, A423–A423, 1998.
171. Janech, M. G. and Piermarini, P. M.: Renal water and solute excretion in the Atlantic stingray in fresh
water, J.Fish Biol., 61, 1053–1057, 2002.
172. Jensen, L. J., Willumsen, N. J., Amstrup, J. and Hviid Larsen, E. H.: Proton pump-driven cutaneous
chloride uptake in anuran amphibia, Biochim.Biophys.Acta, 1618, 120–132, 2003.
173. Jensen, L. J., Willumsen, N. J. and Larsen, E. H.: Proton pump activity is requirred for active uptake
of chloride in isolated amphibian skin exposed to freshwater, J.Comp.Physiol. B., 176, 503–511, 2002.
174. Jensen, M. K., Madsen, S. S. and Kristiansen, K.: Osmoregulation and salinity effects on the expression
and activity of Na+,K+-ATPase in the gills of European sea bass, Dicentrarchus labrax (L.), J.Exp.Zool.,
282, 290–300, 1998.
175. Karasov, W. H. and Hume, I. D.: Vertebrate gastrointestinal system, In: The Handbook of Physiology
— Comparative Physiology. W.H.Dantzler (Ed.), The American Physiology Society, Oxford University
Press., Section 13, Volume 1, 409–480, 1997.
176. Karnaky, K. J. Jr, Kinter, L. B., Kinter, W. B. and Stirling, C. E.: Teleost chloride cell. II Autoradiographic localization of gill Na+,K+-ATPase in killifish (Fundulus heteroclitus) adapted to low and
high salinity environments., J.Cell.Biol., 70, 157–177, 1976.
177. Karnaky, K. J.: Osmotic and ionic regulation, In: The Physiology of Fishes. Evans D. H. (Ed.), Boca
Raton: CRC Press,, 157–176, 1998.
178. Katoh, F., Hyodo, S. and Kaneko, T.: Vacuolar-type proton pump in the basolateral plasma membrane
energizes ion uptake in branchial mitochondria-rich cells of killifish Fundulus heteroclitus, adapted
to a low ion environment., J.Exp.Biol., 206, 793–803, 2003.
179. Katoh, F. and Kaneko, T.: Short-term transformation and long-term replacement of branchial chloride
cells in killifish transferred from seawater to freshwater, revealed by morphofunctional observations
and a newly established “time-differential double fluorescent staining” technique., J.Exp.Biol., 206,
4113–4123, 2003.
2022_C006.fm Page 222 Tuesday, June 7, 2005 5:27 PM
222
au: other
publishing
details?
The Physiology of Fishes
180. Keinanen, M., Peuranen, S., Tigerstedt, C. and Vuorinen, P. J.: Ion regulation in whitefish (Coregonus
lavaretus L.) yolk-sac fry exposed to low pH and aluminum at low and moderate ionic strength.,
Ecotox.Env.Saf., 40, 166–172, 1998.
181. Kempton, R. T.: Studies of the elasmobranch kidney. II. Reabsorption of urea by the smooth dogfish,
Mustelus canis, Biol.Bull., 104, 45–56, 1953.
182. Kent, B. and Olson, K. R.: Blood flow in the rectal gland of Squalus acanthias, Amer.J.Physiol., 24,
R296–R303, 1982.
183. Kerstetter, T. H. and Kirschner, L. B.: Active chloride transport by the gills of rainbow trout (Salmo
gairdneri)., J.Exp.Biol., 56, 263–272, 1972.
184. Kerstetter, T. H., Kirschner, L. B. and Rafuse, D. D.: On the mechanism of sodium ion extrusion by
the gills of rainbow trout (Salmo gairdneri)., J.Gen Physiol., 56, 342–359, 1970.
185. Keys, A. and Willmer, E. N.: “Chloride secreting cells” in the gills of fishes, with special reference
to the common eel., J.Physiol.Lond., 76, 368–378, 1932.
186. Kirsch, R. and Meister, M. F.: Progressive processing of ingested water in the gut of sea-water teleost.,
J.Exp.Biol., 98, 67–81, 1982.
187. Kirschner, L. B.: Water and Ions., In: Comparative Animal Physiology, Environmental and Metabolic
Animal Physiology, 4th Edition, C. L. Prosser, (Ed.), New York: Wiley-Liss, 13–107, 1991.
188. Kirschner, L. B.: Extrarenal Mechanisms in Hydromineral and Acid-Base Regulation in Aquatic
Vertebrates, 577–622, 1997.
189. Kirschner, L. B., Greenwald, L. and Sanders, M.: On the mechanism of sodium extrusion across the
irrigated gill of seawater adapted rainbow trout (Salmo gairdneri), J.Gen.Physiol., 64, 148–165, 1974.
190. Kirschner, L. B.: The mechanism of sodium chloride uptake in hyperregulating aquatic animals,
J.Exp.Biol., 207, 1439–1452, 2004.
191. Kristiansen, H. R. and Rankin, J. C.: Discrimination between endogenous and exogenous water sources
in juvenile rainbow trout fed extruded dry feed, Aquat.Living Resour, 14, 359–366, 2001.
192. Krogh, A.: The active absorption of ions in some freshwater animals, Z.Vergl.Physiol., 25, 335–350,
1938.
193. Lacy, E. R. and Reale, E.: Functional morphology of the elasmobranch nehpron and retention of urea,
In: Cellular and Molecular Approaches to Fish Ionic Regulation, Fish Physiology C. M. Wood and
T.J.Shuttleworth (Eds.), Volume 14, 107–146, 1995
194. Lacy, E. R., Reale, E. and Mackanos, L. A.: Freshwater elasmobranchs do not have a renal countercurrent system, Anat.Rec., 223, 64A,1989.
195. Lacy, E. R., Reale, E., Schlusselburg, D. S., Smith, W. K., and Woodward, D. S.: A renal countercurrent
system in marine elasmobranch fish: a computer-assisted reconstruction., Science, 227, 1351–1354,
1985.
196. Larsen, E. H.: Chloride transport by high-resistance heterocellular epithelia, Physiol.Rev., 71, 235–283,
1991.
197. Laurent, P.: Gill Intern. Morphol. , 1984.
198. Lemire, M. and Lagios, M.: Ultrastructure of the secretory parenchyma of the postanal gland of the
coelacanth, Latimeria chalumnae Smith., Acta Anat (Basel)., 104, 1–15, 1979.
199. Lignot, J. H., Cutler, C. P., Hazon, N. and Cramb, G.: Immunolocalisation of aquaporin 3 in the gill
and the gastrointestinal tract of the European eel Anguilla anguilla (L.), J.Exp.Biol., 205, 2653–2663,
2002.
200. Lin, H., Pfeiffer, D. C., Vogl, A. W. and Randall, D. J.: Immunolocalization of H+-ATPase in the gill
epithelia of rainbow trout. J.Exp.Biol., 195, 169–183, 1994.
201. Lin, H. and Randall, D. J.: Evidence for the presence of an electrogenic proton pump on the trout
gill epithelium., J.Exp.Biol, 161, 119–134, 1991.
202. Lin, H. and Randall, D. J.: H+-ATPase activity in crude homogenates of fish gill tissue — inhibitor
sensitivity and environmental and hormonal regulation, J.Exp.Biol., 180, 163–174, 1993.
203. Lin, L. Y., Weng, C. F. and Hwang, P. P.: Regulation of drinking rate in euryhaline tilapia larvae
(Oreochromis mossambicus ) during salinity challenges, Physiol.Biochem.Zool., 74, 171–177, 2002.
204. Lin, L. Y., Weng, C. F., and Hwang, P. P.: Effects of cortisol and salinity chalenge on water balance
in developing larvae of tilapia (Oreochromis mossambicus), Physiol.Biochem.Zool., 73, 283–289,
2000.
205. Loo, D. D. F., Wright, E. M. and Zeuthen, T.: Water pumps, J.Physiol. London, 542, 53–60, 2002.
2022_C006.fm Page 223 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
223
206. Loretz, C. A. and Bern, H. A.: Ion transport by the urinary bladder of the gobiid teleost, Gillichthys
mirabilis., Amer.J.Physiol., 239, R415–R423, 1980.
207. Loretz, C. A.: Electrophysiology of ion transport in the teleost intestinal cells, In: Cellular and
Molecular Approaches to Fish Ionic Regulation, Fish Physiology C. M. Wood and T. J. Shuttleworth
(Eds.), 14, 25–56, 1995.
208. Loretz, C. A.: Drinking and alimentary transport in teleost osmoregulation, Proceedings of the 14th
International Congress of Comparative Endocrinology, 723–732, 2001.
209. Loretz, C. A. and Fourtner, C. R.: Functional characterization of a voltage-gated anion channel from
teleost fish intestinal epithelium, J.Exp. Biol., 136, 383–403, 1988.
210. Mackay, W. C. and Janicki, R.: Changes in the eel intestine during seawater adaptation, Comp.Biochem.Physiol., 62A, 757–761, 1978.
211. Mackay, W. C. and Lahlou, B.: Relationships between Na+ and Cl- fluxes in the intestine of the
European flounder,Platichthys flesus., Epithel. Trans. Lower Vertebr., 151–162, 1980.
212. Maetz, J.: Branchial sodium exchange and ammonia excretion in the goldfish Carassius auratus.
Effects of ammonia-loading and temperature changes, J.Exp.Biol, 56, 601–620, 1972.
213. Malvin, R. L., Schiff, D. and Eiger, S.: Angiotensin and drinking rates in the euryhaline killifish,
Amer.J.Physiol., 239, R31–R34, 1980.
214. Marshall, E. K. and Smith, H. W.: Glomerular development of the vertebrate kidney in relation to
habitat., Biol.Bull., 59, 135–153, 1930.
215. Marshall, W. S.: Transepithelial potential and shortcircuit current across the isolated skin of Gillichthys
mirabilis (teleostei: gobiidae), acclimated to 5% and 100% sea water., J.Comp.Physiol., 114, 157–165,
1977.
216. Marshall, W. S.: Active transport of Rb+ across the skin of the teleost Gillichthys mirabilis .
Amer.J.Physiol., 241, F482–F486, 1981.
217. Marshall, W. S.: Sodium dependency of active chloride transport across isolated fish skin (Gillichthys
mirabilis)., J.Physiol.Lond, 319, 165–178, 1981.
218. Marshall, W. S.: Paracellular ion transport in trout opercular epithelium models osmoregulatory effects
of acid precipitation., Can.J.Zool., 63, 1816–1822, 1985.
219. Marshall, W. S.: Independent Na+ and Cl– active transport by urinary bladder epithelium of brook
trout. Amer.J.Physiol., 250, R227–R234, 1986.
220. Marshall, W. S.: Passive solute and fluid transport in brook trout (Salvelinus fontinalis) urinary bladder
epithelium., Can.J.Zool., 66, 912–918, 1987.
221. Marshall, W. S.: Na+, Cl–, Ca2+ and Zn2+ transport by fish gills: retrospective review and prospective
synthesis., J.Exp.Zool., 293, 264–283, 2002.
222. Marshall, W. S.: Rapid regulation of NaCl secretion by estuarine teleost fish: coping strategies for
short duration freshwater exposures., Biochim.Biophys.Acta., 1618, 95–105, 2003.
223. Marshall, W. S. and Bryson, S. E.: Intraccellular pH regulation in trout urinary bladder epithelium:Na+H+(NH4+) exchange., Amer.J.Physiol., 261, R652–R658, 1991.
224. Marshall, W. S. and Bryson, S. E.: Transport mechanisms of seawater chloride cells: An inclusive
model of a multifunctional cell., Comp.Biochem.Physiol. 119A, 97–106, 1998.
225. Marshall, W. S., Bryson, S. E., Darling, P., Whitten, M., Wilkie, M. P., Wood, C. M. and BucklandNicks, J.: NaCl transport and ultrastructure of opercular epithelium from a freshwater adapted euryhaline teleost, Fundulus heteroclitus., J.Exp.Zool., 277, 23–37, 1997.
226. Marshall, W. S., Bryson, S. E., Midelfart, A. and Hamilton, W. F.: Low conductance anion channel
activated by cyclic AMP in teleost Cl– secreting cells., Amer.J.Physiol., 268, R963–R969, 1995.
227. Marshall, W. S., Bryson, S.E. and Wood, C. M.: Calcium transport by isolated skin of rainbow trout.,
J.Exp.Biol,, 166, 297–316, 1992.
228. Marshall, W. S., Emberley, T. R., Singer, T. D., Bryson, S. E. and McCormick, S. D.: Time course
of salinity adaptation in a strongly euryhaline estuarine teleost, Fndulus heteroclitus: a multivariable
approach, J.Exp.Biol., 202, 1535–1544, 1999.
229. Marshall, W. S., Lynch, E. M. and Cozzi, R. R. F.: Redistribution of immunofluorescence of CFTR
anion channel and NKCC cotransporter in chloride cells during adaptation of the killifish Fundulus
heteroclitus to sea water, J.Exp.Biol., 205, 1265–1273, 2002.
230. Marshall, W. S. and Nishioka, R. S.: Relation of mitochondria rich chloride cells to anion transport
by marine teleost skin, J.Exp.Zool., 214, 147–156, 1980.
2022_C006.fm Page 224 Tuesday, June 7, 2005 5:27 PM
224
au: volume
and page
numbers?
The Physiology of Fishes
231. Marshall, E. K. J. and Vickers, J. L.: The mechanism of the elimination of phenolsulphonphthalein
by the kidney: a proof of secretion by the convoluted tubules, Bull.Johns Hopkins Hosp., 34, 1–7, 1923.
232. Marshall, J., Martin, K. A., Picciotto, M., Hockfield, S., Nairn, A. C. and Kaczmarek, L. K.: Identification and localization of a dogfish homolog of human cystic-fibrosis transmembrane conductance
regulator, J.Biol.Chem., 266, 22749–22754, 1991.
233. Marshall, W. S., Howard, J. A., Cozzi, R. R. F. and Lynch, E. M.: NaCl and fluid secretion by the
intestine of the teleost Fundulus heteroclitus: involvement of CFTR, J.Exp.Biol, 205, 745–758, 2002.
234. Marvao, P., Emilio, M. G., Ferreira, K. G., Fernandes, P. L., and Ferreira, H. G.: Ion-transport in the
intestine of Anguilla-anguilla — gradients and translocators., J.Exp.Biol., 193, 97–117, 1994.
235. McCormick, S. D.: Ontogeny and evolution of salinity tolerance in anadromous salmonids: hormones
and herterochrony., Estuaries, 17, 26–33, 1994.
236. McCormick, S. D.: Endocrine control of osmoregulation in teleost fish., Amer.Zool., 41, 781–794,
2001.
237. McCormick, S. D., Hasegawa, S., and Hirano, T.: Calcium uptake in the skin of a freshwater teleost,
Proc.Natl.Acad.Sci. U.S.A., 89, 3635–3638, 2004.
238. McCormick, S. D., Sundell, K., Bjornsson, B. T., Brown, C. L. and Hiroi, J.: Influence of salinity on
the localization of Na+/K+-ATPase, Na+/K+/2Cl– cotransporter (NKCC) and CFTR anion channel in
chloride cells of the Hawaiian goby (Stenogobius hawaiiensis)., J.Exp.Biol., 206, 4575–4583, 2003.
239. McDonald, D. G., Hobe, H. and Wood, C. M.: The influence of calcium on the physiological responses
of the rainbow trout, Salmo gairdneri, to low environmental pH., J.Exp.Biol., 88, 109–131, 1980.
240. McDonald, M. D., Walsh, P. J. and Wood, C. M.: Transport physiology of the urinary bladder in
teleosts: a suitable model for renal urea handling?, J.Exp.Zool., 292, 604–617, 2002.
241. McDonald, M. D., Grosell, M., Wood, C. M. and Walsh, P. J.: Branchial and renal handling of urea
in the gulf toadfish, Opsanus beta: the effect of exogenous urea loading., Comp.Biochem.Physiol.,
134A, 763–776, 2003.
242. McDonald, M. D., Walsh, P. J. and Wood, C. M.: Branchial and renal excretion of urea and urea
analogues in the plainfin midshipman, Porichthys notatus, J.Comp.Physiol., 172B, 699–712, 2002.
243. McDonald, M. D. and Wood, C. M.: Reabsorption of urea by the kidney of the freshwater rainbow
trout., Fish Physiol.Biochem., 18, 375–386, 1998.
244. McDonald, M. D., Wood, C. M., Wang, Y. X. and Walsh, P. J.: Differential branchial and renal handling
of urea, acetamide and thiourea in the gulf toadfish Opsanus beta: Evidence for two transporters,
J.Exp.Biol., 203, 1027–1037, 2000.
245. McFarland, W. N. and Munz, F. W.: Regulation of body weight and serum composition by hagfish in
various media., Comp.Biochem.Physiol., 14, 383–398, 1965.
246. McGeer, J. C. and Eddy, F. B.: Ionic regulation and nitrogenous excretion in rainbow trout exposed
to buffered and unbuffered freshwater of pH 10.5, Physiol.Zool., 71, 179–190, 1998.
247. McVicar, A. J. and Rankin, J. C.: Dynamics of glomerular filtration in in the river lamprey, Lampetra
fluviatilis L., Amer.J.Physiol., 249, F132–F138, 1985.
248. Miles, H. M.: Renal function in migrating adult coho salmon, Comp.Biochem.Physiol., 38, 787–826,
1971.
249. Morgan, J. D. and Iwama, G. K.: Energy cost of NaCl transport in isolated gills of cutthroat trout.,
Amer.J.Physiol., 277, R631–R639, 2004.
250. Morgan, R. L., Wright, P. A. and Ballantyne, J. S.: Urea transport in kidney brush-border membrane
vesicles from an elasmobranch, Raja erinacea, J.Exp.Biol, 2003.
251. Morrison-Shetlar, A., Edwards, S. L. and Claiborne, J. B.: Molecular identification and cloning of an
NHE-2 like isoform from the gills of the dogfish shark (Squalus acanthias), Bull.Mt.Desert.Island
Biol.Lab., 41, 11, 2002.
252. Musch, M. W., O’Grady, S. M. and Field, M.: Ion transport of marine teleost intestine, Meth.Enzymol.,
192, 746–753, 1990.
253. Musch, M. W., Orellana, S. A., Kimberg, L.S., Field, M., Halm, D.R., Krasny, E.J. and Frizzell, R.A.:
Na+-K+-2Cl– co-transport in the intestine of a marine teleost, Nature, 300, 351–353, 1982.
254. Natochin, Y. V. and Gusev, G. P.: The coupling of magnesium secretion and sodium reabsorption in
the kidney of teleost, Comp.Biochem.Physiol., 37, 107–111, 1970.
255. Nelson, N. and Harvey, W. R.: Vacuolar and plasma membrane proton-adenosinetriphosphatases.
Physiol Rev, 79, 361–385, 1999.
2022_C006.fm Page 225 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
au: please
check pages
225
256. Newbound, D. R. and O’Shea, J. E.: The microanatomy of the rectal salt gland of the Port Jackson
shark, Heterodontus portusjacksoni (Meyer) (Heterodontidae): Suggestions for a counter-current
exchange system., Cells Tissues Organs, 169, 165–175, 2001.
257. Nishimura, M. and Imai, M.: Control of renal function in freshwater and marine teleosts, Fed.Proc.,
41, 2355–2360, 1982.
258. Nishimura, M., Imai, M. and Ogawa, M.: Sodium chloride and water transport in the renal distal
tubule of the rainbow trout, Amer.J.Physiol., 244, F247–F254, 1982.
259. Nonnotte, G., Nonnotte, L. and Kirsch, R.: Chloride cells and chloride exchange in the skin of a seawater teleost, the shanny (Blennius pholis L.)., Cell Tissue Res., 199, 387–396, 1979.
260. O’Donnell, M. J., Kelly, S. P., Nurse, C. A. and Wood, C. M.: A maxi Cl- channel in cultured pavement
cells from the gills of the freshwater rainbow trout Oncorhynchus mykiss ., J.Exp.Biol., 204,
1783–1794, 2001.
261. Oberleithner, H., Lang, F., Messner, G. and Wang, W.: Mechanism of hydrogen ion transport in the
diluting segment of frog kidney, Pflügers Arch., 272–280, 1984.
262. Oguri, M.: Rectal gland of marine and freshwater sharks, Comp.Histol.J., 144, 1151–1152, 1964.
263. Parmelee, J. T. and Renfro, J. L.: Esophageal desalination of seawater in flounder: role of active
sodium transport., Amer.J.Physiol., 245, R888–R893, 1983.
264. Part, P., Wright, P. A. and Wood, C. M.: Urea and water permeability in dogfish (Squalus acanthias)
gills, Comp.Biochem.Physiol. 119A, 117–123, 1998.
265. Patrick, M. L., Pärt, P., Marshall, W. S. and Wood, C. M.: Characterization of ion and acid-base
transport in the freshwater adapted mummichog (Fundulus heteroclitus)., J.Exp.Zool., 279, 208–219,
1997.
266. Patrick, M. L. and Wood, C. M.: Ion and acid-base regulation in the freshwater mummichog (Fundulus
heteroclitus): a departure from the standard model for freshwater teleosts, Comp.Biochem.Physiol.,
122A, 445–456, 1999.
267. Payan, P., Girard, J. P. and Mayer-Gostan, N.: Branchial ion movements in teleosts: the roles of
respiratory and chloride cells. In: Fish Physiology, Vol X.B. Ion and water transfer. W. S. Hoar and
D. J. Randall (Eds.), 39–63, 1984.
268. Payan, P., Goldstein, L. and Forster, R. P.: Gills and kidneys in ureosmotic regulation in euryhaline
skates., Amer.J.Physiol., 224, 367–372, 1973.
269. Pelis, R. M., Goldmeyer, J. E., Crivello, J. and Renfro, J. L.: Cortisol alters carbonic anhydrasemediated renal sulfate secretion., Amer.J.Physiol., 285, R1430–R1438, 2003.
270. Pelis, R. M. and Renfro, J. L.: Active sulfate secretion by the intestine of winter flounder is through
exchange for luminal chloride., Amer.J.Physiol., 284, R380–R388, 2003.
271. Pelis, R. M. and Renfro, J. L.: Role of tubular secretion and carbonic anhydrase in vertebrate renal
sulfate secretion., Amer.J.Physiol., 287, R479–R501, 2004.
272. Pequeux, A., Gilles, R., and Marshall, W. S.: NaCl transport in epithelia and related structures., In:
Advances in Comparative Environmental Pphysiology I. NaCl transport in epithelia. R. Greger, (Ed.)
Berlin: Springer Verlag,, 1–73, 1988.
273. Perrot, M. N., Grierson, N., Hazon, N. and Balment, R. J.: Drinking behavior in sea water and fresh
water teleosts: the role of the renin-angiotensin system., Fish Physiol.Biochem., 10, 161–1668, 1992.
274. Perry, S. F. and Goss, G. G.: The effects of experimentally altered gill chloride cell surface area on
acid-base regulation in rainbow trout during metabolic alkalosis, J.Comp.Physiol., 164B, 327–336,
1994.
275. Perry, S. F., Shahsavarani, A., Georgalis, T., Bayaa, M., Furimsky, M. and Thomas, S. L.: Channels,
pumps, and exchangers in the gill and kidney of freshwater fishes: their role in ionic and acid-base
regulation., J.Exp.Zool., 300, 53–62, 2003.
276. Perry, S. F.: The chloride cell: structure and function in the gills of freshwater fishes, Ann.Rev.Physiol.,
59, 325–347, 1997.
277. Perry, S. F., Beyers, M. L. and Johnson, D. A.: Cloning and molecular characterisation of the trout
(Oncorhynchus mykiss ) vacuolar H+-ATPase B subunit, J.Exp.Biol., 203, 459–470, 2000.
278. Perry, S. F., Payan, P. and Girard, J. P.: Effects of perfusate HCO3 - and PCO2 on chloride uptake in
perfused gills of rainbow trout (Salmo-Gairdneri ), Can.J.Fish.Aq.Sci., 41, 1768–1773, 1984.
279. Philpott, C. W. and Copeland, D. E.: Fine structure of chloride cells from three species of Fundulus.,
J.Cell.Biol., 18, 389–404, 1963.
2022_C006.fm Page 226 Tuesday, June 7, 2005 5:27 PM
226
au: please
update
au: please
check with
ref. to ref.
299
The Physiology of Fishes
280. Piermarini, P. M. and Evans, D. H.: Effects of environmental salinity on Na+/K+- ATPase in the gills
and rectal gland of a euryhaline elasmobranch (Dasyatis sabina), J.Exp.Biol., 203, 2957–2966, 2000.
281. Piermarini, P. M. and Evans, D. H.: Immunochemical analysis of the vacuolar proton-ATPase Bsubunit in the gills of a euryhaline stingray (Dasyatis sabina): effects of salinity and relation to
Na+/K+– ATPase, J.Exp.Biol., 204, 3251–3259, 2001.
282. Piermarini, P. M. and Evans, D. H.: Osmoregulation of the Atlantic stingray (Dasyatis sabina) from
the freshwater lake Jesup of the St. Johns River, Florida, Phys.Zool., 71, 553–560, 1998.
283. Piermarini, P. M., Verlander, J. W., Royaux, I. E., and Evans, D. H.: Pendrin immunoreactivity in the
gill epithelium of a euryhaline elasmobranch., Amer.J.Physiol., 283, R983–R992, 2002.
284. Pillans, R. D. and Franklin, C. E.: Plasma osmolyte concentrations and rectal gland mass of bull
sharks Carchahinus leucas , captured along a salinity gradient, Comp.Biochem.Physiol., A 138,
363–371, 2004.
285. Pisam, M., LeMoal, C., Auperin, B., Prunet, P. and Rambourg, A.: Apical structures of mitochondriarich a and b cells in euryhaline fish gill: Their behaviour in various living conditions., Anat.Rec., 241,
13–24, 1995.
286. Potts, W. T. W.: The effects of pH and calcium on gill potentials and sodium balance in the brown
trout Salmo trutta., In: Epithelial Transport in Lower Vertebrates , B. Lahlou, (Ed.), London:
Cambridge University Press, 115–120, 1980.
287. Potts, W. T. W.: Transepithelial potentials in fish gills. In: Fish Physiology, Vol XB Gill ion and water
transfer. W. S. Hoar and D.J.Randall (Eds.), New York: Academic Press, 105–128, 1984.
288. Potts, W. T. W. and Eddy, F.B.: Gill potentials and sodium fluxes in the flounder Platichthys flesus.,
J.Comp.Physiol., 87, 29–48, 1973.
289. Potts, W. T. W., Fletcher, C.R. and Hedges, A.J.: The in vivo transepithelial potential in a marine
teleost., J.Comp.Physiol., 161B, 393–400, 1991.
290. Preest, A. M. R., Gonzales, R. J. and Wilson, R. W.: A phamacological examination of Na+ and Cl–
transport in two species of freshwater fish, Physiol.Biochem.Zool., In press, 2004.
291. Randall, D. J., Wood, C. M., Perry, S. F., Bergman, H., Maloiy, G. M., Mommsen, T. P. and Wright,
P. A.: Urea excretion as a strategy for survival in a fish living in a very alkaline environment., Nature,
337, 165–166, 1989.
292. Rankin, J. C., Logan, A. G. and Moriarty, R. J.: Changes in kidney function in the river lamprey,
Lampetra fluviatilis, in response to changes in external salinity, In: Epithelial Transport in the Lower
Vertebrates, B. Lahlou (Ed.),Cambridge: Cambridge University Press, 171–184, 1980.
293. Reid, S. D., Hawkings, G. S., Galvez, F. and Goss, G. G.: Localization and characterization of
phenamil-sensitive Na+ influx in isolated rainbow trout gill epithelial cells., J.Exp.Biol., 206, 551–559,
2003.
294. Renfro, J. L.: Water and ion transport by the urinary bladder of the teleost Pseudopleuronectes
americanus., Amer.J.Physiol., 228, 52–61, 1975.
295. Renfro, J. L.: Interdependence of active Na+ and Cl– transport by the isolated urinary bladder of the
teleost Pseudopleuronectes americanus. , J Exp Zool, 199, 383–390, 1977.
296. Renfro, J. L., Miller, D. S., Karnaky, K. J. Jr. and Kinter, W. B.: Na+,K+-ATPase localization in the
teleost urinary bladder by [3H]ouabain autoradiography, Amer.J.Physiol., 231, 1735–1743, 1976.
297. Renfro, J. L.: Relationship between renal fluid and magnesium secretion in a glomerular marine
teleost, Amer.J.Physiol., 238, F92–F98, 1980.
298. Renfro, J. L. and Pritchard, J. B.: H+-dependent sulfate secretion in the marine teleost renal tubule,
Amer.J.Physiol., 243, F150–F159, 1982.
299. Renfro, J. L. and Pritchard, J. B.: H+-dependent sulfate transport by flounder renal tubule brush border:
presence of anion exchange, Amer.J.Physiol., 244, F488–F496, 1982.
300. Renfro, J. L. and Pritchard, J. B.: Sulfate transport by flounder renal tubule brush border: presence
of anion exchange, Amer.J.Physiol., 244, F488–F496, 1983.
301. Renfro, J. L. and Shustock, E.: Peritubular uptake and brush boarder transport of magnesium-28 by
flounder Pseudopleuronectes americanus renal tubules, Amer.J.Physiol., 249, F497–F506, 1985.
302. Richards, J. G., Semple, J. W., Bystriansky, J. S. and Schulte, P. M.: Na+/K+-ATPase a-isoform
switching in gills of rainbow trout (Oncorhynchus mykiss ) during salinity transfer., J.Exp.Biol., 206,
4475–4486, 2004.
303. Rimmer, D. W. and Wiebe, W. J.: Fermentative microbial digestion in herbivorous fishes, J.Fish.Biol.,
31, 229–236, 1987.
2022_C006.fm Page 227 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
au: publishers?
227
304. Sanders, M. J. and Kirschner, L. B.: Potassium metabolism in seawater teleosts: II. Evidence for active
potassium extrusion across the gill., J.Exp.Biol., 104, 29–40, 1983.
305. Sardet C, Pisam M, and Maetz J.: The surface epithelium of teleost fish gills. Cellular and junctional
adaptations of the chloride cell in relation to salt adaptation., J.Cell.Biol., 80, 96–117, 1979.
306. Schmidt-Nielsen, B.: Renal transport of urea in elasmobranchs., In: Transport Mechanisms in Epithelia, Alfred Benzon Symp.V., H. H. Ussing and N. A. Thorn (Eds.), Copenhagen: Munksgaard, 621,
1972.
307. Schmidt-Nielsen, B. and Rabinowitz, L.: Methylurea and acetamide: active reabsorption by elasmobranch renal tubules., Science, 146, 1587–1588, 1964.
308. Schmidt-Nielsen, B., Truninger, B., and Rabinowitz, L.: Sodium-linked urea transport by the renal
tubule of the spiny dogfish Squalus acanthias, Comp.Biochem.Physiol., 42A, 13–25, 1972.
309. Schofield, J. P., Stephen, D., Jones, C. and Forrest, J. N.: Identification of C-type natriuretic peptide
in heart of spiny dogfish shark (Squalus-Acanthias), Amer.J.Phys., 261, F734–F739, 1991.
310. Seidelin, M., Madsen, S. S., Blenstrup, H., and Tipsmark, C. K.: Time-course changes in the expression
of the Na+, K+-ATPase in gills and pyloric caeca of brown trout (Salmo trutta) during acclimation to
seawater., Physiol.Biochem.Zool., 73, 446–453, 2000.
311. Shannon, J. A.: On the mechanism of the renal tubular excretion of creatinine in the dogfish, Squalus
acanthias., J.Cell.Comp.Physiol., 16, 285–291, 1940.
312. Shehadeh, Z. H. and Gordon, M. S.: The role of the intestine in salinity adaptation of the rainbow
trout, Salmo gairdneri, Comp.Biochem.Physiol., 30, 397–418, 1969.
313. Shepherd, B. S., Sakamoto, T., Nishioka, R. S., Richman, N. H. 3rd., Mori, I., Madsen, S. S., Chen,
T. T., Hirano, T., Bern, H, A. and Grau, E. G.: Somatotropic actions of the homologous growth
hormone and prolactins in the euryhaline teleost, the tilapia, Oreochromis mossambicus .,
Proc.Nat.Acad.Sci. U.S.A., 94, 2068–2072, 1997.
314. Shuttleworth, T. J.: Haemodynamic effects of secretory agents on the isolated elasmobranch rectal
gland, J.Exp.Biol, 103, 193–204, 1983.
315. Shuttleworth, T. J.: Salt and water balance - extrarenal mechanisms, In: The Physiology of Elasmobranch Fishes. Berlin: Springer, 171–199, 1988.
316. Silva, P. and Epstein, F. H.: Role of the cytoskeleton in secretion of chloride by shark rectal gland,
J.Comp.Physiol., 172B, 719–723, 2002.
317. Silva, P., Epstein, J., Myers, M., Stevens, A., and Epstein, F. H.: Inhibition of chloride secretion by
BaCl in the rectal gland of the spiny dogfish, Squalus acanthias, Bull.MDIBL., 21, 12–13, 1981.
318. Silva, P., Solomon, R. J., and Epstein, F. H.: Mode of activation of salt secretion by C-type natriuretic
peptide in the shark rectal gland, Amer.J.Phys., 277, R1725–R1732, 1999.
319. Silva, P., Stoff, J. S., Solomon, R. J., Lear, S., Kniaz, D., Greger, R. and Epstein, F. H.: Atrialnatriuretic-peptide stimulates salt secretion by shark rectal gland by releasing VIP, Amer.J.Phys.,
252, F99–F103, 1987.
320. Singer, T. D., Tucker, S. J., Marshall, W. S. and Higgins, C. F.: A divergent CFTR homologue: highly
regulated salt transport in the euryhaline teleost F. heteroclitus., Amer.J.Physiol., 274, C715–C723,
1998.
321. Skadhauge, E.: Coupling of transmural flows of NaCl and water in the intestine of the eel (Anguilla
anguilla)., J.Exp.Biol, 60, 535–546, 1974.
322. Skou, J. C.: The energy coupled exchange of Na+ for K+ across the cell membrane. The Na+, K+pump., FEBS Lett., 268, 314–324, 1990.
323. Skou, J. C. and Esmann, M.: The Na,K-ATPase, J.Bioenerg.Biomembr., 24, 249–261, 1992.
324. Sleet, R. B. and Weber, L. J.: The rate and manner of seawater ingestion by a marine teleost and
corresponding seawater modification by the gut., Comp.Biochem.Physiol., 72A, 469–475, 1982.
325. Smith, C. P. and Wright, P. A.: Molecular characterization of an elasmobranch urea transporter,
Amer.J.Physiol., 276, R622–R626, 1999.
326. Smith, H. W.: The absorption and excretion of water and salts by marine teleosts, Amer.J.Physiol.,
93, 480–505, 1930.
327. Smith, H. W.: The absorption and excretion of water and salts by the elasmobranch fishes. I. Freshwater
elasmobranchs, Amer.J.Physiol., 98, 279–295, 1931.
328. Smith, H. W.: The absorption and excretion of water and salts by the elasmobranch fishes. II. Marine
elasmobranchs, Amer.J.Physiol., 98, 296–310, 1931.
329. Smith, L. H.: Digestive Functions in Teleost Fishes , 331–421, 2004.
2022_C006.fm Page 228 Tuesday, June 7, 2005 5:27 PM
228
The Physiology of Fishes
330. Smith, N. F., Eddy, F. B., Struthers, A. D. and Talbot, C.: Renin, atrial-natriuretic-peptide and bloodplasma ions in parr and smolts of Atlantic salmon Salmo-Salar L. and rainbow trout Oncorhynchus
mykiss (Walbaum) in fresh-water and after short-term exposure to sea-water, J.Exp.Biol., 157, 63–74,
1991.
331. Smith, N. F., Talbot, C. and Eddy, F. B.: Dietary salt intake and its relevance to ionic regulation in
freshwater salmonids, J.Fish.Biol., 35, 749–753, 1989.
332. Smith, W. W.: The excretion of phenol red in the dogfish, Squalus acanthias., J.Cell.Comp.Physiol.,
14, 357–363, 1939.
333. Solomon, R., Protter, A., Mcenroe, G., Porter, J. G., and Silva, P.: C-Type natriuretic peptides stimulate
chloride secretion in the rectal gland of squalus-acanthias., Amer.J.Physiol., 262, R707–R711, 1992.
334. Solomon, R., Taylor, M., Sheth, S., Silva, P. and Epstein, F. H.: Primary role of volume expansion in
stimulation of rectal gland function., Amer.J.Physiol., 248, R638–R640, 1985.
335. Sterling, D., Alvarez, B. V. and Casey, J. R.: The extracellular component of a transport metabolon.
Extracellular loop 4 of the human AE1 Cl–/HCO3– exchanger binds carbonic anhydrase IV.,
J.Biol.Chem., 277, 25239–25246, 2002.
336. Stolte, H., Galaske, R. G., Eisenbach, G. M., Lechene, C., Schmidt-Nielsen, B., and Boylan, J. W.:
Renal tubule ion transport and collecting duct function in the elasmobranch littel skate., Raja erinacea,
J.Exp.Zool., 199, 403–410, 1977.
337. Sturla, M., Masini, M. A., Prato, P., Grattarola, C. and Uva, B.: Mitochondria-rich cells in gills and
skin of an African lungfish, Protopterus annectens., Cell.Tiss.Res., 303, 351–358, 2001.
338. Sullivan, G., Fryer, J. N. and Perry, S. F.: Immunolocalization of proton pumps (H+-ATPase) in
pavement cells of rainbow trout gill, J.Exp.Biol., 198, 2619–2629, 1995.
339. Suzuki, Y., Itakura, M., Kashiwagi, M., Nakamura, N., Matsuki, T., Sakuta, H., Naito, N., Takano,
K., Fujita, T. and Hirose, S.: Identification by differential display of a hypertonicity-inducible inward
rectifier potassium channel highly expressed in chloride cells., J.Biol.Chem., 274, 11376–11382, 1999.
340. Swenson, E. R.: A comparative approach to carbonic anhydrase: the work of Thomas H. Maren.,
Comp.Biochem.Physiol., 136A, 229–241, 2003.
341. Swenson, E. R. and Maren, T. H.: Roles of gill and red cell carbonic anhydrase in elasmobranch
HCO3– and CO2 excretion., Amer.J.Physiol., 253, R450–R458, 1987.
342. Takei, Y.: Structural and functional evolution of the natriuretic peptide system in vertebrates.,
au: please
Int.Rev.Cytol., 194, 1–66, 2000.
343. Takei, Y. and Tsuchida, T.: Role of the renin-angiotensin system in drinking of the seawater-adapted doublecheck
eels Anguilla japonica: reevaluation., Amer.J.Physiol., 279, R1105–R1111, 2000.
344. Takei, Y.: Comparative physiology of body fluid regulation in vertebrates with special reference to
thirst regulation, Jap.J.Phys., 50, 171–186, 2000.
345. Takei, Y., Hirano, T., and Kobayashi, H.: Angiotensin and water intake in the Japanese eel, Anguilla
japonica, Gen.Comp.Endocrinol., 38, 446–475, 1979.
346. Takei, Y., Okubo, J. and Yamaguchi, K.: Effect of celular dehydration on drinking and plasma
angiotensin II level in the eel, Anguilla japonica, Zool.Sci., 5, 43–51, 1988.
347. Takei, Y., Tsuchida, T., Li, Z. H. and Conlon, J. M.: Antidipsogenic effects of eel bradykinins in the
eel Anguilla japonica, Amer.J.Phys., 281, R1090–R1096, 2001.
348. Thorson, T. B.: Osmoregulation in fresh-water elasmobranchs, In: Sharks, Skates and Rays P. W.
Gilbert, R. F. Mathewson, and D. P. Rall, (Eds.) Baltimore, Maryland: John Hopkins Press, 265–270,
1967.
349. Thorson, T. B.: Freshwater stingrays, Potamotrygon spp: failure to concentrate urea when exposed to
a saline medium., Life Science, 9, 893–900, 1970.
350. Thorson, T. B., Cowan, C. M. and Watson, D. E.: Potamotrygon spp.: Elasmobranchs with low urea
content., Science, 158, 375–377, 1967.
351. Tierney, M. L., Luke, G., Cramb, G., and Hazon, N.: The role of the renin-angiotensin system in the
control of blood-pressure and drinking in the European eel, Anguilla anguilla., Gen.Comp.Endocrinol.,
100, 39–48, 1995.
352. Tipsmark, C. K., Madsen, S. S., Seidelin, M., Christensen, A. S., Cutler, C. P., and Cramb, G.:
Dynamics of Na+,K+,2Cl– cotransporter and Na+,K+-ATPase expression in the branchial epithelium of
brown trout (Salmo trutta) and Atlantic salmon (Salmo salar)., J.Exp.Zool., 293, 106–118, 2002.
353. Tomasso, J. R. and Grosell, M.: Physiological basis for large differences in resistance to nitrite among
freshwater and freshwater acclimated euryhaline fishes, Environ.Sci.Technol., In press.
2022_C006.fm Page 229 Tuesday, June 7, 2005 5:27 PM
Ion Transport, Osmoregulation, and Acid–Base Balance
229
354. Tsuchida, T. and Takei, Y.: Effects of homologous atrial natriuretic peptide on drinking and plasma
ANG II level in eels, Amer.J.Phys., 44, R1605–R1610, 1998.
355. Tufts, B. L., Gervais, M. R., Staebler, M. and Weaver, J.: Subcellular distribution and characterization
of gill carbonic anhydrase and evidence for a plasma carbonic anhydrase inhibitor in Antarctic fish.,
J.Comp.Physiol., 172B, 287–295, 2002.
356. Tytler, P., Tatner, M. and Findley, C.: The ontogeny of drinking in the rainbow trout, Onchorhynchus
mykiss (Walbaum)., J.Fish.Biol., 36, 867–875, 1990.
357. Usher, M. L., Talbot, C. and Eddy, F. B.: Drinking in atlantic salmon smolts transferred to seawater
and the relationship between drinking and feeding, Aquaculture, 73, 237–246, 1988.
358. Usher, M. L., Talbot, C. and Eddy, F. B.: Intestinal water transport in juvenile atlantic salmon (Salmo
salar L.) during smolting and following transfer to seawater., Comp.Biochem.Physiol., 100A, 813–818,
1991.
359. Vince, J. W., Carlsson, U. and Reithmeier, R. A.: Localization of the Cl–/HCO3– anion exchanger binding
site to the amino-terminal region of carbonic anhydrase II., Biochemistry, 39, 13344–13349, 2000.
360. Vince, J. W. and Reithmeier, R. A.: Identification of the carbonic anhydrase II binding site in the
Cl–/HCO3– anion exchanger AE1. Biochemistry, 39, 5527–5533, 2000.
361. Vogel, W., Vogel, V. and Pfautsch, M.: Arterio-venous anastomoses in rainbow trout gill filaments: a
scanning and transmission electron microscopic study., Cell.Tiss.Res., 167, 373–385, 1976.
362. Walsh, P. J., Blackwelder, P., Gill, K. A., Danulat, E. and Mommsen, T. P.: Carbonate deposits in marine
fish intestines: a new source of biomineralization., Limnol.Oceanography, 36, 1227–1232, 1991.
363. Wang, Y. S., Gonzalez, R. J., Patrick, M. L., Grosell, M., Zhang, C., Feng, Q., Du, J., Walsh, P. J.
and Wood, C. M.: Unusual physiology of scale-less carp, Gymnocypris przewalskii , in Lake Qinghai:
a high altitude alkaline saline lake., Comp.Biochem.Physiol., 134A, 409–421, 2003.
364. Weech, S. A., Scheuhammer, A. M., Elliott, J. E. and Cheng, K. M.: Mercury in fish from the Pinchi
Lake Region, British Columbia, Canada., Environ.Pollut., 131, 275–286, 2004.
365. Wendelaar Bonga, S. E.: The stress response in fish., Physiol Rev, 77, 591–625, 1997.
366. Wilkie, M. P.: Mechanisms of ammonia excretion across fish gills, Comp.Biochem.Physiol. A., 118A,
39–50, 1997.
367. Wilkie, M. P.: Ammonia excretion and urea handling by fish gills: present understanding and future
research challenges., J.Exp.Zool., 293, 284–301, 2002.
368. Wilkie, M. P. and Wood, C.: The adaptations of fish to extreme alkaline environments, Comp.Biochem.Physiol., 113B, 665–673, 1996.
369. Wilson, J. M., Laurent, P., Tufts, B. L., Benos, D. J., Donowitz, M., Vogl, A. W. and Randall, D. J.:
NaCl uptake by the branchial epithelium in freshwater teleost fish: and immunological approach to
ion transport protein localization., J.Exp.Biol., 203, 2279–2296, 2000.
370. Wilson, J. M., Randall, D. J., Donowitz, M., Vogl, A. W. and Ip, A. K. Y.: Immunolocalization of ion
transport proteins to branchial epithelium mitochondria rich cells in the mudskipper (Periophthalmodon schlosseri)., J.Exp.Biol., 203, 2297–2310, 2000.
371. Wilson, J. M., Morgan, J. D., Vogl, A. W. and Randall, D. J.: Branchial mitochondria-rich cells in the
dogfish Squalus acanthias, Comp.Biochem.Phys. 132A, 365–374, 2002.
372. Wilson, R. W.: A novel role for the gut of seawater teleosts in acid-base balance, Regulation of AcidBase Status in Animals and Plants, SEB seminar series, Cambridge: Cambridge University Press, 68,
257–274, 1999.
373. Wilson, R. W., Gilmour, K., Henry, R., and Wood, C.: Intestinal base excretion in the seawater-adapted
rainbow trout: a role in acid-base balance?, J.Exp.Biol, 199, 2331–2343, 1996.
374. Wilson, R. W. and Grosell, M.: Intestinal bicarbonate secretion in marine teleost fish — source of
bicarbonate, pH sensitivity, and consequence for whole animal acid-base and divalent cation homeostasis, Biochim.Biophys.Acta, 1618, 163–193, 2003.
375. Wilson, R. W., Wilson, J. M., and Grosell, M.: Intestinal bicarbonate secretion by marine teleost
fish — why and how?, Biochim.Biophys.Acta, 1566, 182–193, 2002.
376. Wilson, R. W., Wright, P. M., Munger, S. and Wood, C. M.: Ammonia excretion in fresh-water rainbowtrout (Oncorhynchus-Mykiss ) and the importance of gill boundary-layer acidification — lack of
evidence for Na+/NH4+ exchange, J.Exp.Biol., 191, 37–58, 1994.
377. Wong, T. M. and Chan, D. K. O.: Physiological adjustments to dilution of the exteransl medium in
the lip-shark Memiscyllium plagiosum (bennet). II. Branchial, renal and rectal gland function,
J.Exp.Zool., 200, 85–96, 1977.
2022_C006.fm Page 230 Tuesday, June 7, 2005 5:27 PM
230
au: please
check. same
as 379
The Physiology of Fishes
378. Wood, C. M., Kelly, S. P., Fletcher, M., Zhou, B., O’Donnell, M., Eletti, B. and Part, P.: Cultured gill
epithelia as models for the freshwater fish gill, Biochim.Biophys.Acta., 1566, 72–83, 2002.
379. Wood, C. M., Matsuo, A. Y., Gonzalez, R. J., Wilson, R. W., Gonzalez, R. J., Patrick, M. L. and Val,
A. L.: Mechanisms of ion transport in Potamotrygon, a stenohaline freshwater elasmobranch native
to the ion-poor black waters of the Rio Negro., J.Exp.Biol. 205, 3039–3054, 2002.
380. Wood, C. M. and Part, P.: Cultured branchial epithelia from freshwater fish gills, J.Exp.Biol., 200,
1047–1059, 1997.
381. Wood, C. M.: Ammonia and urea metabolism and excretion, In: The Physiology of Fishes. Evans D. H.
(Ed.), Boca Raton: CRC Press, 157–176, 1st Edition, 379–425, 1993.
382. Wood, C. M., Matsuo, A. Y. O., Gonzalez, R. J., Wilson, R. W., Patrick, M. L., and Val, A. L.:
Mechanisms of ion transport in Potamotrygon, a stenohaline freshwater elasmobranch native to the
ion-poor blackwaters of the Rio Negro., J.Exp.Biol., 205, 3039–3054, 2002.
383. Wood, C. M. and Randall, D. J.: The effects of anaemia on ion exchange in the southern flounder
(Paralichthys lethostigma), Comp.Biochem.Physiol., A39, 391–402, 1971.
384. Xu, J. C., Lytle, C., Zhu, T. T., Payne, J. A., Benz, E. Jr. and Forbush, B. 3rd: Molecular cloning and
functional expression of the bumetanide-sensitive Na-K-Cl cotransporter., Proc.Natl.Acad.Sci. USA.,
91, 2201–2205, 1994.
385. Yokota, S., Iwata, K., Fujii, Y. and Ando, M.: Ion transport across the skin of the mudskipper
Periophthalmus modestus ., Comp.Biochem.Physiol. 118A, 903–910, 2004.
386. Zadunaisky, J. A., Cardona, S., Au, L., Roberts, D. M., Lowenstein, B., Cragoe, E. J. Jr. and Spring,
K. R.: Chloride transport activation by plasma osmolarity during rapid adaptation to high salinity of
Fundulus heteroclitus., J.Membr.Biol., 143, 207–217, 1995.
387. Zhou, B., Kelly, S. P., Ianowski, J. P. and Wood, C. M.: Effects of cortisol and prolactin on Na+ and
Cl– transport in cultured branchial epithelia from FW rainbow trout., Amer.J.Physiol., 285,
R1305–R1316, 2003.
388. Zydlewski, J. and McCormick, S. D.: Developmental and environmental regulation of chloride cells
in young American shad, Alosa sapidissima., J.Exp.Zool., 290, 73–87, 2001.