Physiological Effects of High Pressures
of Nitrogen and Oxygen
By AVALLACE
0.
FENNN, Pu.D.. D.Sc.
A brief survey is giveen of the effects of different pressures on living organisms. Highpartial pressures inhibit oxidative metabolism and, according to Gersehman, have
effects which summate at some point with the effects of radiation. In a study of the mechanism of the narcotic effect of inert gases, it was found that high pressures of nitrogen and
argon, but not helium, act like other anestheties in favoring water-in-oil rather than oil-inwater emulsion of dilute NaOH solutions and olive oil. The effect is small but appears to
be real. This suggests that inert gases may make the lipoidal surface layer of cells relatively
more continuous and therefore less permeable.
oxygen
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B AROPHYSIOLOGY is a new term.
coined for the purposes of this talk and
arbitrarily defined as anything in physiology
involving the use of pressures from the zero
pressure of infinite space to the maximum
pressure inside the largest of the stars of the
universe. The range thus included varies
from 0 to 1016 atmospheres. In the center of
our sun the pressure is said to be 101" atmospheres,' and in the center of our earth it is
3.6 X 106 atmospheres.2 The highest pressure
attained more or less continuously in the laboratory for experinmental purposes is 2 X 10l
atmospheres. The highest pressure used in
physiological investigations is between 1,000
and 10,000 atmospheres and even this is 10100 times as great as the partial pressures of
the respiratory gases whieh are of physiological importance.
In one sense these high pressures are not
foreign to our bodies, for the intrinsic pressure
of water calculated from the van der Waals's
equation is said to be 11,000 atni. When
an external pressure of 1,000 atm. is applied
to water, it decreases in volume by 20 per
cent.3 At still higher pressures fluids become
solids and electrons become displaced from
their orbits and circulate freelv as in metals.
Such apparently is the situation in the center
of the earth where the pressure is such as;
to reduce iron to half its sea-level volume. At
still higher pressures nuelei iiay fuse with
tremendous liberation of energy, as in the sun
and stars, where hydrogen condenses to helium and helium to bervlliuin and carbon.
Under the maximuml pressure of still larger
suns, the properties of matter and the laws
of chemistrv must be very different froin anything known to us on the surface of the earth.
Here we live in a verv narrow pressure range.
v-arying only from sunny to stormy days and
mountain tops to the sea. Tt is an interesting
qluestion what great purpose is served bv these
great starry masses with sueh inconeeivablv
large pressutres at their eenters, all circulating
around aimlessly in otherwise emptv space or
rushing madly away to the far corners of our
expanding universe.
Be that as it may, I am concerned only with
the physiological aspects of pressure. T propose to say only a few words about pressure
per se in order to put the whole subject into
its proper setting an-d to devote most of my
time to those aspects of the subjeet with which
T have personally been to some degree concerned, e.g., the partial pressuires of some of
the normal respiratory gases. These too are
sometimes encountered at grossly abnormal
total pressures, and they have some very defilite physiological effects. the fulll explanation
of which still eludes us.
The mnaximunr pressurLe (ooinpatible with
life is found at the bottom of the ocean about
From the Department of Physiology, University
of Rochester School of Medicine and Dentistry,
Rochester, N. Y.
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6 to 7 muiles below the surface. Perhaps this
is only because there are no greater pressures
naturally available for adventurous living
organisms. Even man has penetrated recently
in the Trieste to the very bottoin of the ocean
and returned safely, although he ingeniously
carried with him a fairly normal environment.
At pressures much greater than the 1,000
atmospheres found at the bottom of the ocean,
proteins are coagulated, toxins, viruses, and
enzymes are inactivated, red cells are disintegrated, blood coagulates, bimolecular leaflets
are disrupted, and life becomes impossible.
Between 100 and 1,000 atmospheres there is
a twilight zone where rnarked physiological
effects are encountered but many forms of life
are found. Any living organism in the ocean
is likely to sink to the bottom on occasions
if its flotation apparatus fails or if it stops
actively swimming upwards. Some species
have survived such an accident by suitable
mutations, and now an astonishing variety of
species can be brought up from the bottom.4
These have been called barophils, while those
higher up at perhaps 500 atmospheres or less
are called barophobes. Neither group of organisms can survive well in the environment
of the other. Just what mutations are necessary for survival on the bottom we can
only guess, but they must at least produce
proteins and lipid layers which are not
denatured by the high ambient pressures.
Pressure of course favors those reactions
which result in a decrease in volume, and thus
the relative rates of different reactions are
altered so that the steady-state composition
of the tissues is changed. In general, pressure
forces molecules more closely together, while
temperature tends to expand them, so to some
extent these two quantities are antagonistic.
Some reactions however are favored by simultaneous high pressures and high temperatures,
as in the formation of artificial diamonds.
Many of the physiological effects of high
pressures have been reviewed by Dr. Cattell
in his classical summary of the subject of biological pressures published in 1936. There is
for example a cessation of cardiae, ciliary,
aind ameboid activity. The work of Ebbeeke,
Circulation, Volume XXVI, November 1i962
1135
Cattell and Edwards, Brown, Marsland, and
others (see Cattell3 for references) tells us
that pressure has a marked effect also on
skeletal muscles. At a pressure of 400 atm.
or more a muscle goes into a smooth contracture without action potentials, which lasts as
long as the pressure is applied. By electrical
stimulation a twitch can be superimposed
upon this contracture. Brief exposure to
lower pressures will itself produce a twitch
or brief contraction. Apparently pressure can
bypass the excitatory mechanism and activate
the contractile mechanism itself. Of special
interest is the fact that the application of
pressure during the initial (but not the later)
phases of the contraction will intensify the
liberation of energy and the tension produced
(Brown and Cattell). Pressure, like low temperature, apparently prolongs the duration of
the active state so that the total energy release is increased. It seems natural to correlate these effects with the decrease in volume
which results when a muscle contracts, but
the exact explanation is debatable and probably complex.
I cannot, however, spend more time on these
fascinating experiments for which I have the
greatest of admiration. I must nevertheless
call attention to the beautiful work of Johnson, Eyring, Marsland, and others from
Princeton on the effects of pressure and temperature on reaction rates in luminescent
bacteria.5 6 There is an optimum temperature
for luminescence. At temperatures below the
optimum, luminescence increases with rising
temperature because the activation of the enzyme is accelerated. This reaction involves
an increase in volume and is inhibited by
pressure. At temperatures above the optimum,
luminescence falls off because the inactivated
enzyine supply is diminished by a reversible
denaturation which now becomes the limiting
factor in the process. This denaturation is
accelerated by narcotics but is inhibited by
pressure because the volume increases. Hence
in this region pressure has an antinarcotic
effect and increases luminescence. The data
obtained are nicely explained quantitatively
in terms of reaction rates with suitable con-
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stants for the pressure aud the temperature
effects. It is interesting to note that the same
antagonism between narcotics and pressure
has been demonstrated in records of nerveaction potentials by Syropoulos.7 These studies
indicate therefore that pressure as well as
temperature can be a valuable tool in analyzing the molecular processes concerned in
physiological phenomiena.
Inl line with the subject matter of this symposium, it is evideiit that pressure can affect
the permeability of cell membranes. Gerschfeld and Shanes8 have shown, for example,
that nlerves gain sodium and lose potassium
wheni subjected to high pressures. Some gels
change to sols under high pressures9 and Golovina in Russia'0 has shown that isolated brain
cells take up neutral red more easily when
they are subjected to a pressure of 2,000 atm.,
eveen for the short period of 10 minutes. Daniellil" reported that the protoplasmic tentacles
of a niarine protozoan are broken up into
drops when the protoplasmie gel is liquefied
by pressure. I was intrigued, however, to
learn that sonie of the bacteria brought up
from:n the bottom of the ocean by the Danish
Galathea expedition4 and grown under pressure of 600 atm. produced long chains of
incompletely separated cells, while at 1 atm.
pressure they divided into discrete cells.12 In
one case, therefore, pressure unites, while in
another it divides.
I must, however, leave this fascinating subject of the effects of simple hydrostatic pressures, which promises so niuch interest for
the future, and turn to the more mundane and
famniliar problems of some of the partial pressures of oxygen and nitrogen with which so
mnany physiologists have been concerned.
Some of these effects also may prove to have
sonie bearing on problems of the plasma membrane behavior.
MNIy own interest in barophysiology began
when I read two statements in Commander
Ellsbergo's very interesting book entitled Meni
lnder the Sea.13 In discussing the physiology
of divers engaged in underwater salvage work,
he expressed the opinion that under high
oxvgen pressures "the fat in his body is lit-
FENN
erally burned out of him" but the divers were
sonietimes capable of superhuman mnuscular
feats because of high oxygen stimulation;
they had ani "oxygen jag." All these statememits were probably wrong.
Wiith the aid of a graduate studeiit, Elizabeth Cass (now Mrs. Henry Wills), we unidertook (in 1941) to nmeasure the effect of high
oxygen pressures on the mnetabolic rate of frog
musele. To follow this under high pressures.
we decided to measure the output of carbon
dioxide by measuring the electrical conduetivitv of barium hydrate solutions in which
the CO2 was absorbed. The results showed
clearly that the metabolic rate was reversiblv
depressed when the oxygen concentration was
raised to 15 atmospheres. Sometimes there
was an inlitial increase in metabolic rate with
high oxygen, but this occurred also with high
nitrogen. A few years ago Dr. Charles Major
repeated these experiments at Rochester (unpublished) and found that this rise was due
to a contracture of the muscle caused by the
sudden rise in temperature when the gas was
compressed. With a slower rate of pressurization it did not occur. In spite of this complication, the inhibition due to high oxygen
pressure was clearly demonstrated. The experiments were completed in 1943 but were not
published until 1947.'4 In the meantime,
Stadie, Riggs, and Haugaard'5 had found a
sinmilar result by other methods. It still seems
to me likely that the phenomenon of oxygen
poisoning is due directly or imidireetly to this
interference with the oxidizing meehanism in
the cells, resultimig perhaps from an oxidation
of -SH groups.
Some years later Dr. Rebeca Gerschman
was working in my laboratory on oxygen
poisoning. She found that high oxygen, like
low oxygen, is a stressful experience and results in a decrease in the ascorbic acid content of the adrenal gland.16 More significant,
however, was her observation that the rats
which were simultaneously irradiated while
being exposed to 6 atmospheres of oxygen died
sooner than the controls without radiation.
The radiation alone did not kill the rats for
several days while the oxygen was lethal in
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less than 1 hour.'7 Radiation had no effect
if it was completed more than 5 hours before
exposure to oxygen. If still longer periods
elapsed between the end of radiation and the
beginning of oxygen, the oxygen seemed to
have no effect, i.e., previous radiation protected against oxygen poisoning. This, however, was later shown to be due to the
inanition or anorexia which characterizes the
terminal stages of radiation damage.'8 The
rats were already too sick to show signs of
oxygen poisoning. As an interpretation of
these experiments, Dr. Gerschman proposed
that there was some common factor in radiation and oxygen damage which summated
when they were applied more or less simultaneously. This was thought to be the formation of free oxidizing radicals by both radiation and oxygen. The interpretation of this
experiment is perhaps not quite so straightw
forward. Conceivably radiation may act quite
unspecifically, and any untoward event might
well hasten death during an acute exposure
to lethal concentrations of oxygen. In further
support of her thesis, however, Dr. Gerschman found that a number of substances which
protected against radiation would also protect
against oxygen poisoning. Likewise it was
shown that oxygen like radiation had a mutagenic effect on E. coli19 and produced an abnormal percentage of streptomycin-tolerant
mutants. These effects of high oxygen pressure are extremely intriguing and have numerous and far-reaching applications, as for
example in the proposed treatment of cancer
by combined radiation and high 02
So far as I know, the effects of oxygen on
the cell membrane and its permeability have
not been thoroughly studied and might well
repay close investigation. High oxygen would
almost certainly interfere with active transport across membranes, and one of our medical students found that it did interfere with
the transport of sodium by frog skin.20 Likewise, it is known that one of the first effects
of high oxygen pressures is on the pulmonary
epithelium with the development of pulmonary edema. As Dr. Gerschman has repeatedly
pointed out, high oxygen is a much more
Circulation, Volume XXVI, November
1962
1137
toxic substance than is generally believed and
may well be intimately concerned with the
whole process of aging. Indeed it may be
that man would live longer if there were less
oxygen in the air than the concentration
which we now consider normal. Life has developed on the earth in a period when the
oxygen concentration has been gradually increasing from its primeval reduced level, and
it may be that the biological processes of
adaptation are losing ground in the effort
to keep up with the rising oxidative level of
our environment. Such at least is the thesis
which Dr. Gerschman and her collaborator
Dr. Dan Gilbert2' have presented for our consideration. With the exception of the combined radiation and oxygen treatments, the
evidence in favor of it is only indirect and
even the more direct radiation experiments
should be repeated under a variety of different conditions. I do not consider that the
thesis is proved, but I do feel that it should
not be dismissed without further study.
Since oxygen is toxic at only a few atinospheres of pressure, it hardly deserves a place
in a paper on barophysiology. Nitrogen, however, requires much higher pressures before
any physiological effect can be observed and
has therefore a better claim for inclusion in
this discussion. It is generally regarded as
an inert gas, but this is not because the outer
atomic shell contains its full complement of
8 electrons, for it contains only 5, but because
the internal bond energy of the triple bond
of the N2 molecule is so unusually large (226
Kg.-Cal. per mol., compared to 96 for 02;
Pauling22) that the gas is not easily ionized.
Being a constituent of proteins and many
other organic substances, nitrogen is not an
unreactive molecule, but nitrogen gas is certainly unreactive. For this reason it was most
surprising to learn 30 years ago that divers
suffer from something which has come to be
called nitrogen narcoqis, or rapture of the
deep. This it was, in fact, which was presumably responsible for the "oxygen jag" described by Commander Ellsberg in his divers.
My work with nitrogen began in 1946 in
collaboration with Prof. Charlotte Haywood
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of Mt. Holyoke College. We reasoned that if
nitrogen narcosis is a real phenomenon in
divers, it should be possible to produce it in
the laboratory. We tried, therefore, high pressures of nitrogen with normal oxygen supply
on a great variety of phenomena including muscle contraction, membrane potential,
phagoeytosis, cardiac activity, and swimming
movement of Daphnia but without being able
to discover any effect. Later Professor Haywood extended this study to the effect of N2
on cleavage of Arbacia eggs with the sanme negative result.23 Evidently we did not use high
enough pressures or did not have sufficiently
sensitive preparations. Later Dr. Jean Marshall 24 as a graduate student, continued this
work and soon found that reflex activity and
brain waves of frogs could be eliminated reversibly by high pressures of nitrogen or
argon, but sinmilar pressures of helium had no
effect, presumably because the lipoid solubilitv
of helium was too low.* Dr. Frank Carpenter23 continued this work using the inhibition
of electroshock convulsions in mice as his end
point. With a wide variety of ilarcotics, including nitrogen and argon, he was able to
plot the logarithm of the narcotic threshold
of these agents against the log of their lipoid
solubility and obtained a good straight line.
At this point the nareotic potency of inert
gases seemned well established, not only in ouir
laboratory but in nmany other laboratories as
well. It has effects not only on brain waves
and human performance but on insects, the
development of larvae, and the growth of
bacteria. Nitrogen narcosis is therefore to be
regarded as an established fact. like gra-ity7.
*More recently Bennett and Glass in Eniglandl
have carried out an excellent electroencephalographic
study in man, showing the elimination of alpha
blocking by iinert gases (Electroeiieeph. Clin. nenrlophysiol., 13: 91, 1961).
fThe symptoms of nitrogeni narcosis hi (livers are
of course not very marked, and it is easy f or a
particular diver to miimiiiize them or to argue that
they may be due to some other cause. This does not
invalidate however the existence of the physiological
phenomenon. (See Buhlmann, Schweiz. med. Wschr.
9: 774, 1961.)
FENN
anid it seenits unnecessary to drop another
apple to improve the demonstration.t
Since nitrogen does have a narcotic effect
in sufficient concentration, it presumably belongs with the other physical anesthetics
which are effective in proportion to their
lipoid solubility, their oil/water solubility ratio, or their chemical or thermodynamic potential. This does not tell us, however, just
what it does in the cell to interfere with cell
funetions. This has recently been attributed
by Pauling30 to the formation of hydrate microcrystals, but five years ago I was unable
to find evidence of any effect of high pressures of nitrogen gas on physicochemical
systems which might serve in any way as a
clue to its action within the cell. It occurred
to me, therefore, to examine the effects of
nitrogen and other inert gases on oil-wate:r
emulsions, since Clowes26 and later Sullman27
and Hirsehfelder and Serles25 had observed
that narcotics tended to favor the formation
of water drops in oil rather than oil drops in
water. According to this concept, narcosis
would occur when penetration of water soluble substances was prevented by the formation of a continuous lipid layer around the
cell. Someone with a sense of hunlor called
this the "fish and rabbits" theory, because a
system of islands in the sea is permiieable to
fish but not to rabbits while the reverse is
true for a system of lakes in the land.
Dr. D. F. Sears worked on this problem as
a graduate student in my laboratory and confirmed the fact that high pressures of nitrogenl
do have this effect.29 Subsequently I caine to
feel, however, that we had not had time to
get to the bottom of the problem and had nlot
made the demonstration thoroughly convineing. I decided therefore to investigate the
problem again by a totally different method
by measuring the interfacial surface tension
between oil and water under the influence of
high nitrogen pressures. I used the dropcounting method and arranged to allow 10
ml. of dilute NaOH to drop through a capillary tip immersed in olive oil in a large steel
compression chamber equipped with a window
for observing the number of drops. It was
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necessary to allow plenty of time for the saturation of the oil and water, with nitrogen at
pressures up to 1,000 p.s.i., to protect the system from all traces of CO2 and to arrange to
start the flow by closing a switch outside the
pressure chamber. After innumerable difficulties I finally came to the conclusion that nitrogen had no effect on the interfacial surface
tension. The number of drops for 10 ml. of
solution was independent of pressure. This
may have been because the system was not
fully saturated with nitrogen, or because the
falling drops did not have time to come into
equilibrium with the oil, or perhaps merely
because of the insensitivity of the method. In
any event it was the same experience which
Sullman27 reported with other anestheties.
He found that they would reverse the emulsions but had no effect on surface tension as
measured by the drop-counting method.
This negative result seemed to throw doubt
on our original observations concerning emulsion reversal by high pressures of nitrogen,
so- I felt obliged to repeat these experiments.
The new apparatus consists of a teflon chamber holding about 8 ml. and mounted inside
a steel pressure chamber. Inlet and outlet
valves are provided on the teflon chamber for
the gases, but the emulsion is prevented from
escaping while being shaken. The teflon chamber also contains two electrodes which make
contact with external binding posts when the
chamber is screwed into position on the stopper of the steel chamber. With these electrodes
the conductivity of the emulsion was measured with direct current and a galvanometer,
the current being measured first in one direction and then in the other to minimize polarization effects. The method is crude, but I believe quite adequate for the purpose. When
no current flows, it is evident that the oil is
the outer phase and completely encloses all
the conducting NaOH. The mixture consisted
of 2 ml. of olive oil plus 2 ml. of dilute
NaOH, usually about 0.002N. The concentration of NaOH was selected to be near the
critical level where the emulsion is almost
ready to reverse from oil-in-water to waterin-oil. When shaken with water or neutral
Circulation, Volume XXVI, November 1962
ilI3 9-
NaCl or CaCl2, olive oil always forms waterin-oil emulsions. In these experiments it is
particularly important to be sure that the
gases used contain no CO2, because the emulsions will reverse to water-in-oil whenever
enough CO2 is absorbed to convert all the
NaOH to NaHCO3. To avoid this, all the gases
used were stored in small tanks containing a
small amount of strong NaOH solution.
I will not bore you with the details of these
experiments but will merely report that in
my spare time I have tried in vain during
the last two years to prove that high pressures
of inert gases have no effect, and I have come
to the conelusion that there is indeed a small
effect. It is perhaps not quite correct to say
that they produce an actual reversal of the
emulsions. They do, however, produce more
water drops in oil than oil drops in water,
and the conductivity does go to zero somewhat
more often or more quickly when high pressures of nitrogen are in the chamber. Helium
does not have this effect. The emulsions are
extremely sensitive to C02, and even the CO2
in the 12 cc. of air between the teflon chamber
and the steel jacket is enough to influence the
result, if it is driven into the teflon chamber
with the pressurizing gas. The result is best
established with 1,000-1,500 p.s.i. of nitrogen,
but it seems to be true also for argon, N20,
and SF6. The effect is too small to quantitate
accurately for different gases. It is, however,
one established effect of high pressures of
nitrogen on a nonliving system similar in some
respects to protoplasm. Compared to a living
cell it is perhaps a very insensitive way of
detecting this effect, but I am confident that
the effect exists unless it is due to some subtle
artifact which I have been unable either to
detect or to control.
I am not clear about the explanation of
the effect observed. It is not due simply to
pressure per se, because the effect is not produced by helium. Pressure might, however, be
expected to have some effect upon oil-water
emulsions, just as it has some effect on gel-sol
transformations. To study this point further,
I made some measurements of the change in
volume that occurs when oil and water are
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emulsified. For this purpose a layer of oil
was placed on top of a layer of dilute NaOH
in a differential volumeter. After achieving
temperature equilibrium in a water bath, the
oil and water layers were vigorously mixed
with a magnetic stirrer rotating on the bottom
of the volumeter. The result was a rapid increase in volume. The magnitude of the
change increased with the concentration of
NaOH to a maximum of about 0.2 cu. mm.
per ml. of emulsion. A similar curve was obtained for the amount of fatty acid neutralized by the different concentrations of NaOH.
Presumably the greater the amount of soap
formed, the greater the amount of oil-water
interface formed. I was surprised to find,
however, that emulsification with Ca(OH1)2
instead of NaOH, which forms water-in-oil
instead of oil-in-water emulsions, was likewise
accompanied by an increase in volume of the
same order of magnitude. Since both types
of emulsions cause an increase in volume,
pressure per se should favor a clean separation into two layers. It is hard to say, therefore, which type of emulsion is least inhibited
by the pressure itself.
I have made some efforts to measure the
temperature change which accompanies emulsification. There seems to be a slight increase
of 0.10 C. orless, but it is not as large aswould
be expected from the heat of neutralization
of the NaOH by the fatty acid of the oil. Any
heat so produced is presumably counterbalanced to some degree by the cooling effect
which must accompany the great increase in
interface. In any event the increase in temperature is not enough to explain the increase
in volume which occurs.
Narcotics have different effects on permeability of different cells to different substances.
I do not propose to review this complicated
subject here. It is often said, however, that
narcotics decrease permeability in small concentrations and increase it in larger concentrations. In the original concept of Clowes,26
this could be understood if they tended to
make a lipoid layer more continuous. Applying this to the Danielli membrane,31 consisting
of a bimolecular lipoid leaflet with adsorbed
FENN
layers of protein, we should suppose that
there are some watery holes or discontinuities
in the lipoid layer which has a tendency to
adopt an oil-in-water structure. Such holes
would be closed by narcotics, as also by calcium or other divalent cations which tend to
make the oil phase continuous.
Other evidence of effects of high pressures
of nitrogen on physicochemical systems is
certainly desirable. Dr. Sears (personal communication) has found on]y very small
changes in the conductivity of dilute electrolytes when saturated with high partial pressures of argon and nitrogen. Simultaneously
he is making interesting observations on volume changes resulting from solution of the
different gases. Skou32 and Dean et al.33 have
demonstrated some increases in the surface
pressure of monomolecular surface films of
stearic acid from the action of somne narcotic
agents. Dr. Fred Snell and I have some experiments of this sort under way in a modified Langmuir trough in a pressure chamber.
We hope thus to observe an effect of high
nitrogen pressures in monomolecular films,
but we have no results as yet to report. I have
also tried to find out whether high pressures
of nitrogen would mnodify the melting point
of potassium oleates. This was suggested by
the experiments of the Monniers,34 who observed marked changes of melting points from
60 to 750 C. due to variations in the relative
concentrations of Na, K, and Ca oleates. For
this purpose I built a special apparatus to
monitor the solidity and temperature of the
oleate from outside a pressure chamber as the
temperature was slowly increased. Unfortunately, high pressures of nitrogen did not
seem to have any measurable effect on the
melting points in this system. The experiment
seems pertinent because a lowering of the
melting point of a bimolecular lipid leaflet
might permit it to break up into drops, thus
forming holes and so increasing the perme-
ability.
Before leaving the question of emulsions, I
should like to make some comment concerning
the antagonistic effects of Na and Ca on this
system described by Clowes.26 It is certainly
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true that CaCl2 will reverse an emulsion which
is made oil-in-water by dilute NaOH. When
the Ca is just equivalent to the -OH-, the
emulsion is completely reversed. NaCl, however, seems to have no effect whatsoever
upon the state of these emulsions, so the antagonism is not between Na and Ca but rather
between Ca++ and OH-. Anything which "precipitates" the OH- either as HOH or as an
insoluble hydroxide will cause reversal of the
emulsion. In this respect carbonic acid acts
like any other acid. As Sears and Eisenberg35
have recently shown, this may explain its effect on surface membranes.
A better model for the well-known sodiumcalcium antagonism is one which I observed
in gelatine solutions 45 years ago.36 A gelatine
solution can be precipitated by the addition
of ethyl alcohol. Both CaCl2 and NaCl combine with the gelatine, which then requires
more alcohol for precipitation. However, a
mixture of the two salts in ratio of 90 per
cent Na to 10 per cent Ca has less effect and
requires less alcohol than either salt alone, all
having the same ionic strength and the same
pH. Both NaCl and CaCl2 decrease the pH
when added to gelatine, even though both were
originally neutral and the gelatine slightly
acid before the salts were added. Both, therefore, combine with the protein in exchange
for H+ ions. In a similar experiment with
KCI and NaCl only additive effects were observed. The only additional observation is
that in calcium the particles of precipitated
gelatine are aggregated and visible under a
microscope, while in NaCl they are almost too
small to see. I should be interested in a good
explanation of this phenomenon. Both salts
prevent the precipitation of gelatine by alcohol, but they must do so by slightly different
methods which are to some extent antagonistic. Danielli37 has discussed this critical 10/1
ratio for Na-Ca antagonism in biological
systems and has shown that the ratio on the
surface of the protein may be 1/1. While this
may well be true, it does not seem to me that
it represents any explanation of what the two
ions are competing for or why they are antagonistic rather than additive in their effects.
Circulation, Volume XXVI, November 1962
1141
Another good case of Na-Ca antagonism was
observed by the Monniers34 in their study of
the melting points of the oleates in oleic acid.
The melting points of Na and Ca oleates alone
were 180 C. and 140 C., respectively, but this
was increased to 750 C. by appropriate mixtures of the two.
Before leaving this subject, some other aspects of nitrogen physiology deserve mention.
Space scientists are still arguing about the
necessity of including nitrogen in their space
capsules. It would diminish the danger of
fires and would perhaps avoid atelectasis of
the lung. Nevertheless, mice have given birth
to young and weaned them without difficulty
in the complete absence of nitrogen, but with
normal tensions of oxygen.38 A recent report
from Russia, however, tells US39 that chick
embryos cannot live if the nitrogen of the air
is replaced by helium. The lethal effect was
attributed to the fact that chick embryos have
the capacity to fix some nitrogen from the air,
as demonstrated by actual analysis of the
embryos for total nitrogen. Without the possibility of doing this, they cannot develop,
and they die. This indicates at last that this
inert molecule may still have some surprises
in store for us.
Lastly, I think I should mention the important discovery of Ebert, Hornsey, and
Howard40 that high pressures of nitrogen and
other inert gases protect bean seedlings from
radiation injury. It is proposed that nitrogen
displaces oxygen from some site where it exerts its well-known action in potentiating the
radiation effects. High nitrogen, according to
this concept, would produce a local anoxia
even in the presence of ample oxygen. This
effect has been obtained also in Drosophila.4
The relation between this phenomenon and
narcosis remains to be elucidated.
Finally, I should apologize for presenting
such a peculiar array of miscellaneous subjects before this distinguished audience. To
make matters worse, I have ended up by reviving an outworn theory of narcosis when a
newer and much more sophisticated theory30
has only recently been presented and seems
to be widely accepted. I can only hope that
1142
the two theories are not wholly incomipatible
and that it may even happen that our results
with inert gases and emulsions nmay be explained somehow by Pauling's hydrate mierocrystal theory.
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Circulation, Volume XXVI, November 1962
SYMPOSIUM ON THE PLASMA MEMBRANE
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There are those who say that they can extrapolate from
purpose in the organism to purpose in the cosmos, from personality in man to a personality transcending the stars and the
nebulae. This, I must question. Purpose in the organism issues
from its molecular structure, as does personality in man; and
both are transient patterns in the swirling fountain of matter
and energy that in a few thousand million years has spewed
galaxies in inconceivable numbers and at inconceivable speeds
into the impenetrable depths of space.-Homer Smnith. From
Fish to Philosopher. Boston, Little, Brown & Co., 1953.
Circulation, Volume XXVI, November 1962
1143
Physiological Effects of High Pressures of Nitrogen and Oxygen
WALLACE O. FENN
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Circulation. 1962;26:1134-1143
doi: 10.1161/01.CIR.26.5.1134
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