Am J Physiol Lung Cell Mol Physiol 287: L455–L459, 2004;
10.1152/ajplung.00172.2004.
EB2004 FEATURED TOPIC REPORT
Cell-cell interactions in regulating lung function
Scott Boitano,1 Zeenat Safdar,2,3 Donald G. Welsh,4 Jahar Bhattacharya,2 and Michael Koval5
1
Department of Physiology, University of Arizona Health Sciences Center, Tucson, Arizona 85724; 2Lung Biology Laboratory
and 3Division of Pulmonary-Critical Care Medicine, St. Luke’s-Roosevelt Hospital Center, College of Physicians
and Surgeons, Columbia University, New York, New York 10019; 4Department of Physiology and Biophysics, University
of Calgary, Calgary, Alberta, Canada T2N 4N1; and 5Department of Physiology and Institute for Environmental Medicine,
University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
tight junction; gap junction; claudin; connexin; cadherin; calcium
TO FUNCTION AS A COHESIVE TISSUE,
the activities of individual
cells are coordinated at cell-cell contact sites. These sites are
composed of transmembrane and peripheral protein components that provide a scaffold to interlink these elements with
the cytoskeleton and serve to cluster cell adhesion molecules,
ion channels, and junctional components into a functional
complex (29, 48). Cell-cell contact sites provide important
spatial cues to generate cell polarity and enable cells to sense
and respond to adjacent cells (32). Junctional complexes at
cell-cell contact sites are also control points for regulating
solute flow across cell monolayers (through tight junctions)
and from one cell to another (through gap junctions). Progress
in understanding the regulation of pulmonary barrier function
and roles for gap junctional communication by lung epithelium
and endothelium was presented at the 2004 Experimental
Biology Meeting held in Washington, DC.
DIFFERENTIAL CLAUDIN LOCALIZATION BY
ALVEOLAR EPITHELIUM
Disruption of the paracellular alveolar permeability barrier is
a significant pathological consequence of acute lung injury (8).
Transmembrane proteins in the claudin family act in concert
Address for reprint requests and other correspondence: M. Koval, Univ. of
Pennsylvania School of Medicine, Dept. of Physiology, B-400 Richards
Bldg./6085, 3700 Hamilton Walk, Philadelphia, PA 19104 (E-mail:
mkoval@mail.med.upenn.edu).
http://www.ajplung.org
with other transmembrane and peripheral proteins to form the
physical basis for tight junctions (41, 42). There are roughly
two dozen different claudins. Epithelial cells simultaneously
express up to six or more claudin isoforms. Cells expressing
different claudins have different paracellular permeability
characteristics (7, 43– 45). Whereas individual claudins have
been shown to support the paracellular transport of ions, the
mechanisms used by multiple claudins to form a tight junction
barrier has not been well established.
Because cells often express multiple claudins, this raises the
possibility that two or more different claudins in adjacent cells
might interact heterotypically, through head-to-head interactions. A study of transfected fibroblasts suggests that claudin
head-to-head compatibility is limited to specific claudin combinations rather than being universal (14). Although claudin
compatibility is an issue in a homogeneous epithelium, it is a
more critical concern in the mature alveolus, where there are
heterologous contact sites between type II cells and type I cells
that express different claudins (45). In this case, exclusion of
incompatible claudins from type II-type I cell interfaces could
potentially help regulate tight junction composition and thus
paracellular permeability. Whether this is the case remains to
be determined. However, it seems likely that the paracellular
permeability of heterologous type II-type I alveolar epithelial
cell interfaces will differ from that of homologous type I-type
I and type II-type II contact sites. This could have functional
ramifications for maintaining fluid balance in the adult lung.
In contrast to the mature alveolus, which is a heterogeneous
epithelium, the developing air space consists of a more uniform
monolayer of fetal type II cells. A tight seal is important for
alveolar development, since accumulated fetal lung fluid induces mechanical distension and differentiation of fetal alveolar epithelial cells (11, 31). Given this, barrier function of
isolated human fetal alveolar epithelial cells in culture was
examined (16). Isolated fetal alveolar epithelial cells cultured
in medium containing dexamethasone and cAMP plus IBMX
(DCI) differentiate to a type II-like phenotype, whereas cells
cultured in the absence of added hormones remain undifferentiated (16). DCI-treated fetal alveolar epithelial cells cultured
on permeable supports formed high-resistance monolayers
(⬎1,700 ⍀ 䡠cm2), consistent with the ability of fetal type II
cells to form tight junctions. In contrast, undifferentiated fetal
alveolar cells formed leaky monolayers (⬍300 ⍀䡠cm2). At the
mRNA level, the major tight junction proteins upregulated by
DCI treatment were claudin-5 and claudin-18. None of the
other proteins examined showed more than a twofold change in
mRNA expression, including other claudins, occludin, junction
1040-0605/04 $5.00 Copyright © 2004 the American Physiological Society
L455
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Boitano, Scott, Zeenat Safdar, Donald G. Welsh, Jahar Bhattacharya, and Michael Koval. Cell-cell interactions in regulating
lung function. Am J Physiol Lung Cell Mol Physiol 287: L455–L459,
2004; 10.1152/ajplung.00172.2004.—Tight junction barrier formation
and gap junctional communication are two functions directly attributable to cell-cell contact sites. Epithelial and endothelial tight junctions are critical elements of the permeability barrier required to
maintain discrete compartments in the lung. On the other hand, gap
junctions enable a tissue to act as a cohesive unit by permitting
metabolic coupling and enabling the direct transmission of small
cytosolic signaling molecules from one cell to another. These components do not act in isolation since other junctional elements, such as
adherens junctions, help regulate barrier function and gap junctional
communication. Some fundamental elements related to regulation of
pulmonary barrier function and gap junctional communication were
presented in a Featured Topic session at the 2004 Experimental
Biology Conference in Washington, DC, and are reviewed in this
summary.
L456
EB2004 FEATURED TOPIC REPORT
Fig. 1. Differential claudin localization by fetal alveolar epithelial cells.
Isolated human fetal alveolar epithelial cells were cultured for 4 days in
Waymouth medium containing dexamethasone, cAMP, and IBMX to promote
differentiation toward a type II cell phenotype (A) or under control conditions
to remain undifferentiated (B). The cells were then fixed, permeabilized, and
immunostained for claudin-7. Claudin-7 was preferentially localized to the
plasma membrane by differentiated cells; however, undifferentiated cells had
a significant intracellular claudin-7 pool (arrowheads). Other claudins expressed by these cells had a similar intracellular distribution (not shown). This
difference in claudin localization correlated with increased barrier function of
differentiated fetal alveolar epithelial cells. Bar, 10 ␮m.
AJP-Lung Cell Mol Physiol • VOL
claudin incorporation into tight junctions as a posttranslational
means to regulate barrier function. Although the mechanisms
that fetal alveolar cells use to regulate claudin localization
remain to be elucidated, these data suggest that coordinated
increases in fetal type II cell differentiation and barrier function
might provide a positive feedback loop with the potential to
help drive fetal lung development (11, 31).
INTERCELLULAR SIGNALING BETWEEN ALVEOLAR
EPITHELIAL CELLS
Physiological function of the alveolar epithelium requires
intercellular signaling between type I alveolar epithelial cells
and type II alveolar epithelial cells. The overall contribution of
specific cell-cell interactions to lung function has been difficult
to assess due to problems working with whole lung tissue and
the lack of a culture model that contains both type I and type
II cells. In an attempt to develop a heterocellular culture of type
I and type II cells, type II cells were isolated and cultured on
a rat tail collagen/fibronectin matrix supplemented with a
limited amount of another extracellular matrix protein, laminin
5. After 7 days on this matrix, alveolar cell cultures contained
a mixed monolayer of epithelial cells morphologically resembling either type I-like or type II-like cells, based on immunohistochemical staining of cell-specific markers, distribution of
cell types, and cell morphology (24). These heterocellular
cultures of type I-like and type II-like cells provide an accessible in vitro model system to study alveolar epithelial cell
interactions between and among the two alveolar epithelial
phenotypes.
The cells of the alveolar epithelium are interconnected by
gap junction channels that enable the flow of cytoplasmic
metabolites, antioxidants, and signals from one cell to its
nearest neighbor (26). There are at least six gap junction
protein (connexin) isoforms expressed by alveolar epithelial
cells. The connexins expressed by type I-like and type II-like
cells in heterocellular cultures resembled those expressed by
type I and type II cells in situ (25). This contrasts with the
pattern of connexins expressed by alveolar epithelial cells
grown in homogenous cultures and suggests that connexin
expression by alveolar epithelial cells is influenced by neighboring cell phenotype and/or cell matrix interactions (1, 2, 4,
18, 21, 28). The expression of comparable connexins by
heterocellular cultures and cells in situ suggested an improved
model for studying alveolar epithelial cell-cell communication
in vitro. Consistent with the presence of connexins in both
alveolar epithelial cell types, cells in heteroculture were coupled through gap junctions, as measured by transfer of microinjected dyes between cells with similar and distinct phenotype
(25). Connexin mimetic peptides inhibited dye transfer between cells in heteroculture, although dye transfer from type
I-like cells to type II-like cells was less sensitive to peptide
inhibition.
The transmission of stretch-induced Ca2⫹ transients between
alveolar epithelial cells suggests that changes in intracellular
Ca2⫹ concentration ([Ca2⫹]i) can contribute to integrated signaling in lung epithelium. For instance, mechanical stimulation
of type I cells in situ initiates a transient increase in [Ca2⫹]i that
is transmitted to type II cells through gap junctions to stimulate
surfactant secretion (3). Direct mechanical stimulation of type
II cells can also stimulate changes in [Ca2⫹]i and surfactant
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adhesion molecule-1, and scaffold proteins. In addition, at the
total protein level, differences between DCI-treated and untreated fetal alveolar cells were modest.
The difference between DCI-treated and untreated cells was
more dramatic when the cells were examined by immunofluorescence microscopy (Fig. 1). In DCI-treated differentiated
cells, claudin-3, claudin-4, claudin-5, and claudin-7 were localized to the plasma membrane. In contrast, undifferentiated
alveolar epithelial cells had a prominent intracellular claudin
pool and showed discontinuous claudin labeling of the plasma
membrane. The intracellular pool of claudins colocalized with
early endosome antigen-1, suggesting that undifferentiated
cells constitutively internalized claudins from the plasma membrane and that this process might compete for claudin incorporation into tight junction strands. This suggests that fetal
type II cells either inhibit claudin endocytosis or stabilize
EB2004 FEATURED TOPIC REPORT
Fig. 2. Signaling pathways for Ca2⫹ communication between cultured alveolar epithelial cells. Cells were mechanically stimulated to initiate intercellular
communication (A, arrowhead, gray). Increases in cytosolic calcium, [Ca2⫹]i,
are transmitted through homogenous cultures of type I-like cells through gap
junctions. B: homogenous cultures of type II cells use nucleotide trisphosphate
(NTP) release and paracrine stimulation to transmit increases in [Ca2⫹]i. C: in
heterocellular cultures, increases in [Ca2⫹]i generated by stimulation of type
I-like cells are transmitted to both type I-like and type II-like cells through gap
junctions. D: in contrast, type II-like cells stimulated in heterocellular cultures
transmitted increases in [Ca2⫹]i to type I-like cells through NTP release, or to
type II-like cells through both NTP release and gap junctions.
AJP-Lung Cell Mol Physiol • VOL
fibronectin matrix provides a new model for the study of
coordinated cellular physiology of the alveolar epithelium.
Initial studies with this model show distinct connexin profiles
and unique functional coupling pathways between the two cell
phenotypes that may provide insight on interactions used by
type I and type II cells to regulate alveolar epithelial function
in vivo. Further study on cell communication and physiological
outcome will help to elucidate roles for different connexin
isoforms and changes in mechanisms of Ca2⫹ communication
in the alveolar epithelium.
ENDOTHELIAL CA2ⴙ REGULATION BY CONNEXIN 43 IN
ALVEOLAR CAPILLARIES OF RAT LUNG
In lung microvessels, endothelial cells serve a variety of
functions, such as maintenance of the vascular permeability
barrier, establishment of a nonthrombogenic luminal surface,
and secretion of vasodilatory factors such as nitric oxide. Many
microvascular endothelial functions are [Ca2⫹]i dependent, and
their signaling mechanisms involve critical increases in
[Ca2⫹]i. Previous studies using the fura 2 ratio imaging method
to measure [Ca2⫹]i in intact lung microvessels of the subpleural capillary bed demonstrated the transmission of [Ca2⫹]i
along the capillary wall through gap junctions (49). Stimuli
such as increased pressure or histamine increase the amplitude
of [Ca2⫹]i (27, 49). However, the frequency of lung capillary
Ca2⫹ oscillations appears to be controlled by a subset of
endothelial cells, called pacemaker cells, that actively generate
[Ca2⫹]i transients even under resting conditions (49).
Analysis of 20- to 25-␮m-diameter lung venular capillaries
facilitates measurements in a vascular wall consisting purely of
endothelial cells, since lung vessels of ⬍30-␮m diameter lack
smooth muscle, especially in the venous system. Also, the
endothelial phenotype of cells in these vessels was confirmed
by DiI-AcLDL labeling and the lack of smooth muscle actin
expression (49). This helps simplify the analysis of endothelial
cell-cell [Ca2⫹]i transmission, since these vessels lack myoendothelial junctions that can confound analysis of intercellular
communication in the vasculature (5, 38, 46, 47).
Connexin 37 and connexin 40 tend to be uniformly expressed by vascular endothelial cells in situ (39). In general,
large vessel endothelial cells show more connexin 43 expression than microvascular cells, which correlates with the extent
of gap junctional coupling (35). Here, connexin 43 expression
by lung capillaries was confirmed by immunohistochemistry,
consistent with other studies demonstrating connexin 43 expression by microvascular endothelial cells (19, 20). Note that
connexin 43 expression tends to be upregulated in areas with
turbulent flow, such as vessel branch points, although connexin
37 and connexin 40 expression in situ are much less sensitive
to flow (9, 15). Interestingly, endothelial pacemaker cells also
tend to be localized to microvessel branch points (49), raising
the possibility that they might express more connexin 43 than
other capillary endothelial cells.
Transmission of [Ca2⫹]i transients through gap junctions can
occur either through the direct flow of Ca2⫹ or through the flow
of second messengers, such as inositol trisphosphate (13, 33,
34). To examine the transmission of Ca2⫹ through gap junctions, lung capillary endothelial cells in situ were loaded with
a “caged” Ca2⫹ compound and a Ca2⫹-sensitive dye, fluo 4.
UV-induced photolysis increased endothelial Ca2⫹ both at the
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secretion (12). However, alveolar epithelial cells have the
capacity to transmit changes in [Ca2⫹]i both directly (through
gap junctions) and indirectly (through nucleotide secretion and
paracrine stimulation of purinergic receptors). These differences have been observed in alveolar epithelial monocultures,
where mechanical stimulation of type I-like cells induces gap
junction-mediated transmission of changes in [Ca2⫹]i (21),
whereas mechanical stimulation of type II-like cells induces
paracrine signaling (23) (Fig. 2).
To determine the pathway for intercellular Ca2⫹ waves
between phenotypically distinct alveolar cell types in heteroculture, we mechanically stimulated cells to initiate Ca2⫹
waves and applied inhibitors of either gap junctional communication or purinergic receptor stimulation. Initiation of Ca2⫹
waves from type I-like cells communicated increases in
[Ca2⫹]i to neighboring type I-like or type II-like cells via a gap
junctional pathway (Fig. 2). In contrast, communication of
Ca2⫹ waves from type II-like cells in heterocellular culture was
more complex. Stimulated type II-like cells communicated
increases in [Ca2⫹]i to neighboring type I-like and type II-like
cells via extracellular nucleotide release; however, communication to neighboring type II-like cells also occurred via gap
junctions. Similar to the dye-coupling experiments, these Ca2⫹
communication data are suggestive of selective molecular
transfer between and among type I and type II cells (25).
In summary, the heterocellular culture model of type I-like
and type II-like cells grown for 7 days on a laminin 5/collagen/
L457
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EB2004 FEATURED TOPIC REPORT
3.
4.
5.
6.
7.
E-CADHERIN EXPRESSION IN LUNG VENULAR CAPILLARIES
The lung capillary barrier critically regulates fluid flux into
lung tissue (10, 40). Microvascular endothelial cells in culture
have a biphasic response to treatment with hyperosmolar sucrose solution (36). With short-term (1 min) exposure, the cells
shrink and their barrier function decreases. However, with
longer-term exposure (15 min), the microvascular cells recover
and have increased barrier function. In part, this is due to
stimulation of focal adhesion kinase activity which, in turn,
promotes remodeling of the actin cytoskeleton (30, 36). Ecadherin expression is also increased, which further promotes
cell adhesion and provides a cytoskeletal anchor point for actin
at cell-cell contact sites (17). As opposed to the significant
increase in E-cadherin expression, microvascular cells in culture expressed only low levels of vascular endothelial (VE)cadherin, in contrast to previous reports that VE-cadherin is
expressed by endothelial cells of the lung (6).
The cadherin isoforms expressed by lung capillaries in situ
have not been characterized. To examine this, capillaries of the
isolated, blood-perfused lung were immunostained using instilled anti-cadherin antibodies and then viewed by confocal
microscopy (37). E-cadherin was evident in both alveolar
septal and venular capillaries. Costaining for actin with rhodamine phalloidin revealed occasional colocalization of E-cadherin and actin in resting capillaries. However, VE-cadherin
expression was not detected. Consistent with studies on cultured microvascular cells, hyperosmolar infusion for 15 min
increased capillary barrier function immunofluorescence (37).
This increase in barrier function was accompanied by an
increase in detection of E-cadherin at the endothelial cell
surface as measured by in situ immunofluorescence (37). The
level of filamentous actin also increased in response to hyperosmolar infusion, as did the extent of overlap between Ecadherin and actin in the pulmonary capillaries. Significant
levels of VE-cadherin were not detected in hyperosmolar
infused lung capillaries. Together, these data suggest that
E-cadherin is the dominant cadherin expressed by endothelial
cells of lung capillaries.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
23.
REFERENCES
1. Abraham V, Chou ML, DeBolt KM, and Koval M. Phenotypic control
of gap junctional communication by cultured alveolar epithelial cells.
Am J Physiol Lung Cell Mol Physiol 276: L825–L834, 1999.
2. Abraham V, Chou ML, George P, Pooler P, Zaman A, Savani RC, and
Koval M. Heterocellular gap junctional communication between alveolar
AJP-Lung Cell Mol Physiol • VOL
24.
epithelial cells. Am J Physiol Lung Cell Mol Physiol 280: L1085–L1093,
2001.
Ashino Y, Ying X, Dobbs LG, and Bhattacharya J. [Ca2⫹]i oscillations
regulate type II cell exocytosis in the pulmonary alveolus. Am J Physiol
Lung Cell Mol Physiol 279: L5–L13, 2000.
Carson JL, Reed W, Moats-Staats BM, Brighton LE, Gambling TM,
Hu SC, and Collier AM. Connexin 26 expression in human and ferret
airways and lung during development. Am J Respir Cell Mol Biol 18:
111–119, 1998.
Christ GJ, Spray DC, el-Sabban M, Moore LK, and Brink PR. Gap
junctions in vascular tissues. Evaluating the role of intercellular communication in the modulation of vasomotor tone. Circ Res 79: 631– 646,
1996.
Corada M, Zanetta L, Orsenigo F, Breviario F, Lampugnani MG,
Bernasconi S, Liao F, Hicklin DJ, Bohlen P, and Dejana E. A
monoclonal antibody to vascular endothelial-cadherin inhibits tumor angiogenesis without side effects on endothelial permeability. Blood 100:
905–911, 2002.
Coyne CB, Gambling TM, Boucher RC, Carson JL, and Johnson LG.
Role of claudin interactions in airway tight junctional permeability. Am J
Physiol Lung Cell Mol Physiol 285: L1166 –L1178, 2003.
Crandall ED and Matthay MA. Alveolar epithelial transport. Basic
science to clinical medicine. Am J Respir Crit Care Med 163: 1021–1029,
2001.
DePaola N, Davies PF, Pritchard WF Jr, Florez L, Harbeck N, and
Polacek DC. Spatial and temporal regulation of gap junction connexin43
in vascular endothelial cells exposed to controlled disturbed flows in vitro.
Proc Natl Acad Sci USA 96: 3154 –3159, 1999.
Dudek SM and Garcia JG. Cytoskeletal regulation of pulmonary vascular permeability. J Appl Physiol 91: 1487–1500, 2001.
Flecknoe S, Harding R, Maritz G, and Hooper SB. Increased lung
expansion alters the proportions of type I and type II alveolar epithelial
cells in fetal sheep. Am J Physiol Lung Cell Mol Physiol 278: L1180 –
L1185, 2000.
Frick M, Bertocchi C, Jennings P, Haller T, Mair N, Singer W, Pfaller
W, Ritsch-Marte M, and Dietl P. Ca2⫹ entry is essential for cell
strain-induced lamellar body fusion in isolated rat type II pneumocytes.
Am J Physiol Lung Cell Mol Physiol 286: L210 –L220, 2004.
Fry T, Evans JH, and Sanderson MJ. Propagation of intercellular
calcium waves in C6 glioma cells transfected with connexins 43 or 32.
Microsc Res Tech 52: 289 –300, 2001.
Furuse M, Sasaki H, and Tsukita S. Manner of interaction of heterogeneous claudin species within and between tight junction strands. J Cell
Biol 147: 891–903, 1999.
Gabriels JE and Paul DL. Connexin43 is highly localized to sites of
disturbed flow in rat aortic endothelium but connexin37 and connexin40
are more uniformly distributed. Circ Res 83: 636 – 643, 1998.
Gonzales LW, Guttentag SH, Wade KC, Postle AD, and Ballard PL.
Differentiation of human pulmonary type II cells in vitro by glucocorticoid
plus cAMP. Am J Physiol Lung Cell Mol Physiol 283: L940 –L951, 2002.
Gumbiner BM. Regulation of cadherin adhesive activity. J Cell Biol 148:
399 – 404, 2000.
Guo Y, Martinez-Williams C, Yellowley CE, Donahue HJ, and Rannels DE. Connexin expression by alveolar epithelial cells is regulated by
extracellular matrix. Am J Physiol Lung Cell Mol Physiol 280: L191–
L202, 2001.
Gustafsson F, Mikkelsen HB, Arensbak B, Thuneberg L, Neve S,
Jensen LJ, and Holstein-Rathlou NH. Expression of connexin 37, 40
and 43 in rat mesenteric arterioles and resistance arteries. Histochem Cell
Biol 119: 139 –148, 2003.
Haas TL and Duling BR. Morphology favors an endothelial cell pathway
for longitudinal conduction within arterioles. Microvasc Res 53: 113–120,
1997.
Isakson BE, Evans WH, and Boitano S. Intercellular Ca2⫹ signaling in
alveolar epithelial cells through gap junctions and by extracellular ATP.
Am J Physiol Lung Cell Mol Physiol 280: L221–L228, 2001.
Isakson BE, Lubman RL, Seedorf GJ, and Boitano S. Modulation of
pulmonary alveolar type II cell phenotype and communication by extracellular matrix and KGF. Am J Physiol Cell Physiol 281: C1291–C1299,
2001.
Isakson BE, Seedorf GJ, Lubman RL, and Boitano S. Heterocellular
cultures of pulmonary alveolar epithelial cells grown on laminin-5 supplemented matrix. In Vitro Cell Dev Biol Anim 38: 443– 449, 2002.
287 • SEPTEMBER 2004 •
www.ajplung.org
Downloaded from http://ajplung.physiology.org/ by 10.220.33.6 on October 2, 2016
uncaging site as well as at a distant location lying outside the
uncaging area, indicating that the increase of Ca2⫹ at the
uncaging site was communicated to the distant site. Infusion of
peptides that block intercellular communication through connexin 43-containing gap junctions completely blocked the
photolysis-induced Ca2⫹ increase at the distant capillary site
but not at the photo-targeted site. A major conclusion of this
study was that Ca2⫹ increases in endothelial cells of lung
capillaries are rapidly conducted to adjoining endothelial cells
of the capillary. This has the potential to act as a signaling
pathway and also provides a mechanism for decreasing localized increases in [Ca2⫹]i by transmitting Ca2⫹ throughout the
interconnected endothelium. Diffusion of Ca2⫹ through connexin 43-containing gap junctions appears to be the major
mechanism for this protective response.
EB2004 FEATURED TOPIC REPORT
AJP-Lung Cell Mol Physiol • VOL
37. Safdar Z, Wang P, Ichimura H, Issekutz AC, Quadri S, and Bhattacharya J. Hyperosmolarity enhances the lung capillary barrier. J Clin
Invest 112: 1541–1549, 2003.
38. Sandow SL and Hill CE. Incidence of myoendothelial gap junctions in
the proximal and distal mesenteric arteries of the rat is suggestive of a role
in endothelium-derived hyperpolarizing factor-mediated responses. Circ
Res 86: 341–346, 2000.
39. Severs NJ, Rothery S, Dupont E, Coppen SR, Yeh HI, Ko YS,
Matsushita T, Kaba R, and Halliday D. Immunocytochemical analysis
of connexin expression in the healthy and diseased cardiovascular system.
Microsc Res Tech 52: 301–322, 2001.
40. Stevens T, Garcia JG, Shasby DM, Bhattacharya J, and Malik AB.
Mechanisms regulating endothelial cell barrier function. Am J Physiol
Lung Cell Mol Physiol 279: L419 –L422, 2000.
41. Tsukita S, Furuse M, and Itoh M. Multifunctional strands in tight
junctions. Nat Rev Mol Cell Biol 2: 285–293, 2001.
42. Van Itallie C and Anderson JM. The role of claudins in determining
paracellular charge selectivity. Proc Am Thorac Soc 1: 38 – 41, 2004.
43. Van Itallie C, Rahner C, and Anderson JM. Regulated expression of
claudin-4 decreases paracellular conductance through a selective decrease
in sodium permeability. J Clin Invest 107: 1319 –1327, 2001.
44. Van Itallie CM, Fanning AS, and Anderson JM. Reversal of charge
selectivity in cation or anion-selective epithelial lines by expression of
different claudins. Am J Physiol Renal Physiol 285: F1078 –F1084, 2003.
45. Wang F, Daugherty B, Keise LL, Wei Z, Foley JP, Savani RC, and
Koval M. Heterogeneity of claudin expression by alveolar epithelial cells.
Am J Respir Cell Mol Biol 29: 62–70, 2003.
46. Welsh DG and Nelson MT. A case for myoendothelial gap junctions.
Circ Res 87: 427– 428, 2000.
47. Yashiro Y and Duling BR. Integrated Ca2⫹ signaling between smooth
muscle and endothelium of resistance vessels. Circ Res 87: 1048 –1054,
2000.
48. Yeaman C, Grindstaff KK, Hansen MD, and Nelson WJ. Cell polarity:
versatile scaffolds keep things in place. Curr Biol 9: R515–R517, 1999.
49. Ying X, Minamiya Y, Fu C, and Bhattacharya J. Ca2⫹ waves in lung
capillary endothelium. Circ Res 79: 898 –908, 1996.
287 • SEPTEMBER 2004 •
www.ajplung.org
Downloaded from http://ajplung.physiology.org/ by 10.220.33.6 on October 2, 2016
25. Isakson BE, Seedorf GJ, Lubman RL, Evans WH, and Boitano S.
Cell-cell communication in heterocellular cultures of alveolar epithelial
cells. Am J Respir Cell Mol Biol 29: 552–561, 2003.
26. Koval M. Sharing signals: connecting lung epithelial cells with gap
junction channels. Am J Physiol Lung Cell Mol Physiol 283: L875–L893,
2002.
27. Kuebler WM, Ying X, and Bhattacharya J. Pressure-induced endothelial Ca2⫹ oscillations in lung capillaries. Am J Physiol Lung Cell Mol
Physiol 282: L917–L923, 2002.
28. Lee YC, Yellowley CE, Li Z, Donahue HJ, and Rannels DE. Expression of functional gap junctions in cultured pulmonary alveolar epithelial
cells. Am J Physiol Lung Cell Mol Physiol 272: L1105–L1114, 1997.
29. Matter K and Balda MS. Signalling to and from tight junctions. Nat Rev
Mol Cell Biol 4: 225–236, 2003.
30. Mehta D, Tiruppathi C, Sandoval R, Minshall RD, Holinstat M, and
Malik AB. Modulatory role of focal adhesion kinase in regulating human
pulmonary arterial endothelial barrier function. J Physiol 539: 779 –789,
2002.
31. Moessinger AC, Harding R, Adamson TM, Singh M, and Kiu GT.
Role of lung fluid volume in growth and maturation of the fetal sheep lung.
J Clin Invest 86: 1270 –1277, 1990.
32. Nelson WJ. Adaptation of core mechanisms to generate cell polarity.
Nature 422: 766 –774, 2003.
33. Niessen H, Harz H, Bedner P, Kramer K, and Willecke K. Selective
permeability of different connexin channels to the second messenger
inositol 1,4,5-trisphosphate. J Cell Sci 113: 1365–1372, 2000.
34. Paemeleire K, Martin PE, Coleman SL, Fogarty KE, Carrington WA,
Leybaert L, Tuft RA, Evans WH, and Sanderson MJ. Intercellular
calcium waves in HeLa cells expressing GFP-labeled connexin 43, 32, or
26. Mol Biol Cell 11: 1815–1827, 2000.
35. Pepper MS, Montesano R, el Aoumari A, Gros D, Orci L, and Meda
P. Coupling and connexin 43 expression in microvascular and large vessel
endothelial cells. Am J Physiol Cell Physiol 262: C1246 –C1257, 1992.
36. Quadri SK, Bhattacharjee M, Parthasarathi K, Tanita T, and Bhattacharya J. Endothelial barrier strengthening by activation of focal
adhesion kinase. J Biol Chem 278: 13342–13349, 2003.
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