1Department of Physiology, University of Otago Medical School, Dunedin, New Zealand 9001; and 2Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
Submitted 13 June 2003 ; accepted in final form 31 January 2004
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ABSTRACT |
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pigmented ciliary epithelial cells; nonpigmented ciliary epithelial cells; gap junctions; aqueous humor; Na+/K+ exchange pump; rabbit iris-ciliary body
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In our previous microprobe analyses of ciliary epithelial cells, we generally found little difference in average compositions between PE and NPE cells. Although consistent with the syncytial view of the ciliary epithelium, cell composition was altered relatively little in most of these studies. One aim of the present experiments was to examine the relationships between cells displaying the much larger changes in individual composition that follow ouabain inhibition of the Na+/K+ exchange pump. We also used heptanol in an attempt to isolate effects of ouabain on the NPE cells from those on the paired PE cells. Our prediction was that, after incubation in heptanol, effects on cell composition of drugs and other agents applied to one surface of the epithelium should be limited to the cell type on that surface. If so, this would allow examination of the transport characteristics of NPE and PE cells in the intact epithelium without undue modification of the effects by the paired cell.
As illustrated by Fig. 1, studies of ciliary epithelial transport are commonly analyzed within the framework of lumped-parameter models, but some published results have suggested possible regional differences in net secretion (11, 13, 14, 1721, 25). The microprobe technique permits measurement of cell electrolyte composition in individual cells, thus providing a unique opportunity to explore this possibility directly. Recently, we reported evidence of a higher turnover rate of Cl in the anterior ciliary epithelium (22). In addition to examining gap-junctional function, the present study addressed whether cells in the anterior and posterior regions of the ciliary epithelium were equally affected by ouabain.
Our results indicate that there are differences in gap-junctional function within and between the PE and NPE cell layers, that the functional unit of the ciliary epithelium is the PE-NPE cell couplet, and that the turnover of Na and K is substantially faster in the anterior than in the posterior ciliary epithelial cells.
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MATERIALS AND METHODS |
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Cellular model. Dutch black-belted rabbits of either sex and older than 6 wk postweaning were obtained from the Department of Laboratory Animal Sciences, University of Otago Medical School, and were treated in accordance with the Resolution on the Use of Animals in Research of the Association for Research in Vision and Ophthalmology. Animals were anesthetised with 30 mg/kg pentobarbital sodium and killed by injecting air into the marginal ear vein. After enucleation, the iris-ciliary body (ICB) was excised and cut into quarters, and each quarter was bonded with cyanoacrylate to a Mylar support frame on its stromal border. The quadrants with attached frames were mounted in incubation chambers.
Our experimental protocols, in common with many epithelial studies, required the application of different solutions to either side of the ICB. Tissues were mounted between two half-chambers designed to separate the solutions bathing the aqueous and stromal surfaces of the ciliary epithelium. Electrodes were not installed. Each support frame with attached ICB quadrant was aligned by pins between the half-chambers and an indent in the stromal half-chamber, so that the quadrant accurately occluded the common aperture of the two half-chambers. The fluid volume of each half-chamber was 1.5 ml. Fresh solution was constantly infused through each half-chamber at 0.5 ml/min, with higher flow rates during solution changes. Aspiration of excess solution maintained equal levels of fluid on each side of the epithelium, with no pressure gradient. A gas lift in each half-chamber provided gentle aeration and stirring of the solution.
Quadrants of ICB were incubated for 12 h at room temperature (1822°C) under control conditions. Pairs of quadrants (one from each eye) were then incubated for at least 30 min under either control or experimental conditions. After incubation, the tissues were blotted and then plunged into liquid propane at 80°C to freeze the preparation rapidly, thus preventing any redistribution of ions and water. Blocks were fractured from the frozen tissue under a dissecting microscope (x7). Careful attention was paid to the origin and orientation of the block. Thus, after transfer of a block to the cryoultramicrotome and subsequent trimming, we could identify and accurately select the region from which the sections were cut. Generally, sections were cut tangentially. We identified the origins of the sections as either the posterior region (toward retina) or the anterior region (toward iris), respectively, by using criteria established previously (25). Occasionally, sections were cut radially, particularly when we sought to correlate changes in ion content with position along the posterior-anterior axis.
In our initial topological study (25), we analyzed three regions of the rabbit ciliary epithelium: a posterior pars plicata (30) region adjacent to the minimal (in the rabbit) pars plana (30), an anterior region including what has been referred to as the iridial portion of the primary ciliary processes (30), and a middle region between these two. In that study, the responses of the middle region tended to track those of the anterior region but also appeared to display some properties of a region transitional between the well-defined anterior and posterior regions. These two areas are indeed very well defined structurally so that, with experience, the source of the section can be easily identified in cross section by the investigator. The posterior region is characterized by long ciliary processes reaching regularly down to the iris. In contrast, the anterior region displays irregularly shaped cross-sectional areas, whose folds do not necessarily extend to the iris in the section examined but rather reach the iris in an earlier or subsequent section. In the present work, we have compared the elemental compositions of these two structurally well-defined regions: the anterior iridial portion of the primary ciliary processes and the posterior pars plicata region.
Sections of thickness 0.20.4 µm were cut at 80 to 90°C, freeze-dried at 104 Pa (equivalent to 7.5 x 107 Torr), and transferred for analysis to a scanning electron microscope (JEOL JSM 840) equipped with an energy-dispersive X-ray spectrometer.
Solutions and chemicals. The solutions contained (in mM) 145 Na+, 5.9 K+, 122.1 Cl, 15.0 HEPES [4-(2 hydroxyethyl)-1-piperazineethanesulfonic acid], 1.2 Mg2+, 2.5 Ca2+, 1.2 H2PO4, 30 HCO3, and 10 glucose at pH 7.307.45 and 305315 mosmol/kgH2O. Throughout incubation, 95%O2-5%CO2 was bubbled through the solution. All chemicals were reagent grade. Both ouabain and heptanol were added directly to solutions at their final concentrations and dissolved by stirring. In addition, solutions containing heptanol were sonicated for 1 h following stirring.
Data acquisition and reduction. Electron probe X-ray microanalysis permits both quantification and localization of intracellular elements. Using an electron microscope, we target a specific visualized area within the cell. The specimen is irradiated with a beam of electrons, which ionizes a small fraction of the atoms bombarded. After an electron is knocked from an inner atomic shell, an electron from an outer shell can take its place. The relaxation of the electron from a higher to a lower energy state generates a quantum of X-ray energy. Spectroscopic measurement of the characteristic energy and number of these quanta permits identification and quantification of the elements within the sample.
The dried sections were imaged with a transmitted electron detector. X-rays were collected with a Tracor Northern 30-mm2 X-ray detector using a probe current of 140200 pA for 100 s at an accelerating voltage of 20 kV. The intracellular data were obtained by the electron beam scanning a rectangular area within the nucleus of each selected NPE or PE cell, which varied from 0.9 x 1.2 to
2.4 x 3.0 µm depending on the size of the nucleus analyzed. It must be emphasized that a great strength of the electron probe is the capability of directly visualizing those cells and those subcellular targets that are analyzed, thereby ensuring that only the analyzed epithelial cells and not the extracellular compartment or other cellular components contributed data on elemental composition. The individual PE and NPE cells were analyzed in pairs to enable the cellular compositions of the PE and NPE layers to be compared on an individual cell-pair basis.
The elemental peaks were quantified by filtered least-square fitting to a library of monoelemental peaks (3). The library spectra for Na, Mg, Si, P, S, Cl, K, and Ca were derived from microcrystals sprayed onto a Formvar film. In addition to the quantal element-specific X-rays, irradiating sections with an electron beam produces nonquantal white or continuous radiation or "Bremsstrahlung," arising from electron deceleration by coulombic interaction with atomic nuclei. The white counts (w), an index of tissue mass (5), were summed over the range 4.66.0 keV, and corrected for the nontissue contributions arising from the Al specimen holder and Ni grid. As discussed previously (24), the Na, K, and Cl signals were routinely normalized to the P signal obtained in the same scanned area of each cell, yielding molar ratios of these elements. We have previously estimated the P content in this tissue to constitute 500 mmol/kg dry wt (2). P was chosen for normalization because of the constancy of the intracellular signal, which almost entirely reflects the covalently linked fraction in epithelial cells. For example, inorganic phosphate (Pi) is accumulated to only 3 mmol/kg intracellular water in the epithelial cells of frog skin (5). In such cells, the total pool of ATP, ADP, phosphocreatine, and Pi corresponds to only 5% of the total P pool measured in the ciliary epithelial cells (2). The validity of normalizing to P has been experimentally demonstrated by the close linear relationship we have obtained between the two largely intracellular elements K and P (see Fig. 3 in Ref. 2). As illustrated in Table 1, we have found that there is no regional difference in P content. NPE cells had the same values of P/w anteriorly and posteriorly, as did the PE cells.
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RESULTS |
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Despite the very large ouabain-triggered changes in Na and K content of the anterior cells, the median values of Na/P (Fig. 2A) and K/P (Fig. 2B) were the same in both NPE and PE cells. Evidently, when communication through the gap junctions linking the two cell layers is not blocked, paired NPE and PE cells are affected to similar extents under all conditions, as documented by the linear relationship between the elemental contents of PE and NPE cells following exposure to ouabain (Fig. 3, AC).
One striking observation was that the ouabain-induced changes in Na/P and K/P varied markedly from cell to cell within the NPE and PE cell layers. The cells that gained the most Na lost the most K. This is clear from the plots of anterior NPE cell K/P as a function of Na/P following incubation in stromal, aqueous, or bilateral ouabain (Fig. 4, AC). The deviation from linearity of the data points with the very highest Na/P of Fig. 4C likely indicates that bilateral exposure to ouabain produces the largest inhibitions of the Na+ pumps. Under these conditions, there is more complete replacement of K by Na, leading to membrane depolarization and further uptake of Na accompanied by Cl.
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We conclude that application of heptanol alone affects the composition only of the most anterior NPE cells. A possible explanation for this is that these cells rely on their partner PE cells to maintain their Na and K compositions; i.e., these cells cannot maintain their ion composition unaided, because the passive ion movements exceed the capacity of their pump activity.
Time course of responses to ouabain in presence of heptanol. Tissues were incubated in 3 mM heptanol and 100 µM ouabain on both sides and analyzed after 0, 20, 40, and 80 min. The time course reflects both the time taken for ouabain to reach the cells and block the Na+-K+-ATPase, and the rate at which Na is gained by, and K lost from, the cells. As in the absence of heptanol, ouabain exerted greater changes on the Na/P and K/P of the anterior (Fig. 6A) than the posterior (Fig. 6C) ciliary epithelial cells.
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Concentration-response relationship to ouabain in presence of heptanol. The tissues of Fig. 7 were exposed to ouabain on both surfaces for 30 min. As noted with the foregoing protocols, ouabain exerted the greatest effects on anterior NPE cells, with an apparently saturating concentration of 10 µM for the effects on both Na and K over this time period. For the anterior PE cells, only 100 µM ouabain produced changes approaching those of both 10 and 100 µM concentrations on the anterior NPE cells. For the posterior NPE and PE cells, the ouabain effects were much smaller; note the different vertical scale of Na/P in Fig. 7C.
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DISCUSSION |
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Baseline measurements. In the absence of ouabain and heptanol, there was relatively little variation in Na/P and K/P of neighboring cells within a single section (Fig. 5). Under these control conditions, NPE and PE cells displayed similar median values and frequency distributions for Na/P and K/P (Fig. 2). It seems implausible that neighboring pairs of PE and NPE cells in series have precisely the same number and activity of transporters. Therefore, we interpret the relative homogeneity of Na/P, K/P, and Cl/P to reflect the ability of Na+, K+, and Cl to equilibrate by moving from one cell to its neighbor through gap junctions.
Effects of ouabain alone. Application of ouabain to both surfaces of excised rabbit iris-ciliary bodies reduces the intracellular K and increases the intracellular Na contents of the PE and NPE cells (2). In the present study, we have confirmed and extended that observation. In the presence of ouabain without heptanol, the Na, K, and Cl contents of adjoining pairs of PE and NPE cells remained very similar (Fig. 3), as predicted if the PE-NPE gap junctions remain functional. However, the variation in Na/P and K/P among neighboring cell pairs was striking (Fig. 5C). This finding was unexpected in view of structural (27, 28), biochemical (7, 9), and functional (2, 4, 12, 22, 26, 33) evidence for gap-junctional coupling between adjoining cells within the cell layers. The present results clearly indicate that the gap junctions linking PE and NPE cells are different in number or molecular composition from those linking adjoining cells within either the PE or NPE cell layers. This observation is consonant with the original observations of Raviola and Raviola (27), who noted the far greater number of gap junctions between than within the PE and NPE cell layers. Our observation is also in agreement with recent studies of the connexin (Cx) composition of ciliary epithelial gap junctions.
The prominence of Cx43 in ciliary gap junctions was initially reported by Coca-Prados et al. (7) and subsequently confirmed by several laboratories (9, 29, 32). Although Cx50 had been thought to participate in these gap junctions (32), the specificity of the antibody to Cx50 used has been questioned (9). On the basis of a recent careful RT-PCR and immunostaining study of rat ciliary epithelium (9), it is likely that PE and NPE cell couplets are linked by homotypic, homomeric Cx40 and Cx43 gap junctions. In contrast, adjoining NPE cells appear linked by separate homomeric Cx26 and Cx31 gap junctions. Interestingly, Coffey et al. (9) did not detect connexins linking adjoining PE cells, although PE-PE gap junctions have been demonstrated by freeze fracture (27). The negative result of Coffey et al. could reflect either the small plaque size of the PE-PE gap junctions or the participation of as-yet-unidentified connexins.
The inability of PE-PE and NPE-NPE gap junctions to sustain ionic equilibration between adjoining ouabain-treated cells may have reflected simply the limited expression and conductance of these junctions. Alternatively, ouabain may have triggered uncoupling of junctions between adjacent cells in the two layers. Connexins can be selectively up- and downregulated, especially through phosphorylation and dephosphorylation (23). In the current context, ouabain may have triggered a cascade of events leading selectively to interruption of gap junctions linking cells within the PE and NPE layers. For example, the increased Na+ concentration produced by ouabain should increase Ca2+ and proton concentrations secondarily by reducing the electrochemical driving forces for Na+/Ca2+ and Na+/H+ exchange. Indeed, exposure to ouabain either in the aqueous or aqueous and stromal solutions significantly reduced (Na + K Cl)/P, consistent with a fall in intracellular pH (data not shown). Reductions in intracellular pH and increases in intracellular Ca2+ do block gap junctions (32), but future direct measurements of pH and Ca2+ will be needed to test the plausibility of this possibility.
Effects of heptanol alone. Heptanol alone did not result in appreciable changes in ion contents in either the NPE or PE cells (with the exception noted in results in relation to some NPE cells in sections from the most anterior region of the tissue). This observation, illustrated for example in Fig. 5B, indicates either that, under the conditions of the experiments, variations in ion movements into the two cell types are able to be compensated for by movements out of the same cells across their basolateral membranes, or that heptanol is not particularly effective in blocking gap junctions between adjoining PE-PE and NPE-NPE cell pairs.
Effects of ouabain in presence of heptanol. If the observed heptanol-induced reduction in current across rabbit iris-ciliary body (31) indeed reflects interruption of PE-NPE cell gap junctions, heptanol should reveal the differential responsivity of PE and NPE cell composition to ouabain. The present results verify this prediction. Despite the substantial variance in the effects of ouabain on elemental composition of PE-NPE cell pairs (Fig. 5C), the elemental composition of the paired PE and NPE cells tracked one another very well in the absence of heptanol (Fig. 3). In contrast, heptanol abolished this tracking (Figs. 10 and 12). It is evident from the analyses of time and concentration dependence that, on average, the anterior NPE cells responded more strongly to ouabain than their PE cell counterparts did. This suggests that the rate of Na+ extrusion by the NPE cell pumps might exceed the rate of net Na+ transfer from PE to NPE cells. A significant fraction of Na+ extrusion by these pumps may represent recycling across the basolateral membrane abutting the aqueous humor. If so, this recycling through the NPE cells might provide a basis for significantly regulating NaCl reabsorption through the gap junctions and PE cells back to the stroma. This putative reabsorption could then be regulated by modifying Na+ and Cl release across the PE cell basolateral membrane. Indeed, recent electrophysiological studies suggest that cAMP directly activates PE-cell maxi-Cl channels whose open probability and conductance are enhanced in Cl-loaded cells (10, 16).
Topology of net fluid transport.
A number of investigators have observed regional differences in the expression of Na+-K+-activated ATPase and additional proteins and biologically active peptides. Interestingly, NPE cells of young calves display higher expression of 1/
2/
3/
1/
2-isoforms of Na+-K+-activated ATPase anteriorly than posteriorly, but PE cells express a constant relative concentration of
1/
1 throughout the epithelium (8). Thus net vectorial Na+ extrusion through the Na+ pumps is likely higher anteriorly. Whether the net vectorial movement is actually reversed, leading to reabsorption posteriorly (20), has never been tested. We have already obtained intriguing indications of topological differences in transport from electron microprobe analyses of rabbit ciliary epithelium (25). Those indications were that 1) the ratio of K to Na content was higher in the posterior than in the anterior epithelium, consistent with a lower turnover of Na+ and K+ in the posterior region; and 2) three separate perturbations exerted greater effects on the Cl content of the anterior than of the posterior epithelium, consistent with a higher turnover rate of Cl anteriorly. The three perturbation were omission of CO2/HCO3 from the bathing solutions, inhibition of carbonic anhydrase in the presence of CO2/HCO3, and inhibition of Na+-K+-2Cl cotransport with bumetanide.
The present results provide strong support for the possibility that net transport across the ciliary epithelium is region specific. After exposure to ouabain to block the Na+-K+-activated ATPase, the epithelium responded far more vigorously anteriorly than posteriorly. Unstirred layers can play no role in this phenomenon, since the basolateral surfaces of the NPE cells are equally accessible to the aqueous solutions anteriorly and posteriorly. In addition, because the vast majority of cell K behaves as does K in free solution and the plasma membrane is not impermeable to Na, cells must gain Na and lose K if the sodium pump is inhibited. The regional specificity of the responses to ouabain could reflect the isoform distributions of Na+-K+-activated ATPase or the distribution of regulating molecules such as phospholemman (15). The rate of inhibition of the enzyme by ouabain depends on the rate of turnover of the pump. The slower the pump rate, the longer it will take for maximal pump inhibition. However, pump inhibition is not normally the rate-limiting step in determining the consequent rate of change in cell composition; rather, it is the rates at which the cells can gain Na and lose K. As illustrated in Fig. 6, it is apparent that the posterior cells gain Na and lose K continuously throughout the 80 min of incubation but at a much slower rate than the anterior cells. Whether the increased turnover of Na+, K+, and Cl underlies a higher rate of aqueous humor secretion across the anterior region of the ciliary epithelium remains to be determined.
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GRANTS |
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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REFERENCES |
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2. Bowler JM, Peart D, Purves RD, Carré DA, Macknight AD, l, and Civan MM. Electron probe X-ray microanalysis of rabbit ciliary epithelium. Exp Eye Res 62: 131139, 1996.[CrossRef][ISI][Medline]
3. Bowler JM, Purves RD, and Macknight AD. Effects of potassium-free media and ouabain on epithelial cell composition in toad urinary bladder studied with X-ray microanalysis. J Membr Biol 123: 115132, 1991.[ISI][Medline]
4. Carré DA, Tang CS, Krupin T, and Civan MM. Effect of bicarbonate on intracellular potential of rabbit ciliary epithelium. Curr Eye Res 11: 609624, 1992.[ISI][Medline]
5. Civan MM. Epithelial Ions & Transport: Application of Biophysical Techniques. New York: Wiley-Interscience, 1983.
6. Civan MM. Transport components of net secretion of the aqueous humor and their integrated regulation. Current topics in membranes 45. In: The Eye's Aqueous Humor: From Secretion to Glaucoma, edited by Civan MM. San Diego: Academic, 1998, p. 124, 1998.
7. Coca-Prados M, Ghosh S, Gilula NB, and Kumar NM. Expression and cellular distribution of the alpha 1 gap junction gene product in the ocular pigmented ciliary epithelium. Curr Eye Res 11: 113122, 1992.[Medline]
8. Coca-Prados M and Sánchez-Torres J. Molecular approaches to the study of the Na+,K+-ATPase and chloride channels in the ocular ciliary epithelium. In: The Eye's Aqueous Humor: From Secretion to Glaucoma, edited by Civan MM. San Diego: Academic, 1998, p. 2553.
9. Coffey KL, Krushinsky A, Green CR, and Donaldson PJ. Molecular profiling and cellular localization of connexin isoforms in the rat ciliary epithelium. Exper Eye Res 75: 921, 2002.[CrossRef][ISI]
10. Do CW, Peterson-Yantorno K, Mitchell CH, and Civan MM. cAMP-activated maxi-Cl channels in native bovine pigmented ciliary epithelial cells: implications for net secretion of the aqueous humor (Abstract). Soc General Physiologists, Woods Hole, MA: 2003, p. #97.
11. Dunn JJ, Lytle C, and Crook RB. Immunolocalization of the Na-K-Cl cotransporter in bovine ciliary epithelium. Invest Ophthalmol Vis Sci 42: 343353, 2001.
12. Edelman JL, Sachs G, and Adorante JS. Ion transport asymmetry and functional coupling in bovine pigmented and nonpigmented ciliary epithelial cells. Am J Physiol Cell Physiol 266: C1210C1221, 1994.
13. Eichhorn M, Flügel C, and Lütjen-Drecoll E. Regional differences in the ciliary body of cattle: an electron microscopy and histochemical study. Fortschr Ophthalmol 87: 241246, 1990.[Medline]
14. Eichhorn M, and Lütjen-Drecoll E. Distribution of endothelin-like immunoreactivity in the human ciliary epithelium. Curr Eye Res 12: 753757, 1993.[ISI][Medline]
15. Feschenko MS, Donnet C, Wetzel RK, Asinovski NK, Jones LR, and Sweadner KJ. Phospholemman, a single-span membrane protein, is an accessory protein of Na,K-ATPase in cerebellum and choroid plexus. J Neurosci 23: 21612169, 2003.
16. Fleischhauer JC, Mitchell CH, Peterson-Yantorno K, Coca-Prados M, and Civan MM. PGE2, Ca2+, and cAMP mediate ATP activation of Cl channels in pigmented ciliary epithelial cells. Am J Physiol Cell Physiol 281: C1614C1623, 2001.
17. Flügel C, Liebe S, Voorter C, Bloemendal H, and Lütjen-Drecoll E. Distribution of alpha B-crystallin in the anterior segment of primate and bovine eyes. Curr Eye Res 12: 871876, 1993.[ISI][Medline]
18. Flügel C and Lütjen-Drecoll E. Presence and distribution of Na+/K+-ATPase in the ciliary epithelium of the rabbit. Histochemistry 88: 613621, 1988.[ISI][Medline]
19. Flügel C, Lütjen-Drecoll E, Zadunaisk JA, and Wiederholt M. Regional differences in the morphology and enzyme distribution of the spiny dogfish (Squalus acanthias) ciliary epithelium. Exp Eye Res 49: 10971114, 1989.[ISI][Medline]
20. Ghosh S, Freitag AC, Martin-Vasallo P, and Coca-Prados M. Cellular distribution and differential gene expression of the three alpha subunit isoforms of the Na,K-ATPase in the ocular ciliary epithelium. J Biol Chem 265: 29352940, 1990.
21. Ghosh S, Hernando N, Martin-Alonso JM, Martin-Vasallo P, and Coca-Prados M. Expression of multiple Na+,K+-ATPase genes reveals a gradient of isoforms along the nonpigmented ciliary epithelium: functional implications in aqueous humor secretion. J Cell Physiol 149: 184194, 1991.[ISI][Medline]
22. Green K, Bountra C, Georgiou P, and House CR. An electrophysiologic study of rabbit ciliary epithelium. Invest Ophthalmol Vis Sci 26: 371381, 1985.[Abstract]
23. Lampe PD and Lau AF. Regulation of gap junctions by phosphorylation of connexins. Arch Biochem Biophys 384: 205215, 2000.[CrossRef][ISI][Medline]
24. McLaughlin CW, Peart D, Purves RD, Carré DA, Macknight AD, and Civan MM. Effects of HCO3 on cell composition of rabbit ciliary epithelium: a new model for aqueous humor secretion. Invest Ophthalmol Vis Sci 39: 16311641, 1998.[Abstract]
25. McLaughlin CW, Zellhuber-McMillan S, Peart D, Purves RD, Macknight AD, and Civan MM. Regional differences in ciliary epithelial cell transport properties. J Membr Biol 182: 213222, 2001.[CrossRef][ISI][Medline]
26. Oh J, Krupin T, Tang LQ, Sveen J, and Lahlum RA. Dye coupling of rabbit ciliary epithelial cells in vitro. Invest Ophthalmol Vis Sci 35: 25092514, 1994.[Abstract]
27. Raviola G and Raviola E. Intercellular junctions in the ciliary epithelium. Invest Ophthalmol Vis Sci 17: 958981, 1978.[Abstract]
28. Reale E. Freeze-fracture analysis of junctional complexes in human ciliary epithelia. Albrecht Von Graefes Arch Klin Exp Ophthalmol 195: 116, 1975.[ISI][Medline]
29. Sears J, Nakano T, and Sears M. Adrenergic-mediated connexin43 phosphorylation in the ocular ciliary epithelium. Curr Eye Res 17: 104107, 1998.[CrossRef][ISI][Medline]
30. Weingeist TA. The structure of the developing and adult ciliary complex of the rabbit eye: a gross, light, and electron microscopic study. Doc Ophthalmol 28: 205375, 1970.[ISI][Medline]
31. Wolosin JM, Candia OA, Peterson-Yantorno K, Civan MM, and Shi XP. Effect of heptanol on the short circuit currents of cornea and ciliary body demonstrates rate limiting role of heterocellular gap junctions in active ciliary body transport. Exp Eye Res 64: 945952, 1997.[CrossRef][ISI][Medline]
32. Wolosin JM, Schutte M, and Chen S. Connexin distribution in the rabbit and rat ciliary body. A case for heterotypic epithelial gap junctions. Invest Ophthalmol Vis Sci 38: 341348, 1997.[Abstract]
33. Yantorno RE, Carré DA, Coca-Prados M, Krupin T, and Civan MM. Whole cell patch clamping of ciliary epithelial cells during anisosmotic swelling. Am J Physiol Cell Physiol 262: C501C509, 1992.
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