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Chloride-activated water permeability in the frog corneal epithelium.

The Journal of Membrane Biology

Amphotericin B, metabolism, Water, Rana catesbeiana, Osmolar Concentration, Epithelium, Cornea, Chlorides, Cells, Cultured, Cell Membrane Permeability, Biological Transport, drug effects, Basement Membrane, Animals, pharmacology

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      We have previously reported that the isolated frog corneal epithelium (a Cl(-)-secreting epithelium) has a large diffusional water permeability (Pdw approximately 1.8 x 10(-4) cm/s). We now report that the presence of Cl- in the apical-side bathing solution increases the diffusional water flux, Jdw (in both directions) by 63% from 11.3 to 18.4 microliters with 60 mM [Cl] exerting the maximum effect. The presence of Cl- in the basolateral-side bathing solution had no effect on the water flux. In Cl(-)-free solutions amphotericin B increased Jdw by 29% but only by 3% in Cl(-)-rich apical-side bathing solution, suggesting that in Cl(-)-rich apical side bathing solution, the apical barrier is no longer rate limiting. Apical Br- (75 mM) also increased Jdw by 68%. The effect of Cl- on Jdw was observed within 1 min after its addition to the apical-side bathing solution. HgCl2 (0.5 mM) reduced the Cl(-)-increased Pdw by 31%. The osmotic permeability (Pf) was also measured under an osmotic gradient yielding values of 0.34 and 2.88 (x 10(-3) cm/s) in Cl(-)-free and Cl(-)-rich apical-side bathing solutions respectively. It seems that apical Cl-, or Cl- secretion into the apical bath could activate normally present but inactive water channels. In the absence of Cl-, water permeability of the apical membrane seems to be limited to the permeability of the lipid bilayer.

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