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Chloride-activated water permeability in the frog corneal epithelium
Authors:O A Candia  A C Zamudio
Institution:(1) Department of Ophthalmology, Mount Sinai School of Medicine, 100th Street and 5th Avenue, 10029 New York, NY;(2) Department of Physiology and Biophysics, Mount Sinai School of Medicine, 100th Street and 5th Avenue, 10029 New York, NY
Abstract:We have previously reported that the isolated frog corneal epithelium (a Cl-secreting epithelium) has a large diffusional water permeability (Pdw ap 1.8×10–4 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 mgrl min–1 · cm–2 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 apicalside 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.This work was supported by National Eye Institute grants EY-00160 and EY-01867.
Keywords:Water permeability  Frog cornea  Chloride activation  Unidirectional water fluxes  Net water fluxes  Chloride-secreting epithelium
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