Active transport of ions across frog retinal pigment epithelium

Abstract

Ion fluxes across the isolated frog retinal pigment epithelium-choroid preparation were measured in the short circuited state. There was a net flux of ²²Na (0·47[μEq/cm²hr]) in the choroid to retina (basal to apical) direction that was 50–60% inhibited by apical ouabain, 10⁻⁴m. No seasonal variation in this net flux was observed. In contrast, the net retina to choroid ³⁶Cl flux did vary from season to season, being high (0·5–0·74[μEq/cm² hr]) in the spring, and low (0·2–0·5[μEq/cm² hr]) in the summer. The net ²²Na plus ³⁶Cl flux did not account for all the short circuit current in either the spring or summer. The net ³⁶Cl flux was equally inhibited by acetazolamide, 10⁻³m, and by a 10-fold reduction in the bathing solution HCO₃⁻ concentration (27·5–2·75 mm). The ³⁶Cl fluxes were not affected by ouabain. The inhibition of the net ²²Na and ³⁶Cl fluxes exhibited a similar pattern of changes. In both cases the unidirectional flux, in the direction of net transport, was slightly or not at all reduced, and the opposite flux was significantly increased. There was a net flux of ⁴⁵Ca in the choroid to retina direction of 4–5[nm/cm² hr] that was doubled by apical ouabain (10⁻⁴m) and not affected by a 10-fold reduction in [HCO₃⁻]₀ or acetazolamide, 10⁻³m.