The flux ratio of the Na-Cl cotransport mechanism in the frog corneal epithelium

Abstract

The stoichianetry of the Na-Cl ootransport mechanism at the base-lateral membrane of the frog corneal epithelium was studied with the aid of intracellular microelectrodes by analyzing the effects of ouabain on intracellular recordings (PD_SC) and transepithelial short-circuit current (I_SC). Under short-circuit conditions, the total current across the basolateral membrane was equated to the Cl⁻ transport across the apical membrane. Ouabain produces a quick and steep decrease of PD_SC (7.1 mV) and I_SC (3.0 μA/cm²) that was ascribed to a sudden inhibition of the electrogenic component of the Na-K pump. From these effects, and from results in previous studies, the maximum value for the Na⁺ flux via the ootransport mechanism (I^C_Na) was estimated and compared to the apical Cl⁻ transport (a minimum estimate of the Cl⁻ flux cotransported with Na⁺). In all experiments, I_cl was larger than I_Na. Considering that Na⁺ also recirculates across tne basolateral membrane via a passive pathway, the Cl:Na flux ratio of the ootransport system may be as high as 4.