Mernbrane Biology 9 Sprlnger.Vedag New York inc. 1988 Effect of Taurine on the Isolated Retinal Pigment Epithelium of the Frog: Electrophysiologic Evidence for Stimulation of an Apical, Eiectrogenic Na+-K § Pump

Summary. The apical surface of the retinal pigment epithelium (RPE) faces the neural retina whereas its basal surface faces the choroid. Taurine, which is necessary for normal vision, is re-leased from the retina following light exposure and is actively transported from retina to choroid by the RPE. In these experi-ments, we have studied the effects of taurine on the electrical properties of the isolated RPE of the bullfrog, with a particular focus on the effects of taurine on the apical Na~-K + pump. Acute exposure of the apical, but not basal, membrane of the RPE to taurine decreased the normally apical positive trans-epithelial potential (TEP). This TEP decrease was generated by a depolarization of the RPE apical membrane and did not occur when the apical bath contained sodium-free medium. With con-tinued taurine xposure, the initial TEP decrease was sometimes followed by a recovery of the TEP toward baseline. This recov