Hyperosmolarity-induced hyperpolarization of the membrane potential of the retinal pigment epithelium.

The hyperosmolarity-induced changes of the apical (Vap) and basal (Vba) membrane potentials of the retinal pigment epithelium (RPE) were studied in an in-vitro RPE-choroid preparation of the frog. Both Vap and Vba were simultaneously hyperpolarized by hyperosmolarity at either the apical or basal side of the RPE. Hyperosmolarity at the apical side hyperpolarized Vap greater than Vba, and increased the trans-epithelial potential (TEP) across the RPE. Hyperosmolarity at the basal side hyperpolarized Vba, simultaneously hyperpolarized Vap by a smaller amount, and reduced the TEP. The hyperosmolarity response (a decrease of the ocular standing potential induced by an intravenous hypertonicity) is due mainly to a hyperpolarization of Vba.