POTASSIUM CURRENTS IN CULTURED-CELLS OF THE RAT RETINAL-PIGMENT EPITHELIUM

Whole-cell currents were investigated in cultured rat retinal pigment epithelial (RPE) cells. Two voltage-dependent conductances were discri minated. First, at potentials more positive than -30 mV, a time-depend ent outward current was activated. Inhibition by Ba2+ (10 mM) and 4-am inopyridine (10 mM) indicated that this current was carried by potassi um ions. This current showed no inactivation during 5 sec depolarizati ons. Second, an inward current, sensitive to Ba2+ (10 mM) and 4-aminop yridine (10 mM), was activated at potentials more negative than -70mV. Under extra- and intracellular potassium-free conditions, both curren ts disappeared. In summary, cultured rat RPE cells expressed one potas sium conductance similar to the delayed rectifier and one similar to t he inward rectifier. The delayed rectifier expressed characteristics c omparable with those known in mammalian species and different from tho se in non-mammalian species.