Development of voltage-dependent inward currents in dissociated newt retinal pigment epithelial cells in culture

The whole-cell patch-clamp technique was employed to investigate the development of voltage-gated currents in cultured newt retinal pigment epithelial (RPE) cells. Freshly dissociated RPE cells were inexcitable and mainly exhibited a voltage-gated outward K+ current. Within a few days in culture RPE cells began to flatten and gradually became less pigmented. During subsequent time in culture the cells proliferated and formed monolayer colonies containing depigmented cells. About 36% cells (15/42) examined between 6 and 21 days in culture developed the voltage-gated inward currents. In two depigmented cells cultured for more than 17 days, the sustained inward Ca2+ current was developed. The result suggests that RPE cells develop the voltage-gated inward currents responsible for retinal neurones with time in culture.