Three light-evoked responses of the retinal pigment epithelium.

This paper summarizes our findings on light-evoked changes in retinal pigment epithelial cell (RPE) membrane potentials. Experiments were performed on the eye of the anesthetized or decerebrate cat and on isolated tissues from the eyes of a lizard, Gekko gekko, and a frog, Rana catesbeiana. In cat, as was previously shown, the RPE apical membrane potential responds to changes in [K+]0 in the subretinal space. At the onset of illumination it hyperpolarizes to a peak at 4.0 sec as [K+]0 decreases. The next RPE response is a hyperpolarization of the basal membrane that peaks at 20 sec and is also dependent on the decrease in subretinal [K+]0. The last and slowest response is a depolarization of the basal membrane that peaks at 300 sec, and is not obviously associated with K+ changes. The same responses also appear in gecko at a slower time-course, but only the apical-membrane K+-response is present in frog. The three responses also are associated with changes of the opposite polarity at the offset of illumination. These changes in membrane potential are the origin, respectively, of the RPE component of the ERG c-wave, the fast oscillation, and the light peak (slow oscillation).