Dihydropyridine-sensitive calcium currents in freshly isolated human and monkey retinal pigment epithelial cells.

PURPOSE The authors previously reported that rat retinal pigment epithelial (RPE) cells exhibit an ionic current through voltage-operated calcium channels that is dihydropyridine sensitive. They attempted to record the same current from freshly isolated fetal or adult primate RPE cells, as well as from cultured cells. METHODS The whole-cell version of the patch-clamp technique was applied to RPE cells freshly isolated by enzymatic dissociation from fetal human and adult human and monkey eyes, as well as cultured fetal and adult human RPE cells. The cells were loaded with cesium to minimize potassium-related current and were bathed in an extracellular solution containing 40 mM barium to intensify the calcium currents. RESULTS Freshly isolated cells, both fetal and adult, showed sustained and inward-going barium current through voltage-operated calcium channels with membrane depolarizations from a high holding voltage of -60 mV. This current was affected by dihydropyridine compounds. Cultured human RPE cells showed no sign of a calcium current of this type. CONCLUSIONS Freshly isolated fetal and adult human RPE cells, as well as adult monkey, exhibit calcium current through voltage-operated, dihydropyridine-sensitive channels, similar to the neuronal L-type, just as in rat RPE cells.