Voltage-operated calcium channels in fresh and cultured rat retinal pigment epithelial cells.

PURPOSE There is little known about the membrane properties of retinal pigment epithelial (RPE) cells with respect to calcium. The authors attempted to characterize membrane calcium channels from solitary fresh and cultured RPE cells from normal and dystrophic rat retinas. METHODS RPE cells were enzymatically dissociated from eyes of neonatal rats of several strains, including dystrophic RCS strains. Membrane currents were recorded using the whole-cell version of the patch-clamp technique from either fresh or cultured cells. RESULTS The authors observed sustained high-voltage-activated calcium channels that were dihydropyridine sensitive and closely resembled neuronal L-type calcium channels. The RCS-rdy+p+ strain was mainly investigated, but high-voltage-activated calcium channels were also recorded from fresh RPE cells of other rats regardless of age or strain, including RCS p+, RCS rdy+, Long Evans, Sprague Dawley, and also cultured RPE cells taken from a neonatal Long Evans strain. Low-voltage-activated calcium channels were not observed in any of these cells. CONCLUSION Voltage-operated calcium channels of the L-type are the main calcium channels present in rat RPE cells. Cultured cells retained the identical channels. The dystrophic RCS strains (studied until 17 days postnatal) also exhibited these channels.