Ca2+‐conductances in cultured rat retinal pigment epithelial cells

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Abstract
Membrane conductances for Ca2+ in cultured rat pigment epithelial cells were studied in the whole‐cell configuration of the patch‐clamp technique using barium (10 mM) as a charge carrier. Two types of voltage‐dependent and verapamiland diltiazem‐sensitive Ba2+ currents were observed. First, a nearly sustained current was activated by depolarization to potentials more positive than — 30mV and blocked by nifedipine (1 μM). This current was observed in cells of primary cultures less than 13 days old. Second, a transient nifedipine (1 μM) insensitive current was activated by depolarization to potentials more positive than — 55mV in cultures which were more than 13 days old. This current was not carried by sodium and blocked by 1 μM tetrodotoxin (TTX). In summary, cultured rat retinal pigment epithelial cells in younger primary cultures express Ba2+ currents indicating the presence of L‐type Ca2+ channels. In order primary cultures a low‐voltage activated channel was observed with properties different from T‐type calcium channels or TTX‐sensitive calcium conducting sodium channels.