Zusammenfassung
PURPOSE. Ca2+ is a major regulator of cell function. In the retinal pigment epithelium (RPE), intracellular free Ca2+ concentration ([Ca2+](i)) is essential for the maintenance of normal retinal function. Therefore, accurate control of [Ca2+](i) is vital in these cells. Because Ca2+ is permanently extruded from the cytosol, RPE cells need a basal Ca2+ entry pathway that counteracts this Ca2+ ...
Zusammenfassung
PURPOSE. Ca2+ is a major regulator of cell function. In the retinal pigment epithelium (RPE), intracellular free Ca2+ concentration ([Ca2+](i)) is essential for the maintenance of normal retinal function. Therefore, accurate control of [Ca2+](i) is vital in these cells. Because Ca2+ is permanently extruded from the cytosol, RPE cells need a basal Ca2+ entry pathway that counteracts this Ca2+ efflux. The purpose of this study was to identify the molecular basis of basal Ca2+ entry into the RPE. METHODS. [Ca2+](i) was measured using Fura-2-loaded ARPE-19 cells. The expression pattern of TRPC channels was investigated by RT-PCR with RNA extracted from ARPE-19 cells and freshly isolated RPE cells from human donor eyes. RESULTS. In most cells, basal [Ca2+](i) is highly controlled by cell membranes that are only slightly permeable to Ca2+ and by the activity of Ca2+ pumps and transporters. The authors show here that RPE cells have a basal Ca2+ conductance that is dose dependently blocked by La3+. Basal [Ca2+](i) was also strongly reduced by the TRP channel blockers Gd3+, Ni2+, 2-APB, and SKF96365 and was insensitive to blockers of other Ca2+ channels. In confirmation of this pharmacologic profile, RPE cells expressed TRPC1 and TRPC4 channels, as shown by RT-PCR experiments. CONCLUSIONS. Ca2+ is needed for several permanently occurring regulatory processes in RPE cells. The Ca2+ influx pathway identified in this study is essential to define a resting basal [Ca2+](i). This resting [Ca2+](i) may contribute, for example, to basal cytokine secretion essential for the maintenance of normal retinal function.
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