Characterization of calcium uptake in chick retinal pigment epithelium

45Ca uptake was studied in isolated chick retinal pigment epithelial cells. 45Ca was accumulated by a saturable, temperature-dependent system with a KM of 400 microM and a Vmax of 0.13 mumoles2mg protein/min, which depends on the external sodium concentrations. The transport system was present early during embryonic development. RPE cells of three breeds of chicks with different degrees of pigmentation accumulated calcium proportionally to the melanin content of the cells, suggesting that pigment granules participate in the storage and regulation of intracellular calcium.