Calcium stimulates steroidogenesis in permeabilized bovine adrenal cortical cells

The effect of Ca2+ on steroid production was examined in electropermeabilized bovine adrenal zona glomerulosa and fasciculata cells. The cells were superfused with a medium mimicking cytosolic ionic content but deprived of Ca2+. The permeabilized glomerulosa cells produced aldosterone at a low basal rate. Upon addition of NADP+ to the medium, a transient and concentration-dependent (EC50 = 6 microM) peak of aldosterone production occurred. When the superfusion medium was supplemented with buffered Ca2+ at submicromolar concentrations, a concentration-dependent and sustained increase of aldosterone output was observed. The maximal response (2-3 times the basal secretion rate) was achieved with 1-2 microM ambient free Ca2+, and the EC50 for Ca2+ was 0.5 microM. The continuous presence of NADP+ was found to be necessary for a Ca2+ effect. The Ca2+-induced aldosterone response was entirely blocked by ruthenium red (1 microM), an inhibitor of mitochondrial Ca2+ uptake, and by W-7 (5 microM), a calmodulin inhibitor. Qualitatively and quantitatively similar results were obtained for corticosterone production in adrenal fasciculata cells. These results show that permeabilized adrenal cortical cells retain the ability to produce steroids. Moreover, Ca2+ influx into the mitochondria and Ca2+/calmodulin-dependent reactions appear to be critical steps in the activation of steroidogenesis. These studies provide a further direct link between cytosolic free calcium concentration and biological responses induced by steroidogenic, calcium-mobilizing stimulators in the adrenal cortex.