Capacitative calcium entry is involved in steroidogenesis in bovine adrenocortical fasciculata cells

Capacitative Ca2+ entry into bovine adrenocortical fasciculata cells was in vestigated by using the mobilization of intracellular Ca2+ concentration ([ Ca2+](i)) and Ca2+- induced steroidogenesis as the indicators. Bovine adren ocortical fasciculata cells on a glass coverslip were loaded with fura-2. T he [Ca2+](i) mobilization was detected by a change of fura-2 fluorescence i ntensity. In the intracellular Ca2+ store depleted cells, the addition of C a2+ to the incubation medium elicited a marked and sustained increase in [C a2+](i). In the intracellular Ca2+ store non-depleted cells, the addition o f thapsigargin, an endoplasmic reticulum Ca2+-ATPase inhibitor, in the abse nce of extracellular Ca2+, induced a slight and transient increase in [Ca2](i), but an extensive and sustained dincrease in [Ca2+](i) was obtained by adding Ca2+ to the incubation medium after the thapsigargin treatment. The sustained increase induced by thapsigargin was not inhibited by nifedipine , but was inhibited by Zn2+ and Cd2+ in a concentration-dependent manner. T he effect of Zn2+ was more potent than that of Cd2+ Thapsigargin stimulated steroidogenesis in the presence of extracellular Ca2+. The steroidogenic e ffect of thapsigargin was inhibited by Zn2+ and Cd2+ but not by nifedipine. These results suggest that there is, in bovine adrenocortical fasciculata c ells, a steroidogenesis-linked Ca2+ entry process other than that involving voltage-operated Ca2+ channels and that the process might be capacitative Ca2+ entry.