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

Capacitative Ca²⁺ entry into bovine adrenocortical fasciculata cells was investigated by using the mobilization of intracellular Ca²⁺ concentration ([Ca²⁺]_i) and Ca²⁺-induced steroidogenesis as the indicators. Bovine adreno-cortical fasciculata cells on a glass coverslip were loaded with fura-2. The [Ca²⁺]_i mobilization was detected by a change of fura-2 fluorescence intensity. In the intracellular Ca²⁺ store depleted cells, the addition of Ca²⁺ to the incubation medium elicited a marked and sustained increase in [Ca²⁺]_i. In the intracellular Ca²⁺ store non-depleted cells, the addition of thapsigargin, an endoplasmic reticulum Ca²⁺-ATPase inhibitor, in the absence of extracellular Ca²⁺, induced a slight and transient increase in [Ca²⁺]_i, but an extensive and sustained increase 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. The effect of Zn²⁺ was more potent than that of Cd²⁺. Thapsigargin stimulated steroidogenesis in the presence of extracellular Ca²⁺. The steroidogenic effect of thapsigargin was inhibited by Zn²⁺ and Cd²⁺ but not by nifedipine. These results suggest that there is, in bovine adrenocortical fasciculata cells, a steroidogenesis-linked Ca²⁺ entry process other than that involving voltage-operated Ca²⁺ channels and that the process might be capacitative Ca²⁺ entry.