Capacitative Ca²⁺ influx in adrenal glomerulosa cells: Possible role in angiotensin II response

We examined the effect of the depletion of intracellular Ca²⁺ stores on Ca²⁺ influx in rat glomerulosa cells. Depletion of intracellular Ca²⁺ stores was achieved by inhibiting sarco/endoplasmic reticulum-type Ca²⁺- ATPase with thapsigargin or 2,5-di-(t-butyl)-1,4-benzohydroquinone (t-BHQ). Both inhibitors induced a sustained rise in cytoplasmic Ca²⁺ concentration. The initial rise was observed also in Ca²⁺-free medium, while the sustained phase disappeared, indicating that the latter requires Ca²⁺ influx. In Ca²⁺-free medium, the readdition of Ca²⁺ induced a steeper and higher rise in intracellular Ca²⁺ concentration in thapsigargin-treated cells than in controls, supporting the role of Ca²⁺ influx. In normal medium, the addition of Cd²⁺ (80 μM) evoked an immediate inhibition of the sustained phase of thapsigargin response. The response to thapsigargin was insensitive to nifedipine. Thapsigargin failed to enhance Mn²⁺ quenching of fura 2. Our results provide evidence for the existence of capacitative Ca²⁺ influx in rat glomerulosa cells and indicate that dihydropyridine-sensitive Ca²⁺ channels do not participate in capacitative Ca²⁺ entry. High concentrations of thapsigargin and t-BHQ, similar to the reported effects of angiotensin II and vasopressin, inhibited K⁺-induced Ca²⁺ signals. These effects appear, however, to be independent of the depletion of internal Ca²⁺ stores.