The effects of angiotensin II (AII), acetylcholine and vasopressin on the intracellular concentration of Ca2+ have been little studied in adrenocortical cells from the zona fasciculata/reticularis (ZFR).
Primary cultures of bovine ZFR cells maintained in suspension culture for 72 h produce cortisol in response to AII (0·1 µM), acetylcholine (0·1 mM) and vasopressin (1 µM). This response is accompanied by a breakdown of membrane phosphoinositides from [3H]inositol-prelabelled cells.
Using cells loaded with the Ca2+ indicator fura-2, the intracellular concentration of Ca2+ was measured in response to increasing doses of all three agonists and found to increase in a graded fashion in each case. The basal intracellular concentration of Ca2+ was 75±3 nM (mean±S.E.M., n=52), rising to a maximum 1·82±0·14-fold (n=6) for AII (0·1 µM), 1·35±0·05-fold (n=7) for acetylcholine (0·1 mM) and 1·27±0·10-fold (n=6) for vasopressin (1 µM).
In the case of AII and acetylcholine, agonists were added sequentially in medium of normal extracellular Ca2+ concentration (1·2 mM) or in medium in which the Ca2+ concentration was buffered to approximate to the intracellular concentration of Ca2+ (75–100 nM). Evidence was thereby obtained that both AII and acetylcholine mobilize a common intracellular pool of Ca2+.
Our findings suggest that these three agonists, all of which stimulate phospholipase C, increase intracellular Ca2+ through a mechanism which depends, at least in part, on the release of Ca2+ from a common intracellular pool.
