Dihydropyridine calcium agonist and antagonist effects on aldosterone secretion

The effects of the dihydropyridine calcium antagonists nimodipine, nitrendipine, and nisoldipine were studied on K+-induced and angiotensin II (ANG II)-induced aldosterone secretion from isolated calf adrenal glomerulosa cells. These drugs were more effective inhibitors of K+-induced secretion than ANG II-induced secretion. However, when the ANG II-induced release of intracellular calcium was blocked by prior treatment of cells with dantrolene, then nitrendipine was equally as effective in blocking ANG II- as K+-induced secretion. On the other hand, the dihydropyridine agonist, BAY K8644, was found to enhance K+-induced secretion to a greater extent than ANG II-induced secretion when the latter was studied in either the absence or presence of dantrolene. It is concluded that K+ and ANG II mobilize calcium from different sources for stimulus-response coupling in these cells and that there is no difference in the sensitivity to nitrendipine of the plasma membrane calcium channels operated by these two different agonists.