Myosin light chain kinase inhibitors and calmodulin antagonist inhibit Ca(2+)- and ATP-dependent catecholamine secretion from bovine adrenal chromaffin cells.

We have used stage-specific assays for ATP-dependent priming and for Ca(2+)-activated triggering in the absence of ATP to examine the effects of myosin light chain kinase (MLCK) inhibitors, ML-9 and ML-7, and calmodulin antagonists, W-7 and trifluoperazine (TFP), on regulated exocytosis in beta-escin-permeabilized bovine adrenal chromaffin cells. Ca2+ (0.1-30 microM) induced a significantly greater secretion of catecholamines in the presence of MgATP (2 mM) than in the absence of MgATP. ML-9 (30 and 100 microM), ML-7 (30 and 100 microM), W-7 (30 and 100 microM) and TFP (10 and 30 microM) inhibited the Ca(2+)-induced catecholamine secretion in the presence of MgATP, but did not affect the catecholamine response to Ca2+ in the absence of MgATP. In intact cells all these compounds inhibited catecholamine secretion in responses to acetylcholine (100 microM) and high K+ (40 mM). The results obtained in permeabilized cells suggest that the calmodulin-MLCK system plays an essential role in the ATP-requiring priming stage but not in the Ca2(+)-triggered fusion step in the exocytotic process in bovine adrenal chromaffin cells.