Control of exocytosis from adrenal chromaffin cells.
1. Calcium-dependent exocytosis of catecholamines from intact and digitonin-permeabilized bovine adrenal chromaffin cells was investigated. 2. 45Ca2+ uptake and secretion induced by nicotinic stimulation or depolarization in intact cells were closely correlated. The results provide strong support for Ca2+ entry being the trigger for exocytosis. 3. Experiments in which the H+ electrochemical gradient across the intracellular secretory granule (chromaffin granule) membrane was altered indicated that the gradient does not play an important role in exocytosis. 4. Ca2+ entry into the cells is associated with activation of phospholiphase C and a rapid translocation of protein kinase C to membranes. 5. The plasma membrane of chromaffin cells was rendered permeable to Ca2+, ATP, and proteins by the detergent digitonin without disruption of the intracellular secretory granules. In this system in which the intracellular milieu can be controlled, micromolar Ca2+ directly stimulated catecholamine secretion. 6. Treatment of the cells with phorbol esters and diglyceride, which activate protein kinase C, enhanced phosphorylation and subsequent Ca2+-dependent secretion in digitonin-treated cells. 7. Phorbol ester-induced secretion could be specifically inhibited by trypsin. The experiments indicate that protein kinase C modulates but is not necessary for Ca2+-dependent secretion.
Holz
R W
RW
Department of Pharmacology, University of Michigan, Ann Arbor 48109.
D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics* / Q000502:physiology; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D004072:Digitonin / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects*; D010703:Phorbol Esters / Q000494:pharmacology; D010766:Phosphorylation
D002395:Catecholamines; D010703:Phorbol Esters; D004072:Digitonin; D002118:Calcium