The effects of staurosporine, a recently isolated microbial alkaloid, on amylase secretion and protein kinase C activity of guinea pig pancreatic acini were investigated. Staurosporine at a concentration of 1 microM completely inhibited both acinar protein kinase C activity (IC50 = 5.5 +/- 1.4 nM) and amylase secretion induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (IC50 = 4.1 +/- 0.4 nM). At this concentration, staurosporine reduced amylase secretion elicited by maximally effective concentrations of carbachol and cholecystokinin by approximately 50% but did not appreciably alter the potencies of the two secretagogues. In the presence of staurosporine, amylase secretion induced by carbachol was linear for at least 60 min. Staurosporine had no effect on amylase release elicited by the Ca2+ ionophore A23187. It did, however, inhibit secretion induced by vasoactive intestinal peptide, although with a reduced potency relative to its effects on amylase release stimulated by TPA, carbachol, and cholecystokinin (IC50 = 34 +/- 17 nM). These results indicate that staurosporine is a potent inhibitor of protein kinase C activity in pancreatic acini and that protein kinase C has an important role as an intracellular mediator of digestive enzyme secretion induced by cholecystokinin and carbachol in the acinar cell. In addition, a separate staurosporine-insensitive coupling pathway, most likely involving Ca2+, appears to be equally important and can maintain long-term secretion in the absence of functional protein kinase C activity.
Cyclic GMP Does Not Inhibit Protein Kinase C-mediated Enzyme Secretion in Rat Pancreatic Acini
