Effects of H7 and staurosporine on cytosolic free calcium and amylase secretion in rat pancreatic acini.

Pretreatment of rat pancreatic acini with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) for 5 or 10 min reduced cytosolic free calcium and amylase secretion stimulated by submaximal concentration (10(-6) M) of carbachol in a dose-dependent manner. 10(-7) M TPA inhibited initial amylase secretion and had no effect on sustained secretion stimulated by 10(-6) M carbachol. 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7), a protein kinase C inhibitor, partially blocked these inhibitory effects of TPA. Cytosolic calcium concentration and initial amylase secretion were recovered with 10-100 microM H7 in TPA-treated acini. H7 was more effective than N-(2-guanidinoethyl)-5-isoquinoline-sulfonamide hydrochloride in increasing cytosolic free calcium in TPA-treated acini. TPA completely blocked an increase in cytosolic free calcium by 10 mM NaF. These findings indicated that TPA caused the inhibitory effects by means of activating protein kinase C, and suggested that protein kinase C might regulate enzyme secretion by inhibiting calcium mobilization, probably through a postreceptor-mediated mechanism.