Activation of protein kinase activity in pancreatic acini by calcium and cAMP

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Abstract
Regulation of protein kinase activity by Ca and cAMP was investigated in cytosolic and particulate preparations from isolated mouse pancreatic acini. In cytosol, 3 protein kinase activities could be distinguished: a Ca-activated kinase activity that was increased by exogenous calmodulin (CaM) and abolished by treatment of cytosol with a phenothiazine-coupled resin, a Ca-activated kinase activity dependent on phosphatidylserine (PS) and cAMP-activated kinase activity. Phosphorylation of a MW = 92,000 cytosolic protein was greatly increased by both CaM-dependent and cAMP-activated kinases, whereas PS-dependent kinase activity most heavily phosphorylated proteins of MW = 62,000 and 40,000. These kinase activities demonstrated differences in specificity for exogenous protein substrates. CaM- and PS-dependent kinases were completely blocked by trifluoperazine; the inhibitor protein of cAMP-activated protein kinase selectively inhibited cAMP-activated kinase activity. Exogenous CaM decreased the concentration of free Ca for half-maximal activation of CaM-dependent kinase activity from 5.5 .+-. 0.5 to 1.2 .+-. 0.3 .mu.M Ca2+; half-maximal activation of the PS-dependent and cAMP-activated kinase activities was achieved at 12 .mu.M Ca2+ and 40-50 nM cAMP, respectively. In a particulate fraction depleted of endogenous CaM, CaM-dependent and cAMP-activated kinase activities were detected. This study demonstrates the existence of protein kinases in pancreatic acini which may be involved in the action of pancreatic regulatory agents [such as cholecystokinin and cholinergic agonists] that use Ca or cAMP as an intracellular messenger.

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