Regulation of phosphatidylinositol 4-kinase activity in rat pancreatic acini

Previous data showed that carbachol (CCh) elicits a concentration-dependent increase in phosphatidylinositol (PtdIns) 4-kinase activity in homogenates derived from agonist-stimulated pancreatic acini. In the present study CCh elicited a time-dependent increase in PtdIns 4-kinase activity, which was blocked by n-methylscopolamine and mimicked by muscarine. A membrane-associated PtdIns 4-kinase activity was identified that displayed maximal activity in the pH range of 5.5-8.5. The zymogen granule fraction possessed relatively high specific enzyme activity, which was sensitive to CCh stimulation. The enzyme had apparent Km values for PtdIns and ATP of 4 and 60 microM, respectively. CCh caused no discernible change in the Km for either PtdIns or ATP but increased Vmax. Dioctanoylglycerol and oleoyl acetylglycerol augmented PtdIns 4-kinase activity, which was blocked by staurosporine, thus suggesting a possible role for protein kinase C in the regulation of PtdIns 4-kinase. These collective findings demonstrate a muscarinic receptor-mediated regulation of PtdIns 4-kinase activity in exocrine pancreas, involving a protein kinase C-dependent process.