Serine protease inhibitor causes F-actin redistribution and inhibition of calcium-mediated secretion in pancreatic acini

Background & Aims: The present study was undertaken to evaluate the role of serine proteases in regulating digestive enzyme secretion in pancreatic ac inar cells. Methods: Isolated acini were stimulated by various secretagogue s in the presence or absence of cell-permeant serine protease inhibitors 4- (2-aminoethyl)-benzenesulfonyl fluoride and N alpha -p-tosyl-L-phenylalanin e chloromethyl ketone, F-actin distribution was studied after staining with rhodamine phalloidin. Results: Both cell-permeant serine protease inhibito rs blocked amylase secretion in response to secretagogues that use calcium as a second messenger (e.g., cerulein, carbamylcholine, and bombesin) but n ot to those that use adenosine 3',5'-cyclic monophosphate (cAMP) as a secon d messenger (e.g., secretin and vasoactive intestinal polypeptide), Incubat ion of the acini with these inhibitors also resulted in a dramatic redistri bution of the F-actin cytoskeleton, This redistribution was energy dependen t. Similar redistribution of F-actin from the apical to the basolateral reg ion was also observed when acini were incubated with a supramaximally stimu lating concentration of cerulein, which is known to inhibit secretion. Conc lusions: These results suggest that a serine protease activity is essential for maintaining the normal apical F-actin distribution; its inhibition red istributes F-actin from the apical to the basolateral region and blocks sec retion induced by secretagogues that act via calcium. cAMP reverses the F-a ctin redistribution and hence cAMP-mediated secretion is not affected.