SERINE THREONINE PHOSPHATASES PLAY A ROLE IN STIMULUS-SECRETION COUPLING IN PANCREATIC ACINAR-CELLS

The role of serine/threonine phosphatases in Ca2+/IP3- and cAMP- media ted stimulus-secretion coupling was investigated in isolated pancreati c acinar cells. Cyclosporine A, an inhibitor of type 2b serine/threoni ne phosphatases, maximally reduced CCK8-stimulated amylase secretion b y 33%. In contrast, the secretory response to secretin or PACAP-(1-27) was not significantly altered by cyclosporine A independent of the se cretagogue-concentration used. The type 1, 2a and 2b serine/threonine phosphatase inhibitor okadaic acid significantly reduced amylase relea se, induced by Ca2+/IP3-mediated- (CCK-8) or cAMP-mediated agonists (s ecretin, PACAP-(1-27), VIP) at concentrations that primarily inactivat e type 1 and 2b phosphatases. Calyculin A, another type 1 and 2a phosp hatase inhibitor, had a similiar inhibitory effect on CCK-8-, secretin - or PACAP-(1-27)-induced secretion. In permeabilized acini, cyclospor ine A reduced calcium-induced amylase release by 20%, whereas okadaic acid and calyculin A had an inhibitory effect by 55% and 52%, respecti vely. The ultrastructure of CsA-incubated acinar cells was not differe nt from vehicle-incubated control lobules. In contrast, incubation wit h okadaic acid for 60 min resulted in morphological alterations of the Golgi apparatus, leading to a fragmentation of Golgi cisternae into s mall vesicles. Our data suggest a role of type 1 and 2b phospatases in stimulus-secretion coupling of both signal-transduction pathways in p ancreatic acinar cells. These phosphatases might also be important for the maintenance of pancreatic cellular ultrastructure.