STIMULATORY EFFECTS OF VANADATE ON AMYLASE RELEASE FROM ISOLATED RAT PANCREATIC ACINI

The effects of vanadate on exocrine pancreatic function were examined in isolated rat pancreatic acini. Vanadate caused a concentration-depe ndent stimulation of amylase release above a concentration of 1 mM. Go -incubation of vanadate with vasoactive intestinal polypeptide, 8-brom oadenosine 3':5'-cyclic monophosphate, and the Ca2+ ionophore A23187 p roduced a synergistic pattern of amylase release, whereas co-incubatio n with cholecystokinin octapeptide (CCK-8), carbamylcholine, and 12-O- tetradecanoylphorbol 13-acetate produced an additive effect. Vanadate alone had no influence on acinar cyclic AMP content, Ca2+ efflux, or i ntracellular Ca2+ concentration. However, preincubation with vanadate prevented the plateau phase of CCK-8 induced Ca2+ transient increase f rom returning to baseline. Moreover, depletion of the intracellular Ca 2+ pool by pretreatment of acini with CCK-8 in Ca2+-free medium (plus ethyleneglycol bis[beta-aminoethylether]-N,N-1-tetraacetic acid) had n o effect on subsequent stimulation by vanadate, although it abolished the response to both CCK-8 and carbamylcholine stimulation. The protei n kinase C (PKC) inhibitors staurosporine and calphostin C significant ly inhibited vanadate-stimulated amylase release, whereas the protein tyrosine kinase inhibitor genistein had no inhibitory effect. Moreover , vanadate caused a significant translocation of PKC from cytosol to m embrane fraction in pancreatic acinar cells. This translocation was in hibited significantly by staurosporine and calphostin C but not by gen istein. These results suggest that vanadate acts directly on pancreati c acini and stimulates amylase release by activating PKC without an ef fect on Ca2+ mobilization, cyclic AMP, or protein tyrosine kinase. (C) 1998 Elsevier Science Inc.