Interaction of the tyrosine phosphatase inhibitor ortho-vanadate on stimulus-secretion coupling in pancreatic acinar cells

Background: The effect of the tyrosine phosphatase inhibitor ortho-vanadate on stimulus-secretion coupling was investigated in isolated rat pancreatic acini. Methods and Results: Ortho-vanadate (10(-3) M) reduced cholecystoki nin (CCK)-8 (10(-10) M)-stimulated amylase release by 40% (IC50 = 5 x 10(-4 ) M). In contrast, preincubation with 10(-3) M ortho-vanadate increased sec retin (5 x 10(-9) M) and vasoactive intestinal peptide (VIP) (10(-7) M)-ind uced amylase release by 65% and 80% (IC50 = 3 x 10(-4) M). respectively. 8- Bromo-cyclic adenosine-5-monophosphate (cAMP) (10(-4) M) and phorbol ester( 10(-5) M)induced secretion was increased by 60% and 50%, respectively, wher eas thapsigargin-induced amylase release was not affected. Ortho-vanadate d id not affect CCK-S binding or VIP-induced cAMP synthesis in isolated acini . In contrast, preincubation with 10(-4) M ortho-vanadate resulted in a sig nificant reduction of CCK-8-induced intracellular calcium release. In strep tolysin-O-permeabilized acini, ortho-vanadate reduced calcium-induced amlya se secretion by 50%. Conclusions: The present data provide indirect evidenc e of a differential involvement of protein tyrosine dephosphorylation in bo th cAMP- and IP3/Ca2+ mediated pancreatic secretion. The differential effec ts of ortho-vanadate on cAMP- versus calcium-mediated secretion correspond to the results obtained with receptor-independent intracellularly acting se cretagogues. Further experiments must define the tyrosine phosphatases invo lved in both signal-transduction pathways.