Oxidizing effects of vanadate on calcium mobilization and amylase release in rat pancreatic acinar cells

The effects of vanadate were examined by monitoring intracellular free calc ium concentration ([Ca2+](i)) and amylase secretion in collagenase-disperse d rat pancreatic acinar cells. Vanadate increased [Ca2+](i) by mobilizing c alcium from agonist releasable intracellular calcium stores, since this inc rease was observed in the absence of extracellular calcium and vanadate fai led to increase [Ca2+](i) after treatment with thapsigargin in calcium-Free medium. Moreover, pretreatment of acinar cells with vanadate prevented the cholecystokinin octapeptide (CCK-8)-induced signal of [Ca2+](i), whereas c o-incubation with CCK-8 potentiated the plateau phase of calcium response t o CCK-8 without modifying the transient calcium spike. The effects of vanad ate on calcium mobilization were reversed by the presence of the sulfhydryl reducing agent dithiothreitol. Vanadate also activated the calcium influx, since an additional enhancement of calcium influx induced by thapsigargin- evoked intracellular store depletion was observed and vanadate reversed the inhibitory effect of lanthanum (an inhibitor of calcium entry) into acinar cells. In addition, vanadate evoked a concentration-dependent release of a mylase From pancreatic acinar cells and moreover, reduced the secretory res ponse to CCK-8. We conclude that, in pancreatic acinar cells, vanadate rele ases calcium from the agonist-releasable intracellular calcium pool and con sequently induces amylase secretion. These effects are likely due to the ox idizing effects of this compound. BIOCHEM PHARMACOL 58;1:77-84, 1999. (C) 1 999 Elsevier Science Inc.