Effects of phosphotyrosine phosphatase inhibition on insulin secretion andintracellular signaling events in rat pancreatic islets

Isolated rat pancreatic islets were incubated at 3.3 (low) and 16.7 thigh) mM glucose with different concentrations of the phosphotyrosine phosphatase (PTP) inhibitor, peroxovanadate (pV). At low glucose, pV stimulated insuli n secretion 2- to 4-fold, but it inhibited insulin secretion at 16.7 mM. Th e latter effect was not due to an inhibition of glucose metabolism, nor was it inhibited by pertussis toxin pretreatment. In addition, pV stimulated i nsulin secretion similar to3-fold in depolarized cells at both low and high glucose. pV markedly increased the tyrosine phosphorylation of several pro teins, including IRS-l and -2, and also increased the phosphorylation of th e downstream kinases PKB/Abt and MAPK. PKB/Akt, but not MAPK, was also phos phorylated in the absence of pV. Intracellular pV-stimulated tyrosine phosp horylation, including that of IRS-2, was generally increased by high glucos e suggesting a further inhibition of PTP and/or enhanced tyrosine kinase ac tivity. Thus, these data suggest that intracellular tyrosine and serine (PK B/Akt) phosphorylation are related to insulin secretion but they do not sup port a unique and direct link between IRS-2 tyrosine phosphorylation and gl ucose-stimulated insulin secretion, (C) zool academic Press.