Potentiation by glucose metabolites of inositol trisphosphate-induced calcium mobilization in permeabilized rat pancreatic islets.

Saponin-permeabilized rat pancreatic islets degraded exogenously added inositol 1,4,5-trisphosphate (IP3), and degradation was inhibited in the presence of either fructose 1,6-bisphosphate or diphosphoglycerate. The addition of either fructose-1,6-P2 or diphosphoglycerate to 45Ca2+-labeled permeabilized islets potentiated 45Ca2+ release caused by IP3 (by either exogenously added IP3 or IP3 generated endogenously in the presence of carbachol or guanosine 5'-3-O-(thio)triphosphate (GTP gamma S). The effect of diphosphoglycerate and fructose-1,6-P2 on 45Ca2+ release correlated well with the effects of these agents on the recovery of radioactivity in IP3. These results further support our previous proposal that in pancreatic islets intracellular calcium mobilization may be sustained in part via the inhibition of IP3 degradation by metabolites produced during stimulation with insulinotropic concentrations of glucose (Rana, R.S., Sekar, M.C., Hokin, L.E., and MacDonald, M.J. (1986) J. Biol. Chem. 261, 5237-5240).