Effects of thapsigargin, an intracellular CA2+ pump inhibitor, on insulin release by rat pancreatic B-cell.

This is the first report as to the effects of thapsigargin (Tg), an inhibitor of intracellular Ca2+ pumps, on insulin release by pancreatic B-cells. Tg does not alter basal insulin release by the isolated islets, with 3 mM glucose. However, it potentiates high glucose-induced insulin release: potentiation of the first phase response is dose-related in a concentration range of 1.3-40 microM. In isolated B-cells, Tg causes a minimal rise in basal cytosolic free calcium concentration ([Ca2+]i) and eliminates high glucose-induced initial lowering of [Ca2+]i. Tg does not alter glucose oxidation by the islets and the islet insulin content. An elimination of glucose-induced sequestration of Ca2+ into Tg-sensitive intracellular pool(s) is considered to be the cause of Tg potentiation of glucose effect on insulin release.