Regulation of Ca2+ homeostasis by islet endoplasmic reticulum and its role in insulin secretion.

Changes in intracellular Ca2+ concentrations have a major role in the regulation of insulin secretion by islet beta-cells. It has recently become apparent that the endoplasmic reticulum plays a prominent role in the regulation of intracellular Ca2+ concentrations under basal conditions and during insulin secretion. This review describes biochemical properties of the endoplasmic reticulum that contribute to intracellular Ca2+ homeostasis including 1) an ATP-dependent Ca2+ uptake pump associated with a Ca2+-ATPase located in the endoplasmic reticulum; 2) Ca2+ release from the endoplasmic reticulum induced by the second messengers inositol trisphosphate and arachidonic acid as well as the guanine nucleotide GTP; and 3) a Ca2+ sequestration mechanism localized to the endoplasmic reticulum that is regulated by glucose 6-phosphate and glucose-6-phosphatase. The hypothesis is developed that these biochemical mechanisms participate in the regulation of intracellular Ca2+ concentrations and represent central intracellular events involved in the first phase of glucose-induced insulin secretion.