Glucose-induced pulsatile insulin release from single islets at stable and oscillatory cytoplasmic Ca21

Bergsten, Peter. Glucose-induced pulsatile insulin release from single islets at stable and oscillatory cytoplasmic Ca21. Am. J. Physiol. 274 (Endocrinol. Metab. 37): E796– E800, 1998.—The cytoplasmic Ca21 concentration ([Ca]i) and insulin release were measured simultaneously in mouse pancreatic islets cultured overnight. [Ca]i was 105 nM and insulin release 3 pmol ·g21 ·s21 at 3 mM glucose. An increase to 7 mM glucose reduced [Ca]i transiently, whereas insulin release doubled and was pulsatile with a frequency of 0.47 min21. [Ca]i oscillations with similar frequency appeared at 11 mM glucose associated with increased amplitude of the insulin oscillations, raising the secretory rate 10-fold. In the presence of 16 and 20 mM glucose [Ca]i was .300 nM and showed no oscillations apart from two islets, which demonstrated [Ca]i oscillations with small amplitude at 16 mM glucose. Insulin release with maintained frequency increased by 46 and 31%, respectively. When the glucose concentration was increased from 3 to 11 mM, [Ca]i decreased with a nadir that appeared significantly earlier than when the glucose concentration was raised from 3 to 7 mM. Glucose-induced insulin release from the isolated islet is pulsatile both at stable and oscillatory [Ca]i, with changes in secretory rate caused by the sugar also when [Ca]i is unchanged.