SYNCHRONOUS OSCILLATIONS OF CYTOPLASMIC CA2-STIMULATED PANCREATIC-ISLETS( AND INSULIN RELEASE IN GLUCOSE)

The cytoplasmic Ca2+ concentration ([Ca2+](i)) was measured in single pancreatic mouse islets superfused in a system allowing concomitant re cordings of insulin release. When glucose was raised from 3 to 11 mM, [Ca2+](i) responded by a transient lowering followed by a rise to an a verage level of 192 +/- 11 nM. In 77% of the islets the rise was assoc iated with the gradual appearance of oscillations, which were either f ast (2-7/min), slow (0.3-0.9/min), or a combination of both types. The characteristics of the fast [Ca2+](i) oscillations were those expecte d from a relationship with the electrical burst activity in islets. Ac cordingly, in most cases the fast oscillations were remarkably regular . The slow [Ca2+](i) oscillations had characteristics similar to the l arge amplitude ones in individual beta-cells. Whereas glucagon and dib utyryl cAMP could transform slow islet oscillations into fast ones, th e alpha(2)-adrenergic agonist clonidine had the opposite effect. The r apid islet oscillations were also facilitated by elevated concentratio ns of extracellular Ca2+. Reinforcing the arguments for [Ca2+](i) osci llations as responsible for a pulsatile insulin secretion it was possi ble to demonstrate that the release of the hormone from single islets is synchronized with the slow [Ca2+](i) oscillations.