Activation of insulin-secreting cells by pyruvate and halogenated derivatives.
Addition of pyruvate to rat islets perifused in the presence of 5 mM-glucose elicited an immediate pronounced biphasic stimulation of insulin secretion. At lower concentrations of glucose (2.5 mM), only the initial, transient, phase of secretion was observed. Pyruvate inhibited 45Ca2+ efflux from islets at 2.5 mM-glucose and stimulated efflux at 5 mM-glucose. Pyruvate also decreased the rate of efflux of 86Rb+ from perifused islets. A marked stimulation of insulin secretion and 45Ca2+ efflux rate was observed in response to 3-fluoropyruvate and 3-bromopyruvate, compounds which inhibited oxidative metabolism of [14C]glucose and [14C]pyruvate in islets. The stimulatory effects of 3-fluoro- and 3-bromo-pyruvate were associated with enhanced 86Rb+ efflux. Withdrawal of pyruvate or halogenated analogues from the perfusate resulted in a secondary stimulation of insulin release, 45Ca2+ efflux and, to some extent, 86Rb+ efflux rates. Pyruvate, 3-fluoropyruvate and 3-bromopyruvate were all effective in promoting intracellular acidification and a rise in cytosolic Ca2+ concentration, as judged from fluorescence measurements in HIT-T15 cells loaded with 2',7'-biscarboxyethyl-5'(6')-carboxyfluorescein and Quin 2 respectively. It is proposed that oxidative metabolism of pyruvate is not a prerequisite for its stimulatory actions on pancreatic beta-cells. An alternative mechanism of activation by pyruvate and its halogenated derivatives is proposed, based on the possible electrogenic flux of these anions across the cell membrane.
Yates
A P
AP
Department of Clinical Endocrinology, Manchester Royal Infirmary, U.K.
Lynch
A M
AM
Best
L
L
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007515:Islets of Langerhans / Q000187:drug effects*; D008928:Mitochondria / Q000378:metabolism; D010084:Oxidation-Reduction; D011773:Pyruvates / Q000494:pharmacology*; D051381:Rats
D011773:Pyruvates; C017319:3-fluoropyruvate; C017092:bromopyruvate; D005947:Glucose