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.
Department of Clinical Endocrinology, Manchester Royal Infirmary, U.K.
A P
AP
Yates
A M
AM
Lynch
L
L
Best
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