Stimulation by d-glucose of the synthesis of polyphosphoinositides in pancreatic islets

Abstract

d-glucose (16.7 mM) stimulates the synthesis of polyphosphoinositides in in intact pacreatic islets prelabelled with tritiated myo-inositol and incubated in the absence of extracellular Ca 2+. ATP (1.0 mM) exerts a comparable effect in sonicates of prelabelled normal or tumoral islet cells. In the acellular system, ATP fails to affect the generation of tritiated inositol phosphates in the absence of Ca 2+, but augments the Ca 2+-stimulated production of inositol mono-, bis- and triphosphates. The latter effect is not reproduced by α, ß-methylene ATP, suggesting that it is not attributable to a purinergic mechanism. Whether in the absence or presence of ATP, the Ca 2+-induced increment in inositol phosphates production coincides with a comparable decrease in tritiated polyphosphoinositides. It is proposed, therefore, that the increased production of inositol phosphates in intact islets stimulated by nutrient secretagogues is attributable, in part at least, to an accelerated generation of polyphosphoinositides, possibly resulting from a rise in cytosolic ATP concentration.