Effect of D‐glucose on the incorporation of 32 P into phospholipids of mouse pancreatic islets

Exposure of P-cells to D-glucose induces a prompt discharge of insulin and stimulates the synthesis of proinsulin and the formation of new secretory granules [I] . These processes engage P-cell membranes, and as phospholipids are integral parts of all cell membranes, it seemed possible that insulin secretion might be accompanied by an alteration in the metabolism of membrane phospholipids. We have therefore studied the composition of, and the incoproration of 32P-orthophosphate into, phosphclipids of isolated pancreatic islets from obese-hyperglycemic mice. These islets consist to more than 90% of Pcells [2], whose secretory pattern in response to D-glucose is well known [3]. We found that the islets contained 115 nmoles phospholipid per mg dry weight, with phosphatidyl choline as the major component. Insulin release, but not the incorporation of 32P into islet phospholipids, was stimulated when islets were exposed to 20 mM D-glucose for 5 min. However, after 60 and 120 min incubation, the stimulated insulin release was accompanied by an increased 32P-labelling of the islets phospholipids. The combined phosphatidyl inositol/phos phatidyl serine fraction incorporated most of the label. These experiments suggest that D-glucose stimulates the metabolism of &cell phospholipids, predominantly the acidic phospholipids phosphatidyl inositol and/or phosphatidyl serine. * To whom to address correspondence.