Production of [H-3]choline-labelled metabolites from endogenously H-3-labelled phosphatidylcholine in mouse pancreatic islets

The involvement of phosphatidylcholine (PC) hydrolysis in the regulation of insulin secretion was studied in mouse pancreatic islets prelabelled with [H-3]choline. Phospholipase C (PLC) and phospholipase D (PLD) activities were demonstrated and also that of an enzyme that removes both fatty acids from PC and thus catalyses the production of [H-3]glycerophosphorylcholine (GroPCho). After 2 min of incubation with 20 mM glucose a 35% increase in the content of [H-3]GroPCho was observed in prelabelled islets, whereas the amount of [H-3]lysoPC, [H-3]phosphorylcholine (PCho) and [H-3]choline was unaffected. After 30 min of incubation with 20 mM glucose, 0 . 2 mM tolbutamide 40 mM KCl, 10 mM succinic acid monomethyl ester (SME) or 10 mM NaF, a 25-50% increase in [H-3]GroPCho was observed. In the presence of 100 mu M diazoxide or 35 mu M RHC 80267 the glucose activation was attenuated. PLC was stimulated slightly by tolbutamide and 100 mu M isoprenaline (isoproterenol), whereas SME decreased the amount of [H-3]PCho by 10%. [H-3]Choline content was increased by 25-40% in the presence of 0 . 16 mu M 12-O-tetradecanoylphorbol 13-acetate (TPA), 10 mM NaF or 100 mu M carbachol. This effect of fluoride was potentiated in the presence of 20 mM glucose. It is concluded that metabolism of PC to GroPCho may be involved in the regulation of glucose-stimulated insulin secretion, and that PLD may participate in insulin secretion evoked by TPA, carbachol and fluoride.