Increase in Diacylglycerol Mass in Isolated Glomeruli by Glucose From De Novo Synthesis of Glycerolipids

An increase in glucose concentration in the medium from 5 to 30 mM transiently enhanced diacylglycerol mass and activated protein kinase C in glomeruli isolated from nondiabetic rats as assessed by translocation of enzyme activity from the soluble to particulate fraction. Effects of glucose on both diacylglycerol mass and protein kinase C were evident at 5 and 15 min but waned by 30 min. An increase in glucose concentration in the medium also increased the incorporation of 14Cglucose into the glycerol backbone of diacylglycerol, triacylglycerol, and phospholipids. Several observations implied that 14Cglucose was being incorporated into diacylglycerol through the de novo pathway for glycerolipid synthesis rather than being derived from phospholipids. 1) 14Cglucose incorporation into all the lipids was suppressed by 2-deoxyglucose. 2) The incorporation of 14Cglucose into diacylglycerol and triacylglycerol was evident by 1 min and increased linearly for at least 30 min. In contrast, incorporation into phosphatidylcholine occurred with a lag of at least 5 min. 3) Although only 10% of the 14Cglucose incorporated into lipids was present in diacylglycerol versus greater than 50% in phospholipids, the specific activity of 14Cglucose in diacylglycerol was fivefold higher than that in phospholipid when expressed as a function of mass. 4) Glucose had no effect on labeled diacylglycerol or phosphatidic acid production in glomeruli that had been prelabeled with 3Hglycerol. Glucose-induced increases in diacylglycerol may contribute to the activation of glomerular protein kinase C observed in early diabetes.