Insulin Rapidly Increases Diacylglycerol by Activating De Novo Phosphatidic Acid Synthesis

The mechanisms whereby insulin increases diacylglycerol in BC3H-1 myocytes were examined. When 3Harachidonate labeling of phospholipids was used as an indicator of phospholipase C activation, transient increases in 3Hdiacylglycerol were observed between 0.5 and 10 minutes after the onset of insulin treatment. With 3Hglycerol labeling as an indicator of de novo phospholipid synthesis, 3Hdiacylglycerol was increased maximally at 1 minute and remained elevated for 20 minutes. 3HGlycerol-labeled diacylglycerol was largely derived directly from phosphatidic acid. Insulin increased de novo phosphatidic acid synthesis within 5 to 10 seconds; within 1 minute, this synthesis was 60 times greater than that of controls. Thus, the initial increase in diacylglycerol is due to both increased hydrolysis of phospholipids and a burst of de novo phosphatidic acid synthesis. After 5 to 10 minutes, de novo phosphatidic acid synthesis continues as a major source of diacylglycerol. Both phospholipid effects of insulin seem important for generating diacylglycerol and other phospholipid-derived intracellular signaling substances.