Insulin Rapidly Increases Diacylglycerol by Activating De Novo Phosphatidic Acid Synthesis

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Abstract
The mechanisms whereby insulin increases diacylglycerol in BC3H-1 myocytes were examined. When [ 3 H]arachidonate labeling of phospholipids was used as an indicator of phospholipase C activation, transient increases in [ 3 H]diacylglycerol were observed between 0.5 and 10 minutes after the onset of insulin treatment. With [ 3 H]glycerol labeling as an indicator of de novo phospholipid synthesis, [ 3 H]diacylglycerol was increased maximally at 1 minute and remained elevated for 20 minutes. [ 3 H]Glycerol-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.

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