We evaluated the possibility that diacylglycerol may function as a second messenger in insulin action. To thisend, we employed 12-O-tetradecanoyl phorbol 13-acetate (TPA)to mimic diacylglycerol in BC3H-1 myocytes. Like insulin, TPAprovoked rapid increases in 2-deoxyglucose transport and pyruvatedehydrogenase activity in mature insulin-responsive BC3H-1 cultured myocytes. TPA also stimulated amino acid uptake, asevidenced by uptake of a-methylaminoisobutyric acid; the relativelyslow time course of this effect paralleled that of insulin.In contrast, the effects of TPA were not apparent in undifferentiatedBC3H-1 myoblasts, which were also unresponsive toinsulin. The insulin-like effects in the myocytes appeared to bespecific for TPA, the biologically active phorbol diester whichactivates protein kinase C, as other tested phorbol derivativeswere without effect. Effects of maximally effective concentrationsof TPA and insulin were nonadditive. Two syntheticdiacylglycerols, 1, 2-diolien and l-oleoyl-2-acetyl-sn-glycerol, also provoked insulin-like effects on 2-deoxyglucose transport.Since insulin rapidly increases diacylglycerol levels in these cells, and TPA mimics diacylglycerol biochemically, it is possible thatinsulin may control cellular processes through changes in diacylglycerol.
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