Further Evidence Implicating Diacylglycerol Generation and Protein Kinase C Activation in Agonist-Induced Increases in Glucose Uptake: Insulin-Like Effects of Phenylephrine in BC3H-1 Myocytes

Abstract

We have previously suggested that insulin effects on 2-deoxyglucose (2-DOG) uptake in BC3H-1 myocytes are due to increases in de novo phospholipid synthesis, diacylglycerol generation, and protein kinase C activation. To test this hypothesis further, we examined the effects of phenylephrine, an agonist that increases diacylglycerol and protein kinase C activity through phospholipase C activation. As evidence for phospholipase activation in BC3H-1 myocytes, we found that phenylephrine increased acute 32PO4 incorporation into phosphatidic acid and phosphatidylinositol, generation of [3H]inositol phosphates from prelabeled [3H]inositol phospholipids, cytosolic Ca2+, and membrane-bound protein kinase C. Phenylephrine also provoked dose-related increases in [3H]2-DOG uptake that were similar in magnitude and time course to those induced by insulin. As with insulin, phenylephrine effects on 2-DOG uptake were not apparent in myocytes that were maximally stimulated with 12-O-tetradecanoylphorbol-13-acetate, a diacylglycerol analogue that activates protein kinase C. These findings support our hypothesis that diacylglycerol generation and protein kinase C activation may be important in the stimulation of glucose uptake by agents such as phenylephrine and insulin that activate the phosphoinositide cycle.