Abstract
Abstract
Previous experimental data documenting an insulin like-effect of 12-O-tetradecanoyl phorbol 13-acetate (TPA), a specific activator of protein kinase C, on glucose transport in adipocytes prompted us to test the hypothesis that TPA might display another insulin-like effect, i.e., antagonize catecholamine-induced lipolysis. TPA (100 nM) led to a decrease of both free fatty acid (41%) and glycerol (58%) release due to 1 μM norepinephrine stimulation in isolated rat adipocytes. TPA also diminished the antilipolytic effect of insulin (5 ng·ml-1) in the presence of 1 μM norepinephrine. Thus, the residual lipolysis with insulin was 25% for free fatty acids and 24% for glycerol release. In the presence of TPA, these values increased to 50% and 45%, respectively. TPA (100 nM) addition to isolated adipocytes induced protein kinase C translocation from the cytosol to the membrane fraction. In control cells, 94.7 ± 2.9% of the enzyme was found in the cytosol, with the rest found in the membrane. At 10 min after TPA (100 nM) addition, the corresponding value was 43.6 ± 17.4%, with the rest in the membrane (n = 6, P < 0.05). These findings indicate that protein kinase C might be involved not only in the insulin action on glucose transport, but also in the mechanism of insulin's antilipolytic action.
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