Effects of insulin-glucagon interactions on glycogenolysis and protein kinase activity in rat hepatocytes

The effects of insulin and glucagon on cAMP accumulation, protein kinase activation, and glycogenolysis were investigated in isolated rat hepatocytes. Glucagon (0.01 nM to 10 micro M) increased the activation state of protein kinase and the rate of glucose accumulation. Addition of 1.0 nM insulin to cells preincubated with 0.1 nM glucagon attenuated the rate of glucose accumulation, but did not alter the protein kinase activity ratio. Addition of 0.1 nM glucagon to cells preincubated with 1.0 nM insulin caused a rapid activation of protein kinase; however, glycogenolysis was not immediately affected. These effects were enhanced with pharmacological concentrations of glucagon and insulin. These data indicate that the degree of protein kinase activation does not always correlate temporally or quantitatively with rates of glycogenolysis in liver cells exposed to insulin and glucagon.