Electrical stimulation of the liver cell: activation of glycogenolysis

To examine the role of ionic factors in the regulation of glycogen metabolism, we examined the effects of electrical stimulation on liver glycogen cycle enzymes. Passage of electric current through a suspension of rat hepatocytes caused the conversion of glycogen phosphorylase to its active (a) form and the simultaneous conversion of glycogen synthase to its inactive (D) form. The rise in phosphorylase a activity was dependent on the magnitude of current flow, was detectable after 5 s of current flow, and was rapidly reversible on cessation of stimulation. The activation of phosphorylase by shocking was completely eliminated by depletion of cellular Ca2+ and was restored by readdition of Ca2+. Cyclic AMP and cyclic GMP levels were unaffected by shocking. It is concluded that shocking, in the absence of any hormone or exogenous chemical, causes an increase in cytosol Ca2+, which in turn leads to activation of phosphorylase and inactivation of synthase. Electrical stimulation may serve as a model system for studying the role of ions in metabolic regulation.