AJP - Endocrinology and Metabolism, Vol 240, Issue 3 226-E232, Copyright © 1981 by American Physiological Society
Electrical stimulation of the liver cell: activation of glycogenolysis
K. A. Freude, L. S. Sandler and F. J. Zieve
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.
