AJP - Heart and Circulatory Physiology, Vol 262, Issue 3 649-H653, Copyright © 1992 by American Physiological Society
Adrenergic activation of glycogen phosphorylase in primary culture diabetic cardiomyocytes
J. A. Buczek-Thomas, S. R. Jaspers and T. B. Miller Jr
Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester 01655.
The basis of catecholamine-induced activation of glycogen phosphorylase was
investigated in adult rat cardiomyocytes isolated from normal and
alloxan-diabetic animals. Cells derived from diabetic animals exhibited a
hypersensitive response to epinephrine stimulation that was apparent 3 h
after cell isolation and was further enhanced on maintenance of the
myocytes in culture for 24 h. Normal cells initially lacked the
hypersensitive response to epinephrine stimulation, although on maintenance
of these cells in culture for 24 h, the hypersensitive response was
acquired in vitro. To assess alpha- and beta-adrenergic mediation of the
response, normal and diabetic cardiomyocytes were incubated with
propranolol, a beta-blocker, before direct alpha 1-receptor stimulation
with phenylephrine. Both normal and diabetic myocytes failed to undergo
activation of phosphorylase in 3- or 24-h cell cultures. In addition, the
effects of epinephrine on phosphorylase activation were completely
inhibited by propranolol, whereas prazosin, an alpha-blocker, was
unsuccessful. The present data suggest that the hypersensitive response of
glycogen phosphorylase in normal and diabetic cardiomyocytes is solely
mediated through beta-adrenergic receptor activation.
