AJP - Cell Physiology, Vol 262, Issue 5 C1284-C1291, Copyright © 1992 by American Physiological Society
Appearance of alpha 1-adrenergic receptors in soleus muscles from SHR
J. G. Pickar, S. D. Gray and R. C. Carlsen
Department of Human Physiology, University of California, Davis 95616.
The depressed functional capabilities of spontaneously hypertensive rat
(SHR) muscles, reported previously (Exp. Neurol. 95: 249-264, 1987), may
reflect a decrease in muscle responsiveness to catecholamines occurring as
a consequence of exposure to the elevated level of plasma catecholamines in
SHR. Responsiveness to applied catecholamines was determined in SHR and
Wistar-Kyoto rat (WKY) soleus by measuring muscle resting membrane
potentials (RMP) in vitro. Epinephrine (10(-6) M) produced a similar
membrane hyperpolarization in SHR and WKY fibers. Pretreatment with the
beta-antagonist propranolol completely blocked the epinephrine-induced
hyperpolarization in WKY, but not in SHR. SHR soleii from both young and
old rats contained a population of alpha 1-adrenergic receptors also
associated with membrane hyperpolarization. The alpha-receptors appeared to
be associated with a ligand-gated Ca(2+)-influx pathway, since the
alpha-agonist-induced membrane hyperpolarization required the presence of
Ca2+ in the extracellular medium. The alpha-induced hyperpolarization was
also blocked by apamin, a derivative of bee venom which blocks a
Ca(2+)-activated K(+)-efflux pathway in a variety of tissues. The possible
role of these novel alpha-receptors in skeletal muscle function, and their
relationship to the development of hypertension, is uncertain.
