Appearance of alpha 1-adrenergic receptors in soleus muscles from SHR.
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.
Pickar
J G
JG
Department of Human Physiology, University of California, Davis 95616.
Gray
S D
SD
Carlsen
R C
RC
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D004594:Electrophysiology; D004837:Epinephrine / Q000494:pharmacology; D006614:Hindlimb; D008297:Male; D009132:Muscles / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D011918:Rats, Inbred SHR / Q000378:metabolism*; D011921:Rats, Inbred WKY; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D013566:Sympathomimetics / Q000494:pharmacology
D011942:Receptors, Adrenergic, alpha; D013566:Sympathomimetics; D001030:Apamin; D004837:Epinephrine