Location of alpha 1-adrenoceptors relative to beta-adrenoceptors in rat myocardium.
Electrically driven rat papillary muscles (1 Hz) were examined for the location of their alpha 1-adrenoceptor and beta-adrenoceptor populations relative to each other. We determined the horizontal position of the dose-response curves for the positive inotropic effects exerted by noradrenaline in the absence and presence of the neuronal uptake blocker cocaine and in the absence and presence of the beta-adrenoceptor antagonist timolol and of the alpha 1-adrenoceptor antagonist prazosin. Cocaine slightly shifted the dose-response curves for alpha 1-adrenoceptor stimulation to a lower concentration of agonist. In contrast, the dose-response curve for beta-adrenoceptor stimulation was markedly shifted by cocaine to a lower concentration of agonist. Experiments with corticosterone (an extraneuronal uptake blocker) revealed no differential shift of either of the dose-response curves. Together, these data indicate that the alpha 1-adrenoceptor population is located more distantly from the adrenergic nerve terminals than the beta 1-adrenoceptor population in rat myocardium.
Dybvik
T
T
Department of Pharmacology, University of Oslo, Norway.
Osnes
J B
JB
Skomedal
T
T
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D003345:Corticosterone / Q000494:pharmacology; D004347:Drug Interactions; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000648:ultrastructure*; D009411:Nerve Endings / Q000502:physiology; D009474:Neurons / Q000187:drug effects; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010210:Papillary Muscles / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000032:analysis* / Q000187:drug effects; D018342:Receptors, Adrenergic, beta-1 / Q000032:analysis* / Q000187:drug effects; D013268:Stimulation, Chemical; D013564:Sympathetic Nervous System / Q000502:physiology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D002316:Cardiotonic Agents; D014179:Neurotransmitter Uptake Inhibitors; D018340:Receptors, Adrenergic, alpha-1; D018342:Receptors, Adrenergic, beta-1; D003042:Cocaine; D003345:Corticosterone; D009638:Norepinephrine