title: Slow responses mediated by alpha-adrenoceptors in the cardiac muscles of the monkey (Macaca fuscata).
abstract: The effects of phenylephrine on force of contraction and on slow action potentials were studied in the cardiac muscles of the Japanese monkey (Macaca fuscata). 1) The concentration-response curves for the positive inotropic effect of phenylephrine in the left atria and right ventricular papillary muscles were shifted to the right by either prazosin (10(-7) M) or propranolol (10(-6) M), and were further shifted in the presence of both prazosin and propranolol. 2) Phenylephrine (10(-5) M) restored the tension development in the left atria and right ventricular papillary muscles which were depolarized and rendered inexcitable by elevating K+ concentration to 22 mM. The restored contractions with phenylephrine were abolished or diminished by either prazosin (10(-6) M), phenylephrine (10(-5) M) restored action potentials in 4 of 6 K+-depolarized right ventricular muscle preparations; the restored action potentials were abolished or diminished by prazosin (10(-6) M). These results indicate that alpha-adrenoceptors as well as beta-adrenoceptors are involved in inducing slow responses in the monkey heart.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D004594:Electrophysiology; D005260:Female; D006321:Heart / Q000294:innervation*; D066298:In Vitro Techniques; D008251:Macaca; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D010210:Papillary Muscles / Q000187:drug effects; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013268:Stimulation, Chemical
chemical_list: D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D011188:Potassium