[Effect of myocardial alpha 1-adrenoceptor stimulation on the guinea-pig ventricular papillary muscle].
The alpha-adrenoceptor agonist phenylephrine (5.0 x 10(-6) mol/L) was used to stimulate myocardial alpha-adrenoceptors of the guinea-pig ventricular papillary muscle, and changes of transmembrane action potential and contractile force of the muscle were observed. The alpha 1-adrenoceptor blocker prazosin (5.0 x 10(-7) mol/L) and the alpha 2-adrenoceptor blocker yohimbine (5.0 x 10(-7) mol/L) were used to determine which subtype of alpha-adrenoceptor is responsible for the effects. The beta-adrenoceptor blocker propranolol (1.0 x 10(-6) mol/L) was used throughout the experiment. The results show that the myocardial alpha 1-adrenoceptor stimulation (1) increases the contractile force of the guinea-pig ventricular papillary muscle, (2) prolongs the time to peak contractile force while the duration of relaxation is not altered, (3) prolongs the fast response action potential duration, and (4) increases the maximal rate of depolarization during the phase 0 of the slow response action potential. It is suggested that the electrophysiological and positive inotropic effects of myocardial alpha 1-adrenoceptor stimulation might be due to the activation of the slow inward current and an increase in Ca2+ influx.
Shi
Q
Q
Zhang
H D
HD
Xu
Y Q
YQ
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D015220:Calcium Channels; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D010210:Papillary Muscles / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*
D015220:Calcium Channels; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine