Effects of alpha-adrenoceptor stimulation on electrophysiological properties and mechanics in rat papillary muscle.
1. Electrophysiological and inotropic responses to stimulation of alpha-adrenoceptors were examined in isolated rat papillary muscles. 2. Stimulation of alpha-adrenoceptors caused two major electrophysiological changes, i.e. prolongation of action potential duration (APD) and hyperpolarization of resting membrane potential. 3. The time course of the inotropic responses to alpha-adrenoceptor stimulation was composed of an initial, short-lasting and small positive phase followed by a negative phase and then a second increasing phase. 4. Nifedipine abolished the alpha-adrenoceptor-mediated positive inotropic effect whereas unaffecting the negative inotropic effect, the APD prolongation and the hyperpolarization. 5. In quiescent muscles alpha-adrenoceptor stimulation also produced hyperpolarization, which was blocked by Ba2+.
D000200:Action Potentials / Q000187:drug effects; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D000317:Adrenergic alpha-Antagonists; D010656:Phenylephrine; D001464:Barium; D009543:Nifedipine