Muscarinic receptors mediating the positive inotropic effect of carbachol in embryonic chick ventricle have a low affinity for pirenzepine.
Electrically driven ventricular strips from 3 day old chick embryos were used to investigate the ability of pirenzepine, a muscarinic antagonist that distinguishes between subtypes of muscarinic receptors, to antagonize the positive inotropic effect of carbachol. A low pA2 value was found for pirenzepine (6.40) whereas the pA2 value for atropine was 1000-fold higher (9.36). It can be concluded that the positive inotropic effect of carbachol on this tissue is mediated by muscarinic receptors others than M1-receptors.
Protas
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LL
Sechenov Institute of Evolutionary Physiology and Biochemistry, USSR Academy of Sciences, Leningrad.
D000818:Animals; D002217:Carbachol / Q000037:antagonists & inhibitors*; D002316:Cardiotonic Agents / Q000494:pharmacology; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects*; D006352:Heart Ventricles / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D010890:Pirenzepine / Q000494:pharmacology*; D011976:Receptors, Muscarinic / Q000502:physiology*; D013268:Stimulation, Chemical
D002316:Cardiotonic Agents; D011976:Receptors, Muscarinic; D010890:Pirenzepine; D002217:Carbachol