title: Differential blockade of potassium and carbachol contractures of toad isolated rectus abdominis muscle by calcium entry blockers, ketamine and hydrallazine.
abstract: Contractures of the rectus abdominis muscle of Buffo regularis evoked by carbachol were inhibited in concentration-dependent fashion by verapamil, nifedipine, hydrallazine and ketamine, whereas KCI-induced contractures were relatively resistant to blockade by these compounds. The order of potency in blocking carbachol-induced responses was: verapamil greater than nifedipine greater than hydrallazine greater than ketamine, verapamil being over 10 times more potent than nifedipine. In high K+-depolarized muscles, carbachol elicited contractural responses which were inhibited by verapamil, nifedipine, hydrallazine and ketamine; these compounds exhibited similar blocking potencies against carbachol responses in high K+-depolarized muscles as in the polarized muscles. In Ca2+-free EGTA-Ringer's solution, both KCl and carbachol contractures were abolished, but were restored on readmission of Ca2+. d-Tubocurarine competitively antagonized carbachol, but not KCl contractures. It is suggested that (i) extracellular Ca2+-influx occurs during contractures of the toad rectus abdominis muscle induced by carbachol and KCl; (ii) there probably exists more than one pathway for Ca2+-entry into this muscle--one pathway is stimulated by high K+-depolarization, and another which is linked to the activation of nicotinic cholinoceptors. Verapamil, nifedipine, hydrallazine and ketamine appear to preferentially inhibit Ca2+-influx stimulated via a pathway linked to nicotinic cholinoceptors.
authors: Department of Pharmacology and Therapeutics, College of Medicine, University of Ibadan, Nigeria.
authors: A O
authors: AO
authors: Savage
authors: N A
authors: NA
authors: Olokodana
mesh_terms: D000818:Animals; D002025:Bufonidae; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002217:Carbachol / Q000037:antagonists & inhibitors*; D005260:Female; D006830:Hydralazine / Q000494:pharmacology*; D066298:In Vitro Techniques; D007649:Ketamine / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000037:antagonists & inhibitors*; D011189:Potassium Chloride / Q000494:pharmacology*; D014403:Tubocurarine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D006830:Hydralazine; D011189:Potassium Chloride; D007649:Ketamine; D002217:Carbachol; D014700:Verapamil; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D014403:Tubocurarine