title: Comparison of the effects of nifedipine, diltiazem and verapamil on the mechanical activity of rabbit papillary muscles induced by barium chloride.
abstract: Isolated rabbit papillary muscles that do not present pacemaker activity under physiological conditions develop a spontaneous activity in the presence of 2 mmol/l BaCl2. Ba-induced contractions were unaffected by high concentrations of the Na antagonist procainamide (10(-5) mol/l). Tetrodotoxin (10(-5) mol/l), a specific blocker of the fast Na current, only slightly increased the amplitude of contractions. In contrast, the calcium entry blockers nifedipine, diltiazem, and verapamil strongly depressed the mechanical activity in a time- and dose-dependent manner. The concentrations that decreased the amplitude and frequency of contractions by 50% were determined. The order of potency was nifedipine much greater than diltiazem greater than or equal to verapamil. Ba-induced automaticity is a particularly useful model on which the potency of calcium entry blockers could be assessed.
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology*; D017609:Barium Compounds; D001552:Benzazepines / Q000494:pharmacology*; D002712:Chlorides; D004110:Diltiazem / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology*; D010210:Papillary Muscles / Q000187:drug effects* / Q000502:physiology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D017609:Barium Compounds; D001552:Benzazepines; D002712:Chlorides; C024986:barium chloride; D001464:Barium; D012964:Sodium; D014700:Verapamil; D004110:Diltiazem; D009543:Nifedipine