title: Positive inotropic effects of the calcium channel activator Bay K 8644 on guinea-pig and human isolated myocardium.
abstract: 1. The positive inotropic effects of the dihydropyridine calcium activator Bay K 8644 were studied in guinea-pig isolated contracting myocardium and human papillary muscle strips obtained from patients undergoing mitral valve replacement or cardiac transplantation. 2. Bay K 8644 produced a slowly developing, concentration-dependent positive inotropic response in all cardiac tissues studied. In guinea-pig papillary muscle, the increase in force of contraction was half-maximal at 3.9 x 10(-8) mol/l and the maximal inotropic effect was comparable to that obtained with ouabain, dobutamine or calcium. The guinea-pig left atrium (EC50, 2.1 x 10(-7) mol/l) was fivefold less sensitive than the papillary muscle. 3. The maximal inotropic response to dihydroouabain was significantly increased after preincubation with Bay K 8644 (1 x 10(-6) mol/l) in papillary muscles from both guinea-pig and human. In guinea-pig papillary muscles, the maximal inotropic response to dobutamine was not changed by preincubation with Bay K 8644 whereas in human papillary muscle strips, Bay K 8644 increased the inotropic response to dobutamine. 4. Bay K 8644 increased force of contraction (EC50, 4 x 10(-8) mol/l) in human papillary muscle strips from patients undergoing mitral valve replacement. However, the maximal inotropic response to Bay K 8644 was reduced to 32 +/- 4.4% that of calcium (15 mmol/l) measured in the same muscle strips. 5. A further reduction in maximal inotropic response to Bay K 8644 to 13 +/- 1.2% that of calcium (15 mmol/l) with no change in potency was measured in human papillary muscle strips taken from terminally failing hearts of cardiac transplant recipients.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004071:Digitalis Glycosides / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013268:Stimulation, Chemical
chemical_list: D000318:Adrenergic beta-Agonists; D004071:Digitalis Glycosides; D010726:Phosphodiesterase Inhibitors; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium