The positive inotropic action of the nifedipine analogue, Bay K 8644, in guinea‐pig and rat isolated cardiac preparations

• Published in: British journal of pharmacology 1985-09, Vol.86 (1), p.27-32
• Main Authors: Finet, M., Godfraind, T., Khoury, G.
• Format: Article
• Language: English
• Subjects: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Animals; Biological and medical sciences; Calcium - deficiency; Calcium - pharmacology; Cardiotonic agents; Cardiovascular system; In Vitro Techniques; Medical sciences; Myocardial Contraction - drug effects; Nifedipine - analogs & derivatives; Nifedipine - pharmacology; Pharmacology. Drug treatments; Rats; Rats, Inbred Strains; Stimulation, Chemical
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1985.tb09431.x

1 The inotropic effect of Bay K 8644 has been studied in rat and guinea‐pig atria and ventricular strips stimulated at 1 Hz, in a medium containing CaCl2 1.8 mM. The positive inotropic effect at maximal effective concentrations of Bay K 8644 was in the following order: guinea‐pig ventricle > rat ventricle > guinea‐pig atria >> rat atria. 2 In rat preparations, the tension recorded at maximum effective concentrations of Bay K 8644 was similar at three different calcium concentrations (0.7, 1.8, 3.0 mM). The amplitude of the positive inotropic effect evoked by Bay K 8644 increased when atrial and ventricular contractions were reduced by lowering the external calcium concentration. 3 The contractile tension reached in the presence of maximum effective concentrations of Bay K 8644 (3 × 10−7 − 1 × 10−6 M) was greater than that produced by the maximum effective concentration of external calcium (3 mM) in rat ventricles but not in rat atria. 4 High doses of nifedipine (3 × 10−7 − 1 × 10−6 M) depressed the contraction of rat atria more than the contraction of rat ventricles. 5 In rat ventricles, nifedipine shifted to the right the inotropic dose‐effect curve of Bay K 8644. 6 It is concluded that the interaction between nifedipine and Bay K 8644 occurred at the same binding sites. These sites have some characteristics of the low affinity binding sites of nifedipine and other related dihydropyridines.