Positive inotropic and chronotropic effects of the calcium ionophore A23187 (calimycin) on guinea-pig atria.
The inotropic and chronotropic effects of the calcium ionophore A23187 (calimycin = CA) in isolated, superfused, electrically driven, auxotonically contracting left and spontaneously beating right guinea-pig atria were examined at different Ca2+ concentrations. 10(-6) to 10(-5) mol/l CA shows significantly positive inotropic and chronotropic effects. The inotropic effect of CA can be significantly diminished by relatively high concentrations of Ca2+ channel antagonists and relatively low concentrations of ryanodine. The positive chronotropic effect of CA can be reduced slightly, but significantly, by beta-adrenoceptor antagonists and histamine H2-receptor antagonists. From this we infer that the positive inotropic effect of CA is mainly due to the release of Ca2+ from cardiac sarcoplasmic reticulum, whereas catecholamine and histamine release appear to contribute to the positive chronotropic effect of the ionophore.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D013268:Stimulation, Chemical
D002413:Cations, Divalent; D012433:Ryanodine; D000001:Calcimycin; D002118:Calcium