Temperature-dependent inotropic action of A23187 on guinea-pig ventricular muscles.
The effects of the Ca2+ ionophore, A23187, on the contraction and membrane action potential of the isolated guinea-pig papillary muscle were examined at various temperatures (30-16 degrees C) and compared to those of isoprenaline and a high calcium medium. A23187 caused a marked positive inotropic effect with a significant prolongation of the action potential duration at an early repolarization phase but not a late repolarization phase at normal temperature (30 degrees C). Such an inotropic effect was completely abolished at low temperature (16 degrees C) where a marked positive inotropic effect of isoprenaline (5 X 10(-8) M) and a high calcium medium (6.2 mM) still remained. These results suggest that the cardiac responsiveness to A23187 was sensitive to a low temperature at which a membrane lipid phase transition may occur.
Kondo
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D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D002316:Cardiotonic Agents; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D013696:Temperature; D016276:Ventricular Function
D002316:Cardiotonic Agents; D000001:Calcimycin; D007545:Isoproterenol; D002118:Calcium