Temperature-dependent inotropic action of A23187 on guinea-pig ventricular muscles

Abstract

1. The effects of the Ca 2+ ionophore, A23187, on the contraction and membrane action potential of the isolated guinea-pig papillary muscle were examined at various temperatures (30–16°C) and compared to those of isoprenaline and a high calcium medium. 2. A23187 caused a marked positive ionotropic 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°C). 3. Such an inotropic effect was completely abolished at low temperature (16°C) where a marked positive inotropic effect of isoprenaline (5 × 10 −8 M) and a high calcium medium (6.2 mM) still remained. 4. These results suggest that the cardiac responsiveness to A23187 was sensitive to a low temperature at which a membrane lipid phase transition may occur.