A23187: a calcium ionophore that directly increases cardiac contractility (38704).

The effect of the calcium ionophore A23187 on contractility in guinea pig left atria was studied. This ionophore increased both the force of contraction and the rate of tension development in a concentration dependent manner. The positive inotropic effect of A23187 is not mediated by activation of beta-receptors or by the release of endogenous catecholamines since neither propranolol nor pretreatment with reserpine altered the inotropic effect of this agent. Our studies of the dependence of contractile force on external calcium indicate that A23187 enhances the response of atrial muscle to external calcium ions. Since A23187 is known to facilitate the movement of calcium across biological membranes, we believe the ionophore may be acting either by increasing calcium influx across the myocardial cell membrane or by facilitating calcium release from sarcoplasmic reticulum.