Effects of amrinone, a cardiotonic drug, on calcium movements in dog erythrocytes.

Dog erythrocytes (RBC) have a system for passive Ca and Na movements that resembles the Ca-Na exchanger first described in cardiac muscle. Amrinone, a new cardiotonic drug active in humans with congestive heart failure, is shown to stimulate net Ca uptake by dog RBC. Amrinone's action is on Ca influx rather than efflux. The influence of Amrinone on Ca uptake is enhanced when the cells are placed in low Na media; raising external Na or lowering intracellular Na both abolish the effect of the drug. The data suggest that amrinone potentiates passive Ca entry into the cells by a Na-dependent pathway. If Ca moves through myocardial sarcolemma as it does through dog RBC membranes, then the inotropic action of amrinone can be explained on the basis that the drug increases intracellular Ca levels.