Amiloride-sensitive net Mg2+ efflux from isolated perfused rat hearts.

Coronary blood vessels of isolated spontaneously beating rat hearts were perfused with an Mg2+-free solution at a rate of 3 ml/min. 1.5-ml fractions were sampled. Net Mg2+ efflux from heart muscle cells was measured by the increase of Mg2+ concentration in the perfusate. Addition of 0.3 microM isoproterenol to the perfusate resulted in a rapidly occurring transient Mg2+ efflux which was inhibited by amiloride.