[Effect of extracellular magnesium on reperfused rat heart and intracellular calcium concentration of the myocardium].

Isolated rat hearts were subjected to 30 min global ischemia followed 20 min reperfusion with various concentration of Mg2+ Krebs-Henseleit-bicarbonate buffer (KHB buffer) (Mg2+:1.2 mM, 2.5 mM, 5 mM, 10 mM) and 20 min reperfusion with original KHB buffer (Mg2+:1.2 mM) at 37 degrees C, respectively. Cardiac function and the incidence of ventricular arrhythmia were measured during pre-ischemia and reperfusion, and intracellular Ca2+ concentration was measured during pre-ischemia, ischemia and reperfusion period. The hearts reperfused with 1.2 mM Mg2+ presented a significantly higher frequency of ventricular fibrillation (VF) and ventricular tachycardia (VT) than the other groups. Percent recoveries of LVDP (Left ventricular developed pressure) at the Mg2+ concentration of 1.2, 2.5, 5, 10 mM after 40 min reperfusion were 64.3 +/- 5.7%, 108.4 +/- 6.1%, 100.4 +/- 6.1%, 101.5 +/- 5.5%, respectively. Intracellular Ca2+ concentration of the hearts with Mg2+ 1.2 mM revealed 248.9 +/- 15.6% at reperfusion, and that the other groups did not increased during reperfusion. These data suggest that extracellular Mg2+ inhibits reperfusion arrhythmia and Ca2+ overload during reperfusion, and improves cardiac function of reperfused heart.