CALCIUM OVERLOAD AND MECHANICAL FUNCTION IN POST-HYPOXIC MYOCARDIUM - BIPHASIC EFFECT OF PH DURING HYPOXIA

Abstract

Mechanical function and Ca accumulation in the myocardium during and after hypoxia were examined in the isolated but arterially perfused interventricular rabbit septum. The pH of the perfusate during hypoxia was varied from 7.4 to 6.6 by increase of the pCO2 [CO2 partial pressure]. All septa were reoxygenated for 30 min at pH 7.4. In the posthypoxic period, the recovery of developed tension was greatest and the magnitude of contracture least in those septa perfused at pH 6.8 during hypoxia; Ca overload did not occur. Marked Ca overload (3.5 .mu.mol/g wet wt) occurred in septa perfused at pH 7.4 during hypoxia. Reduction of pH to 6.6 during hypoxia did not result in a greater degree of recovery of developed tension or compete reversal of contracture in the posthypoxic period, and marked Ca overload was not prevented. Partial recovery of mechanical function in the posthypoxic period can occur concurrent with a net gain of Ca. The beneficial effects on recovery in the posthypoxic period in septa perfused at pH 6.8 during hypoxia may be related to prevention of Ca overload; The beneficial effects of acidosis are lost when the perfusate pH is reduced to 6.6 during hypoxia.