Prevention by hypothermia of paradoxical calcium necrosis in cardiac muscle

Abstract

Isolated rat hearts were perfused with calcium-free medium at either 37° or 4°C, and electrical and mechanical phenomena recorded. The calcium-free perfusion of the isolated rat heart at 37°C for periods in excess of 3 min, caused quick cessation of contractile activity with electro-mechanical dissociation. When calcium was restored to the perfusate at 37°C irreversible electro-mechanical dissociation and myocytolysis occurred, accompanied by a massive efflux of intracellular constituents into the perfusate. When the isolated rat heart was perfused with calcium-free medium at 4°C, both the electrocardiogram and contractility disappeared within 15–20 s. The restoration of calcium to these hearts perfused with calcium-free medium at 4°C, permitted rapid recovery of cardiac function upon warming to 37°C. Electron microscopy of hearts perfused with calcium after calcium-free perfusion at 37°C and 4°C showed that at 37°C extensive alteration and lysis of the cardiac organelles occurred, whereas at 4° they were well protected. Uptake of 45Ca 2+ by the myocardium subsequent to calcium-free perfusion at 37°C was approximately 20 times greater than that observed in hearts subjected to calcium deprivation at 4°C. These findings lend support to the view that the paradoxical calcium necrosis of cardiac muscle at 37°C is due to the massive influx of calcium into the cardiac muscle cells following damage to the sarcolemma. It is suggested that the damage to the sarcolemma observed at 37° consists of loss of membrane-bound proteins responsible for the physiologic “calcium channel”. At 4°C their escape from the bilayer appears to beretarded by a more sluggish shift in conformation from the calcium-bound to the calcium-free state, and a more crystalline membrane.