Ultrastructural influence of reperfusing dog myocardium with calcium-free blood after coronary artery occlusion.

The ultrastructural effects of perfusing ischemic myocardium with calcium-free blood were determined in 12 dogs. In 6 dogs, the left anterior descending coronary artery was ligated for 45 minutes and was released for 5, 10, or 20 minutes. In 6 other dogs, the ischemic zone was perfused with blood free of calcium which was chelated with EGTA (ethylene glycol bis [B-aminoethylether-N,N'-tetraacetic acid] for 5, 10, or 20 minutes. After reperfusion with whole blood, the sarcomeres either were mildly contracted or formed contracted bands. The cells were usually pulled apart at the intercalated disk. The mitochondria were swollen and contained electron-dense deposits. Lanthanum was used as a marker for monitoring changes in cell membrane permeability and permeated into many ischemic myocardial cells. The hearts treated with calcium-free plasma showed well preserved morphology. Mitochondria were slightly swollen, their cristae were occasionally disrupted, and they lacked electron-dense deposits. No lanthanum leaked into these cells, with a few scattered exceptions. Even in the leaky cells, the mitochondria did not show any deposits. It is suggested that calcium overload plays a significant role in the pathogenesis of cell injury and that reduction in plasma levels of calcium, at least for a limited period may delay the onset of calcium overload and improve cell morphology. Alterations in the cell membrane are followed by lethal intracellular changes leading to events associated with cell death.