Ultrastructural damage and Ca2(+)-shifts in the canine myocardium subjected to regional incomplete ischemia.

The role of Ca2+ in the pathogenesis leading to ischemic myocardial cell death is still controversial. To gain insight into this phenomenon a cytochemical procedure, the phosphate pyroantimonate method, was used to localize different subcellular Ca2+-pools at the ultrastructural level. After 45 min of left anterior descending coronary artery (LAD) occlusion, the coronary arteries were perfused with triphenyltetrazoliumchloride staining (TTC) to identify viable ischemic and infarcted tissue. In non-ischemic tissue, Ca2+-deposits were confined to the sarcolemma, sarcolemma-derived vesicles, transverse tubules, and intercalated disks. In infarcted tissue (TTC-negative), the sarcolemma lost its Ca2+-binding capacity and mitochondria were either overloaded with Ca2+-precipitate or they contained amorphous densities. In viable ischemic areas (determined with the TTC-technique) the sarcolemma was virtually devoid of Ca2+-deposits. Mitochondria in this area frequently showed clumping of the cristae, associated with an accumulation of Ca2+-precipitate in between the clustered cristae. The results of this study indicate that Ca2+-shifts occur in ischemic myocardial cells before the occurrence of other ultrastructural signs of irreversible injury which, therefore, narrows the possibility that Ca2+-overload is only a consequence of ischemic cell death.