[Transmural differences between damaged cardiomyocytes due to post-ischemic reperfusion and calcium paradox].

Normothermic 3 min lasting perfusion of the isolated rat heart by Krebs--Henseleit solution in which Ca2+ was replaced by EDTA and subsequent perfusion with a Ca2+ containing medium induced structural and metabolic changes demonstrated electron microscopically and histochemically. In contrast to the ischemic reperfusion damage, in calcium paradox, the histochemically studied enzymes alpha-glucan-phosphorylase, lactate dehydrogenase, succinic dehydrogenase, beta-hydroxybutyric dehydrogenase, and ATPases were better preserved in the subendocardial region of the left ventricle. Ultrastructural analysis of this phenomenon showed good correlation with histochemical findings. A large portion of cardiomyocytes in the subendocardial layer exhibited but small changes. On the other hand, myocytes in the subepicardial region and in the midmyocardium were markedly damaged and all characteristic signs of calcium paradox were present, including hypercontraction bands with myofilament fusion, extrusion and accumulation of edematous mitochondria with occurrence of electron dense material in mitochondrial cristae, ruptures of the sarcolemma in all its layers, separation of intercalated discs, etc. The better preservation of the subendocardial region in experiments with calcium paradox is attributable to inadequate perfusion of this region by calcium free medium due to transmural anatomic inhomogeneity of capillary supply whose insufficiency in the subendocardial region results in a better protection of these myocytes from Ca2+ paradox.