[Myocardial cell ultrastructure of yaks dwelling at high altitudes]

The ultrastructure of myocardial cells of the left, right ventricle, and the ventricular septum was studied in the Altai and Pamir Yaks permanently living at the altitude of 3000-3600 m. Electron microscopic studies of myocardial cells revealed, along with the normal mitochondria, the ones with a peculiar structure of the cristae; these had the appearance of polyhedral wavy membranes in some groups of the mitochondria, and of polyhedral netted structures - in the others. Considerable accumulations of glycogen granules were found beneath the sarcolemma, in the perinuclear cytoplasmic zone and between the myofibrils. The results suggest that by undulating and creating a certain structural regularity the mitochondrial cristae increased their active area ensuring the efficacy of the mitochondrial function. Considerable accumulation of glycogen granules in the majority of myocardial cells seems to maintain the energy potential of the myocardium preventing the development of hypoxia.