[Stereological analysis of the ultrastructural organization of the cardiomyocytes in the red-cheeked suslik in different seasons of the year].

The myocardium of red-cheeked sousliks was studied at different seasons with the use of stereological analysis. The volume and surface densities of the myofibrils, mitochondria, T system, sarcoplasmic reticulum as well as the surface-volume ratios of the main organelles were measured. Pronounced seasonal changes in physiological activity of the heterothermal animals were accompanied by marked reorganization of the spatial ultrastructure of the cardiomyocytes. The seasonal regression of the heart weight and diminution of the cardiomyocyte diameter were recorded during hibernation. The authors believe that the increased volume ratio of the cytoplasmic organelles to the myofibrils forms the basis for a rapid adaptive reaction of the heart during hibernation and waking up.