Ultrastructural characteristics of the formation and development of the intercalated disc in the rat left and right working ventricular myocardium on the postnatal ontogenetic stages

Abstract

Background. Maintenance of the normal distribution of intercellular contacts between cardiomyocytes and preservation of the correct geometry of the intercalated disc are essential conditions for the proper functioning of the heart. Objective. To provide complex ultrastructural evaluation of the mechanism of formation and development of the intercalated disc in rat ventricular myocardium on postnatal stages of development. Methods. Rats at the age of 1, 3, 7, 14, 30 days after birth and mature individuals were used as an object. Transmission electron microscopy, morphometric and statistical methods were applied. In particular, the convolution index was evaluated to characterize quantitative changes of the dynamics of configuration of intercalated disc. Results. It was found that the redistribution of adherens junctions from the lateral surface of cardiomyocytes occurs most rapidly from 3rd to 14th days after birth. The gap junctions trimming occurs due to their internalization with subsequent formation of the annular gap junction profile in the sarcoplasm; these profiles are inserted into the intercalated disc at the last turn. The process of complication of the geometry of intercalated disc is accompanied by the consistent increase of convolution index in the mature myocardium of the left and right ventricles up to 2,46±0,17 and 1,94±0,14, respectively. The predominance of the convolution index in the left ventricle over the levels in the right ventricle was the most prominent on the 14th day of postnatal development (38,1%; p<0,05) and in the mature myocardium – 26,8% (p<0,05). Conclusion. As the result of physiological hypertrophy and adaptive remodeling of cardiomyocyte in the postnatal rat cardiogenesis redistribution of diffusely located intercellular junctions from the periphery to the terminal areas of the cell occurs. The formation of a definitive pattern of distribution of intercellular junctions is completed at the puberty