ULTRASTRUCTURAL FEATURES OF THE STRUCTURE OF THE HEART OF A NORMAL WHITE RAT

Abstract

SUMMURY. The aim – to conduct an ultrastructural study of the myocardium and the microcirculatory channel of the heart of healthy white rats.

Material and Methods. The material for research is heart biopsies of white male rats weighing 180–230 g. The study was carried out using transmission electron microscopy.

Results. Using the method of transmission electron microscopy, it was confirmed that the heart muscle of a white rat is formed by muscle fibers. The structure of rat myocardium at the ultrastructural level corresponds to the structure of cardiac muscle tissue. The muscle component is formed by closely interconnected striated cells – cardiomyocytes [2,3]. Myocardial muscle fibers are formed by mono- or binucleate cardiomyocytes, which are rectangular in cross-section. Contractile cardiomyocytes are formed by bundles of parallel myofibrils bounded by the sarcolemma. Myofibrils, in turn, consist of a number of sarcomeres bounded by Z-lines, each of which has 2–3 mitochondria. Cardiomyocytes are connected to each other with the help of intercalated discs. The intercellular space between cardiomyocytes is filled with loose connective tissue with nerves and links of the microcirculatory channel. In the myocardium, the microcirculatory channel is represented by: arterioles, precapillary arterioles, hemocapillaries of the somatic, unfenestrated type, postcapillary venules and venules. In addition to typical contractile cardiomyocytes, a second type of myocardial cells is also distinguished - atypical conducting cardiomyocytes, which form the conducting system of the heart. Secretory cardiomyocytes are secreted in the atria and on the atrioventricular septum. Gap junctions alternate with desmosomes and are found between the lateral surfaces of atrial cardiomyocytes. Multiple thin fibrils were found along the lateral surface of muscle cells, one end of which is woven into the basal membrane of a cardiomyocyte, and the other into the basal membrane of an endotheliocyte of a capillary or a neighboring cardiomyocyte. Collagen fibrils were found in the spaces between the muscle fibers of the myocardium. A significant number of small vesicles was found on the surface of cardiomyocytes. Atrial cardiomyocytes have many mitochondria and myofibrils. The most dense arrangement of myofibrils was observed on the periphery of cardiomyocytes, while the nucleus, tubules of the agranular endoplasmic reticulum, Golgi complex, mitochondria and secretory granules are located in the central zone. Mitochondria are round in shape with numerous cristae and a light matrix. Elements of the agranular endoplasmic reticulum [4,5], the Golgi apparatus, and numerous secretory granules are located in the spaces between mitochondria. The sarcoplasm contains a small amount of glycogen granules and single lipid inclusions [6,7].

Conclusions. 1. The structure of rat myocardium at the ultrastructural level have a similar structure of cardiac muscle tissue. The muscle component is formed by closely interconnected striated cells – cardiomyocytes. 2. Myocardial muscle fibers are formed by uni- or binucleate cardiomyocytes. 3. Contractile cardiomyocytes are formed by bundles of parallel myofibrils bounded by the sarcolemma. 4. The nuclei are mostly round and oval in shape, contain 1–2 nucleoli and 3 types of chromatin in the form of large granules, optically dense interchromatin granules and finely dispersed chromatin.