[Ultrastructure of the contacts between conducting and also between working myocytes in the sino-auricular region of the heart of the intact rat].

Ultrastructural investigation of cellular contacts of sinus node (SN), conducting myocytes of types I and II and working myocytes of right atrium (RA) perinodular myocardium was performed in rat heart. Lateral contacts between myocytes and intercalated discs are the basic in this area. Desmosomes and nexuses were found in lateral contacts apart from regions of simple abutment of plasmalemma. Incidence of different elements of the contacts varied in different types of myocytes. Nexuses were not found in contacts between type 1 myocytes in SN but were encountered in contacts between RA working myocytes and SN type II myocytes. Proportion of intercalated discs in intercellular contacts increases almost 3.5 fold from SN type I and II myocytes to RA working myocytes. In working myocytes lateral contact desmosomes were of different length as well; they were located not only in linear areas of contacts but also in finger-like processes of adjacent myocytes. Desmosomes and fasciae adherentes of intercalated discs, the proportion of which in contacts between type I and II SN myocytes was 72.9, 73.7 and 71.2% respectively, were likely to perform the main mechanic connections of specialized cells. These figures indicate equal mechanical strength of the connections of different type myocytes in sino-auricular region of rat heart. The role of the elements of cellular contacts detected in realization of mechanical, barrier and communication functions is discussed.