Fluorescence and electron-microscopic analysis of differentiation of the myocytes of the ventricles and atria of the avaian heart in ontogenesis]

The histogenesis of the ventricle and atria myocardium was studied in 240 chick embryos of from 30--34 hours up to 20 days of incubation and in 66 chickens at the age of 1--90 days. Fixators were the Bouin's Carnoy's and Newkomer's fluids and the 100% solution of neutral formalin. The paraffin sections were stained by histological and histochemical methods. RNA, DNA, glycogen and lipids were detected. The ultrafine sections of the material fixed in 1% buffer solution of osmium tetroxide (pH 7,2) and embedded in araldite were prepared for electron microscopy. The contrasting was made in solutions of acetic uranium and lead citrate. Electron microscope--UEMB-100K, accelarating voltage--75 kV. The prefunctional period of cardiogenesis is characterized by most intensive processes of specific differentiation of cardiac myocytes and by accumulation of energetic material. With the growing functional activity of the tubular heart the amount and size of lipid drops in the cytoplasm of differentiating cardiomyocytes diminished suggesting the use of lipids as the main source of energy. In the period of formation of the heart the trabecular myocardium of ventricles and the atria myocardium, seeming to perform the main functional load, are characterized by a better developed contracting apparatus and a considerable content of glycogen granules. A sharp decrease of the glycogen content at the end of the embryonic period is likely to be due to growing hypoxia, the appearance of lung respiration and transition to the other type of energy metabolism.