[Quantitative electron microscopic research on the structure of the myocytes in the atrioventricular node and perinodal myocardium of the rat interatrial septum].

A quantitative electron microscopical examination of specialized conducting myocytes of types II and III in the atrioventricular node and working myocytes in perinodal region was performed. The volume fractions of myofibrils, mitochondria, nuclei, sarcoplasmic reticulum, glycogen, atrial granules and "clear" cytoplasm were measured, in addition to the diameters of conducting and working myocytes. These data were compared with those for conducting myocytes of types I, II, and III from sinoatrial region and internodal tracts of the rat heart, and with evidence for atrioventricular node of other animals. Principles of an universal classification of conducting myocytes of the heart are discussed.