PRESENCE OR ABSENCE OF GLYCOGEN-BETA PARTICLES IN SINOATRIAL NODE CELLS

The sinoatrial node is formed by specialized cells, the main ultrastru ctural differences of which, as compared with ordinary atrial myocardi um, are a pale cytoplasm and sparse myofibrils. Moreover, nodal cells have been described to contain large amounts of glycogen particles in their pale cytosol; these glycogen inclusions are often used as the ma in criterion for identifying nodal cells. Nevertheless, the presence o f glycogen cytosolic inclusions has been discussed by several authors. This paradox was solved by the description of some undesirable effect s of uranyl acetate when used en bloc. To prove the presence of glycog en granules in nodal cells and the effects of uranyl acetate en bloc, we performed an ultrastructural study of the sinoatrial node in rats o f different ages using different staining techniques. Our results do n ot reveal any beta-particles in nodal cells in tissues processed by ei ther general or glycogen-specific methods. Uranyl acetate staining did not cause any change of appearance in the nodal or ordinary myocardiu m. From these results, one could conclude that, on the one hand, sinoa trial nodal cells do not show deposits of beta-particles of glycogen w hich can be detected with ultrastructural techniques, and, on the othe r hand, that uranyl acetate does not cause any morphological artifacts .