Electron and fluorescence microscopic study of specific granules in rat atrial muscle cells.

Many dense granules have been found in the cardiac muscle cells and in the specific cells which are present in the interstitial tissue of the cyclostome heart by electron microscopy (OSTLUND et al. 1960, BLOOM et al. 1961). Chemical analysis of these granules revealed a large amount of catecholamine contained in the granules (BLOOM et al. 1961). On the other hand, the presence of spherical, electron-opaque granules within the atrial muscle of the mammals has been reported by a few investigators in recent years (KISCH 1956, POCHE 1958, BOMPIANI et al. 1959, VIRAGH et al. 1960, BATTIG et al. 1961, JAMIESON et al. 1964). In addition, the granules are constantly present in the atrial muscle fibers of various mammals (JAMIESON et al. 1964). Concerning the functional significance of these granules, PALADE (1961) suggested that the atrial granules contained catecholamine as in granules seen in cyclostome heart based on the decrease of the number of granules in the atrial muscle cells in responce to reserpine administration. However, whether the specific dense granules in the mammalian atrial muscle cell contain catecholamine as in those in the cyclostome heart has not been decided as yet. The present study was undertaken in order to elucidate this problem. The atria of rats in which drugs related to catecholamine metabolism were administered were subjected to histochemical fluorescence method for the detection of catecholamines as well as to electron microscopy.