Small granule-containing cells in the heart of the toad (Bufo melanostictus)

This study reveals the presence of small granule-containing cells in the heart of the toad, Bufo melanostictus. The cells were small in size (5-25 microns in diameter) and located in the interatrial septum. The small cells occurred singly or in small clusters within the cardiac ganglia or near the myocardial cells. They were characterized by numerous large dense core vesicles (80-300 nm) in their cytoplasm. With 5-hydroxydopamine treatment, the granularity of the large dense core vesicles was greatly intensified. The large dense core vesicles were variable in size and shape and extended into the long and short processes of the cells. Some of these processes were in close contact with myocardial cells. Other cytoplasmic organelles included rough endoplasmic reticulum, free ribosomes, randomly distributed mitochondria and glycogen particles. Individual cells or cell clusters were usually ensheathed by a thin layer of cytoplasm from sheath cells. The small granule-containing cells in the present study correspond to the catecholamine-containing (SIF) cells described by earlier workers. These cells presumably regulate muscular and ganglionic activities by virtue of their close association.