Two populations of microvesicles in the SGC (small granule chromaffin) cells of the mouse adrenal medulla.

A second population of cytoplasmic microvesicles was constantly recognized in the SGC (small granule chromaffin) cells of the mouse adrenyl medulla by means of transmission electron microscopy in glutaldehyde/osmium tetroxide-fixed material. The microvesicles were rendered in shape and of mean profile diameter of between 30, 40 nm: some contained several dense precipitates. The vesicles were usually dispersed throughout the cytoplasm among the typical secretory granules of 100-230 nm in profile diameter, though they occasionally formed aggregations. The SGC cells were also characterized by a high nucleus to cytoplasm ratio, rich innervation, and long cytoplasmic processes which were traced up to 30 micrometer. Co-existence of the synaptic-like vesicles and secretory granules in the SGC cells suggests that they may represent an intermediate position between the chromaffin and sympathetic nerve cells.