Two Populations of Microvesicles in the SGC (Small Granule Chromaffin) Cells of the Mouse Adrenal Medulla

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Abstract
A 2nd population of cytoplasmic microvesicles was constantly recognized in the SGC (small granule chromaffin) cells of the mouse adrenal medulla by means of transmission electron microscopy in glutaraldehyde/osmium tetroxide-fixed material. The microvesicles were rounded in shape and of a 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 .mu.m. 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.