Morphological aspects of exocytosis in the adrenal medulla

In the adrenal medulla of the hamster, we have clearly observed profiles which show exocytosis. Such profiles have been seen on all surfaces of the chromaffin cells, near the large extracellular spaces which are mainly occupied by the blood vessels and connective tissue and also near the narrow intercellular cleft of about 20 to 25 nm which separates neighbouring chromaffin cells. (1) Near the large extracellular spaces, the plasma membrane shows granule-containing invaginations. An electron-translucent space separates the plasma membrane and the granule which is alone in the invagination. The same diversity in size and shape may be seen among the expelled granules and the intracellular granules (see figures 1 to 7 and, plates 47 to 50). These figures look like the exocytosis aspects which have been already described in other types of cells, in particular adenohypophysis (Farquhar 1961).