Exocytosis in the adrenal medulla demonstrated by freeze-etching

Replicas of fractured chromaffin cells are indicative of a range of activities thought to characterize exocytosis, including attachment of secretory vesicles to the plasma membrane, fusion, extrusion of contents, and membrane retrieval. Exocytosis sites are abundant on stimulated cells but are infrequent when calcium is omitted from the system.