Ultrastructure of isolated human mast cells during histamine release induced by ionophore A 23187

In the presence of calcium, the ionophore A 23187 (10(-7) TO 10(-6) M) causes a dose-dependent histamine release from isolated human mast cells. The accompanying degranulation process is characterized by a formation of channels of fused mast cell granules and by an exocytotic extrusion of altered granule material. Simultaneously, large numbers of newly formed 70 A filaments occur. These filaments probably have a key function in secreting human mast cells.