Distribution of actin filaments in rat mast cells and its role in histamine release

The distribution of actin filaments was confirmed by immunofluorescence microscopy and immuno-electron microscopy in nonsecreting and secreting rat peritoneal mast cells. In a resting cell, immunofluorescence of the actin showed up as a net-like formation surrounding each granule. After stimulation with compound 48/80 or A-23187, the distribution of the actin filaments became very irregular and disordered, disappearing completely in some areas within the cell and expanding in conjunction with the swelling of the granules. Similar changes are seen in a passively sensitized mast cell exposed to antigen. When cells were pretreated with cytochalasin B or colchicine, the distribution of actin filaments was not greatly affected by stimulation. The results clearly show that actin filaments exist in mast cells.