FREEZE-FRACTURE IMMUNOCYTOCHEMISTRY FOR INTRACELLULAR-LOCALIZATION OFSEROTONIN IN MAST-CELLS STIMULATED WITH COMPOUND-48 80/

Changes of intracellular localization of serotonin in rat mast cells w ere examined by freeze-fracture immunocytochemistry, to prevent the tr anslocation of the serotonin antigen. Rat peritoneal cells including m ast cells were stimulated in vitro with compound 48/80, at 17 degrees C for 0, 30 or 60 s for exocytosis to occur. The mast cells were fixed , quickly frozen and freeze-fractured to expose the antigen on the fra ctured surface. They were immunostained with serotonin antibody, and t he immunoreactions on the fractured surface were examined on ultrathin sections by electron microscopy. Unstimulated mast cells exhibited se rotonin localization mostly in each intragranular matrix. In contrast, mast cells stimulated for 30 s exhibited increased serotonin in their intergranular cytoplasm. Mast cells showed more distinct immunoreacti ons in the cytoplasm where degranulation would be promoted after 60 s. It is suggested that intracellular release of serotonin occurred in t he stimulated mast cells.