MORPHOLOGICAL-STUDY OF RAT MAST-CELLS STIMULATED WITH COMPOUND-48 80 AT DIFFERENT TEMPERATURES/

Changes of mast cells stimulated with compound 48/80 were morphologica lly investigated at different temperatures. Peritoneal mast cells of m ale rats were stimulated in vitro at 4 or 17 degrees C. At 17 degrees C, mast cells stimulated for 10 s gave decreased fluorescent reactions for phalloidin. At 30 s stimulation, they showed typical exocytosis i nitiated by fusions of peripherally located secretory granules to the plasma membrane. In contrast, mast cells stimulated at 4 degrees C exh ibited neither decrease of phalloidin reactions nor typical excytosis even after 30 s. It was inferred that the fusions were mediated by cyt oplasmic elements, probably the actin filaments previously suggested t o prevent release of secretory granules. Furthermore, the space betwee n the perigranular membrane and granular contents was enlarged in some mast cells stimulated at 4 degrees C. The morphological changes sugge sted that equivocal events occurred also in the cytoplasm of these cel ls. The mast cells showed no typical exocytosis at 4 degrees C.