QUANTITATIVE-ANALYSIS OF EXOCYTOSIS VISUALIZED BY A VIDEO-ENHANCED LIGHT FLUORESCENCE MICROSCOPE REVEALS 2 DISTINCT COMPONENTS OF EXOCYTOSIS IN RBL-2H3 CELLS/

Rat basophilic leukemia (RBL-2H3) cells, which exhibit Ca2+-dependent secretion of granules when stimulated with antigen or the Ca2+-ionopho re A23187, were observed under a video-enhanced light/fluorescence mic roscope. Exocytotic events of individual granules were visualized in i ndividual cells stimulated with antigen or A23187. Exocytosis of granu les stimulated,vith A23187 showed two peaks in the time course. The ea rlier one was inhibited by selective inhibitors of protein kinase C (R o31-8425, Ro31-8220, and chelerythrine) and the other was inhibited by an inhibitor of phosphatidate hydrolase, propranolol. Exocytosis by a ntigen stimulation, however, showed only one peak, which was inhibited by the selective inhibitors of protein kinase C, but not by propranol ol. These results indicate that at least two distinct components of ex ocytosis exist in RBL-2H3 cells.