Adriamycin induces exocytosis in rat and beige mouse peritoneal mast cells: an ultrastructural, morphometric and biochemical study

The process of exocytosis was studied in rat and beige mouse peritoneal mas t cells stimulated by adriamycin (ADR) at 37 degrees C and 22 degrees C. AD R induces a non cytotoxic histamine release that is followed by a significa nt uptake of the drug. Examination was performed by transmission electron m icroscopy and, at the same time, histamine release and ADR uptake were meas ured by spectrofluorimetry. ADR accumulation in mast cells was investigated also by fluorescence microscopy. In rat mast cells stimulated at 37 degree s C, the secretory process developed abruptly and was virtually complete af ter 30 sec. Electron microscopy showed rapid intracytoplasmic channel forma tion and extrusion of secretory granules; spectrofluorimetry revealed a mas sive release of histamine and rapid uptake of ADR. In addition, fluorescenc e microscopy showed mast cells exhibiting an intense orange-yellow fluoresc ent signal localized at the secretory granules. At 22 degrees C, rat mast c ells showed alteration of the granules, cavity formation by fusion of the p erigranular membrane and granule discharge due to fusion of the cavity memb rane with the cell membrane. Histamine release and ADR uptake proceeded les s quickly than at 37 degrees C. Quantitative analysis of rat mast cell ultr astructure demonstrated that histamine release induced by ADR stimulation w as achieved by sequential exocytosis. This process presents both morphologi cal and biochemical affinities with the exocytosis induced by basic secreta gogues such as compound 48/80. In beige mouse mast cells the process of exo cytosis progressed more slowly and was completed after 20 min at 37 degrees C. By electron microscopy, the cytoplasm presented a rigid structure due t o abundance of actin-like fibrils. Granule fusion was an uncommon feature a nd exocytosis was mostly the result of single granule opening to the cell e xterior without extrusion of granule matrices.