IMMUNOCYTOCHEMICAL LOCALIZATION OF CHYMASE TO CYTOPLASMIC VESICLES AFTER RAT PERITONEAL MAST-CELL STIMULATION BY COMPOUND-48 80/

The subcellular events responsible for release of mediators by mast ce lls may help to clarify roles for mast cells in health and disease. In this study we show that the granule-associated protease chymase is al so within cytoplasmic vesicles in appropriately stimulated rat periton eal mast cells. Rat peritoneal mast cells were recovered before or 1-1 0 sec after exposure to the secretogogue compound 48/80 (10 mu g/ml) a nd then were examined by radioimmunoassay to quantify histamine releas e or were processed, using routine methods for postembedding immunoele ctron microscopy, to identify the subcellular localization of chymase. In comparison to unstimulated cells, compound 48/80 stimulated cells in two independent experiments showed an increase (15%, 28%) in the su rface area of the cell and a decrease (12%, 6%) in the surface area of the total granule compartment before degranulation channel formation. These global cellular changes occurred in a background of transient b ut significant (p<0.01) increases in the area and number of chymase-im munoreactive vesicles per mu m(2) cytoplasm. These changes were detect able at 5 or 7 sec after stimulation with compound 48/80 but returned to near prestimulation levels by 9 or 10 sec after addition of compoun d 48/80 (total cumulative histamine release was 28% by 8 sec and 47% b y 14 sec). These observations suggest that vesicles participate in the early stages of regulated secretion of chymase from rat peritoneal ma st cells.