title: Rat serosal mast cell degranulation mediated by chymase, an endogenous secretory granule protease: active site-dependent initiation at 1 degree C.
abstract: Exposure at 37 degrees C of rat serosal mast cells (RSMC) to chymase, an endogenous secretory granule serine protease, results in exocytosis as determined by the release of another secretory granule enzyme, beta-hexosaminidase. Chymase-mediated RSMC degranulation does not occur at 1 degree C; however, exposure of RSMC to chymase at 1 degree C followed by the removal of buffer and the resuspension of the cells in buffer alone at 37 degrees C results in exocytosis equivalent to that obtained by direct exposure of RSMC to chymase at 37 degrees C. Maximal chymase-mediated RSMC degranulation at 37 degrees C is Ca2+-dependent and Mg2+-independent. The dose-dependent degranulation-inducing interaction of chymase and alpha-chymotrypsin with RSMC at 1 degree C is Ca2+-independent, whereas subsequent exocytosis at 37 degrees C in new buffer without added enzyme still requires Ca2+. Specific binding of 125I-labeled alpha-chymotrypsin to RSMC does not occur at 1 degree C, implying that the inducing action of chymase is not a simple ligand-receptor binding. The enzyme inhibitors diisopropyl fluorophosphate and lima bean trypsin inhibitor inhibit subsequent exocytosis at 37 degrees C only if they are added within the first 10 min of the interaction of RSMC and chymase at 1 degree C, implying that an active site-dependent inducing event occurs between RSMC and chymase at 1 degree C. Thus, chymase-induced coupled activation-secretion can be divided into a cation- and temperature-independent initiation phase, which is dependent on the active site of exogenously added chymase and a subsequent temperature-dependent and calcium-augmented cellular secretion phase.
mesh_terms: D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D002118:Calcium / Q000502:physiology; D053818:Chymases; D002918:Chymotrypsin / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D005089:Exocytosis; D006596:Hexosaminidases / Q000378:metabolism; D007073:Immunoglobulin E / Q000276:immunology; D007700:Kinetics; D008407:Mast Cells / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D012697:Serine Endopeptidases; D013696:Temperature; D001619:beta-N-Acetylhexosaminidases
chemical_list: D000888:Antibodies, Anti-Idiotypic; D011480:Protease Inhibitors; D007073:Immunoglobulin E; D006596:Hexosaminidases; D001619:beta-N-Acetylhexosaminidases; D010450:Endopeptidases; D012697:Serine Endopeptidases; D002918:Chymotrypsin; D053818:Chymases; D002118:Calcium