Mechanism of Histamine Release by Alpha-Chymotrypsin from Isolated Rat Mast Cells

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Abstract
.alpha.-Chymotrypsin (CT) was modified chemically and physically by treatments with diisopropyl fluorophosphate, L-(1-tosylamide-2-phenyl) ethylchloromethylketone, hydrogen peroxide and heat. After these treatments, CT lost or decreased both the enzymic activity and ability of releasing histamine from rat mast cells. Ca2+ was essential for histamine release by CT, while it enhanced only slightly the enzymic activity. The process of histamine release by CT could be separated into 2 stages: CT-dependent but not CA2+-dependent, and Ca2+-dependent but not CT-dependent. The activated state of mast cells produced by CT decayed rapidly at 37.degree. C in the absence of Ca2+, but these cells responded to Ca2+ by adding CT once again, suggesting reconstitution of cell membrane structure affected by CT. Isoproterenol, epinephrine, prostaglandin E1 and dibutyryl-cyclic AMP (0.01-0.1 mM) did not inhibit release of histamine induced by CT. Neither theophylline (0.01-0.1 mM) alone nor the combinations of these cyclic AMP-active agents with theophylline inhibited the release of histamine. In the presence of papaverine (0.01-0.1 mM) a marked, dose-dependent inhibition was observed. Release of histamine by CT from rat mast cells may be causally related to its hydrolytic activity. This activity may cause a reversible change on mast cell membrane which probably facilitates Ca2+-influx through the cell membrane. There may be subtle differences among CT, compound 48/80 [p-methoxyphenthyl methylamine formaldehyde product] and antigens concerning the effect of cyclic AMP-active agents in histamine-releasing mechanisms in mast cells.