Abstract
Rat peritoneal mast cells were stimulated to generate superoxide anion (02-) by the addition of compound 48/80 (48/80), a typical histamine releaser. Biphasic elevation of [Ca2+]i was also induced by 48/80. The first phase was inhibited by TMB-8 and the second by diltiazem. And 48/80-induced O2- generation was inhibited by TMB-8, forskolin, isoprenaline, dibutyryl cAMP, KT-5926, a MLCK inhibitor, and manoalide, a phospholipase A2 inhibitor, and enhanced by KT-5720, an A-kinase inhibitor. Our data suggest the followings: (1) 48/80-induced 02- generation may be initiated by an increase of [Ca2+]i via cAMP-dependent protein phosphorylation such as MLCK phosphorylation; (2) the mechanisms of O2- generation in mast cells may be similar to that in neutrophils (NADPH-oxidase system). Epinastine, ketotifen, oxatomide and mequitazine dose-dependently prevented the N-formyl-Met-Leu-Phe and phorbol 12-myristate 13-acetate-induced O2- generation from rat neutrophils, but cromolyn sodium did not prevent it. When membrane and cytosol fractions were incubated with each drug, epinastine, ketotifen and mequitazine prevented O2- generation. On the other hand, when only the membrane fraction was incubated with each drug, ketotifen and mequitazine prevented O2- generation, but epinastine did not. Epinastine may inhibit the NADPH oxidase system through the obstruction of NADPH oxidase-associated cytosol components. In conclusion, our studies suggest that the inhibitory effects on O2- generation may be useful as a new marker in the evaluation of innovative antiallergic drugs.
