Reduction of Antigen-Induced Contraction of Sensitized Guinea-Pig Tracheal Smooth Muscle in vitro by Calmodulin Inhibitors

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Abstract
The effect of two calmodulin inhibitors, 1-[bis(p-chlorophenyl)methyl]-3-[2,4-dichloro-β-(2,4-dichlorobenzyloxy)phenethyl]imidazolinium chloride (R 24571) and chlorpromazine (CPZ) on antigen-induced contraction of guinea-pig tracheal smooth muscle was studied. Ketotifen, an anti-allergic compound, was used as a comparative drug. Contraction of sensitized guinea-pig trachea induced by antigen challenge was reduced by all three agents. The two calmodulin inhibitors effected relaxation of contraction of guinea-pig trachea induced by histamine and leukotriene D4 (LTD4). Ketotifen relaxed histamine-induced contraction, but hardly affected LTD4-induced tone. Contrary to chemical mediator induced tone, all examined agents had no effect on resting tone. These three agents shifted histamine- and LTD4-induced concentration-contraction curves to the right. They produced a downward displacement of the maximum, without a parallel shift in histamine- and LTD4-induced concentration-contraction curves. The two calmodulin inhibitors did not affect the antigen-induced release of histamine and SRS-A from sensitized guinea-pig lung tissue. Ketotifen slightly inhibited the release of histamine. These results suggest that R 24571 and CPZ, calmodulin inhibitors, reduced an antigen-induced contraction of sensitized guinea-pig trachea in vitro mainly by affecting the contractility of tracheal smooth muscle by chemical mediators but not by interfering with the release of mediators.

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