EFFECT OF CROMAKALIM AND SALBUTAMOL ON HISTAMINE-INDUCED AND METHACHOLINE-INDUCED CONTRACTION OF THE ISOLATED GUINEA-PIG TRACHEAL CHAIN

The relaxant effect of cromakalim on histamine- and methacholine-induc ed contraction was investigated in guinea-pig trachea in vitro with an d without epithelial cells present. The isolated tracheas of four to s ix guinea-pigs were used in each experiment and suspended in organ bat hs, filled with Krebs-Henseleit solution and gassed with 95% O-2 and 5 % CO2. Cromakalim (3 x 10(-5) M) produced a relaxation of 68.2 +/- 8.7 % after histamine-induced contraction and 71.0 +/- 4.0% after methacho line-induced contraction as compared to salbutamol (100%). At higher c oncentrations. cromakalim produced a relaxation of 86.2 +/- 9.6% (10(- 4) M cromakalim) for histamine-induced contraction and 90.8 +/- 9.9% ( 10(-3) M cromakalin) for methacholine-induced contraction. Epithelial cell removal had minimal effects. A non-significant increase in the re laxant effect of cromakalim was noted for both agonists. Glibenclamide pre-incubation (10(-6) M) had no ef feet on the relaxant effect of cr omakalim for methacholine-contracted preparations, but depressed the r elaxant effect of cromakalim significantly for histamine-contracted pr eparations. All these findings suggest that the relaxant effect of cro makalim involves different K+ channels for different agonists.