The effect of a novel benzopyran derivative, KC 399, on the isolated guinea-pig trachealis and human bronchi.

1. In isolated guinea-pig trachealis, KC 399, BRL 38227 and salbutamol suppressed the spontaneously generated tone in a concentration-dependent manner with pD2 values of 8.89 +/- 0.09 (n = 14), 6.18 +/- 0.07 (n = 11) and 7.72 +/- 0.12 (n = 8), respectively. 2. The bronchodilator effects of KC 399 and BRL 38227 were antagonized by glibenclamide but not by charybdotoxin or apamin. The effect of salbutamol was antagonized by charybdotoxin but not by glibenclamide or apamin. 3. KC 399 and BRL 38227 failed to inhibit the tone evoked by 90 mM K+ in guinea-pig trachealis, whereas salbutamol did inhibit it, in a concentration-dependent manner. 4. These bronchodilators also relaxed the tone of isolated guinea-pig trachealis supported by histamine, carbachol, U46619 or leukotriene D4. Their order of potency was always KC 399 > salbutamol > BRL 38227. 5. KC 399 and BRL 38227 relaxed isolated human bronchi contracted with histamine or carbachol. 6. We conclude that KC 399 is a potent relaxant of isolated guinea-pig trachealis and human bronchi in vitro. The relaxant action of KC 399 could be due to the opening of glibenclamide-sensitive K+ channels.