ROLE OF K-K+ ATPASE ACTIVITY IN AIRWAY RELAXATION INDUCED BY SALBUTAMOL( CHANNEL OPENING AND NA+)

To determine the role of K+ channel opening and Na+-K+ ATPase activity in the beta-adrenoceptor-mediated relaxation of airway smooth muscle, we studied canine bronchial segments under isometric conditions in vi tro. Relaxant responses to salbutamol were not altered by glibenclamid e or apamin but inhibited by charybdotoxin, where significant inhibiti on was observed only at salbutamol concentrations of less than 10(-6) M. In contrast, only the relaxations induced by salbutamol at 3 x 10(- 6) M and greater were sensitive to ouabain. Relaxations produced by lo w and high concentrations of salbutamol were selectively attenuated by charybdotoxin and ouabain, respectively, in a concentration-dependent manner. These results suggest that both Ca2+-activated K+ channel and Na+-K+ ATPase may be operative in the airway relaxation induced by lo w and high concentrations of the beta-adrenergic agonist, respectively .