Involvement of K+ channel in procainamide-induced relaxation of bovine tracheal smooth muscle

The relaxant effect of procainamide, a class Ia antiarrhythmic agent, was e xamined in bovine tracheal smooth muscle. Procainamide produced concentrati on-dependent decreases in tension and full relaxation in the preparations c ontracted with methacholine (0.3 mu M). By comparison, in preparations cont racted with 40 mM K+, procainamide had only slight relaxant effects. The re laxant effects of cromakalim and salbutamol on 40 mM K+-contracted preparat ions were significantly (P < 0.01) smaller than those on 0.3 mu M methachol ine-contracted ones. On the other hand, the concentration-response relation ships for quinidine, lidocaine, mexiletine and propafenone were not so dram atically different between 0.3 mu M methacholine- and 40 mM K+-contracted p reparations. Tetraethylammonium (300 mu M), iberiotoxin (30 nM) and Ba2+ (1 mM) significantly (P < 0.05) attenuated the relaxant effects of procainami de on methacholine-induced contractions, whereas apamin (100 nM), 4-aminopy ridine (300 mu M), and glibenclamide (10 mu M) did not affect them. The inh ibitory effect of a combination of iberiotoxin and Ba2+ was greater than th at of iberiotoxin or Ba2+ alone (P < 0.01). These results suggest that the activation of at least two types of K+ (maxi-K+ and inward rectifier K+) ch annels contributes to the procainamide-induced relaxation of bovine trachea l smooth muscle. (C) 2000 Elsevier Science B.V. All rights reserved.