The role of K+ channels in B-adrenoceptor agonists- and phosphodiesterase inhibitors- induced relaxation in the rabbit tracheal smooth muscle

The aim of this in vitro study was to investigate the inhibitory effects of K+ channel blockers, tetraethylammonium (TEA) and glibenclamide, on the isoprenaline-, salbutamol-, theophylline- and aminophylline- induced relaxation in the rabbit trachea. İn the tracheal strlps pre-contracted with carbachol (W 3 M), isoprenaline (10~9 -10~4 M), salbutamol (3x10 '7-10'3 M), theophylline (10'9 -10~4 M) and aminophylline (10'9 -10~4 M) each produced concentration- dependent relaxation. Mean maximal relaxant responses to isoprenaline, salbutamol, theophylline and aminophylline in the tracheal strips vvere 87.83 ± 2.89 %, 75.83 ± 2.04 %, 73.33 ±2.55% and 69.83 ± 2.36 %, respectively. Relaxant responses of these agents vvere significantly inhibited by K+ channel blockers, TEA (W 4 M) and glibenclamide (W 6 M). The inhibitory ef­ fects of K+ channel blockers on teophylline- and aminophylllne-induced relaxations vvere lovver than those of isop­ renaline and salbutamol. The rank order of potency of these compounds was isoprenaline > aminophylline > te­ ophylline > salbutamol and K+ channel blockers caused a displacement to the right of the dose response curves to these agents. Results indicate that the K^ channels play an important role in the relaxant effects of B-adrenoceptor agonists me­ an vvhile their role in the teophylline- and aminophylline- induced relaxation is less.