Printed in U.S.A. Non-Neurogenic Electrically Evoked Relaxation in Canine Airway Muscle Involves Action of Free Radicals on K

Cyclopiazonic acid (selective blocker of the internal Ca pump) evoked tonic contraction in canine bronchial smooth muscle (BSM) and tracheal smooth muscle. This contraction was biphasic, including an initial component that was relatively insensitive to blockade of Ca influx (e.g., removal of external Ca nifedipine; hyperpolarization using lemakalim) followed by a component that was sensitive to all such interventions. In BSM, but not in tracheal smooth muscle, electrical field stim-ulation (EFS) evoked relaxations that were not affected by interventions designed to prevent release of autacoids from nerve endings or the epithelium, Na/Ca exchange or Ca -ATPase activities (internal or plasmalemmal). EFS evoked little or no relaxant response in carbachol-precontracted BSM in the presence of propranolol. After Ca was replaced with Sr