Effect of electrical field stimulation on muscle strips from chicken crop

The effect of electrical field stimulation (EFS) on smooth muscle strips from the chicken crop was investigated. The EFS (5 Hz, 2 ms, 400 mA; 10 Hz, 2 ms, 400 mA; 5 Hz, 2 ms, 500 mA; 10 Hz, 2 ms, 500 mA) produced contractions in all preparations. Atropine (10(-5) mol l-1) diminished muscle contraction in response to EFS. Tetrodotoxin (5 X 10(-6) mol l-1) fully suppressed the contractile responses to EFS. A serotonin antagonist (methysergide, 10(-4) mol l-1) did not alter contractions elicited by EFS. Propranolol (10(-5) mol l-1) led to an increase of contractions induced by EFS. Noradrenaline (10(-6)-10(-4) mol l-1) reduced acetylcholine-induced (1.1 X 10(-6) mol l-1) contraction of the crop smooth muscle strips. Propranolol (10(-5) mol l-1) abolished noradrenaline-induced relaxation almost fully. Tetrodotoxin (5 X 10(-6) mol l-1) did not change the relaxing effect of noradrenaline. These results suggested that the responses of crop smooth muscle to EFS involve excitatory cholinergic and non-cholinergic (probably peptidergic) as well as inhibitory adrenergic nerves.