Abstract
In guinea pig ileal circular muscle, electrical stimulations by a train of 10-100 pulses (0.05-msec duration, 10 Hz) produced tetrodotoxin-sensitive "off" contractions that were initiated upon the termination of stimulations. Atropine at 10-6M did not inhibit the "off" contractions. FK224 at 10-5M, a dual antagonist for NK1 and NK2-receptors, but not 10-7M CP-96, 345, an antagonist for NK1-receptors, almost abolished the "off" contractions in the presence of atropine. These results suggest that the neurogenic "off" contraction was mediated mainly by NK2-receptors in the circular muscle of guinea pig ileum.
