Contractions and Acetyicholine Release in Rat Isolated Tracheal Smooth Muscle1

The aim of this study was to assess the influence of endothe-lin-1 (Er-i) on cholinergic nerve-mediated contractions in rat isolated tracheal smooth muscle by use of electrical-field stim-ulation (EFS) and rH]choline efflux studies. EFS (80 V, 0.5 ms, 0.1-30 Hz for 10 s) evoked transient, frequency-dependent contractions of isolated tracheal preparations. Contractions were abolished in the presence of atropine or tetrodotoxin, which suggests they were mediated by acetylcholine (ACh) release from cholinergic nerves. The ETB receptor-selective agonist sarafotoxin S6c (1 nM) augmented EFS (0.6-1 Hz)-induced contractions by 1 79%. These effects were significantly attenuated in the presence of the ETB receptor-selective antagonist N-cis-2,6-dimethylpiperidinocarbonyl-L-’y-methyl-leucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine (BQ