Abstract
That endothelin-1(ET-1) plays a mediator role in asthma is consistent with reports of ET-1-induced potentiation of cholinergic nerve-mediated contraction in airways from various animal species. This study examined the effect of ET-1 on cholinergic contractions in human isolated bronchus. Macroscopically nondiseased human bronchial tissue was obtained from 23 patients with respiratory tumours. An electrical field stimulation (EFS) frequency that produced one third of the contraction at 30 Hz (EFS30) was estimated. The effect of ET-1 on these EFS-evoked contractions was assessed. EFS-evoked contractions were frequency-dependent and abolished by either atropine or tetrodotoxin. Thus, EFS-induced contractions were mediated by acetylcholine from cholinergic nerves. ET-1 (3 nM) potentiated EFS-evoked contractions by 10+/-2% EFS30 (p<0.05) without any significant effect on contractions induced by exogenous acetylcholine. Neither the ET(A) receptor-selective antagonist BQ-123 (3 microM) nor the ET(B) receptor-selective antagonist BQ-788 (10 microM) alone significantly altered ET-1-induced potentiation of EFS-evoked contractions. However, in the combined presence of both BQ-123 and BQ-788, ET-1-induced potentiation of EFS-evoked contractions was abolished. Thus, prejunctional endothelinA and endothelinB receptors appear to mediate endothelin-1-induced potentiation of electrical field stimulation-evoked cholinergic contractions in human bronchus. This suggests another potentially important mechanism through which endothelin-1 could increase bronchial tone in asthma.
