Characterization of neural control and contractile function in airway smooth muscle of the ferret.

Several recent studies have characterized neuroanatomical and neurophysiological aspects of ferret airways, but regional differences in reactivity and cholinergic, adrenergic and non-adrenergic-non-cholinergic (NANC) neural responses have not been examined. The aim of this study was to characterize the contractile and relaxant response elicited by electrical field stimulation (EFS), and the contractions induced by cholinergic agonists in isolated ferret tracheal and bronchial preparations. EFS produced frequency-dependent contractions and relaxations. Contractions in both the trachea and bronchi were inhibited by atropine and potentiated by neostigmine. Tracheal relaxations were found to be entirely adrenergic, but bronchial relaxations were mediated by a combination of adrenergic and inhibitory NANC (i-NANC) innervations. Trachea and bronchi were more sensitive to methacholine (MCh) and carbachol than to acetylcholine (ACh); middle tracheal segments being more sensitive to ACh than distal segments, however, in the presence of neostigmine ACh potency was equal in both segments. The results suggest that regional differences exist in cholinergic responsiveness of ferret trachea and bronchi, resulting from differences in ACh degradation.