Regional effects of autonomic agents on ion transport across excised canine airways

The effects of cholinergic and adrenergic agonists and antagonists on ion transport and bioelectric properties of excised canine trachea, main-stem bronchi, and subsegmental bronchi were studied. Acetylcholine (ACh) induced in bronchi a dose-dependent reduction in net Na+ absorption, maximal (30%) at 10(-5) M, that reflected a raised Na+ flux from submucosa to mucosa. Because conductance (G) did not change we speculate that the increased flow in the "passive" direction represents the induction of bidirectional Na+ transport. ACh (10(-4) M) increased net Cl- secretion in the trachea and main-stem bronchi and reduced Na+ absorption. ACh effects in all regions were blocked by atropine. In bronchi, alpha- or beta-adrenergic agonists, 10(-5) and 10(-3) M, raised G and unidirectional Cl- fluxes without affecting short-circuit current (Isc) or inducing Cl- secretion. Small reductions in Na+ absorption were noted at 10(-5) M. In contrast, adrenergic agents increased Isc and Cl- secretion in the trachea. We concluded that neurohumoral agonists induce different patterns of effects on ion transport in central compared with more distal airways. Agonists of both classes induced Cl- secretion in the trachea and reduced but did not abolish net NaCl absorption in the bronchi.