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

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Abstract
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.