Regional differences in bioelectric properties and ion flow in excised canine airways

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Abstract
Absorption of airway liquid, as it moves from the large surface area of distal airways to more central airway surfaces, is considered to be essential for regulation of the depth of airway liquid. The short-circuited excised canine trachea, however, secretes Cl- and absorbs a lesser amount of Na+. We compared bioelectric properties and unidirectional ion flows across epithelia excised from trachea and mainstem and 4th- to 6th-generation bronchi. Compared with trachea, 4th- to 6th-generation bronchi exhibited a lower potential difference (8.9 compared with 35 mV) and higher direct-current conductance (6.9 compared with 2.1 mS . cm-2). Corresponding values for main-stem bronchus were intermediate. Under short-circuit conditions, the trachea secreted Cl- (1.75 mueq . cm-2 . h-1) and absorbed Na+ (1.15 mueq . cm-2 . h-1). K+ fluxes were symmetric. Main-stem bronchus exhibited a similar pattern of ion flow. Subsegmental bronchi absorbed 2.0 mueq Na+ . cm-2 . h-1 and secreted 0.04 mueq K+ . cm-2 . h-1, but net Cl- transport was absent. Under open circuit, Na+ absorption persisted in all regions, but net Cl- secretion disappeared in the trachea and main-stem bronchi. Na+ absorption was uniformly abolished by addition of ouabain (3 x 10(-5) M) to the submucosal bath. We conclude that NaCl absorption dominates resting ion translocation in canine bronchi and that liquid absorption probably occurs at these sites in vivo.