Fluid transport across the canine tracheal epithelium

We measured the rate of fluid movement across the tracheal epithelium of the dog by an electrical method, modified from that originally described by Wiedner (Rev. Sci. Instrum. 47: 775-6, 1976). These base-line volume flow (J(v) from the submucosa to the mucosa was 44 ± 23 nl·min^-1·cm^-2 (mean ± SE; n = 6). In only three of the tissues was the resting J(v) significantly greater than zero. Stimulation with 2 x 10^-3 M aminophylline (a drug that we have shown stimulates Cl secretion under short-circuit conditions) increased J(v) in all tissues to a mean of 137 ± 29 nl·min^-1·cm^-2 (P < 0.001). We also measured the unidirectional fluxes of Cl with the tissue at its spontaneous electrical potential. During the base-line period, the net flux of Cl was not significantly different from zero. During stimulation with aminophylline, Cl secretion increased to a mean of 1.44 ± 0.50 μeq·cm^-2·h^-1. Comparison of the stimulated values of J(v) and net Cl secretion suggest that fluid secretion by the trachea is isotonic during stimulation with aminophylline.