Oxidant injury alters barrier function of ferret tracheal epithelium

To understand the influence of oxidant stress on the barrier function of airway epithelium, we conducted studies to determine the effects of chemically generated reactive oxygen species on permeability, permselectivity, and active ion transport of ferret trachea. We examined the consequences of oxidant injury using ferret trachea mounted in Ussing-type chambers and bathed with a modified Krebs-Henseleit solution containing mannitol and xanthine. We added xanthine oxidase to the luminal bathing solution, which reacted with the xanthine to generate reactive oxygen species. Tissue electrical conductance and short-circuit current were significantly increased after the addition of xanthine oxidase. Simultaneous measurement of mannitol flux (as a marker of paracellular conductance) and the backflux of chloride (lumen to submucosa) demonstrated a significant oxidant-induced increase in mannitol flux and backflux of chloride. Mannitol flux and the backflux of sodium (submucosa to lumen) also increased after oxidant stress. Comparison of the diffusion of sodium relative to the diffusion of chloride in relation to predicted diffusion in free solution indicated that the paracellular pathway was cation selective after oxidant stress. Active ion transport, as reflected by the short-circuit current, was significantly increased transiently after oxidant stress. Studies with furosemide, amiloride, and diphenylamine-2-carboxylate are suggestive that oxidant stress transiently stimulates the Na-K-ATPase. These studies demonstrated that exposure to reactive oxygen species significantly altered the permeability of the tracheal epithelium as well as active ion transport.