The effects of sodium substitution and ouabain on ion transport by dog tracheal epithelium.

Using ouabain and sodium removal, we studied the mechanism of chloride transport by dog tracheal epithelium. When applied to the submucosal side of the tissue, 2 x 10(-4) M ouabain decreased the short-circuit current, the net chloride flux toward the lumen, and the net sodium flux toward the submucosa to zero after 30 min. Applied to the luminal side, ouabain had little effect. Potassium-free medium, like ouabain, decreased the short-circuit current when present in the submucosal bath; on the luminal side ti produced a slight increase (7.0 +/- 1.5 per cent; n = 6) in short-circuit current. Replacement of sodium in the submucosal bathing medium by choline led to a decrease in net chloride flux of 84 per cent. Sodium replacement in the luminal bath produced no change in net chloride flux. It is proposed that chloride secretion by this tissue depends on active basolateral sodium pumps, and that a component of chloride entry into the transporting cells from the submucosal medium may be sodium-linked.