Characteristics of sodium transport by excised rabbit trachea

We studied factors that might be expected to influence Na+ absorption, the major active ion transport by excised rabbit trachea. Transepithelial electric potential difference (PD), short-circuit current (I(sc)), conductance (G), and unidirectional 22Na+ and 36Cl- flows were measured before and during exposure to a drug or after a change in bathing solution composition. Ouabain (3 x 10-4 M) in the submucosal bath abolished I(sc) and Na+ absorption but increased G and unidirectional Cl- flows. Luminal amiloride (10-3 M) abolished net Na+ absorption but reduced I(sc) by only 40%. Residual I(sc) was accounted for by induction of net Cl- secretion, which resulted from a reduction in mucosal (m)-to-submucosal (s) Cl- flux (J). Replacement of liminal Na+ by choline induced effects similar to those of amiloride. Residual I(sc) was not reduced by mucosal indomethacin (10-6 M). Replacement of luminal Cl- by gluconate raised transepithelial PD fourfold, raised I(sc) 50%, decreased G 60%, and abolished net Na+ absorption by decreasing J(m→s) and increasing J(m→s). Luminal amphotericin B affected bioelectric properties and ion flows minimally, whereas monensin (10-4 M) decreased I(sc) and net Na+ transport. Antidiuretic hormone (ADH, 1 U/ml) or aldosterone (10-6 M) did not affect in I(sc) or PD after exposure up to 6 h. We conclude that (1) Na+ absorption across the rabbit trachea is ouabain sensitive, (2) the entry step for Na+ across the luminal membrane is amiloride sensitive, (3) Cl- secretion induced by amiloride or luminal Na+ replacement probably reflects a more favorable chemical gradient for basolateral coupled NaCl entry and/or electrical gradient for Cl- efflux across the liminal membrane, (4) the coupling of Na+ entry to the presence of Cl- in the mucosal solution is probably an electrical rather than a chemical cotransport process, and (5) the tracheal epithelium of the rabbit is not a target for aldosterone and ADH.