Characteristics of sodium transport by excised rabbit trachea

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Abstract
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 (Isc), 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 Isc and Na+ absorption but increased G and unidirectional Cl- flows. Luminal amiloride (10(-3) M) abolished net Na+ absorption but reduced Isc by only 40%. Residual Isc 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 luminal Na+ by choline induced effects similar to those of amiloride. Residual Isc was not reduced by mucosal indomethacin (10(-6) M). Replacement of luminal Cl- by gluconate raised transepithelial PD fourfold, raised Isc 50%, decreased G 60%, and abolished net Na+ absorption by decreasing Jm leads to s and increasing Js leads to m. Luminal amphotericin B affected bioelectric properties and ion flows minimally, whereas monensin (10(-4) M) decreased Isc and net Na+ transport. Antidiuretic hormone (ADH, 1 U/ml) or aldosterone (10(-6) M) did not affect in Isc 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 luminal 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.