Liquid transport properties of porcine tracheal epithelium

Because of its possible importance to the etiology of cystic fibrosis lung disease, the ion and water transport properties of tracheal epithelium were studied. Net liquid flux (J(V)) across porcine tracheal epithelium was measured in vitro using blue dextran as a volume probe. Luminal instillation of isosmotic sucrose solution (280 mM) induced a small net secretion of liquid (7.0 +/-1.7 nl.cm(-2).s(-1)), whereas luminal hyposmotic sucrose solutions (220 or 100 mM) induced substantial and significant (p < 0.05) liquid absorption (34.5<plus/minus>12 and 38.1 +/-7.3 nl.cm(-2).s(-1), respectively). When the luminal solution was normal (isosmotic) Krebs buffer, liquid was absorbed at 10.2 +/-1.1 nl.cm(-2).s(-1). Absorptive JV was abolished by 100 mM amiloride in the luminal solution and significantly reduced when the luminal solution was Na+-free Krebs solution. Absorptive JV was not significantly affected by 300 muM 5-nitro-2-(3-phenylpropylamino) benzoate or 100 muM diphenylamine-2-carboxylic acid, both cystic fibrosis transmembrane conductance regulator protein (CFTR) inhibitors, in the instillate but was significantly reduced by 60% when the luminal solution was Cl--free Krebs solution. We conclude that water freely permeates porcine tracheal epithelium and that absorption of liquid is normally driven by active transcellular Na+ transport and does not require the CFTR.