Bioelectric properties and ion transport of excised rabbit trachea

Bioelectric properties and 22Na+ and 36Cl- isotopic flows across rabbit trachea, an airway epithelium without submucosal glands, were measured in vitro. One hundred twenty-two excised tracheas exhibited a mean transepithelial electric potential difference (PD) of 12 mV (lumen negative), a conductance (G) of 8.5 mS · cm-2, and a short-circuit current (I(sc)) of 90 μA · cm-2. G remained stable for more than 3 hr, but I(sc) and PD fell slowly (10%/h). G was inversely correlated with PD, but I(sc) and G were not correlated. Na+ was absorbed under both open-circuit (1.7 μeq · cm-2 · h-1) and short-circuit (2.2 μeq · cm-2 · h-1) conditions. Net Na+ transport accounted for 70% of I(sc) of the short-circuited trachea. Net Cl- flow in the absorptive direction approximated that of Na+ under open-circuit conditions (1.6 μeq · cm-2 · h-1). Under short-circuit conditions the small net flow of Cl- in the direction of secretion (0.4 μeq · cm-2 · h-1) was not significant. Both unidirectional Cl- fluxes were correlated with G; [14C]mannitol permeability and Na+ flows were weakly or not correlated with G. We found no evidence of net HCO3- or proton transport. Acetylcholine (10-4 M), phenylephrine (10-5 M), or isoproterenol (10-5 M) induced no change in bioelectric properties or ion flows. We conclude that the rabbit trachea is primarily a Na+ absorbing epithelium. The absence of a correlation between mannitol permeability and G suggests that much of the Cl- conductance is transcellular. Whereas insensitivity of rabbit trachea to cholinergic and α-adrenergic agents is compatible with the absence of glands, the lack of response to β-adrenergic agonists demotes a species difference (compared with canine trachea) in airway-surface epithelial cell function.