Human cystic fibrosis airway epithelia have reduced Cl ^- conductance but not increased Na ⁺ conductance

Loss of cystic fibrosis transmembrane conductance regulator (CFTR) anion channel function causes cystic fibrosis (CF) lung disease. CFTR is expressed in airway epithelia, but how CF alters electrolyte transport across airway epithelia has remained uncertain. Recent studies of a porcine model showed that in vivo, excised, and cultured CFTR ^-/- and CFTR ^{ΔF508/ΔF508} airway epithelia lacked anion conductance, and they did not hyperabsorb Na ⁺. Therefore, we asked whether Cl ^- and Na ⁺ conductances were altered in human CF airway epithelia. We studied differentiated primary cultures of tracheal/bronchial epithelia and found that transepithelial conductance (Gt) under basal conditions and the cAMP-stimulated increase in Gt were markedly attenuated in CF epithelia compared with non-CF epithelia. These data reflect loss of the CFTR anion conductance. In CF and non-CF epithelia, the Na ⁺ channel inhibitor amiloride produced similar reductions in Gt and Na ⁺ absorption, indicating that Na ⁺ conductance in CF epithelia did not exceed that in non-CF epithelia. Consistent with previous reports, adding amiloride caused greater reductions in transepithelial voltage and short-circuit current in CF epithelia than in non-CF epithelia; these changes are attributed to loss of a Cl ^- conductance. These results indicate that Na ⁺ conductance was not increased in these cultured CF tracheal/bronchial epithelia and point to loss of anion transport as key to airway epithelial dysfunction in CF.