Minor Role of Cl– Secretion in Non-Cystic Fibrosis and Cystic Fibrosis Human Nasal Epithelium
Na<sup>+</sup> and Cl<sup>–</sup> currents were studied in primary cultures of human nasal epithelium derived from non-cystic fibrosis (non-CF) and cystic fibrosis (CF) patients. We found that Na<sup>+</sup> absorption dominates transepithelial transport and the Na<sup>+</sup> current contains an amiloride-sensitive and amiloride-insensitive component. In non-CF tissue both components contribute about equally to the entire short-circuit current (I<sub>SC</sub>), whereas in CF tissues the major part of the current is amiloride-sensitive. Na<sup>+</sup> removal reduced I<sub>SC</sub> to values close to zero. Several Cl<sup>–</sup> channel blockers were used to identify the remaining tiny Na<sup>+</sup>-independent current. Under unstimulated, physiological conditions in the presence of Cl<sup>–</sup> on both sides and amiloride on the apical side of the epithelium diphenylamine-2-carboxic acid (DPC), 4,4′-diisothiocyanatostilbene-2,2′- disulfonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) failed to induce clearcut inhibition of I<sub>SC</sub>. cAMP as well as ATP did not affect I<sub>SC</sub> either in CF or in non-CF epithelia. Reduction of apical Cl<sup>–</sup> increased I<sub>SC</sub> and depolarized transepithelial potential; however, the observed increase was insensitive to DIDS, DPC and NPPB. From these data we conclude that Cl<sup>–</sup> conductances in primary cultures of human nasal epithelium derived from CF patients as well as from non-CF patients are present only in low numbers or do not contribute significantly to transepithelial ion transport.