No abstract

Na⁺ and Cl^– 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⁺ absorption dominates transepithelial transport and the Na⁺ 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_SC), whereas in CF tissues the major part of the current is amiloride-sensitive. Na⁺ removal reduced I_SC to values close to zero. Several Cl^– channel blockers were used to identify the remaining tiny Na⁺-independent current. Under unstimulated, physiological conditions in the presence of Cl^– 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_SC. cAMP as well as ATP did not affect I_SC either in CF or in non-CF epithelia. Reduction of apical Cl^– increased I_SC and depolarized transepithelial potential; however, the observed increase was insensitive to DIDS, DPC and NPPB. From these data we conclude that Cl^– 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.

Nitric oxide (NO) has been reported to activate Cl- secretion via the cystic fibrosis transmembrane conductance regulator (CFTR) and inhibit epithelial Na+ absorption mediated by amiloride-sensitive epithelial Na+ channels (ENaC). These ion transport systems are defective in cystic fibrosis (CF): Cl- secretion by CFTR is impaired and Na+ absorption by ENaC is dramatically increased. By activating CFTR and depressing ENaC, NO is a potentially beneficial therapeutic agent for ion transport defects in human CF respiratory epithelia. To assess the effects of NO on human respiratory epithelial cells, the NO donors sodium nitroprusside (SNP) and spermine NONOate were applied to primary cultured nasal cells, surgically obtained from non-CF and CF patients. Measurements of transepithelial short-circuit current (ISC) showed that NO has no inhibitory potency against amiloride-sensitive nasal ENaC (nENaC) or amiloride-insensitive Na+-absorbing mechanisms in non-CF and CF epithelia. Furthermore, NO had no stimulatory effect on Cl- secretion by CFTR or any other Cl- conductance pathway in either tissue. Although NO elevated the intracellular Ca2+ concentration, we did not detect any activation of Ca2+-dependent Cl- channels. These results demonstrate that NO has no beneficial effect on CF epithelial cells of the upper airways.