Minor Role of Cl^– Secretion in Non-Cystic Fibrosis and Cystic Fibrosis Human Nasal Epithelium

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 has no beneficial effects on ion transport defects in cystic fibrosis human nasal epithelium

“…It was reported recently [22] that this is not the case for HNE. We used the NO donors SNP and spermine NONOate to boost the tiny Cl -secretion via CFTR or other Cl -channels in HNE, as has been shown for other cells [9].…”

“…Thus, it is possible that nENaC differs in structure or regulation from NO-sensitive ENaCs. On the other hand, nENaC is not sensitive to cGMP while most ENaC are responsive to that compound [22]. Therefore, it is possible that non-CF and CF HNE lack the necessary signal transduction pathways that are the prerequisite for NO's interaction with nENaC, or the nENaC molecule itself is not sensitive to these signal transduction mechanisms.…”

“…Our method of culturing human nasal epithelium was similar to that outlined recently [22]. Briefly, tissues were treated with 0.1% pronase (type XIV protease) in Ca 2+ -free Jokliks MEM medium supplemented with penicillin (100 U/ml), streptomycin (100 µg/ml) and gentamycin (50 µg/ml) for 24 h rotating at 4°C.…”

Sildenafil Acts as Potentiator and Corrector of CFTR but Might be not Suitable for the Treatment of CF Lung Disease

“…Moreover, sildenafil is reported to inhibit Na + absorption through epithelial Na + channels (ENaC) [29]. This could be of therapeutic benefit since CF patients suffer from Na + hyperabsorption in the respiratory tract leading to massive loss of water in the airway surface liquid and increased viscosity of the mucus [51]. Furthermore, there are attempts underway to investigate chemical modifications of sildenafil to enhance the biochemical potency and selectivity of the compound, thereby offering the possibility to apply the newly developed drug in lower concentrations with fewer putative adverse effects [52].…”

Differential roles of NHERF1, NHERF2, and PDZK1 in regulating CFTR-mediated intestinal anion secretion in mice

“…CFTR functional activity in vivo is assessed by nasal potential difference measurements (44), but these measurements are confounded by the very active Na + conductance in these epithelia (45)(46)(47). In the duodenum, CFTR expression is particularly high within the gastrointestinal tract (48), and murine duodenal HCO 3 -secretion and its agonist-mediated regulation are virtually completely dependent on CFTR expression (33)(34)(35)(36).…”