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

Abstract

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.chloride secretion | epithelial Na + channels

Relationships among CFTR expression, HCO 3 − secretion, and host defense may inform gene- and cell-based cystic fibrosis therapies

“…2F). These results are consistent with an effect of the Cl − conductance on ΔIsc (amiloride) , rather than changes in ENaC activity (42,43). Those data and that conclusion predicted that removing Cl − would eliminate the relationship between percentage of WT cells and ΔIsc (amiloride).…”

“…In porcine and human epithelia, apical amiloride produces a greater change in Isc in CF than non-CF because of the lack of a Cl − conductance (42,43). Previous studies used gene transfer vectors to overexpress CFTR in human CF epithelia and measured basal transepithelial electrical properties or the amiloride-induced reduction in Isc [ΔIsc (amiloride) ].…”

SYVN1, NEDD8, and FBXO2 Proteins Regulate ΔF508 Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Ubiquitin-mediated Proteasomal Degradation

“…Electrophysiology Studies-Transepithelial Cl Ϫ current measurements were made in Ussing chambers Ն2 weeks postseeding as reported (66). Briefly, primary air-liquid interface cultures of airway epithelia or polarized CFBE cultures were mounted in Ussing chambers (EasyMount P2300 chamber system, Physiologic Instruments, San Diego, CA), voltageclamped (model VCCMC8-4S, Physiologic Instruments), and connected to a computerized data acquisition system (Acquire & Analyze 2.3.181, Physiologic Instruments) to record short circuit currents and transepithelial resistance.…”

Status of Fluid and Electrolyte Absorption in Cystic Fibrosis

“…Furthermore, recent studies involving human airway epithelia (Itani et al 2011), the CFTR 2/2 , and CFTR DF508/DF508 (Chen et al 2010;Ostedgaard et al 2011) have shown reduced Cl 2 but not Na þ conductance in CF airways. Furthermore, a recent study on the relationship between airway epithelial Cl 2 secretion and Na þ absorption balance has led to the conclusion that hCFTR overexpression increases basal secretion but does not regulate Na þ transport in wildtype mice (Grubb et al 2012).…”