Abnormal surface liquid pH regulation by cultured cystic fibrosis bronchial epithelium

Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, NC 27599-7248, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 01/2004; 100(26):16083-8. DOI: 10.1073/pnas.2634339100
Source: PubMed


Cystic fibrosis (CF) transmembrane conductance regulator (CFTR)-dependent airway epithelial bicarbonate transport is hypothesized to participate in airway surface liquid pH regulation and contribute to lung defense. We measured pH and ionic composition in apical surface liquid (ASL) on polarized normal (NL) and CF primary bronchial epithelial cell cultures under basal conditions, after cAMP stimulation, and after challenge with luminal acid loads. Under basal conditions, CF epithelia acidified ASL more rapidly than NL epithelia. Two ASL pH regulatory paths that contributed to basal pH were identified in the apical membrane of airway epithelia, and their activities were measured. We detected a ouabain-sensitive (nongastric) H+,K+-ATPase that acidified ASL, but its activity was not different in NL and CF cultures. We also detected the following evidence for a CFTR-dependent HCO3- secretory pathway that was defective in CF: (i). ASL [HCO3-] was higher in NL than CF ASL; (ii). activating CFTR with forskolin/3-isobutyl-1-methylxanthine alkalinized NL ASL but acidified CF ASL; and (iii). NL airway epithelia more rapidly and effectively alkalinized ASL in response to a luminal acid challenge than CF epithelia. We conclude that cultured human CF bronchial epithelial pHASL is abnormally regulated under basal conditions because of absent CFTR-dependent HCO3- secretion and that this defect can lead to an impaired capacity to respond to airway conditions associated with acidification of ASL.

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Available from: Larry G. Johnson, Feb 12, 2015
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    • "Efficient anion secretion in the airways is paramount to maintain ASL hydration and pH, as well as efficient mucus secretion and expansion (Garcia et al. 2009;Chen et al. 2010;Gustafsson et al. 2012;Ridley et al. 2014). Loss of functional expression of CFTR at the apical membrane of HCO 3 − -secreting epithelia underlies the hereditary disease cystic fibrosis (CF) and airways dehydration and impaired ASL alkalinisation have been reported in CF airways (Coakley et al. 2003;Song et al. 2006;Boucher, 2007) consistent with a key role for CFTR "
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    ABSTRACT: Hypercapnia is clinically defined as an arterial blood partial pressure of CO2 of above 40 mmHg and is a feature of chronic lung disease. In previous studies we have demonstrated that hypercapnia modulates agonist-stimulated cAMP levels through effects on transmembrane adenylyl cyclase activity. In the airways, cAMP is known to regulate cystic fibrosis transmembrane conductance regulator (CFTR)-mediated anion and fluid secretion, which contributes to airway surface liquid homeostasis. The aim of the current work was to investigate if hypercapnia could modulate cAMP-regulated ion and fluid transport in human airway epithelial cells. We found that acute exposure to hypercapnia significantly reduced forskolin-stimulated elevations in intracellular cAMP as well as both adenosine and forskolin-stimulated increases in CFTR-dependent transepithelial short-circuit current, in polarised cultures of Calu-3 human airway cells. This CO2 -induced reduction in anion secretion was not due to a decrease in HCO3 (-) transport given that neither a change in CFTR-dependent HCO3 (-) efflux, nor Na(+) /HCO3 (-) cotransporter-dependent HCO3 (-) influx were CO2 -sensitive. Hypercapnia also reduced the volume of forskolin-stimulated fluid secretion over 24 h, yet had no effect on the HCO3 (-) content of the secreted fluid. Our data reveal that hypercapnia reduces CFTR-dependent, electrogenic Cl(-) and fluid secretion, but not CFTR-dependent HCO3 (-) secretion, which highlights a differential sensitivity of Cl(-) and HCO3 (-) transporters to raised CO2 in Calu-3 cells. Hypercapnia also reduced forskolin-stimulated CFTR-dependent anion secretion in primary human airway epithelia. Based on current models of airways biology, a reduction in fluid secretion, associated with hypercapnia, would be predicted to have important consequences for airways hydration and the innate defence mechanisms of the lungs. This article is protected by copyright. All rights reserved.
    Full-text · Article · Nov 2015 · The Journal of Physiology
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    • "This protein pumps one cellular proton and one PCL K þ against their osmotic gradient, via the binding of ATP, and is localised to the apical membrane of lung epithelia (Coakley et al., 2003). The HKATPase pump provides basal proton secretion and K þ absorption across the apical membrane in airway epithelia (Fischer, 2012; Fischer et al., 2002; Poulsen and Machen, 1996; Smith and Welsh, 1993). "
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    ABSTRACT: The genetic disease cystic fibrosis (CF) is a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and results in viscous mucus and impaired mucociliary clearance leading to chronic recurring pulmonary infections. Although extensive experimental research has been conducted over the last few decades, CF lung pathophysiology remains controversial. There are two competing explanations for the observed depletion of periciliary liquid (PCL) in CF lungs. The low volume hypothesis assumes fluid hyperabsorption through surface epithelia due to an over-active Epithelial Na(+) Channel (ENaC), and the low secretion hypothesis assumes inspissated mucins secreted from glands due to lack of serous fluid secreted from gland acini. We present a spatial mathematical model that reflects in vivo fluid recycling via submucosal gland (SMG) secretion, and absorption through surface epithelia. We then test the model in CF conditions by increasing ENaC open probability and decreasing SMG flux while simultaneously reducing CFTR open probability. Increasing ENaC activity only results in increased fluid absorption across surface epithelia, as seen in in vitro experiments. However, combining potential CF mechanisms results in markedly less fluid absorbed while providing the largest reduction in PCL volume, suggesting that a compromise in gland fluid secretion dominates over increased ENaC activity to decrease the amount of fluid transported transcellularly in CF lungs in vivo. Model results also indicate that a spatial model is necessary for an accurate calculation of total fluid transport, as the effects of spatial gradients can be severe, particularly in close proximity to the SMGs. Copyright © 2015. Published by Elsevier Ltd.
    Full-text · Article · Jul 2015 · Journal of Theoretical Biology
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    • "First, loss of CFTR impairs HCO 3 – secretion across airway epithelia cultured from humans [4] [5] and pigs with a disrupted CFTR gene [6]; CF pigs spontaneously develop lung disease that mimics human CF [7]. Second, loss of CFTR reduces the pH of airway surface liquid (ASL) in cultured human airway epithelia [5], of secretions from human submucosal glands studied ex vivo [8], and of ASL studied in vivo, ex vivo, and in epithelial cultures from CF pigs [9]. Third, a reduced pH decreases the activity of antimicrobials in ASL in vivo and in vitro, thereby "
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    ABSTRACT: Disrupted HCO3(-) transport and reduced airway surface liquid (ASL) pH in cystic fibrosis (CF) may initiate airway disease. We hypothesized that ASL pH is reduced in neonates with CF. In neonates with and without CF, we measured pH of nasal ASL. We also measured nasal pH in older children and adults. In neonates with CF, nasal ASL (pH5.2±0.3) was more acidic than in non-CF neonates (pH6.4±0.2). In contrast, nasal pH of CF children and adults was similar to values measured in people without CF. At an age when infection, inflammation and airway wall remodeling are minimal, neonates with CF had an acidic nasal ASL compared to babies without CF. The CF:non-CF pH difference disappeared in older individuals, perhaps because secondary manifestations of disease increase ASL pH. These results aid understanding of CF pathogenesis and suggest opportunities for therapeutic intervention and monitoring of disease.
    Full-text · Article · Jan 2014 · Journal of cystic fibrosis: official journal of the European Cystic Fibrosis Society
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