Evaluation of secretory and transport processes which determine the composition of airway surface liquid

The average thickness and distribution of airway surface liquid (ASL) on the luminal surface of peripheral airways were measured in normal guinea pig lungs frozen at functional residual capacity (FRC) and total lung capacity (TLC). Tissue blocks containing cross sections of airways of internal perimeter 0.188–3.342 mm were cut from frozen lungs and imaged by low-temperature scanning electron microscopy (LTSEM). Measurements made from LTSEM images were found to be independent of freezing rate by comparison of measurements at rapid and slow freezing rates. At both lung volumes, the ASL was not uniformly distributed in either the circumferential or longitudinal direction; there were regions of ASL where its thickness was < 0.1 micron, whereas in other regions ASL collected in pools. Discernible liquid on the surfaces of airways frozen at FRC followed the contours of epithelial cells and collected in pockets formed by neighboring cells, a geometry consistent with a low value of surface tension at the air-liquid interface. At TLC airway liquid collected to cover epithelial cells and to form a liquid meniscus, a geometry consistent with a higher value of surface tension. The average ASL thickness (h) was approximately proportional to the square root of airway internal perimeter, regardless of lung volume. For airways of internal perimeter 250 and 1,800 microns, h was 0.9 and 1.8 microns at FRC and 1.7 and 3.7 microns at TLC, respectively. For a given airway internal perimeter, h was 1.99 times thicker at TLC than at FRC; the difference was statistically significant (P < 0.01; 95% confidence interval 1.29–3.08).(ABSTRACT TRUNCATED AT 250 WORDS)

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SPLUNC1 degradation by the cystic fibrosis mucosal environment drives airway surface liquid dehydration

European Respiratory Journal ◽

10.1183/13993003.00668-2018 ◽

2018 ◽

Vol 52 (4) ◽

pp. 1800668 ◽

Cited By ~ 10

Author(s):

Megan J. Webster ◽

Boris Reidel ◽

Chong D. Tan ◽

Arunava Ghosh ◽

Neil E. Alexis ◽

...

Keyword(s):

Cystic Fibrosis ◽

Airway Surface Liquid ◽

The Novel ◽

Pulmonary Tissue ◽

Tissue Samples ◽

Protein Levels ◽

Surface Liquid ◽

Protease Degradation ◽

Mucosal Secretions ◽

Cystic Fibrosis Transmembrane

The multi-organ disease cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane regulator gene (CFTR) that lead to diminished transepithelial anion transport. CF lungs are characterised by airway surface liquid (ASL) dehydration, chronic infection/inflammation and neutrophilia. Dysfunctional CFTR may upregulate the epithelial Na+ channel (ENaC), further exacerbating dehydration. We previously demonstrated that short palate lung and nasal epithelial clone 1 (SPLUNC1) negatively regulates ENaC in normal airway epithelia.Here, we used pulmonary tissue samples, sputum and human bronchial epithelial cells (HBECs) to determine whether SPLUNC1 could regulate ENaC in a CF-like environment.We found reduced endogenous SPLUNC1 in CF secretions, and rapid degradation of recombinant SPLUNC1 (rSPLUNC1) by CF secretions. Normal sputum, containing SPLUNC1 and SPLUNC1-derived peptides, inhibited ENaC in both normal and CF HBECs. Conversely, CF sputum activated ENaC, and rSPLUNC1 could not reverse this phenomenon. Additionally, we observed upregulation of ENaC protein levels in human CF bronchi. Unlike SPLUNC1, the novel SPLUNC1-derived peptide SPX-101 resisted protease degradation, bound apically to HBECs, inhibited ENaC and prevented ASL dehydration following extended pre-incubation with CF sputum.Our data indicate that CF mucosal secretions drive ASL hyperabsorption and that protease-resistant peptides, e.g. SPX-101, can reverse this effect to rehydrate CF ASL.

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Control of pH of airway surface liquid of the ferret trachea in vitro

Journal of Applied Physiology ◽

10.1152/jappl.1990.68.1.135 ◽

1990 ◽

Vol 68 (1) ◽

pp. 135-140 ◽

Cited By ~ 36

Author(s):

H. Kyle ◽

J. P. Ward ◽

J. G. Widdicombe

Keyword(s):

Interstitial Fluid ◽

Ex Situ ◽

Co2 Production ◽

Limiting Factor ◽

Organ Bath ◽

Airway Surface Liquid ◽

Tracheal Lumen ◽

Surface Liquid ◽

External Ph

We measured the pH of airway surface liquid (ASL) secreted by the ferret trachea in vitro by using a catheter-tipped pH electrode implanted in a collecting cannula close to the airway epithelium. Mucus secretion was promoted by methacholine (0.02 mmol/l) in the organ bath. The pH of the ASL was 6.85 +/- 0.03 (SE) compared with a bath value of 7.39 +/- 0.01, when the bath was bubbled with 5.65% CO2. Changing the bath CO2 from 0 to 20.93% CO2 altered the bath pH from 8.06 to 6.96, but the ASL pH only varied from 6.92 to 6.85. This homeostasis of ASL pH was not the result of the buffering powers of the ASL, because ex situ buffer curves for secreted ASL were similar to those for Krebs-Henseleit solution. Changing the luminal CO2 content by blowing gases through the trachea changed ASL pH by values similar to that ex situ. However, when external organ bath CO2 was changed, the luminal CO2 changes were proportionately far smaller. Measurement of rates of diffusion of CO2 across the tracheal wall indicated that this was not a limiting factor in the results. Similarly, measurement of metabolic rate CO2 production in the tracheal lumen indicated that this did not significantly affect the results. We conclude that the pH of ASL is significantly on the acid side of the pH or interstitial fluid and plasma and that it is maintained relatively constant despite large changes in external pH.

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Hypertonic Saline in Treatment of Pulmonary Disease in Cystic Fibrosis

The Scientific World JOURNAL ◽

10.1100/2012/465230 ◽

2012 ◽

Vol 2012 ◽

pp. 1-11 ◽

Cited By ~ 43

Author(s):

Emer P. Reeves ◽

Kevin Molloy ◽

Kerstin Pohl ◽

Noel G. McElvaney

Keyword(s):

Cystic Fibrosis ◽

Hypertonic Saline ◽

Mucociliary Clearance ◽

Inflammatory Cells ◽

Liquid Volume ◽

Airway Surface Liquid ◽

Beneficial Effects ◽

Therapeutic Benefits ◽

Surface Liquid ◽

Subsequent Failure

The pathogenesis of lung disease in cystic fibrosis is characterised by decreased airway surface liquid volume and subsequent failure of normal mucociliary clearance. Mucus within the cystic fibrosis airways is enriched in negatively charged matrices composed of DNA released from colonizing bacteria or inflammatory cells, as well as F-actin and elevated concentrations of anionic glycosaminoglycans. Therapies acting against airway mucus in cystic fibrosis include aerosolized hypertonic saline. It has been shown that hypertonic saline possesses mucolytic properties and aids mucociliary clearance by restoring the liquid layer lining the airways. However, recent clinical and bench-top studies are beginning to broaden our view on the beneficial effects of hypertonic saline, which now extend to include anti-infective as well as anti-inflammatory properties. This review aims to discuss the described therapeutic benefits of hypertonic saline and specifically to identify novel models of hypertonic saline action independent of airway hydration.

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