Journal
JOURNAL OF GENERAL PHYSIOLOGY
Volume 117, Issue 6, Pages 573-582Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1085/jgp.117.6.573
Keywords
water permeability; trachea; airway surface liquid; ventilator; fluorescence microscopy
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Funding
- NHLBI NIH HHS [HL59198, HL60288, HL51854, R01 HL051854, R01 HL059198] Funding Source: Medline
- NIDDK NIH HHS [R37 DK035124, R01 DK035124, DK43840, DK35124] Funding Source: Medline
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Several aquaporin-type water channels are expressed in mammalian airways and lung: AQP1 in microvascular endothelia, AQP3 in upper airway epithelia, AQP4 in upper and lower airway epithelia, and AQP5 in alveolar epithelia. Novel quantitative methods were developed to compare airway fluid transport-related functions in wild-type mice and knockout mice deficient in these aquaporins. Lower airway humidification, measured from the moisture content of expired air during mechanical ventilation with dry air through a tracheotomy, was 54-56% efficient in wild-type mice, and reduced by only 3-4% in AQP1/AQP5 or AQP3/AQP4 double knockout mice. Upper airway humidification, measured from the moisture gained by dry air passed through the upper airways in mice breathing through a tracheotomy, decreased from 91 to 50% with increasing ventilation from 20 to 220 ml/min, and reduced by 3-5% in AQP3/AQP4 knockout mice. The depth and salt concentration of the airway surface liquid in trachea was measured in vivo using fluorescent probes and confocal and ratio imaging microscopy Airway surface liquid depth was 45 +/- 5 mum and [Na+] was 115 +/- 4 mM in wild-type mice, and not significantly different in AQP3/AQP4 knockout mice. Osmotic water permeability in upper airways, measured by an in vivo instillation/sample method, was reduced by similar to 40% by AQP3/AQP4 deletion. In doing these measurements, we discovered a novel amiloride-sensitive isosmolar fluid absorption process in upper airways (13% in 5 min) that was not affected by aquaporin deletion. These results establish the fluid transporting properties of mouse airways, and indicate that aquaporins play at most a minor role in airway humidification, ASL hydration, and isosmolar fluid absorption.
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