Lung fluid transport in aquaporin-5 knockout mice

Aquaporin-1 (AQP1) water channels are expressed widely in epithelia and capillary endothelia involved in fluid transport. To test whether AQP1 facilitates water movement from capillaries into the peritoneal cavity, osmotically induced water transport rates were compared in AQP1 knockout [(−/−)], heterozygous [(+/−)], and wild-type [(+/+)] mice. In (+/+) mice, RT-PCR showed detectable transcripts for AQP1, AQP3, AQP4, AQP7, and AQP8. Immunofluorescence showed AQP1 protein in capillary endothelia and mesangium near the peritoneal surface and AQP4 in adherent muscle plasmalemma. For measurement of water transport, 2 ml of saline containing 300 mM sucrose (600 mosM) were infused rapidly into the peritoneal cavity via a catheter. Serial fluid samples (50 μl) were withdrawn over 60 min, with albumin as a volume marker. The albumin dilution data showed significantly decreased initial volume influx in AQP1 (−/−) mice: 101 ± 8, 107 ± 5, and 42 ± 4 (SE) μl/min in (+/+), (+/−), and (−/−) mice, respectively [ n = 6–10, P < 0.001, (−/−) vs. others]. Volume influx for AQP4 knockout mice was 100 ± 8 μl/min. In the absence of an osmotic gradient,3H2O uptake [half time = 2.3 and 2.2 min in (+/+) and (−/−) mice, respectively], [14C]urea uptake [half time = 7.9 and 7.7 min in (+/+) and (−/−) mice, respectively], and spontaneous isosmolar fluid absorption from the peritoneal cavity [0.47 ± 0.05 and 0.46 ± 0.04 ml/h in (+/+) and (−/−) mice, respectively] were not affected by AQP1 deletion. Therefore, AQP1 provides a major route for osmotically driven water transport across the peritoneal barrier in peritoneal dialysis.

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Inhibition of CLC-2 chloride channel expression interrupts expansion of fetal lung cysts

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00113.2003 ◽

2004 ◽

Vol 286 (2) ◽

pp. L420-L426 ◽

Cited By ~ 12

Author(s):

Carol J. Blaisdell ◽

Marcelo M. Morales ◽

Ana Carolina Oliveira Andrade ◽

Penelope Bamford ◽

Michael Wasicko ◽

...

Keyword(s):

Chloride Channel ◽

Fluid Transport ◽

Fetal Lung ◽

Chloride Secretion ◽

Normal Lung ◽

Apical Surface ◽

Lung Cysts ◽

Lung Fluid ◽

Lung Morphogenesis ◽

Channel Expression

Normal lung morphogenesis is dependent on chloride-driven fluid transport. The molecular identity of essential fetal lung chloride channel(s) has not been elucidated. CLC-2 is a chloride channel, which is expressed on the apical surface of the developing respiratory epithelium. CLC-2-like pH-dependent chloride secretion exists in fetal airway cells. We used a 14-day fetal rat lung submersion culture model to examine the role of CLC-2 in lung development. In this model, the excised fetal lung continues to grow, secrete fluid, and become progressively cystic in morphology ( 26 ). We inhibited CLC-2 expression in these explants, using antisense oligonucleotides, and found that lung cyst morphology was disrupted. In addition, transepithelial voltage ( Vt) of lung explants transfected with antisense CLC-2 was inhibited with Vt = -1.5 ± 0.2 mV (means + SE) compared with -3.7 ± 0.3 mV (means + SE) for mock-transfected controls and -3.3 ± 0.3 mV (means + SE) for nonsense oligodeoxynucleotide-transfected controls. This suggests that CLC-2 is important for fetal lung fluid production and that it may play a role in normal lung morphogenesis.

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Description of dynamic lung fluid transport phenomena by linear non-equilibrium thermodynamic equations

Journal of Biomedical Engineering ◽

10.1016/0141-5425(90)90114-3 ◽

1990 ◽

Vol 12 (1) ◽

pp. 46-50

Author(s):

V.V. Rosenthal ◽

V.B. Serikov ◽

N.A. Belyakov ◽

S.A. Symbirtsev

Keyword(s):

Fluid Transport ◽

Transport Phenomena ◽

Equilibrium Thermodynamic ◽

Lung Fluid ◽

Thermodynamic Equations ◽

Non Equilibrium

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Lung Epithelial Fluid Transport and the Resolution of Pulmonary Edema

Physiological Reviews ◽

10.1152/physrev.00003.2002 ◽

2002 ◽

Vol 82 (3) ◽

pp. 569-600 ◽

Cited By ~ 478

Author(s):

Michael A. Matthay ◽

Hans G. Folkesson ◽

Christine Clerici

Keyword(s):

Pulmonary Edema ◽

Fluid Transport ◽

Convincing Evidence ◽

Lung Epithelium ◽

Molecular Transporters ◽

Lung Fluid ◽

Lung Fluid Balance ◽

Pathological Conditions ◽

Distal Airway ◽

Distal Lung

The discovery of mechanisms that regulate salt and water transport by the alveolar and distal airway epithelium of the lung has generated new insights into the regulation of lung fluid balance under both normal and pathological conditions. There is convincing evidence that active sodium and chloride transporters are expressed in the distal lung epithelium and are responsible for the ability of the lung to remove alveolar fluid at the time of birth as well as in the mature lung when pathological conditions lead to the development of pulmonary edema. Currently, the best described molecular transporters are the epithelial sodium channel, the cystic fibrosis transmembrane conductance regulator, Na+-K+-ATPase, and several aquaporin water channels. Both catecholamine-dependent and -independent mechanisms can upregulate isosmolar fluid transport across the distal lung epithelium. Experimental and clinical studies have made it possible to examine the role of these transporters in the resolution of pulmonary edema.

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Localization of aquaporin‐5 in sweat glands and functional analysis using knockout mice

The Journal of Physiology ◽

10.1113/jphysiol.2001.020180 ◽

2002 ◽

Vol 541 (2) ◽

pp. 561-568 ◽

Cited By ~ 68

Author(s):

Yuanlin Song ◽

Nitin Sonawane ◽

A. S. Verkman

Keyword(s):

Functional Analysis ◽

Knockout Mice ◽

Sweat Glands ◽

Aquaporin 5

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Invited Review: Active fluid clearance from the distal air spaces of the lung

Journal of Applied Physiology ◽

10.1152/japplphysiol.01210.2001 ◽

2002 ◽

Vol 93 (4) ◽

pp. 1533-1541 ◽

Cited By ~ 73

Author(s):

Michael A. Matthay ◽

Christine Clerici ◽

Georges Saumon

Keyword(s):

Fluid Transport ◽

Critical Role ◽

In Vivo Studies ◽

Lung Epithelium ◽

Lung Fluid ◽

Lung Fluid Balance ◽

Active Ion Transport ◽

Remarkable Progress

Active ion transport drives iso-osmolar alveolar fluid clearance, a hypothesis originally suggested by in vivo studies in sheep 20 yr ago. Over the last two decades, remarkable progress has been made in establishing a critical role for active sodium transport as a primary mechanism that drives fluid clearance from the distal air spaces of the lung. The rate of fluid transport can be increased in most species, including the human lung, by cAMP stimulation. Catecholamine-independent mechanisms, including hormones, growth factors, and cytokines, can also upregulate epithelial fluid clearance in the lung. The new insights into the role of the distal lung epithelium in actively regulating lung fluid balance has important implications for the resolution of clinical pulmonary edema.

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Role of Aquaporin Water Channels in Airway Fluid Transport, Humidification, and Surface Liquid Hydration

The Journal of General Physiology ◽

10.1085/jgp.117.6.573 ◽

2001 ◽

Vol 117 (6) ◽

pp. 573-582 ◽

Cited By ~ 76

Author(s):

Yuanlin Song ◽

Sujatha Jayaraman ◽

Baoxue Yang ◽

Michael A. Matthay ◽

A.S. Verkman

Keyword(s):

Knockout Mice ◽

Fluid Transport ◽

Upper Airway ◽

Lower Airway ◽

Wild Type ◽

Upper Airways ◽

Airway Epithelia ◽

Airway Humidification ◽

Surface Liquid

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 μm 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 ∼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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Mammalian aquaporins: diverse physiological roles and potential clinical significance

Expert Reviews in Molecular Medicine ◽

10.1017/s1462399408000690 ◽

2008 ◽

Vol 10 ◽

Cited By ~ 87

Author(s):

A. S. Verkman

Keyword(s):

Knockout Mice ◽

Fluid Transport ◽

Water Movement ◽

Skin Resistance ◽

Fluid Secretion ◽

Neural Function ◽

Tumour Metastasis ◽

Phenotype Analysis ◽

Obesity And Cancer

Aquaporins have multiple distinct roles in mammalian physiology. Phenotype analysis of aquaporin-knockout mice has confirmed the predicted role of aquaporins in osmotically driven transepithelial fluid transport, as occurs in the urinary concentrating mechanism and glandular fluid secretion. Aquaporins also facilitate water movement into and out of the brain in various pathologies such as stroke, tumour, infection and hydrocephalus. A major, unexpected cellular role of aquaporins was revealed by analysis of knockout mice: aquaporins facilitate cell migration, as occurs in angiogenesis, tumour metastasis, wound healing, and glial scar formation. Another unexpected role of aquaporins is in neural function – in sensory signalling and seizure activity. The water-transporting function of aquaporins is likely responsible for these roles. A subset of aquaporins that transport both water and glycerol, the ‘aquaglyceroporins’, regulate glycerol content in epidermal, fat and other tissues. Mice lacking various aquaglyceroporins have several interesting phenotypes, including dry skin, resistance to skin carcinogenesis, impaired cell proliferation, and altered fat metabolism. The various roles of aquaporins might be exploited clinically by development of drugs to alter aquaporin expression or function, which could serve as diuretics, and in the treatment of brain swelling, glaucoma, epilepsy, obesity and cancer.

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