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Role of aquaporin-4 in airspace-to-capillary water permeability in intact mouse lung measured by a novel gravimetric method.

Song Y, Ma T, Matthay MA, Verkman AS - J. Gen. Physiol. (2000)

Bottom Line: Transcapillary osmotic water permeability was greatly reduced by AQP1 deletion, as measured by the same method except that the airspace saline was replaced by an inert perfluorocarbon.At 5 cm H(2)O outflow pressure, the filtration coefficient was 4.7 cm(3) s(-1) mOsm(-1) and reduced 1.4-fold by AQP1 deletion.The significant reduction in P(f) in AQP1 vs.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, California 94143, USA.

ABSTRACT
The mammalian peripheral lung contains at least three aquaporin (AQP) water channels: AQP1 in microvascular endothelia, AQP4 in airway epithelia, and AQP5 in alveolar epithelia. In this study, we determined the role of AQP4 in airspace-to-capillary water transport by comparing water permeability in wild-type mice and transgenic mice lacking AQP1, AQP4, or AQP1/AQP4 together. An apparatus was constructed to measure lung weight continuously during pulmonary artery perfusion of isolated mouse lungs. Osmotically induced water flux (J(v)) between the airspace and capillary compartments was measured from the kinetics of lung weight change in saline-filled lungs in response to changes in perfusate osmolality. J(v) in wild-type mice varied linearly with osmotic gradient size (4.4 x 10(-5) cm(3) s(-1) mOsm(-1)) and was symmetric, independent of perfusate osmolyte size, weakly temperature dependent, and decreased 11-fold by AQP1 deletion. Transcapillary osmotic water permeability was greatly reduced by AQP1 deletion, as measured by the same method except that the airspace saline was replaced by an inert perfluorocarbon. Hydrostatically induced lung edema was characterized by lung weight changes in response to changes in pulmonary arterial inflow or pulmonary venous outflow pressure. At 5 cm H(2)O outflow pressure, the filtration coefficient was 4.7 cm(3) s(-1) mOsm(-1) and reduced 1.4-fold by AQP1 deletion. To study the role of AQP4 in lung water transport, AQP1/AQP4 double knockout mice were generated by crossbreeding of AQP1 and AQP4 mice. J(v) were (cm(3) s(-1) mOsm(-1) x 10(-5), SEM, n = 7-12 mice): 3.8 +/- 0. 4 (wild type), 0.35 +/- 0.02 (AQP1 ), 3.7 +/- 0.4 (AQP4 ), and 0.25 +/- 0.01 (AQP1/AQP4 ). The significant reduction in P(f) in AQP1 vs. AQP1/AQP4 mice was confirmed by an independent pleural surface fluorescence method showing a 1.6 +/- 0.2-fold (SEM, five mice) reduced P(f) in the AQP1/AQP4 double knockout mice vs. AQP1 mice. These results establish a simple gravimetric method to quantify osmosis and filtration in intact mouse lung and provide direct evidence for a contribution of the distal airways to airspace-to-capillary water transport.

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Osmotic gradient dependence of airspace-capillary water transport in perfused lungs of wild-type mice. (A) Representative original weight recordings obtained with indicated perfusate osmolalities. The airspace compartment was filled with isosmolar HBS (0.5 ml) and the pulmonary artery perfused at constant pressure (20 cm H2O, flow 2.5–3 ml/min) at room temperature. (B) Initial water flow (mean ± SEM, n = 3–6 lungs) as a function of perfusate osmolality. Positive water flow corresponds to movement out of the airspace. (C) Net lung weight increase as a function of 300/mOsm−1, where mOsm is perfusate osmolality. See text for details.
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Figure 3: Osmotic gradient dependence of airspace-capillary water transport in perfused lungs of wild-type mice. (A) Representative original weight recordings obtained with indicated perfusate osmolalities. The airspace compartment was filled with isosmolar HBS (0.5 ml) and the pulmonary artery perfused at constant pressure (20 cm H2O, flow 2.5–3 ml/min) at room temperature. (B) Initial water flow (mean ± SEM, n = 3–6 lungs) as a function of perfusate osmolality. Positive water flow corresponds to movement out of the airspace. (C) Net lung weight increase as a function of 300/mOsm−1, where mOsm is perfusate osmolality. See text for details.

Mentions: The gravimetric method measures total lung weight and thus the sum of fluids contained in the airspace, interstitial, and capillary compartments. Averaged information is obtained for the whole lung rather than surface alveoli/vessels, and no exogenous fluorescent probe is used. When the airspace compartment is filled with an isosmolar saline solution, changes in perfusate osmolality result in water movement across endothelial and epithelial barriers, producing changes in interstitial and airspace water content observed as changes in lung weight. Fig. 2 B shows representative gravimetric data for the same changes in perfusate osmolality studied by the fluorescence method. Increasing perfusate osmolality to 400 mOsm (left) produced a decrease in lung weight as water is extracted from the extravascular spaces of the lung; decreasing perfusate osmolality to 200 mOsm (right) had the opposite effect. A 100-mg weight calibration was done in every experiment, as well as real-time measurement of perfusate flow. Detailed characterization of the gravimetric method for measurement of airspace-capillary osmotic water transport is provided below in Fig. 3 and Fig. 4.


Role of aquaporin-4 in airspace-to-capillary water permeability in intact mouse lung measured by a novel gravimetric method.

Song Y, Ma T, Matthay MA, Verkman AS - J. Gen. Physiol. (2000)

Osmotic gradient dependence of airspace-capillary water transport in perfused lungs of wild-type mice. (A) Representative original weight recordings obtained with indicated perfusate osmolalities. The airspace compartment was filled with isosmolar HBS (0.5 ml) and the pulmonary artery perfused at constant pressure (20 cm H2O, flow 2.5–3 ml/min) at room temperature. (B) Initial water flow (mean ± SEM, n = 3–6 lungs) as a function of perfusate osmolality. Positive water flow corresponds to movement out of the airspace. (C) Net lung weight increase as a function of 300/mOsm−1, where mOsm is perfusate osmolality. See text for details.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1887782&req=5

Figure 3: Osmotic gradient dependence of airspace-capillary water transport in perfused lungs of wild-type mice. (A) Representative original weight recordings obtained with indicated perfusate osmolalities. The airspace compartment was filled with isosmolar HBS (0.5 ml) and the pulmonary artery perfused at constant pressure (20 cm H2O, flow 2.5–3 ml/min) at room temperature. (B) Initial water flow (mean ± SEM, n = 3–6 lungs) as a function of perfusate osmolality. Positive water flow corresponds to movement out of the airspace. (C) Net lung weight increase as a function of 300/mOsm−1, where mOsm is perfusate osmolality. See text for details.
Mentions: The gravimetric method measures total lung weight and thus the sum of fluids contained in the airspace, interstitial, and capillary compartments. Averaged information is obtained for the whole lung rather than surface alveoli/vessels, and no exogenous fluorescent probe is used. When the airspace compartment is filled with an isosmolar saline solution, changes in perfusate osmolality result in water movement across endothelial and epithelial barriers, producing changes in interstitial and airspace water content observed as changes in lung weight. Fig. 2 B shows representative gravimetric data for the same changes in perfusate osmolality studied by the fluorescence method. Increasing perfusate osmolality to 400 mOsm (left) produced a decrease in lung weight as water is extracted from the extravascular spaces of the lung; decreasing perfusate osmolality to 200 mOsm (right) had the opposite effect. A 100-mg weight calibration was done in every experiment, as well as real-time measurement of perfusate flow. Detailed characterization of the gravimetric method for measurement of airspace-capillary osmotic water transport is provided below in Fig. 3 and Fig. 4.

Bottom Line: Transcapillary osmotic water permeability was greatly reduced by AQP1 deletion, as measured by the same method except that the airspace saline was replaced by an inert perfluorocarbon.At 5 cm H(2)O outflow pressure, the filtration coefficient was 4.7 cm(3) s(-1) mOsm(-1) and reduced 1.4-fold by AQP1 deletion.The significant reduction in P(f) in AQP1 vs.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, California 94143, USA.

ABSTRACT
The mammalian peripheral lung contains at least three aquaporin (AQP) water channels: AQP1 in microvascular endothelia, AQP4 in airway epithelia, and AQP5 in alveolar epithelia. In this study, we determined the role of AQP4 in airspace-to-capillary water transport by comparing water permeability in wild-type mice and transgenic mice lacking AQP1, AQP4, or AQP1/AQP4 together. An apparatus was constructed to measure lung weight continuously during pulmonary artery perfusion of isolated mouse lungs. Osmotically induced water flux (J(v)) between the airspace and capillary compartments was measured from the kinetics of lung weight change in saline-filled lungs in response to changes in perfusate osmolality. J(v) in wild-type mice varied linearly with osmotic gradient size (4.4 x 10(-5) cm(3) s(-1) mOsm(-1)) and was symmetric, independent of perfusate osmolyte size, weakly temperature dependent, and decreased 11-fold by AQP1 deletion. Transcapillary osmotic water permeability was greatly reduced by AQP1 deletion, as measured by the same method except that the airspace saline was replaced by an inert perfluorocarbon. Hydrostatically induced lung edema was characterized by lung weight changes in response to changes in pulmonary arterial inflow or pulmonary venous outflow pressure. At 5 cm H(2)O outflow pressure, the filtration coefficient was 4.7 cm(3) s(-1) mOsm(-1) and reduced 1.4-fold by AQP1 deletion. To study the role of AQP4 in lung water transport, AQP1/AQP4 double knockout mice were generated by crossbreeding of AQP1 and AQP4 mice. J(v) were (cm(3) s(-1) mOsm(-1) x 10(-5), SEM, n = 7-12 mice): 3.8 +/- 0. 4 (wild type), 0.35 +/- 0.02 (AQP1 ), 3.7 +/- 0.4 (AQP4 ), and 0.25 +/- 0.01 (AQP1/AQP4 ). The significant reduction in P(f) in AQP1 vs. AQP1/AQP4 mice was confirmed by an independent pleural surface fluorescence method showing a 1.6 +/- 0.2-fold (SEM, five mice) reduced P(f) in the AQP1/AQP4 double knockout mice vs. AQP1 mice. These results establish a simple gravimetric method to quantify osmosis and filtration in intact mouse lung and provide direct evidence for a contribution of the distal airways to airspace-to-capillary water transport.

Show MeSH
Related in: MedlinePlus