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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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Characterization of airspace-capillary osmotic water transport. (A) Dependence of osmotically driven water transport on osmolyte size. The airspace compartment was filled with isosmolar HBS and the perfusate solutions switched between HBS and hyperosmolar HBS containing 300 mOsm NaCl, urea, glycine, or sucrose as indicated. Original gravimetric recordings are shown at the left and averaged water flow data at the right. (B) Temperature-dependence measurements were done as in A, using NaCl as osmolyte, in wild-type and AQP1  mice. Original gravimetric recordings are shown at the left and an Arrhenius plot at the right. (C and D) Effect of pulmonary artery (PA) perfusion pressure and left atrial (LA) outflow pressure. Perfusate osmolalities were changed from 300 to 200 mOsm at indicated perfusion pressures. (E) Effect of AQP1 deletion on microvascular water permeability. The airspace was filled with an inert perfluorocarbon and the pulmonary artery perfused with solutions of indicated osmolalities. See text for explanations.
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Figure 4: Characterization of airspace-capillary osmotic water transport. (A) Dependence of osmotically driven water transport on osmolyte size. The airspace compartment was filled with isosmolar HBS and the perfusate solutions switched between HBS and hyperosmolar HBS containing 300 mOsm NaCl, urea, glycine, or sucrose as indicated. Original gravimetric recordings are shown at the left and averaged water flow data at the right. (B) Temperature-dependence measurements were done as in A, using NaCl as osmolyte, in wild-type and AQP1 mice. Original gravimetric recordings are shown at the left and an Arrhenius plot at the right. (C and D) Effect of pulmonary artery (PA) perfusion pressure and left atrial (LA) outflow pressure. Perfusate osmolalities were changed from 300 to 200 mOsm at indicated perfusion pressures. (E) Effect of AQP1 deletion on microvascular water permeability. The airspace was filled with an inert perfluorocarbon and the pulmonary artery perfused with solutions of indicated osmolalities. See text for explanations.

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)

Characterization of airspace-capillary osmotic water transport. (A) Dependence of osmotically driven water transport on osmolyte size. The airspace compartment was filled with isosmolar HBS and the perfusate solutions switched between HBS and hyperosmolar HBS containing 300 mOsm NaCl, urea, glycine, or sucrose as indicated. Original gravimetric recordings are shown at the left and averaged water flow data at the right. (B) Temperature-dependence measurements were done as in A, using NaCl as osmolyte, in wild-type and AQP1  mice. Original gravimetric recordings are shown at the left and an Arrhenius plot at the right. (C and D) Effect of pulmonary artery (PA) perfusion pressure and left atrial (LA) outflow pressure. Perfusate osmolalities were changed from 300 to 200 mOsm at indicated perfusion pressures. (E) Effect of AQP1 deletion on microvascular water permeability. The airspace was filled with an inert perfluorocarbon and the pulmonary artery perfused with solutions of indicated osmolalities. See text for explanations.
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Related In: Results  -  Collection

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

Figure 4: Characterization of airspace-capillary osmotic water transport. (A) Dependence of osmotically driven water transport on osmolyte size. The airspace compartment was filled with isosmolar HBS and the perfusate solutions switched between HBS and hyperosmolar HBS containing 300 mOsm NaCl, urea, glycine, or sucrose as indicated. Original gravimetric recordings are shown at the left and averaged water flow data at the right. (B) Temperature-dependence measurements were done as in A, using NaCl as osmolyte, in wild-type and AQP1 mice. Original gravimetric recordings are shown at the left and an Arrhenius plot at the right. (C and D) Effect of pulmonary artery (PA) perfusion pressure and left atrial (LA) outflow pressure. Perfusate osmolalities were changed from 300 to 200 mOsm at indicated perfusion pressures. (E) Effect of AQP1 deletion on microvascular water permeability. The airspace was filled with an inert perfluorocarbon and the pulmonary artery perfused with solutions of indicated osmolalities. See text for explanations.
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