Salt and water transport across alveolar and distal airway epithelia in the adult lung

1996 ◽  
Vol 270 (4) ◽  
pp. L487-L503 ◽  
Author(s):  
M. A. Matthay ◽  
H. G. Folkesson ◽  
A. S. Verkman
Keyword(s):  
Water Transport ◽  
Water Permeability ◽  
Fluid Transport ◽  
Water Channels ◽  
Molecular Water ◽  
Alveolar Epithelial ◽  
Distal Airway ◽  
Injured Lung

Substantial progress has been made in understanding the role of the distal airway and alveolar epithelial barriers in regulating lung fluid balance. Molecular, cellular, and whole animal studies have demonstrated that reabsorption of fluid from the distal air spaces of the lung is driven by active sodium transport. Several different in vivo, in situ, and isolated lung preparations have been used to study the mechanisms that regulate fluid transport in the normal and injured lung. Catecholamine-dependent and -independent regulatory mechanisms have been identified that modulate fluid transport, probably by acting on apical sodium channel uptake or the activity of the Na, K-ATPase pumps. Recently, a family of molecular water channels (aquaporins) has been identified that are small (approximately 30 kDa) integral membrane proteins expressed widely in fluid-transporting epithelia and endothelia. At present, four different water channels have been identified in trachea and lung. Measurements of osmotic water permeability in in situ perfused lung and isolated perfused airways suggest a significant contribution of these molecular water channels to measured water permeability. However, further studies are required to determine the role of these water channels in normal pulmonary physiology and disease. Recent studies have provided new insights into the role of the alveolar epithelial barrier in clinical and experimental acute lung injury. Unlike the lung endothelium, the alveolar epithelium is resistant to several clinically relevant types of injury, including endotoxemia and bacteremia as well as aspiration of hyperosmolar solutions. In addition, even when the alveolar barrier has been injured, its capacity to transport edema fluid from the distal air spaces of the lung recovers rapidly. Future studies need to integrate new insights into the molecular mechanisms of alveolar epithelial sodium and water transport with functional studies in the normal and injured lung.

Water transport across mammalian cell membranes

1996 ◽  
Vol 270 (1) ◽  
pp. C12-C30 ◽  
Author(s):  
A. S. Verkman ◽  
A. N. van Hoek ◽  
T. Ma ◽  
A. Frigeri ◽  
W. R. Skach ◽  
...  
Keyword(s):  
Water Transport ◽  
Cell Membranes ◽  
Water Channel ◽  
Water Channels ◽  
Channel Structure ◽  
Level Information ◽  
Selective Channel ◽  
Transcriptional Units ◽  
Measurement Strategies

This review summarizes recent progress in water-transporting mechanisms across cell membranes. Modern biophysical concepts of water transport and new measurement strategies are evaluated. A family of water-transporting proteins (water channels, aquaporins) has been identified, consisting of small hydrophobic proteins expressed widely in epithelial and nonepithelial tissues. The functional properties, genetics, and cellular distributions of these proteins are summarized. The majority of molecular-level information about water-transporting mechanisms comes from studies on CHIP28, a 28-kDa glycoprotein that forms tetramers in membranes; each monomer contains six putative helical domains surrounding a central aqueous pathway and functions independently as a water-selective channel. Only mutations in the vasopressin-sensitive water channel have been shown to cause human disease (non-X-linked congenital nephrogenic diabetes insipidus); the physiological significance of other water channels remains unproven. One mercurial-insensitive water channel has been identified, which has the unique feature of multiple overlapping transcriptional units. Systems for expression of water channel proteins are described, including Xenopus oocytes, mammalian and insect cells, and bacteria. Further work should be directed at elucidation of the role of water channels in normal physiology and disease, molecular analysis of regulatory mechanisms, and water channel structure determination at atomic resolution.

New Insights into the Physiology of Peritoneal Fluid Transport

2008 ◽  
Vol 28 (3_suppl) ◽  
pp. 144-149
Author(s):  
Raymond T. Krediet ◽  
Annemieke M. Coester ◽  
Alena Parikova ◽  
Watske Smit ◽  
Dirk G. Struijk
Keyword(s):  
Water Transport ◽  
Fluid Transport ◽  
Free Water ◽  
Osmotic Gradient ◽  
Ultrafiltration Failure ◽  
Ultra Filtration ◽  
Relationship Of ◽  
The Relationship

A review is given on the mechanisms of free water transport, the various methodologies for its measurement, its dependency on the osmotic gradient, and the assessment of osmotic conductance in individual patients. The importance of impaired free water transport in long-term ultra-filtration failure is discussed, relative to peritoneal solute transport status. Furthermore, the relationship of free water transport with locally released potassium is considered, together with a potential role of impaired K+ channel function with peritoneal alterations. Finally, the role of impaired osmotic conductance to glucose and its effects on free water transport in long-term patients with ultrafiltration failure is reviewed.

Preservation of alveolar epithelial fluid transport mechanisms in rewarmed human lung after severe hypothermia

1996 ◽  
Vol 80 (5) ◽  
pp. 1681-1686 ◽  
Author(s):  
T. Sakuma ◽  
S. Suzuki ◽  
K. Usuda ◽  
M. Handa ◽  
G. Okaniwa ◽  
...  
Keyword(s):  
Fluid Transport ◽  
Human Lung ◽  
Ex Vivo ◽  
Transport Mechanisms ◽  
Alveolar Fluid Clearance ◽  
Alveolar Epithelial ◽  
Severe Hypothermia ◽  
Human Lungs ◽  
Channel Transport

Although hypothermia abolishes alveolar fluid clearance in the in situ goat lung and in the ex vivo human lung, it is unknown whether alveolar fluid clearance resumes in lungs that are rewarmed after severe hypothermia. An isosmolar albumin solution was instilled into resected human lungs that were rewarmed to 37 degrees C after hypothermia (7 +/- 3 degrees C), and then alveolar fluid clearance was measured by the concentration of albumin in the alveolar fluid sample after 4 h. In control experiments in lungs that had not been cooled and rewarmed, alveolar fluid clearance was 11 +/- 2% over 4 h. In separate experiments, hypothermia completely abolished alveolar fluid clearance. However, alveolar fluid clearance resumed to a normal level of 12 +/- 1% over 4 h in the lungs that were rewarmed after hypothermia. Amiloride decreased alveolar fluid clearance by 47% in the rewarmed lungs. Terbutaline increased alveolar fluid clearance by nearly 300% in 2-h experiments in the rewarmed lungs (P < 0.05). The results of this study indicate that alveolar sodium-channel transport mechanisms are preserved in resected human lungs that are exposed to rewarming after hypothermia.

Water and Solute Transport through Different Types of Pores in Peritoneal Membrane in Capd Patients with Ultrafiltration Failure

2009 ◽  
Vol 29 (6) ◽  
pp. 664-669 ◽  
Author(s):  
Jacek Waniewski ◽  
Malgorzata Debowska ◽  
Bengt Lindholm
Keyword(s):  
Hydraulic Conductivity ◽  
Water Transport ◽  
Fluid Transport ◽  
Free Water ◽  
Sodium Concentration ◽  
Convective Transport ◽  
Fluid Absorption ◽  
Ultrafiltration Failure ◽  
Kinetics Of

Free water transport, an estimate of aquaporin function, was evaluated in 7 continuous ambulatory peritoneal dialysis (CAPD) patients with permanent ultrafiltration failure. In 3 patients, peritoneal transport was studied also before the onset of ultrafiltration failure. Transcapillary ultrafiltration and fluid absorption rates were assessed using radiolabeled albumin, and free water transport by kinetics of sodium concentration in dialysis fluid. Diffusive and convective transport rates of small solutes were estimated using the modified Babb–Randerson–Farrell model. Increased diffusive transport of small solutes was found in 5 patients and increased peritoneal fluid absorption in 2 patients. The 3-pore model was fitted to these data. Overall, hydraulic conductivity and the fractional contributions of aquaporins to hydraulic conductivity were either decreased or normal. We conclude that the quantitative role of aquaporins in overall fluid transport may vary substantially in normal patients as well in patients with ultrafiltration failure.

scholarly journals Role of Aquaporin-4 in Airspace-to-Capillary Water Permeability in Intact Mouse Lung Measured by a Novel Gravimetric Method

1999 ◽  
Vol 115 (1) ◽  
pp. 17-27 ◽  
Author(s):  
Yuanlin Song ◽  
Tonghui Ma ◽  
Michael A. Matthay ◽  
A.S. Verkman
Keyword(s):  
Water Transport ◽  
Water Permeability ◽  
Gravimetric Method ◽  
Mouse Lung ◽  
Wild Type ◽  
Capillary Water ◽  
Double Knockout ◽  
Lung Weight ◽  
Intact Mouse

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 null 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 (Jv) 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. Jv in wild-type mice varied linearly with osmotic gradient size (4.4 × 10−5 cm3 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 H2O outflow pressure, the filtration coefficient was 4.7 cm3 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 null mice. Jv were (cm3 s−1 mOsm−1 × 10−5, SEM, n = 7–12 mice): 3.8 ± 0.4 (wild type), 0.35 ± 0.02 (AQP1 null), 3.7 ± 0.4 (AQP4 null), and 0.25 ± 0.01 (AQP1/AQP4 null). The significant reduction in Pf in AQP1 vs. AQP1/AQP4 null mice was confirmed by an independent pleural surface fluorescence method showing a 1.6 ± 0.2-fold (SEM, five mice) reduced Pf in the AQP1/AQP4 double knockout mice vs. AQP1 null 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.

scholarly journals Role of multiple phosphorylation sites in the COOH-terminal tail of aquaporin-2 for water transport: evidence against channel gating

2009 ◽  
Vol 296 (3) ◽  
pp. F649-F657 ◽  
Author(s):  
Hanne B. Moeller ◽  
Nanna MacAulay ◽  
Mark A. Knepper ◽  
Robert A. Fenton
Keyword(s):  
Plasma Membrane ◽  
Water Transport ◽  
Water Permeability ◽  
Laser Scanning Microscopy ◽  
Apical Plasma Membrane ◽  
Phosphorylation Sites ◽  
Osmotic Water Permeability ◽  
Aquaporin 2 ◽  
Osmotic Water

Arginine vasopressin (AVP)-regulated phosphorylation of the water channel aquaporin-2 (AQP2) at serine 256 (S256) is essential for its accumulation in the apical plasma membrane of collecting duct principal cells. In this study, we examined the role of additional AVP-regulated phosphorylation sites in the COOH-terminal tail of AQP2 on protein function. When expressed in Xenopus laevis oocytes, prevention of AQP2 phosphorylation at S256A (S256A-AQP2) reduced osmotic water permeability threefold compared with wild-type (WT) AQP2-injected oocytes. In contrast, prevention of AQP2 single phosphorylation at S261 (S261A), S264 (S264A), and S269 (S269A), or all three sites in combination had no significant effect on water permeability. Similarly, oocytes expressing S264D-AQP2 and S269D-AQP2, mimicking AQP2 phosphorylated at these residues, had similar water permeabilities to WT-AQP2-expressing oocytes. The use of high-resolution confocal laser-scanning microscopy, as well as biochemical analysis demonstrated that all AQP2 mutants, with the exception of S256A-AQP2, had equal abundance in the oocyte plasma membrane. Correlation of osmotic water permeability relative to plasma membrane abundance demonstrated that lack of phosphorylation at S256, S261, S264, or S269 had no effect on AQP2 unit water transport. Similarly, no effect on AQP2 unit water transport was observed for the 264D and 269D forms, indicating that phosphorylation of the COOH-terminal tail of AQP2 is not involved in gating of the channel. The use of phosphospecific antibodies demonstrated that AQP2 S256 phosphorylation is not dependent on any of the other phosphorylation sites, whereas S264 and S269 phosphorylation depend on prior phosphorylation of S256. In contrast, AQP2 S261 phosphorylation is independent of the phosphorylation status of S256.

Neural control of distal tubular bicarbonate and fluid transport

1989 ◽  
Vol 257 (1) ◽  
pp. F72-F76
Author(s):  
T. Wang ◽  
Y. L. Chan
Keyword(s):  
Neural Control ◽  
Fluid Transport ◽  
Distal Tubule ◽  
Transport Processes ◽  
Distal Convoluted Tubule ◽  
Renal Nerve ◽  
Renal Nerve Activity ◽  
Proximal Tubular

Although previous studies have shown that inhibition of proximal tubular reabsorption of bicarbonate and fluid partially accounts for bicarbonaturia and diuresis observed in the denervated kidney, the role of the distal convoluted tubule in the neural regulation of electrolyte excretion has not been defined. This study was designed to examine the effects of denervation on bicarbonate and fluid reabsorption in the distal convoluted tubules by using in situ microperfusion methods. Early distal tubules were perfused with a solution containing 15 mM bicarbonate at a rate of 12 nl/min, and fluid samples were collected from the late distal tubule. Bicarbonate concentrations were measured as total CO2 by microcalorimetry. The rate of fluid absorption (Jv) was determined using [methoxy-3H]inulin as a volume marker. Before denervation, the rate of bicarbonate absorption (JHCO3-) was 24.7 +/- 2.6 peq.min-1.mm-1, and Jv was 1.80 +/- 0.14 nl.min-1.mm-1. After denervation, marked reductions in JHCO3- (51%) and Jv (60%) were observed. In contrast, sham denervation did not affect JHCO3- or Jv significantly. Our results indicate that the distal convoluted tubule can reabsorb bicarbonate and fluid under physiological conditions. We conclude that the transport processes in this segment of the nephron are regulated by renal nerve activity.

Sign in / Sign up

Export Citation Format

Share Document