High Osmotic Water Permeability Research Articles

Aquaporin‐Based Biomimetic Membranes for Low Energy Water Desalination and Separation Applications

AbstractThe emergence of biomimetic materials developed using nature's inspiration and biological domains can drive a paradigm shift in the design and operation of future‐generation materials in separation applications. In recent years, biomimetic membranes have drawn interest of many researchers for water treatment applications. Among the biomimetic membranes, protein‐based membranes, specifically those synthesized by aquaporin, have received much attention in recent years due to their high osmotic water permeability and excellent ability to remove small molecules, thereby overcoming the trade‐off between the water flux and the contaminant's rejection. The separation efficiency and fouling properties are significantly improved by taking advantage of the strategies evolved in nature. This review provides a comprehensive overview of the state‐of‐the‐art aquaporin‐based biomimetic membranes (ABMs), mainly focusing on their synthesis, characterization, and performance as selective layer in composite membranes for reverse osmosis, nanofiltration, and forward osmosis for water desalination. Fabrication methods and characterization techniques of ABMs and their performance in water desalination are also reviewed, while the main obstacles for their successful commercial viability in wastewater treatment are provided. The applications of ABMs in various separation processes other than water desalination and their potential market are presented to inspire future researchers in this versatile area.

A comparative study of endothelial cell transport in pig and human cornea

Purpose. To study the basic transport characteristics of human and pig corneal endothelial cells, including osmotic water permeability, activation of sodium transport from the cell after conservation, and the ability of the cells to restore their volume when transport mechanisms of the endothelial cells are activated at 37°C.Material and methods. The experiments were held on the primary cell culture of human and pig cornea endothelia. Changes in cell volume were determined by a method based on quenching of Calcein fluorescence probe by the cytosol proteins. Changes in intracellular sodium ion concentration were studied using Sodium Green as a fluorescent probe. Restoration dynamics of cell volume and intracellular sodium concentration were studied under medium temperature changes from 20 to 37°C. Osmotic water permeability was calculated from the rate of cell volume changes under medium osmolality decreasing from 560 to 280 mOsm/kg H2 O.Results. It was established that human endothelial cells plasma membrane has a significantly higher osmotic water permeability than pig endothelial cells (Pf = 1.90E-01 ± 4.66E-02 and 1.31E-01 ± 1.16E-02 cm/s, respectively; p < 0.01, n = 17). Human cells after the temperature restored to 37°C, sodium ions removal from human cells occurs more intensely than from pig cells (-3.2E-3 ± 3.1E-4 с-1 и -6.5E-4 ± 1.2E-5 s-1, respectively; p < 0.01, n = 6). The study of cell volume drop has shown that heat activation of cellular transport restores the endothelial cell volume in humans more slowly (-1,7E-4 ± 5,5E-5 с-1, n = 9) than that of pig cells (-1.7E-3 ± 4E-4 s-1, n = 4, p < 0.05).Conclusion. When using the endothelium of pig cornea as an experimental model of human endothelium, we need to take into account the significant difference in parameters that determine cell volume regulation.

Benign Pleural Mesothelial Cells Have Higher Osmotic Water Permeability than Malignant Pleural Mesothelioma Cells and Differentially Respond to Hyperosmolality.

Cell volume regulation is a critical mechanism for cell homeostasis and depends on the osmotic water permeability (Pf) of the cell plasma membrane. The Pf of human mesothelial cells is unknown although they contribute to serosal fluid turnover. In this study we measured the osmotic water permeability of benign human mesothelial cells (MeT-5A) and of epithelioid (M14K) and sarcomatoid (ZL34) malignant pleural mesothelioma (MPM) cells in response to acute hyperosmotic stress. We also assessed the changes in their Pf after preconditioning with 4% glucose for 24 hours. In both cases we also assessed the role of AQP1 inhibition (0.1 mM HgCl2) on the Pf. Finally, we assessed corresponding changes in the AQP1 plasma membrane availability by immunofluorescence. We report that MeT-5A cells have a significantly higher Pf as compared to M14K and ZL34 MPM cells [4.85E-03±2.37E-03 cm/sec (n=17) versus 2.74E-03±0.74E-03 cm/sec (n=11) and 2.86E-03±0.11E-03 cm/sec (n=11)]. AQP1 inhibition significantly decreased the Pf in all cells lines (p<0.001 in all cases). High glucose preconditioning for 24 hours significantly increased MeT-5A Pf (p<0.001), did not influence M14K Pf (p=0.19) and significantly reduced ZL34 Pf (p=0.02). Comparing cell lines after high glucose preconditioning, MeT-5A Pf was significantly higher than that of M14K and ZL34 MPM cells and the AQP1 inhibition effect was significant in MeT-5A and M14K cells. These results were corroborated by AQP1 immunofluorescence. We provide evidence for a differential regulation of Pf in benign and MPM cells that require further mechanistic investigation.

Metal-Organic Framework Nanocomposite Thin Films with Interfacial Bindings and Self-Standing Robustness for High Water Flux and Enhanced Ion Selectivity.

Metal-organic framework (MOF)-based materials are promising candidates for a range of separation applications. However, the fabrication of self-standing MOF-based thin films remains challenging. Herein, a facile solution casting strategy is developed for fabricating UiO-66 nanocomposite thin films (UiO66TFs) with thicknesses down to ∼400 nm. Nanosizing UiO-66 and incorporating sulfonated polysulfone additives render high dispersity and interfacial bindings between MOFs and polymer matrices, so UiO66TFs are more mechanically robust and thermally stable than their pure-polymer counterparts. Enhanced microporosity with sub-nanometer pore sizes of the self-standing membranes enables the direct translation of UiO-66-based sorption and ion-sieving properties, thus increasing water flux and separation performance (Na2SO4 rejection of 94-96%) under hydraulic pressure-driven processes and eliminating internal concentration polarization in osmotic pressure-driven processes. Enhanced separation performances are achieved with water/Na2SO4 permselectivity of 13.5 L g-1 and high osmotic water permeability up to 1.41 L m-2 h-1 bar-1, providing 3-fold higher water/Na2SO4 permselectivity and 56-fold-higher water flux than polymer membranes for forward osmosis.

Plasma membrane aquaporins mediates vesicle stability in broccoli.

The use of in vitro membrane vesicles is attractive because of possible applications in therapies. Here we aimed to compare the stability and functionality of plasma membrane vesicles extracted from control and salt-treated broccoli. The impact of the amount of aquaporins was related to plasma membrane osmotic water permeability and the stability of protein secondary structure. Here, we describe for first time an increase in plant aquaporins acetylation under high salinity. Higher osmotic water permeability in NaCl vesicles has been related to higher acetylation, upregulation of aquaporins, and a more stable environment to thermal denaturation. Based on our findings, we propose that aquaporins play an important role in vesicle stability.

Construction of Luciferase Reporter Plasmid with Human AQP1 Gene Promoter

Aquaporins (AQPs), a family of water channels, function as a water-selective transporting protein in cell membranes. Aquaporin 1 (AQP1) was first discovered in human erythrocytes as a water channel for high osmotic water permeability. AQP1 promoter is responsible for regulation of its transcription and expression. In this study, molecular biology and genetic engineering knowledge and principles of construction of AQP1 promoter plasmid, and recombinant plasmids were identified and measured for luciferase, for promoter function. Our study successfully constructed AQP1 promoter luciferase reporter gene expression plasmid and successfully carry out the functions of its detection, provides a new foundation for the transcription expression and function regulation of the AQP1

Deletion of Aquaporin 5 Aggravates Acute Lung Injury Induced by Pseudomonas aeruginosa

Aquaporin (AQP) is a membrane protein that facilitates osmotic water transport. Aquaporin 5 (AQP5) expresses at type I alveolar epithelia of apical membrane that confers high osmotic water permeability. Osmosis or stretch challenge in alveoli significantly up-regulates AQP5 expression, which suggests that AQP5 may play a role in the maintenance of epithelia barrier function. Pseudomonas aeruginosa (PA), a leading gram-negative bacterial frequently isolated from ventilation-associated pneumonia patients, disrupts alveolar and airway epithelial cells and subsequently leads to blood dissemination. In this study, we hypothesized that AQP5 might be protective in acute lung injury induced by PA, and deletion of AQP5 might lead to aggravated lung injury. Lung injury model was induced by intratracheal instillation of PA (1 × 10(6) colony-forming unit) in wild-type and AQP5 knockout mice, 2 hours and 6 hours later, blood and lung lysate were cultured to detect blood dissemination, bronchoalveolar lavage fluid and lung tissue were collected for histology analysis. Lung injury assessment, wet/dry weight ratio, protein leakage, and Evan's blue dye extravasation were evaluated for pulmonary barrier function. AQP5 deficiency led to increased bacterial blood dissemination and aggravated lung injury during PA infection, and AQP5 deletion also reduced mucin production in lung. Moreover, AQP5 deficiency showed declined activation of mitogen-activated protein kinase and nuclear factor-kappa B pathways in lungs before and after PA infection. Our data demonstrated that AQP5 plays a protective role in the maintenance of pulmonary barrier function against PA infection.

Expression of aquaporin 5 increases proliferation and metastasis potential of lung cancer

Water channel aquaporin 5 (AQP5) is highly expressed at the apical membrane of alveolar type I epithelial cells and confers high osmotic water permeability. AQP5 is also expressed in lung cancer tissue. Previous studies showed there was an up-regulation of AQP5 expression in cancer tissue compared to surrounding normal tissue. In addition, expression of AQP5 in lung cancer tissue was associated with poor prognosis. Herein, we tested the role of AQP5 in lung cancer oncogenesis and development. Lung cancer cells with different expression of AQP5 were used to study cell proliferation and migration, two important parameters for tumour cell biology. We found enhanced proliferation and migration potential in cancer cells with high AQP5 expression, while reduced proliferation and metastasis potential in cancer cells with low AQP5 expression. Oncogene analysis showed significantly increased PCNA and c-myc expression in AQP5 transfected cells. AQP5 transfected cells also showed significant increased MUC5AC mucin expression, which might contribute to the enhanced metastasis potential of lung cancer. AQP5 overexpression resulted in enhanced activation of the epidermal growth factor receptor (EGFR), extracellular receptor kinase (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) pathway in cancer cells. Moreover, deletion of AQP5 demonstrated decreased activation of the EGFR/ERK/p38 MAPK pathway in AQP5 knockout mice lungs, while deletion of AQP1 or AQP3 did not exhibit significant changes on activation of the EGFR/ERK/p38 MAPK pathway in lung tissue. In conclusion, our results provide evidence for AQP5-facilitated lung cancer cell proliferation and migration, possibly through activation of the EGFR/ERK/p38 MAPK signalling pathway, but why AQP5 but not other aquaporin expression affects the EGFR/ERK/p38 MAPK pathway still needs further exploration.

Aquaporin 1-expressing MCF-7 mammary carcinoma cells show enhanced migration in vitro

Recent studies have demonstrated that aquaporin (AQP) expression facilitates cell migration and promotes angiogenesis and neutrophil motility. Migration of tumor cells is a crucial step in tumor invasion and metastasis. Here we investigated the expression of AQP in MCF-7 human mammary carcinoma cells and characterized its function in cell migration. Reverse Transcription–Polymerase Chain Reaction, Immunoblot and Immunofluorescence analysis demonstrated two populations of MCF-7 cell clones with low (AQP1L) and high (AQP1H) AQP1 expression and the AQP1 protein expression patterns in the plasma membrane of MCF-7 cells. MCF-7 cell clones (AQP1L and AQP1H) with low and about two-fold higher osmotic water permeability were identified by functional assays with corresponding low and high AQP1 expression. Cell migration rate was remarkably higher in AQP1H cells as compared to AQP1L cells, assessed by wound healing and transwell migration assays. Adenoviral-mediated mRNA and protein expression of AQP1 in AQP1L cells increased their water permeability and migration rate to the level similar to AQP1H cells. The results provided direct evidence that aquaporin-mediated plasma membrane water permeability played an important role in mammary carcinoma cell migration and may be associated with mammary carcinoma invasion and metastasis.

Aquaporin 1 water channel is overexpressed in the plasma membranes of pancreatic ducts in patients with autoimmune pancreatitis

Chronic pancreatitis with all kinds of etiologies is characterized by pancreatic exocrine dysfunction especially impaired fluid secretion from pancreatic ducts. However, the molecular mechanism of this impaired fluid secretion in chronic pancreatitis is largely unknown. Aquaporin water channels are intrinsic membrane proteins expressed most of the cell types which have high osmotic water permeability. Among them aquaporin 1 (AQP1) is a predominant water channel expressed in the plasma membranes of human pancreatic ducts. Exocrine function test revealed that fluid secretion was severely impaired in AIP. immunohistochemical analysis revealed that AQP1 is localized mainly in the apical and lateral membranes of small pancreatic ducts in control subjects. AQP1 expression was significantly increased in plasma membranes of pancreatic ducts in AIP. Upregulation of AQP1 expression seen in pancreatic ducts of patient with AIP may be caused by the reduced fluid secretion from the pancreas as compensation. Further study would be required to elucidate the precise molecular mechanism for the role of AQP1 in pancreatic fluid secretion from the pancreas in diseases characterized by the impaired ductal fluid secretion such as cystic fibrosis.

Awards and changes at the Journal of Plant Research

I am very pleased to announce that the paper contributed by Dr. Mari Murai-Hatano and Dr. Tsuneo Kuwagata (MuraiHatano and Kuwagata 2007) won the JPR Best Paper Award 2008. This award-winning work was selected from all the original papers published in the Journal of Plant Research in 2007, by a vote of the editorial board members according to the JPR Awards Selection Procedure. In this study, the authors, Dr. Murai-Hatano and Dr. Kuwagata, investigated the osmotic water permeability of both plasma membrane (Pf1) and vacuolar membrane (Pf2), as well as the bulk osmotic water permeability of a protoplast [Pf(bulk)] isolated from radish roots. They successfully determined these values by measuring the swelling/shrinking rate of protoplasts and isolated vacuoles under hypoor hypertonic conditions. This experimental approach is based on the ‘‘three-compartment model,’’ which describes the theoretical relationship among Pf1, Pf2, and Pf(bulk) (Kuwagata and Murai-Hatano 2007). By using this novel experimental approach based on a robust theoretical background, the authors found high osmotic water permeability of more than 500 lm s both in the plasma membrane and vacuolar membrane in radish root cells. These results are surprising because it is widely accepted that the activity of aquaporins in plants is much higher in the vacuolar membrane compared with that in the plasma membrane. This new finding extends our knowledge about the water relation of plants and significantly contributes to our understanding of plant growth and function. On a different note, the winner of the Most-Cited Paper Award was to have been selected from all the papers published in 2005 by reference to the ISI database. It is unfortunate that no paper won the award for this year, because no paper published in 2005 was cited as frequently as those published in 2004 or in 2006. This does not mean a decreasing trend in citation of JPR. Despite lower levels of citation in 2005 papers, the ISI impact factor as well as total citation of JPR papers has been steadily increasing since 2006, with the score for 2007 being 1.415.

Thyroid Transcription Factor-1 Facilitates Cerebrospinal Fluid Formation by Regulating Aquaporin-1 Synthesis in the Brain

In the brain, aquaporin-1 (AQP-1), a water channel for high osmotic water permeability, is mainly expressed in the apical membrane of the ventricular choroid plexus and regulates formation of cerebrospinal fluid (CSF). Although the physiology of AQP-1 has been the subject of several publications, much less is known about the trans-acting factors involved in the control of AQP-1 gene expression. Here we report that TTF-1, a homeodomain-containing transcriptional regulator, is coexpressed with AQP-1 in the rat brain choroid plexus and enhances AQP-1 gene transcription by binding to conserved core TTF-1-binding motifs in the 5'-flanking region of the AQP-1 gene. Intracerebroventricular administration of an antisense TTF-1 oligodeoxynucleotide significantly decreased AQP-1 synthesis and reduced CSF formation. In addition, blockade of TTF-1 synthesis increased survival of the animals following acute water intoxication-induced brain edema. These results suggest that TTF-1 is physiologically involved in the transcriptional control of AQP-1, which is required for CSF formation.

Osmotic water permeability of plasma and vacuolar membranes in protoplasts I. High osmotic water permeability in radish (Raphanus sativus) root cells as measured by a new method

Osmotic water permeability of plasma and vacuolar membranes in protoplasts I. High osmotic water permeability in radish (Raphanus sativus) root cells as measured by a new method

Osmotic water permeability of plasma and vacuolar membranes in protoplasts I. High osmotic water permeability in radish (Raphanus sativus) root cells as measured by a new method

Intra- and transcellular water movements in plants are regulated by the water permeability of the plasma membrane (PM) and vacuolar membrane (VM) in plant cells. In the present study, we investigated the osmotic water permeability of both PM (P ( f1)) and VM (P ( f2)), as well as the bulk osmotic water permeability of a protoplast (P ( f(bulk))) isolated from radish (Raphanus sativus) roots. The values of P ( f(bulk)) and P ( f2) were determined from the swelling/shrinking rate of protoplasts and isolated vacuoles under hypo- or hypertonic conditions. In order to minimize the effect of unstirred layer, we monitored dropping or rising protoplasts (vacuoles) in sorbitol solutions as they swelled or shrunk. P ( f1) was calculated from P ( f(bulk)) and P ( f2) by using the 'three-compartment model', which describes the theoretical relationship between P ( f1), P ( f2) and P ( f(bulk)) (Kuwagata and Murai-Hatano in J Plant Res, 2007). The time-dependent changes in the volume of protoplasts and isolated vacuoles fitted well to the theoretical curves, and solute permeation of PM and VM was able to be neglected for measuring the osmotic water permeability. High osmotic water permeability of more than 500 mum s(-1), indicating high activity of aquaporins (water channels), was observed in both PM and VM in radish root cells. This method has the advantage that P ( f1) and P ( f2) can be measured accurately in individual higher plant cells.

Cloning and characterization of porcine aquaporin 1 water channel expressed extensively in gastrointestinal system

To clone and characterize the porcine aquaporins (AQPs) in the gastrointestinal system. A PCR-based cloning strategy and RACE were used to clone full-length AQP coding sequence from reversely transcribed pig liver cDNA. Stopped-flow light scattering and a YFP-based fluorescence method were used to measure the osmotic water permeability of erythrocytes and the stably transfected CHO cells. RT-PCR, Northern blot, and immunohistochemistry were used to determine the gastrointestinal expression and localization of cloned AQPs. Protein expression in transfected cells and red blood cells was analyzed by Western blot. An 813 bp cDNA encoding a 271 amino acid porcine aquaporin (designated pAQP1) was cloned from liver mRNA (pAQP1 has a 93% identity with human AQP1 and contains two NPA motifs conserved in AQP family, one consensus sequence for N-linked glycosylation, and one mercury-sensitive site at cysteine 191). RT-PCR analysis revealed extensive expression of pAQP1 mRNA in porcine digestive glands and gut. Northern blot showed a single 3.0 kb transcript in selected digestive organs. pAQP1 protein was localized at central lacteals of the small intestine, microvessles of salivary glands, as well as epithelium of intrahepatic bile ducts by immunoperoxydase. High osmotic water permeability that is inhibitable by HgCl2 was detected in porcine erythrocytes and CHO cells stably transfected with pAQP1 cDNA. Immunoblot analysis of porcine erythrocytes and pAQP-transfected CHO cells revealed an unglycosylated 28 ku band and larger glycosylated proteins. pAQP1 is the first porcine aquaporin that can be molecularly identified so far. The broad distribution of pAQP1 in epithelium and endothelium of porcine digestive organs may suggest an important role of channel-mediated water transport in fluid secretion/absorption as well as in digestive function and pathophysiology of the gastrointestinal system.

Aquaporins in skeletal muscle: reassessment of the functional role of aquaporin-4.

Aquaporin-4 (AQP4) is the major water channel of the neuromuscular system, but its physiological function in both perivascular astrocytes and skeletal muscle sarcolemma is unclear. The purpose of this study was to assess the following in skeletal muscle: a) the expression of all cloned water cannels; b) the functional role of AQP4 using sarcolemma vesicles purified by means of several fractionation methods, and c) the functional effect of AQP4 reduction in mdx mice, the animal model of Duchenne muscular dystrophy (DMD). Immunofluorescence and immunoblot experiments performed with affinity purified antibodies revealed that only AQP1 and AQP4 are expressed in mouse skeletal muscle: AQP1 in endothelial cells of continuous capillaries and AQP4 on the plasma membrane of muscle fiber. Plasma membrane vesicle purification was performed with a procedure extensively used to purify and characterize dystrophin-associated proteins (DAPs) from rabbit skeletal muscle. Western blot analysis showed strong co-enrichment of the analyzed DAPs and AQP4, indicating that the membrane vesicle preparation was highly enriched in sarcolemma. Stopped-flow light-scattering measurements showed high osmotic water permeability of sarcolemma vesicles (approximately 150 microm/s) compatible with the AQP-mediated pathway for water movement. Sarcolemma vesicles prepared from mdx mice revealed, in parallel with AQP4 disappearance from the plasma membrane, a strong reduction in water permeability compared with wild-type mice. Altogether, these results demonstrate high AQP4-mediated water permeability of the skeletal muscle sarcolemma. Expression of sarcolemmal AQP4 together with that of vascular AQP1 may be responsible for the fast water transfer from the blood into the muscle during intense activity. These data imply an important role for aquaporins in skeletal muscle physiology as well as an involvement of AQP4 in the molecular alterations that occur in the muscle of DMD patients.

Overexpression of a lily PIP1 gene in tobacco increased the osmotic water permeability of leaf cells

ABSTRACTMembrane intrinsic proteins (MIP) facilitate the osmotic water transport across biomembranes and are involved in the transcellular and intracellular water flow in plants. An aquaporin‐like gene, AqpL1, was isolated from lily flower using reverse transcriptase‐polymerase chain reaction. Phylogenetic analysis showed that AqpL1 was a member of PIP1 subfamily. The results of northern hybridization indicated AqpL1 expressed in the whole plant but most strongly in young petal. Its expression decreased remarkably with flower age. AqpL1 gene could be properly expressed by in vitro translation and showed a 26 kDa monomer band revealed by autoradiography. Injection of AqpL1 cRNA into Xenopus oocytes resulted in an increase of the osmotic water permeability (Pf = 0.72 × 10−2 ± 0.05 cm s−1) for about 2–3 times compared to that (Pf = 0.24 × 10−2 ± 0.07 cm s−1) of the cells injected with water. Overexpression of AqpL1 in tobacco could greatly increase osmotic water permeability of leaf protoplasts (Pos‐WT : Pos‐L1 = 0.7 × 10−1 cm s−1 : 4.3 × 10−1 cm s−1) and water conductivity of leaf cells (RWL‐WT : RWL‐L1 = 3.3% : 13.2%). It is concluded that AqpL1 is a water channel gene. However, it demonstrated much higher osmotic water permeability in tobacco cells than in oocytes. These results are consistent with the notion that AqpL1 is involved in regulating water and/or other solutes transport across the plant cell membrane.

Ontogeny of water transport in the rabbit proximal tubule.

Water transport across cell membranes is a fundamental biological problem. In the kidney, many nephron segments have mechanisms for transporting large quantities of water with minimal energy input. The proximal tubule reabsorbs two-thirds of the glomerular filtrate with a small transepithelial osmotic gradient as the driving force. In the adult proximal tubule, this is accomplished by the expression of aquaporin 1 (AQP1), the water channel located on the apical and basolateral membranes of the proximal tubule. The neonatal tubule has a much lower expression of AQP1, yet can still transport water with a small osmotic gradient. Thus, tubule properties other than AQP1 expression must allow for this to occur. There are two primary differences that account for this unexpectedly high osmotic water permeability of the neonatal proximal tubule. First, the lipid membrane of the neonatal tubule is more fluid than the adult tubule and therefore a larger fraction of the water can pass through the lipid bilayer. The second property is the fact that the neonatal tubule cells have a smaller cell volume, and thus, the intracellular compartment provides less resistance for the movement of water. This review will discuss postnatal maturation of proximal tubule water transport.

Channel-mediated water movement across enclosed or perfused mouse intrahepatic bile duct units.

We previously reported the development of reproducible techniques for isolating and perfusing intact intrahepatic bile duct units (IBDUs) from rats. Given the advantages of transgenic and knockout mice for exploring ductal bile formation, we report here the adaptation of those techniques to mice and their initial application to the study of water transport across mouse intrahepatic biliary epithelia. IBDUs were isolated from livers of normal mice by microdissection combined with enzymatic digestion. After culture, isolated IBDUs sealed to form intact, polarized compartments, and a microperfusion system employing those isolated IBDUs developed. A quantitative image analysis technique was used to observe a rapid increase of luminal area when sealed IBDUs were exposed to a series of inward osmotic gradients reflecting net water secretion; the choleretic agonists secretin and forskolin also induced water secretion into IBDUs. The increase of IBDU luminal area induced by inward osmotic gradients and choleretic agonists was reversibly inhibited by HgCl2, a water channel inhibitor. With the use of a quantitative epifluorescence technique in perfused mouse IBDUs, a high osmotic water permeability (P(f) = 2.5-5.6 x 10(-2) cm/s) was found in response to osmotic gradients, further supporting the presence of water channels. These findings suggest that, as in the rat, water transport across intrahepatic biliary epithelia in mice is water channel mediated.

Regulation of ion and fluid transport across the distal pulmonary epithelia: new insights

this issue of the American Journal of Physiology-Lung Cellular and Molecular Physiology features nine articles that provide new insights into the mechanisms and the cellular pathways that regulate ion transport across the distal pulmonary epithelia in both the adult and fetal lung. Although much has