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Water Channels (water + channel)
Terms modified by Water Channels Selected AbstractsInvolvement of vH+ -ATPase in synaptic vesicle swellingJOURNAL OF NEUROSCIENCE RESEARCH, Issue 1 2010Leah Shin Abstract Secretory vesicle swelling is central to cell secretion, but the underlying mechanism of vesicle swelling, particularly synaptic vesicles, is not completely understood. The G,i3 -PLA2-mediated involvement of water channel AQP-1 in the regulation of secretory vesicle swelling in exocrine pancreas and the G,o -mediated AQP-6 involvement in synaptic vesicle swelling in neurons have previously been reported. Furthermore, the role of vH+ -ATPase in neurotransmitter transport into synaptic vesicles has also been shown. Using nanometer-scale precision measurements of isolated synaptic vesicles, the present study reports for the first time the involvement of vH+ -ATPase in GTP-G,o -mediated synaptic vesicle swelling. Results from this study demonstrate that the GTP-G,o -mediated vesicle swelling is vH+ -ATPase dependent and pH sensitive. Zeta potential measurements of isolated synaptic vesicles further demonstrate a bafilomycin-sensitive vesicle acidification, following the GTP-G,o -induced swelling stimulus. Water channels are bidirectional and the vH+ -ATPase inhibitor bafilomycin decreases both the volume of isolated synaptic vesicles and GTP-mastoparan stimulated swelling, suggesting that vH+ -ATPase is upstream of AQP-6, in the pathway leading from G,o -stimulated swelling of synaptic vesicles. Vesicle acidification is therefore a prerequisite for AQP-6-mediated gating of water into synaptic vesicles. © 2009 Wiley-Liss, Inc. [source] Existence of a tightly regulated water channel in Saccharomyces cerevisiaeFEBS JOURNAL, Issue 2 2001Valérie Meyrial The Saccharomyces cerevisiae strain ,1278b possesses two putative aquaporins, Aqy1-1p and Aqy2-1p. Previous work demonstrated that Aqy1-1p functions as a water channel in Xenopus oocyte. However, no function could be attributed to Aqy2-1p in this system. Specific antibodies were used to follow the expression of Aqy1-1p and Aqy2-1p in the yeast. Aqy1-1p was never detected whatever the growth phase and culture conditions tested. In contrast, Aqy2-1p was detected only during the exponential growth phase in rich medium containing glucose. Aqy2-1p expression was repressed by hyper-osmotic culture conditions. Both immunocytochemistry and biochemical subcellular fractionation demonstrated that Aqy2-1p is located on the endoplasmic reticulum (ER) as well as on the plasma membrane. In microsomal vesicles enriched in ER, a water channel activity due to Aqy2-1p was detected by stopped-flow analysis. Our results show that the expression of aquaporins is tightly controlled. The physiological relevance of aquaporin-mediated water transport in yeast is discussed. [source] Experimental investigation of turbulent boundary layer flow with surfactant additives using PIV and PDAHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2005Wang Dezhong Abstract Drag reduction of turbulent water flow with surfactant (CTAC) additives was experimentally investigated. By using PIV and PDA measurements, the spatial velocity distribution of surfactant solution flow was clarified in a two-dimensional water channel. With an increasing Reynolds number, it was found that drag reduction of surfactant solution flow is enhanced within the region of drag reduction. However, in the region of post drag reduction, the drag-reducing coefficient approaches one without surfactant when Reynolds number is increased. In the near-wall region, velocity profiles of the drag-reducing fluid are similar to, but not the same as, the laminar profiles of the Newtonian fluid. When compared to the case of water flow without surfactant, the velocity contour lines of the drag-reducing fluid run approximately parallel to the wall. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 99,107, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20047 [source] Glucagon induces the plasma membrane insertion of functional aquaporin-8 water channels in isolated rat hepatocytesHEPATOLOGY, Issue 6 2003Sergio A. Gradilone Although glucagon is known to stimulate the cyclic adenosine monophosphate (cAMP)-mediated hepatocyte bile secretion, the precise mechanisms accounting for this choleretic effect are unknown. We recently reported that hepatocytes express the water channel aquaporin-8 (AQP8), which is located primarily in intracellular vesicles, and its relocalization to plasma membranes can be induced with dibutyryl cAMP. In this study, we tested the hypothesis that glucagon induces the trafficking of AQP8 to the hepatocyte plasma membrane and thus increases membrane water permeability. Immunoblotting analysis in subcellular fractions from isolated rat hepatocytes indicated that glucagon caused a significant, dose-dependent increase in the amount of AQP8 in plasma membranes (e.g., 102% with 1 ,mol/L glucagon) and a simultaneous decrease in intracellular membranes (e.g., 38% with 1 ,mol/L glucagon). Confocal immunofluorescence microscopy in cultured hepatocytes confirmed the glucagon-induced redistribution of AQP8 from intracellular vesicles to plasma membrane. Polarized hepatocyte couplets showed that this redistribution was specifically to the canalicular domain. Glucagon also significantly increased hepatocyte membrane water permeability by about 70%, which was inhibited by the water channel blocker dimethyl sulfoxide (DMSO). The inhibitors of protein kinase A, H-89, and PKI, as well as the microtubule blocker colchicine, prevented the glucagon effect on both AQP8 redistribution to hepatocyte surface and cell membrane water permeability. In conclusion, our data suggest that glucagon induces the protein kinase A and microtubule-dependent translocation of AQP8 water channels to the hepatocyte canalicular plasma membrane, which in turn leads to an increase in membrane water permeability. These findings provide evidence supporting the molecular mechanisms of glucagon-induced hepatocyte bile secretion. [source] p.R254Q mutation in the aquaporin-2 water channel causing dominant nephrogenic diabetes insipidus is due to a lack of arginine vasopressin-induced phosphorylation,HUMAN MUTATION, Issue 10 2009Paul JM Savelkoul Abstract Vasopressin regulates human water homeostasis by re-distributing homotetrameric aquaporin-2 (AQP2) water channels from intracellular vesicles to the apical membrane of renal principal cells, a process in which phosphorylation of AQP2 at S256 by cAMP-dependent protein kinase A (PKA) is thought to be essential. Dominant nephrogenic diabetes insipidus (NDI), a disease in which the kidney is unable to concentrate urine in response to vasopressin, is caused by AQP2 gene mutations. Here, we investigated a reported patient case of dominant NDI caused by a novel p.R254Q mutation. Expressed in oocytes, AQP2-p.R254Q appeared to be a functional water channel, but was impaired in its transport to the cell surface to the same degree as AQP2-p.S256A, which mimics non-phosphorylated AQP2. In polarized MDCK cells, AQP2-p.R254Q was retained and was distributed similarly to that of unstimulated wt-AQP2 or AQP2-p.S256A. Upon co-expression, AQP2-p.R254Q interacted with, and retained wt-AQP2 in intracellular vesicles. In contrast to wild-type AQP2, forskolin did not increase AQP2-p.R254Q phosphorylation at S256 or its translocation to the apical membrane. Mimicking constitutive phosphorylation in AQP2-p.R254Q with the p.S256D mutation, however, rescued its apical membrane expression. These date indicate that a lack of S256 phosphorylation is the sole cause of dominant NDI here, and thereby, p.R254Q is a loss of function instead of a gain of function mutation in dominant NDI. © 2009 Wiley-Liss, Inc. [source] The formation of dunes, antidunes, and rapidly damping waves in alluvial channelsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2001L.-H. Huang Abstract Under the effect of a constant current for a long time, a water channel of infinitely long and constant depth interacting with a uniform sandbed of infinite thickness is used to simulate the formation of dunes, antidunes and rapidly damping waves in alluvial channels. The theory of potential flow is applied to the channel flow, while Biot's theory of poroelasticity is adopted to deal with erodible bed material. The governing equations, together with free surface, bed surface, and far field boundary conditions, form a complete boundary-value problem without applying empirical sediment discharge formulas as in conventional researches. The comparison of the present result with Kennedy's (Journal of Fluid Mechanics, 1963; 16: 521,544) instability analysis not only indicates the appropriateness of the present work, but also reveals the advantage of the present study due to its ability to find all kinds of bed forms (including the rapidly damping waves that Kennedy could not find) and of solving for the unclear lagged distance , introduced in Kennedy's work. Copyright © 2001 John Wiley & Sons, Ltd. [source] Sex- and region-specific alterations of basal amino acid and monoamine metabolism in the brain of aquaporin-4 knockout miceJOURNAL OF NEUROSCIENCE RESEARCH, Issue 4 2005Yi Fan Abstract Aquaporin-4 (AQP4), a predominant water channel of the brain, mediates transmembrane water movement at the blood,brain barrier and brain,cerebrospinal fluid interface. A broad pattern of evidence indicates that AQP4 and regulators of its expression are potential targets for treatment of brain swelling, but whether it participates in the regulation of neurotransmission has not been reported. We examined neurochemical differences between AQP4-knockout and wild-type mice with particular focus on neurotransmission. Basal tissue neurotransmitter and metabolite levels were measured by high-performance liquid chromatography. Significant sex- and region-specific differences of amino acids and monoamines were found in the brain of wild-type and AQP4-knockout mice. In cortex, striatum, and hippocampus of male AQP4-knockout mice, an increase of glutamine and decrease of aspartate were observed. Glutamate was increased only in female AQP4-knockout mice. The lack of AQP4 failed to affect the levels of ,-aminobutyric acid and taurine. In the medial prefrontal cortex of AQP4-knockout mice, the levels of serotonin and norepinephrine were increased, but no significant change in dopamine level was found. In the striatum of male AQP4-knockout mice, the levels of dopamine and serotonin were remarkably increased, which was not found in female mice. In the hypothalamus of AQP4-knockout mice, only the serotonin level was altered. These results provide the first evidence that the lack of AQP4 expression is accompanied by sex- and region-specific alterations in brain amino acid and monoamine metabolism. © 2005 Wiley-Liss, Inc. [source] Expression of aquaporin 8 is diversely regulated by osmotic stress in amnion epithelial cellsJOURNAL OF OBSTETRICS AND GYNAECOLOGY RESEARCH (ELECTRONIC), Issue 6 2009Hongbo Qi Abstract Aim:, Water absorption across fetal chorioamniotic membranes is a critical regulatory pathway for amniotic fluid volume homeostasis. Aquaporin 8 (AQP8) is a water channel regulating osmotic water travel across membranes. This study was to investigate the distribution and expression of AQP8 in amnion epithelial cells (AEC) in response to different osmotic stresses. Methods:, Cells derived from the amnion were subjected to different osmotic culture media. Reverse transcriptase,polymerase chain reaction, Western blotting and immunofluorescence analysis were used to determine expression and localization of AQP8. Results:, Immunofluorescent staining confirmed the expression of AQP8 on cytomembrane and in cytoplasm. Hypotonic media increased AQP8 on cytomembrane of AEC. Compared to isosmolar media, hypotonic media significantly enhanced AQP8 mRNA and protein expression (P < 0.05), while hypertonic media significantly decreased expression (P < 0.05). Conclusion:, The expression and distribution of AQP8 in AEC are diversely regulated by osmotic loads suggesting a role for AQP8 in intramembranous water transport and the balance of amniotic fluid. [source] Astroglial structures in the zebrafish brain,THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 21 2010Larissa Grupp Abstract To understand components shaping the neuronal environment we studied the astroglial cells in the zebrafish brain using immunocytochemistry for structural and junctional markers, electron microscopy including freeze fracturing, and probed for the water channel protein aquaporin-4. Glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) showed largely overlapping immunoreactivity: GFAP in the main glial processes and GS in main processes and smaller branches. Claudin-3 immunoreactivity was spread in astroglial cells along their major processes. The ventricular lining was immunoreactive for the tight-junction associated protein ZO-1, in the telencephalon located on the dorsal, lateral, and medial surface due to the everting morphogenesis. In the tectum, subpial glial endfeet were also positive for ZO-1. Correspondingly, electron microscopy revealed junctional complexes between subpial glial endfeet. However, in freeze-fracture analysis tight junctional strands were not found between astroglial membranes, either in the optic tectum or in the telencephalon. Occurrence of aquaporin-4, the major astrocytic water channel in mammals, was demonstrated by polymerase chain reaction (PCR) analysis and immunocytochemistry in tectum and telencephalon. Localization of aquaporin-4 was not polarized but distributed along the entire radial extent of the cell. Interestingly, their membranes were devoid of the orthogonal arrays of particles formed by aquaporin-4 in mammals. Finally, we investigated astroglial cells in proliferative areas. Brain lipid basic protein, a marker of early glial differentiation but not GS, were present in some proliferation zones, whereas cells lining the ventricle were positive for both markers. Thus, astroglial cells in the zebrafish differ in many aspects from mammalian astrocytes. J. Comp. Neurol. 518:4277,4287, 2010. © 2010 Wiley-Liss, Inc. [source] Air,sea exchanges in the equatorial area from the EQUALANT99 dataset: Bulk parametrizations of turbulent fluxes corrected for airflow distortionTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 610 2005A. Brut Abstract Turbulent fluxes of momentum, sensible heat and water vapour were calculated using both the eddy covariance (EC) and the inertial dissipation (ID) methods applied to data collected on board the research vessel La Thalassa during 40 days of the EQUALANT99 oceanographic campaign. The aim of this experiment was to establish accurate parametrizations of air,sea fluxes for the equatorial Atlantic area from a large dataset. However, the accuracy of turbulent fluxes measured aboard ships is strongly affected by the distortion of airflow patterns generated by obstacles such as the ship and mast. For the EQUALANT99 experiment, the effects of airflow distortion were estimated using physical simulations in a water channel. To reproduce the conditions of the campaign, a neutral boundary layer was simulated in the water channel and a detailed model of the ship La Thalassa was built. Correction coefficients for the mean wind speed were evaluated from these physical simulations. They show a dependence on both the azimuth angle of the flow (i.e. the horizontal direction of the flow with respect to the ship's longitudinal axis) and the angle of incidence of the wind. The correction for airflow distortion was applied to the measured wind speed and also included in the flux computation using the ID method. Compared with earlier studies which applied a single correction per flux sample, it appears that our results for the corrected transfer coefficients present greater dependence on neutral wind speed than the previous parametrizations; the method also shows encouraging results, with a decrease in the scatter of the transfer coefficients parametrization. However, the distortion could not be corrected for in the fluxes calculated using the EC method, because this technique integrates a wide range of turbulence scales for which the airflow distortion cannot be simulated in a water channel. Fluxes computed using the ID and EC methods are presented and compared in order to determine which method, in the configuration of the EQUALANT99 experiment, provides the best resulting transfer coefficients. According to the results, fluxes of momentum and latent heat computed by ID were better for deriving the drag and humidity coefficients. The EC method seemed better adapted to calculate sensible-heat fluxes than the ID method, although a high scatter remained on the Stanton neutral number. Copyright © 2005 Royal Meteorological Society [source] Intrathecal pathogenic anti,aquaporin-4 antibodies in early neuromyelitis optica,ANNALS OF NEUROLOGY, Issue 5 2009Jeffrey L. Bennett MD Objective The serum of most neuromyelitis optica (NMO) patients contains autoantibodies (NMO-IgGs) directed against the aquaporin-4 (AQP4) water channel located on astrocyte foot processes in the perivessel and subpial areas of the brain. Our objectives were to determine the source of central nervous system (CNS) NMO-IgGs and their role in disease pathogenesis. Methods Fluorescence-activated cell sorting and single-cell reverse transcriptase polymerase chain reaction were used to identify overrepresented plasma cell immunoglobulin (Ig) sequences in the cerebrospinal fluid (CSF) of an NMO patient after a first clinical attack. Monoclonal recombinant antibodies (rAbs) were generated from the paired heavy and light chain sequences and tested for target specificity and Fc effector function. The effect of CSF rAbs on CNS immunopathology was investigated by delivering single rAbs to rats with experimental autoimmune encephalomyelitis (EAE). Results Repertoire analysis revealed a dynamic, clonally expanded plasma cell population with features of an antigen-targeted response. Using multiple independent assays, 6 of 11 rAbs generated from CSF plasma cell clones specifically bound to AQP4. AQP4-specific rAbs recognized conformational epitopes and mediated both AQP4-directed antibody-dependent cellular cytotoxicity and complement-mediated lysis. When administered to rats with EAE, an AQP4-specific NMO CSF rAb induced NMO immunopathology: perivascular astrocyte depletion, myelinolysis, and complement and Ig deposition. Interpretation Molecular characterization of the CSF plasma cell repertoire in an early NMO patient demonstrates that AQP4-specfic Ig is synthesized intrathecally at disease onset and directly contributes to CNS pathology. AQP4 is now the first confirmed antigenic target in human demyelinating disease. Ann Neurol 2009;66:617,629 [source] Neuromyelitis optica: Pathogenicity of patient immunoglobulin in vivo,ANNALS OF NEUROLOGY, Issue 5 2009Monika Bradl PhD Objective Severe inflammation and astrocyte loss with profound demyelination in spinal cord and optic nerves are typical pathological features of neuromyelitis optica (NMO). A diagnostic hallmark of this disease is the presence of serum autoantibodies against the water channel aquaporin-4 (AQP-4) on astrocytes. Methods We induced acute T-cell,mediated experimental autoimmune encephalomyelitis in Lewis rats and confronted the animals with an additional application of immunoglobulins from AQP-4 antibody,positive and ,negative NMO patients, multiple sclerosis patients, and control subjects. Results The immunoglobulins from AQP-4 antibody,positive NMO patients are pathogenic. When they reach serum titers in experimental animals comparable with those seen in NMO patients, they augment clinical disease and induce lesions in the central nervous system that are similar in structure and distribution to those seen in NMO patients, consisting of AQP-4 and astrocyte loss, granulocytic infiltrates, T cells and activated macrophages/microglia cells, and an extensive immunoglobulin and complement deposition on astrocyte processes of the perivascular and superficial glia limitans. AQP-4 antibody containing NMO immunoglobulin injected into naïve rats, young rats with leaky blood,brain barrier, or after transfer of a nonencephalitogenic T-cell line did not induce disease or neuropathological alterations in the central nervous system. Absorption of NMO immunoglobulins with AQP-4,transfected cells, but not with mock-transfected control cells, reduced the AQP-4 antibody titers and was associated with a reduction of astrocyte pathology after transfer. Interpretation Human anti,AQP-4 antibodies are not only important in the diagnosis of NMO but also augment disease and induce NMO-like lesions in animals with T-cell,mediated brain inflammation. Ann Neurol 2009;66:630,643 [source] Functional Studies of Synthetic Gramicidin Hybrid Ion Channels in CHO CellsCHEMBIOCHEM, Issue 5 2007Ryszard Wesolowski Abstract The function of a gramicidin hybrid ion channel in living Chinese hamster ovary (CHO) cells was investigated by the patch clamp method. The synthetic ion channel 1 consists of two cyclohexyl ether amino acids that link two minigramicidin strands. With 1 at a concentration of 1.0 ,M, an increase in the whole-cell membrane conductance was observed after 1.37 min. The conductance showed larger currents when Cs+ was used as charge carrier than when Na+ and K+ were used. In single-channel recordings with Cs+ as charge carrier, the substance showed comparable single-channel amplitudes in the membrane of living cells and artificial black lipid bilayers. In addition to functioning as a cation channel, compound 1 appeared to be a water channel. Exposure of the CHO cells to an extracellular hypoosmotic solution did not substantially change the cell volume. Extracellular hypoosmotic conditions in the presence of 1 increased the cell size to 146.5,% that of the control. Thus, the synthetic hybrid channel 1 can function as a cation channel with some Cs+ specificity, and as a water channel in CHO cells. [source] Urinary excretion of the aquaporin-2 water channel exaggerated in pathological states of impaired water excretionCLINICAL ENDOCRINOLOGY, Issue 2 2001Takako Saito OBJECTIVE The present study was undertaken to determine whether the hydro-osmotic action of arginine vasopressin (AVP) is exaggerated in pathological states of impaired water excretion by measuring urinary excretion of the aquaporin-2 (AQP-2) water channel. PATIENTS AND MEASUREMENTS Eighteen hyponatraemic patients with impaired water excretion and 12 control subjects were studied during an acute oral water load (20 ml/kg body weight). RESULTS In the patient group plasma AVP levels were 1·6 pmol/l, relatively high compared to plasma osmolality of 279·8 mmol/kg. Urinary excretion of AQP-2 under ad libitum water drinking was 41·1 fmol/umol creatinine in the patient group, a value significantly greater than that of 21·7 fmol/,mol creatinine in the control subjects. The acute water load verified the impairment in water excretion in the patient group, as the excretion of the water load was only 28·2% (control, 77·3%, P < 0·001) and the minimum urinary osmolality was as high as 437·3 mmol/kg (control, 122·9 mmol/kg, P < 0·001). Also, the minimum urinary excretion of AQP-2 was significantly greater in the patient group than that in the control. There was a positive correlation between plasma AVP levels and urinary excretion of AQP-2 in the control subjects (r = 0·56, P < 0·01). In contrast, the urinary excretion of AQP-2 was exaggerated compared to the respective plasma AVP levels in the patient group, and thus the positive correlation disappeared. CONCLUSION These results indicate that hydroosmotic action of AVP is exaggerated more than that expected from plasma AVP levels in pathological states of impaired water excretion, with non-suppressible, but normal, arginine vasopressin levels in spite of the hypo-osmotic condition. [source] AQP4 expression in striatal primary cultures is regulated by dopamine , implications for proliferation of astrocytesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2008Eva Küppers Abstract Proliferation of astrocytes plays an essential role during ontogeny and in the adult brain, where it occurs following trauma and in inflammation and neurodegenerative diseases as well as in normal, healthy mammals. The cellular mechanisms underlying glial proliferation remain poorly understood. As dopamine is known to modulate proliferation in different cell populations, we investigated the effects of dopamine on the proliferation of striatal astrocytes in vitro. We found that dopamine reduced proliferation. As proliferation involves, among other things, a change in cell volume, which normally comes with water movement across the membrane, water channels might represent a molecular target of the dopamine effect. Therefore we studied the effect of dopamine on aquaporin 4 (AQP4) expression, the main aquaporin subtype expressed in glial cells, and observed a down-regulation of the AQP4-M23 isoform. This down-regulation was the cause of the dopamine-induced decrease in proliferation as knockdown of AQP4 using siRNA techniques mimicked the effects of dopamine on proliferation. Furthermore, stimulation of glial proliferation by basic fibroblast growth factor was also abolished by knocking down AQP4. In addition, blocking of AQP4 with 10 ,m tetraethylammonium inhibited osmotically induced cell swelling and stimulation of glial cell proliferation by basic fibroblast growth factor. These results demonstrate a clear-cut involvement of AQP4 in the regulation of proliferation and implicate that modulation of AQP4 could be used therapeutically in the treatment of neurodegenerative diseases as well as in the regulation of reactive astrogliosis by preventing or reducing the glia scar formation, thus improving regeneration following ischemia or other trauma. [source] Potassium channel Kir4.1 macromolecular complex in retinal glial cellsGLIA, Issue 2 2006Nathan C. Connors Abstract A major role for Müller cells in the retina is to buffer changes in the extracellular K+ concentration ([K+]o) resulting from light-evoked neuronal activity. The primary K+ conductance in Müller cells is the inwardly rectifying K+ channel Kir4.1. Since this channel is constitutively active, K+ can enter or exit Müller cells depending on the state of the [K+]o. This process of [K+]o buffering by Müller cells ("K+ siphoning") is enhanced by the precise accumulation of these K+ channels at discrete subdomains of Müller cell membranes. Specifically, Kir4.1 is localized to the perivascular processes of Müller cells in animals with vascular retinas and to the endfeet of Müller cells in all species examined. The water channel aquaporin-4 (AQP4) also appears to be important for [K+]o buffering and is expressed in Müller cells in a very similar subcellular distribution pattern to that of Kir4.1. To gain a better understanding of how Müller cells selectively target K+ and water channels to discrete membrane subdomains, we addressed the question of whether Kir4.1 and AQP4 associate with the dystrophin,glycoprotein complex (DGC) in the mammalian retina. Immunoprecipitation (IP) experiments were utilized to show that Kir4.1 and AQP4 are associated with DGC proteins in rat retina. Furthermore, AQP4 was also shown to co-precipitate with Kir4.1, suggesting that both channels are tethered together by the DGC in Müller cells. This work further defines a subcellular localization mechanism in Müller cells that facilitates [K+]o buffering in the retina. © 2005 Wiley-Liss, Inc. [source] Glucagon induces the plasma membrane insertion of functional aquaporin-8 water channels in isolated rat hepatocytesHEPATOLOGY, Issue 6 2003Sergio A. Gradilone Although glucagon is known to stimulate the cyclic adenosine monophosphate (cAMP)-mediated hepatocyte bile secretion, the precise mechanisms accounting for this choleretic effect are unknown. We recently reported that hepatocytes express the water channel aquaporin-8 (AQP8), which is located primarily in intracellular vesicles, and its relocalization to plasma membranes can be induced with dibutyryl cAMP. In this study, we tested the hypothesis that glucagon induces the trafficking of AQP8 to the hepatocyte plasma membrane and thus increases membrane water permeability. Immunoblotting analysis in subcellular fractions from isolated rat hepatocytes indicated that glucagon caused a significant, dose-dependent increase in the amount of AQP8 in plasma membranes (e.g., 102% with 1 ,mol/L glucagon) and a simultaneous decrease in intracellular membranes (e.g., 38% with 1 ,mol/L glucagon). Confocal immunofluorescence microscopy in cultured hepatocytes confirmed the glucagon-induced redistribution of AQP8 from intracellular vesicles to plasma membrane. Polarized hepatocyte couplets showed that this redistribution was specifically to the canalicular domain. Glucagon also significantly increased hepatocyte membrane water permeability by about 70%, which was inhibited by the water channel blocker dimethyl sulfoxide (DMSO). The inhibitors of protein kinase A, H-89, and PKI, as well as the microtubule blocker colchicine, prevented the glucagon effect on both AQP8 redistribution to hepatocyte surface and cell membrane water permeability. In conclusion, our data suggest that glucagon induces the protein kinase A and microtubule-dependent translocation of AQP8 water channels to the hepatocyte canalicular plasma membrane, which in turn leads to an increase in membrane water permeability. These findings provide evidence supporting the molecular mechanisms of glucagon-induced hepatocyte bile secretion. [source] Altered aquaporin 9 expression and localization in human hepatocellular carcinomaHPB, Issue 1 2009Srikanth Padma Abstract Background:, In addition to the biochemical components secreted in bile, aquaporin (AQP) water channels exist in hepatocyte membranes to form conduits for water movement between the sinusoid and the bile canaliculus. The aim of the current study was to analyse AQP 9 expression and localization in human hepatocellular carcinoma (HCC) and non-tumourigenic liver (NTL) tissue from patients undergoing hepatic resection. Methods:, Archived tissue from 17 patients was sectioned and analysis performed using an antibody raised against AQP 9. Slides were blind-scored to determine AQP 9 distribution within HCC and NTL tissue. Results:, Aquaporin 9 was predominantly expressed in the membranes of hepatocytes and demonstrated zonal distribution relative to hepatic sinusoid structure in normal liver. In HCC arising in the absence of cirrhosis AQP 9 remained membrane-localized with zonal distribution in the majority of NTL. By contrast, AQP 9 expression was significantly decreased in the HCC mass vs. pair-matched NTL. In HCC in the presence of cirrhosis, NTL was characterized by extensive AQP 9 staining in the membrane in the absence of zonal distribution and AQP 9 staining in NTL was significantly greater than that observed in the tumour mass. Conclusions:, These data demonstrate that human HCC is characterized by altered AQP 9 expression and AQP 9 localization in the NTL mass is dependent on underlying liver pathology. Given the central role of AQPs in normal liver function and the potential role of AQPs during transformation and progression, these data may prove valuable in future diagnostic and/or therapeutic strategies. [source] p.R254Q mutation in the aquaporin-2 water channel causing dominant nephrogenic diabetes insipidus is due to a lack of arginine vasopressin-induced phosphorylation,HUMAN MUTATION, Issue 10 2009Paul JM Savelkoul Abstract Vasopressin regulates human water homeostasis by re-distributing homotetrameric aquaporin-2 (AQP2) water channels from intracellular vesicles to the apical membrane of renal principal cells, a process in which phosphorylation of AQP2 at S256 by cAMP-dependent protein kinase A (PKA) is thought to be essential. Dominant nephrogenic diabetes insipidus (NDI), a disease in which the kidney is unable to concentrate urine in response to vasopressin, is caused by AQP2 gene mutations. Here, we investigated a reported patient case of dominant NDI caused by a novel p.R254Q mutation. Expressed in oocytes, AQP2-p.R254Q appeared to be a functional water channel, but was impaired in its transport to the cell surface to the same degree as AQP2-p.S256A, which mimics non-phosphorylated AQP2. In polarized MDCK cells, AQP2-p.R254Q was retained and was distributed similarly to that of unstimulated wt-AQP2 or AQP2-p.S256A. Upon co-expression, AQP2-p.R254Q interacted with, and retained wt-AQP2 in intracellular vesicles. In contrast to wild-type AQP2, forskolin did not increase AQP2-p.R254Q phosphorylation at S256 or its translocation to the apical membrane. Mimicking constitutive phosphorylation in AQP2-p.R254Q with the p.S256D mutation, however, rescued its apical membrane expression. These date indicate that a lack of S256 phosphorylation is the sole cause of dominant NDI here, and thereby, p.R254Q is a loss of function instead of a gain of function mutation in dominant NDI. © 2009 Wiley-Liss, Inc. [source] Role of aquaporins in endothelial water transportJOURNAL OF ANATOMY, Issue 5 2002A. S. Verkman The aquaporins (AQP) are a family of homologous water channels expressed in many epithelial and endothelial cell types involved in fluid transport. AQP1 protein is strongly expressed in most microvascular endothelia outside of the brain as well as in endothelial cells in cornea, intestinal lacteals, and other tissues. AQP4 is expressed in astroglial foot processes adjacent to endothelial cells in the central nervous system. Transgenic mice lacking aquaporins have been useful in defining their role in mammalian physiology. Mice lacking AQP1 manifest defective urinary concentrating ability, in part because of decreased water permeability in renal vasa recta microvessels. These mice also show a defect in dietary fat processing that may involve chylomicron absorption by intestinal lacteals. There is preliminary evidence that AQP1 might play a role in tumour angiogenesis and in renal microvessel structural adaptation. However AQP1 in most endothelial tissues does not appear to have a physiological function despite its role in osmotically driven water transport. For example mice lacking AQP1 have low alveolar capillary water permeability but unimpaired lung fluid absorption, as well as unimpaired saliva and tear secretion, aqueous fluid outflow, and pleural and peritoneal fluid transport. In the central nervous system mice lacking AQP4 are partially protected from brain oedema in water intoxication and ischaemic models of brain injury. Therefore although the role of aquaporins in epithelial fluid transport is in most cases well understood there remain many questions about the role of aquaporins in endothelial cell function. It is unclear why many leaky microvessels strongly express AQP1 without apparent functional significance. Improved understanding of aquaporin endothelial biology may lead to novel therapies for human disease, such as pharmacological modulation of tumour angiogenesis, renal fluid clearance and intestinal absorption. [source] Factors affecting the formation of fingering in water-assisted injection-molded thermoplasticsADVANCES IN POLYMER TECHNOLOGY, Issue 2 2006Shih-Jung Liu Abstract Water-assisted injection-molding technology has received extensive attention in recent years, due to the lightweight of plastic parts, relatively low-resin cost per part, faster cycle time, and flexibility in the design and manufacture. However, there are still some unsolved problems that confound the overall success of this technology. One of these is the water "fingering" phenomenon, in which the water bubbles penetrate outside designed water channels and form finger-shape branches. This study has investigated the effects of various processing parameters on the formation of fingering in water-assisted injection-molded thermoplastic parts. Both amorphous and semicrystalline polymers were used to mold the parts. The influence of water channel geometry, including aspect ratio and fillet geometry, on the fingering was also investigated. It was found that water-assisted injection-molded amorphous materials gave less fingering, while molded semicrystalline parts gave more fingering when compared to those molded by gas-assisted injection molding. For the water channels used in this study, the channels with a rib on the top produced parts with the least water fingering. Water fingering in molded parts decreases with the height-to-thickness ratio of the channels. The water pressure, water injection delay time and short-shot size were found to be the principal parameters affecting the formation of water fingering. In addition, a numerical simulation based on the transient heat conduction model was also carried out to help better explain the mechanism for the formation of fingering in water-assisted injection-molded thermoplastics. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 98,108, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20062 [source] The Peritoneal Microcirculation in Peritoneal DialysisMICROCIRCULATION, Issue 5 2001BENGT RIPPE ABSTRACT This paper deals with the peritoneal microcirculation and with peritoneal exchange occurring in peritoneal dialysis (PD). The capillary wall is a major barrier to solute and water exchange across the peritoneal membrane. There is a bimodal size-selectivity of solute transport between blood and the peritoneal cavity, through pores of radius ,40,50 Å as well as through a very low number of large pores of radius ,250 Å. Furthermore, during glucose-induced osmosis during PD, nearly 40% of the total osmotic water flow occurs through molecular water channels, termed "aquaporin-1." This causes an inequality between 1,, and the sieving coefficient for small solutes, which is a key feature of the "threepore model" of peritoneal transport. The peritoneal interstitium, coupled in series with the capillary walls, markedly modifies small-solute transport and makes large-solute transport asymmetric. Thus, although severely restricted in the blood-to-peritoneal direction, the absorption of large solutes from the peritoneal cavity occurs at a high clearance rate (,1 mL/min), largely independent of molecular radius. True absorption of macromolecules to the blood via lymphatics, however, seems to be occurring at a rate of ,0.2 mL/min. Several controversial issues regarding transcapillary and transperitoneal exchange mechanisms are discussed in this paper. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 8 2009The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive). Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 1 2009The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive). Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 11-12 2008The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive). Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 11-12 2007The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive). Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 1 2007The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive). Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 12 2006The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive. Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 11 2006The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive. Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] Cover Picture: QSAR Comb.MOLECULAR INFORMATICS, Issue 10 2006The transmembrane protein aquaporin spans biological membranes and forms channels that allow the passage of water molecules. The water channels consist of alpha helices (purple cylinders) and are shown as a Conolly surface,in which the electrostatic potential is represented by colors (blue: negative, red: positive. Peter Agre and Roderick MacKinnon were awarded the 2003 Nobel Prize in chemistry for the discovery of water channels and for structural and mechanistic studies on ion channels, respectively. Cover illustration by courtesy of Prof. Dr. Jürgen Brickmann, Dr. Thorsten Borosch, MOLNET e.V. [source] | |||||||||||||||||||