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Water Permeability (water + permeability)
Selected AbstractsAquaporin-1 and aquaporin-2 urinary excretion in cirrhosis: Relationship with ascites and hepatorenal syndrome,HEPATOLOGY, Issue 6 2006Christina Esteva-Font Several experimental models of cirrhosis have shown dysregulation of renal aquaporins in different phases of liver disease. We investigated the urinary excretion of both aquaporin-1 and aquaporin-2 in patients with cirrhosis at different stages of the disease. Twenty-four-hour urine was collected from 11 healthy volunteers, 13 patients with compensated cirrhosis (without ascites), and 20 patients with decompensated cirrhosis (11 with ascites without renal failure and 9 with hepatorenal syndrome). Aquaporin-1 and aquaporin-2 excretion was analyzed by immunoblotting. Urinary aquaporin-2 excretion was reduced in patients with cirrhosis compared to healthy subjects. A progressive decrease in urinary aquaporin-2 excretion was observed as the severity of cirrhosis increased, from compensated cirrhosis to cirrhosis with ascites and hepatorenal syndrome. Patients with hyponatremia had lower urinary aquaporin-2 excretion than patients without hyponatremia. Vasopressin plasma level did not correlate with aquaporin-2 excretion. There were no differences between healthy subjects and patients with cirrhosis with or without ascites in urinary excretion of aquaporin-1, but urinary aquaporin-1 excretion of those with hepatorenal syndrome was extremely low. In conclusion, patients with cirrhosis appear to exhibit a decreased abundance of renal aquaporin-2 and therefore lower water permeability in the collecting tubules. This may represent an adaptive renal response to sodium retention, with expansion of extracellular fluid volume and dilutional hyponatremia observed in those who have cirrhosis with ascites. Finally, aquaporin-1 does not appear to play a role in the progressive dysregulation of extracellular fluid volume in cirrhosis. (HEPATOLOGY 2006;44:1555,1563.) [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] 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] Fluoropassivation and gelatin sealing of polyester arterial prostheses to skip preclotting and constrain the chronic inflammatory responseJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2010Xingyi Xie Abstract Fluoropassivation and gelatin coating have been applied to polyethylene terephthalate (PET) vascular prosthesis to combine the advantages of both polytetrafluoroethylene (PTFE) and PET materials, and to eliminate the preclotting procedure. The morphological, chemical, physical, and mechanical properties of such prostheses were investigated and compared with its original model. Fluoropassivation introduced OCF3, CF3, and CFCF2 structures onto the surface of the polyester fibers. However, the surface fluorine content was only 28,32% compared to the 66% in expanded PTFE (ePTFE) grafts. The fluoropassivation decreased the hydrophilicity, slightly increased the water permeability, and marginally lowered the melting point and the crystallinity of the PET fibers. After gelatin coating, the fluoropassivated and nonfluoropassivated prostheses showed similar surface morphology and chemistry. While gelatin coating eliminated preclotting, it also renders the prostheses slightly stiffer. The original prosthesis had the highest bursting strength (275 N), with the fluoropassivated and gelatin-sealed devices showing similar bursting strength between 210 and 230 N. Fluoropassivation and gelatin coating lowered the retention strength by 23 and 30% on average, respectively. In vitro enzymatic incubation had only marginal effect on the surface fluorine content of the nongelatin-sealed prostheses. However, the gelatin-sealed ones significantly lost their surface fluorine after in vitro enzymatic incubation (by 69,85%) or in vivo 6-month implantation (by 51,60%), showing the lability of the fluoropolymer layer under the hostile biological environment. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Polyamide-imide nanofiltration hollow fiber membranes with elongation-induced nano-pore evolutionAICHE JOURNAL, Issue 6 2010Shi Peng Sun Abstract The molecular design of nanoporous membranes with desired morphology and selectivity has attracted significant interest over the past few decades. A major problem in their applications is the trade-off between sieving property and permeability. Here, we report the discovery of elongation-induced nano-pore evolution during the external stretching of a novel polyamide-imide nanofiltration hollow fiber membrane in a dry-jet wet-spinning process that simultaneously leads to a decreased pore size but increased pure water permeability. The molecular weight cutoff, pore size, and pore size distribution were finely tuned using this approach. AFM and polarized FTIR verified the nano-pore morphological evolution and an enhanced molecular orientation in the surface skin layer. The resultant nanofiltration membranes exhibit highly effective fractionation of the monovalent and divalent ions of NaCl/Na2SO4 binary salt solutions. More than 99.5% glutathione can be rejected by the nanofiltration membranes at neutral pH, offering the feasibility of recovering this tripeptide. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Some cesium and potassium salts increase the water permeability of astomatous isolated plant cuticlesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2007Salem Elshatshat Abstract Salts were applied as aqueous solution to the outer surfaces of astomatous isolated cuticles, and the water was allowed to evaporate. Effects of salt residues on the surfaces of cuticles on water permeability of cuticles were measured at 25°C. A surface dose of 0.2 mol m,2 Cs2CO3 and K2CO3 increased the water permeability of pear leaf cuticles by factors of 9.9 and 3.9, respectively. Na2CO3 was barely effective, and Li2CO3 as well as (NH4)2CO3 had no influence on water permeability. Potassium applied as sulfate, nitrate, or chloride had no effect on the water permeability of pear leaf cuticles, while K+ salts of weak acids (0.2 mol m,2) were effective, as they increased water permeability by factors of 5.4 (K+ -acetate), 3.9 (K2CO3), and 2.0 (K2HPO4), respectively. Sensitivity of Idesia polycarpa leaf cuticles to treatment with K2CO3 at 0.2 mol m,2 was greatest as water permeability was increased 35-fold, while the water permeability of cuticles from other species tested (astomatous leaf cuticles from Hedera helix, Citrus aurantium, Prunus laurocerasus, Pyrus communis, and Populus canescens; fruit cuticles from Capsicum annuum and Lycopersicon esculentum) increased only by factors ranging from 1.7 to 3.9. Data are discussed in relation to swelling and ion-exchange properties of cuticles. [source] Permeability and Conductivity Studies on Ionomer-Polysilsesquioxane Hybrid MaterialsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3 2006Chedarampet S. Karthikeyan Abstract Summary: Hybrid materials based on sulphonated poly(ether ether ketone) (SPEEK, ionomer) and (RSiO1.5)n network (polysilsequioxane) were prepared by sol-gel process. Two different precursors namely aminopropyl trimethoxysilane (APTMS) and imidazoleglycidoxypropyl trimethoxysilane (IGPTMS) were utilized to generate (RSiO1.5)n in SPEEK matrix by sol-gel process. 29Si MAS NMR confirmed the formation of RSiO3/2 network structure inside the matrix. Characterisation of the hybrid materials showed lower methanol and water permeability compared to the plain SPEEK. They are therefore promising materials as membranes for direct methanol fuel cells applications. The hybrid material derived from amino group was more effective in decreasing the permeability than the material derived from imidazole group. However, the proton conductivity of the latter was higher than the material derived from amino group. The results indicate that hybrid material prepared from imidazole containing silane is more suitable as a membrane for direct methanol fuel cell than the one prepared from amino carrying silane because it fulfils the two main requirements, namely low methanol permeability and reasonably good proton conductivity. Figure shows a network of silica phase in SPEEK matrix. [source] Hyperglycemia Stimulates a Sustained Increase in Hydraulic Conductivity In Vivo without Any Change in Reflection CoefficientMICROCIRCULATION, Issue 7 2007RACHEL M. PERRIN ABSTRACT Objective: Increased microvascular permeability contributes to the development of diabetic microvascular complications and diabetic vasculopathy is correlated with blood glucose levels. The mechanisms underlying increased permeability, however, are poorly understood. Methods: The Landis-Michel technique was used to measure water permeability (hydraulic conductivity, Lp) and macromolecular permeability (reflection coefficient, ,) of exchange capillaries in frogs and rats. Results: Dialysed normoglycemic plasma from diabetic patients had no effect on Lp. The same plasma with 20 mM glucose increased hydraulic conductivity from (mean ± SEM × 10,7 cm · s,1· cm H2O,1) 5.73 ± 2.01 to 13.09 ± 2.67 (P < .01). Nondiabetic control plasma did not affect Lp, but addition of 20 mM glucose increased Lp to a similar degree. The effect of glucose alone was examined. Glucose at 20 mM increased Lp, from 2.82 ± 0.61 to 4.71 ± 1.35 × 10, 7 cm · s, 1· cm H2O,1 (P = .002, n = 13). A similar increase was seen in rat mesenteric microvessels, from 1.04 ± 0.40 in control perfusions to 2.18 ± 0.56, P < .05. The microvascular macromolecular reflection coefficient in all the above experiments was unaltered. The use of specific inhibitors indicated that the glucose-induced increased Lp did not appear to be mediated through protein kinase C (PKC), free radical generation, glucose metabolism, or albumin glycation. Conclusions: These data suggest that hyperglycemia induced increased apparent protein permeability may be secondary to a glucose-mediated change in macromolecular convective flux rather than any change in protein permeability per se. The authors speculate that the increased microvascular permeability to water in vivo is mediated by direct interaction of glucose with the endothelial cells (perhaps with the glycocalyx). [source] Oxidative gating of water channels (aquaporins) in Chara by hydroxyl radicalsPLANT CELL & ENVIRONMENT, Issue 9 2004T. HENZLER ABSTRACT Hydroxyl radicals (*OH) as produced in the Fenton reaction (Fe2+ + H2O2 = Fe3+ + OH, + *OH) have been used to reversibly inhibit aquaporins in the plasma membrane of internodes of Chara corallina. Compared to conventional agents such as HgCl2, *OH proved to be more effective in blocking water channels and was less toxic to the cell. When internodes were treated for 30 min, cell hydraulic conductivity (Lp) decreased by 90% or even more. This effect was reversed within a few minutes after removing the radicals from the medium. In contrast to HgCl2, radical treatment reduced membrane permeability of small lipophilic organic solutes (ethanol, acetone, 1-propanol, and 2-propanol) by only 24 to 52%, indicating some continued limited movement of these solutes across aquaporins. The biggest effect of *OH treatment on solute permeability was found for isotopic water (HDO), which largely used water channels to cross the membrane. Inhibition of aquaporins reduced the diffusional water permeability (Pd) by about 70%. For the organic test solutes, which mainly use the bilayer to cross the membrane, channel closure caused anomalous (negative) osmosis; that is, cells had negative reflection coefficients (,s) and were transiently swelling in a hypertonic medium. From the ratio of bulk (Lp or osmotic permeability coefficient, Pf) to diffusional (Pd) permeability of water, the number (N) of water molecules that align in water channels was estimated to be N = Pf/Pd = 46 (on average). Radical treatment decreased N from 46 to 11, a value still larger than unity, which would be expected for a membrane lacking pores. The gating of aquaporins by *OH radicals is discussed in terms of a direct action of the radicals when passing the pores or by an indirect action via the bilayer. The rapid recovery of inhibited channels may indicate an easy access of cytoplasmic antioxidants to closed water channels. As hydrogen peroxide is a major signalling substance during different biotic and abiotic stresses, the reversible closure of water channels by *OH (as produced from H2O2 in the apoplast in the presence of transition metals such as Fe2+ or Cu+) may be downstream of the H2O2 signalling. This may provide appropriate adjustments in water relations (hydraulic conductivity), and a common response to different kinds of stresses. [source] Climatic factors affecting the occurrence of cloudy stain on the fruit skin of ,Triumph' Japanese persimmonANNALS OF APPLIED BIOLOGY, Issue 3 2010C. Reig Cloudy stain is a physiological disorder of the Japanese persimmon blemishing the skin and causing a great reduction of fruit quality, thus decreasing its commercial value. The stain starts at or just prior to the fruit colour-break stage, coinciding with the presence of cuticular cracks which increase cuticle water permeability and expose subepidermal cells to air and water, causing oxidation of polyphenol substances of large skin areas that turn almost black. The incidence of the disorder examined over four consecutive years in two growing areas of Spain revealed significant differences from year to year, between areas and even the tree face examined. The data consistently showed that cooler groves and fruit located on the northern face of the canopy were more prone to develop the stain. During the 4 years of the study, the average daily minimum temperature of a period of 15,25 days prior to the onset of staining followed the same order as the yearly staining rate, and accumulated hours below 13°C correlated significantly with the percentage of fruit starting the disorder. No relationship was found between the time-course of relative humidity (RH) and the onset of staining, but once the stain started the lower RH resulted in the lower percentage of affected fruit. Dew point, wind speed, rainfall and evapotranspiration did not correlate either with the onset of staining or with its incidence. Rind of cloudy-stained fruit had higher concentration of N, K, Mg and Fe and lower concentration of Ca than that of healthy fruit, but it is not the cause of the disorder. Accordingly, we conclude that cloudy stain of Japanese persimmon starts after a period of low temperature (, 13°C) and, afterwards, RH is responsible for its development and severity. [source] Performance Characteristics of Nanoporous Carbon Membranes for Protein UltrafiltrationBIOTECHNOLOGY PROGRESS, Issue 5 2007Tapan N. Shah Nanoporous carbon membranes could be very attractive for applications of ultrafiltration in the biotechnology industry because of their greater mechanical strength and longer membrane life. The objective of this study was to obtain quantitative data on the performance characteristics of nanoporous carbon membranes formed within a stainless steel support that was first modified by deposition of silica particles within the macroporous support. The nanoporous carbon membrane effectively removed small solutes from a protein solution using diafiltration, with performance comparable to that of commercial polymeric membranes. Protein fouling was evident, although the nanoporous carbon membranes were easily regenerated; cleaning with 0.5 N NaOH at 50 °C completely restored the water permeability for multiple cycles. The nanoporous carbon membranes were also compatible with steam sterilization. Significant increases in process flux could be obtained using periodic back-pulsing, with no evidence of any structural alterations in the membrane. These results clearly demonstrate the potential benefits and opportunities for using nanoporous carbon membranes for protein ultrafiltration. [source] Selection and Basic Properties of the Buffer Material for High-Level Radioactive Waste Repository in ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2008WEN Zhijian Abstract Radioactive wastes arising from a wide range of human activities are in many different physical and chemical forms, contaminated with varying radioactivity. Their common features are the potential hazard associated with their radioactivity and the need to manage them in such a way as to protect the human environment. The geological disposal is regarded as the most reasonable and effective way to safely disposing high-level radioactive wastes in the world. The conceptual model of geological disposal in China is based on a multi-barrier system that combines an isolating geological environment with an engineered barrier system. The buffer is one of the main engineered barriers for HLW repository. It is expected to maintain its low water permeability, self-sealing property, radio nuclides adsorption and retardation properties, thermal conductivity, chemical buffering property, canister supporting property, and stress buffering property over a long period of time. Bentonite is selected as the main content of buffer material that can satisfy the above requirements. The Gaomiaozi deposit is selected as the candidate supplier for China's buffer material of high level radioactive waste repository. This paper presents the geological features of the GMZ deposit and basic properties of the GMZ Na-bentonite. It is a super-large deposit with a high content of montmorillonite (about 75%), and GMZ-1, which is Na-bentonite produced from GMZ deposit is selected as the reference material for China's buffer material study. [source] | |||||||||||||||||||