Changes In Water Permeability Research Articles

Методология влияния свободной порозности и водоотдачи на процессы, происходящие в почвогрунтах оросительных каналов с земляным руслом

Purpose of the research: to consider the influence of free porosity and water loss on the filtration of water from channels with an earthen bed. Explore existing calculation methods taking into account the parameters of free porosity and fluid loss. Collect calculation material that can form the basis of a program for calculating the filtration of channels with an earthen bed, taking into account the factors influencing the first and second stages of filtration in the channels. Materials and research methods: The work used theoretical methods for calculating filtration in channels with an earthen bed, presented the calculation of the loss of flow rate Qf for filtration per 1 km of length with a steady free surface for different types of channel cross-sections, considered the basic formulas proving that water supply changes with changes in transverse cross-section of the canal, the change in the stability of the canal slopes is shown, a test calculation of the canal for filtration strength according to the maximum pressure gradients is presented, the need to compare the excess of the critical filtration pressure gradient with the permissible pressure gradient is considered. Results and its discussion. The relationship between the total, capillary and minimum moisture capacity and water yield in the thickness of soils is presented, the dependence of free porosity on the groundwater level, and the change in water permeability of soils over time are considered. As a result of the research, material was collected on the influence of free porosity and water loss on the movement of water in soils and the influence on the increase in groundwater levels in the zone of influence of canals, a methodology was presented for the influence of free porosity and water loss on the processes occurring in the soils of irrigation canals in an earthen channel, which will allow its use for modeling these processes on a computer.

RESEARCH OF SOME ASPECTS OF WATER PERMEABILITY OF FIRE-RETARDANT FABRIC FOR TENTS

The development of reliable methods for studying the conditions of fire protection of fabrics leads to the creation of new types of fireproof materials. At the same time, there is a need to determine the conditions for the formation of a barrier to water mass transfer and to establish a mechanism for inhibiting water penetration through the material. As a result of the conducted researches the influence of intumescent coating on water resistance was determined and the criterion relationswere obtained, which allow to obtain the change of water permeability on the fabric surface, ie the value of water exposure over time, characterized by the amount of absorbed water. . The water penetration time of the sample of the fireproof element of the tent exceeds the data, compared to the untreated sample by more than 30 times.Peculiarities of inhibition of the mass transfer process under the action of water are the isolation of the surface of the fire-retardant fabric by insoluble complexes of the intumescent coating. Thus, a sample of fire-retardant fabric with an intumescent coating on the reverse side after exposure to water showed the amount of absorbed water not more than0.00011 kg, and a sample of uncoated fabric absorbed 0.01 kg.Thus, the obtained data on the influence of intumescent coating on the process of inhibition of water absorption suggest that the main regulator of the process is not so much the formation of a significant number of water-insoluble complexes, as some fireretardant coatings are destroyed by moisture. In this case, a significant impact on the process of protection of natural combustible material in the application of fire-retardant coating is carried out in the direction of waterproofing the fabric surface with a polymer shell resistant to destruction by moisture. 

Numerical simulation of perimeter drainage system considering peat water permeability change over time

A reliable forecast of water depression in waterlogged areas depends on the due consideration of specific peat properties: a considerable change in the water permeability of peat once water hydrostatic uplift is removed, clogging over time, decomposition and other factors. The article presents an example of numerical simulation in Plaxis software of a perimeter drainage system, where groundwater level has been monitored for 1 year. Piezometers were installed on site at the distance of 7, 17 and 30 m from the drain pipe of a building under construction. Deformation-strength properties and filtration properties of peat were determined on samples taken from excavated pits. Besides, the samples were tested using filtration tubes to identify changes in water permeability of peat over time and depending on the amount of water filtered through peat. The survey took 90 days at the ambient temperature of 6 to 12 °C, which allowed avoiding rapid peat decomposition. The laboratory test results have shown that water permeability of natural-state peat samples has decreased by a factor of 2.7 to 3.1 with 450 to 580 liters of water filtered. The deviation of the design groundwater level calculated in Plaxis from its actual position did not exceed 0.07 m. Numerical simulation with due consideration of decreased water permeability of peat over time allows obtaining forecast results closer to the actual groundwater level.

Increased blood-brain barrier permeability to water in the aging brain detected using noninvasive multi-TE ASL MRI.

PurposeA fundamental goal in the drive to understand and find better treatments for dementia is the identification of the factors that render the aging brain vulnerable to neurodegenerative disease. Recent evidence indicates the integrity of the blood–brain barrier (BBB) to be an important component of functional failure underlying age‐related cognitive decline. Practical and sensitive measurement is necessary, therefore, to support diagnostic and therapeutic strategies targeted at maintaining BBB integrity in aging patients. Here, we investigated changes in BBB permeability to endogenous blood water in the aging brain.MethodsA multiple‐echo‐time arterial spin‐labeling MRI technique, implemented on a 9.4T Bruker imaging system, was applied to 7‐ and 27‐month‐old mice to measure changes in water permeability across the BBB with aging.ResultsWe observed that BBB water permeability was 32% faster in aged mice. This occurred along with a 2.1‐fold increase in mRNA expression of aquaporin‐4 water channels and a 7.1‐fold decrease in mRNA expression of α‐syntrophin protein, which anchors aquaporin‐4 to the BBB.ConclusionAge‐related changes to water permeability across the BBB can be captured using noninvasive noncontrast MRI techniques.

Gas injection test of remolded saturated soil with consolidation

Investigation of gas migration in saturated soil is of great theoretical and practical significance in marine science and engineering. The transport of gas bubbles in soil and its effects on soil physical and mechanical properties can be further studied. Gas injection and permeability tests were conducted using a self-developed oedometer with gas injection and water infiltration. Before the gas injection test, the remolded saturated soil was consolidated in an oedometer device to an effective vertical stress of 100 kPa. Gas injection tests were then performed to investigate the transport mechanism of bubbles in saturated soil and the changes in water permeability after gas injection. The results show that it is difficult for gas to migrate through capillary invasion and fracturing from the pore scale owing to the high gas entry pressure in fine-grained sediments. Hence, initial gas migration mechanism in pore scale is elastic-plastic expansion. The scale of cavities expands from micron to millimeter during gas injection, and gas pressure for fracturing reduces with the expansion of cavities. The fracturing initiated in millimeter scale and gas invades further into the soil. Interconnections of cavities and cracks resulting in an increasing of drainage rate and coefficient of permeability.

MSCS is a Critical Component for Osmotic Survival of Vibrio Cholerae

Vibrio cholerae (Vc), an opportunistic pathogen, adapts to a wide range of osmotic environments. In events of drastic osmotic down-shifts, Vc avoids mechanical rupture by releasing ions and small osmolytes through MscS and MscL, the two major bacterial mechanosensitive (MS) channel species. To investigate contributions of these channels to Vibrio’s osmotic permeability response, we generated DmscL, DmscS and double DmscL DmscS mutants in Vc O395. Patch-clamp recordings confirmed large and generally homogenous populations of MscS in DmscL and MscL in DmscS, whereas in the double mutant we observed low densities of minor MS channels resembling MscS or MscM. Stopped-flow experiments and analysis of light-scattering kinetics detected no change in water permeability. The DmscL strain, however, showed a moderate slowdown of the osmolyte release kinetics and a drastically increased osmotic survival, exceeding WT. The DmscS mutant exhibited markedly slower osmolyte release, increased fraction of permeable osmolytes, and lowest survival. Deletion of both channels changed the release characteristics suggesting the presence of permeant structures which do not reseal (membrane cracks), also producing low survival. qPCR experiments indicated that mscS transcription is about 1.4 fold upregulated in DmscL compared to WT. This is consistent with the higher density of MscS channels observed by electrophysiology in this strain and with the highest rescuing efficiency. The up-regulation of MscS in the absence of MscL also suggests a special crosstalk mechanism in mechanosensitive channel expression. Modeling of the scattering kinetics accurately predicts separate stages of cell swelling, tension generation, osmolyte release, and termination of permeation resulting in a stable level of cell population scattering. In the absence of inactivating MscS, the final level is unstable, signifying incomplete resealing of the membrane. We conclude that MscS is the most critical component in the Vibrio permeability response.

Study on Application of Simulated Air Pollution Dust the Permeable Concrete

Impermeable pavement is usually adopted in pavement construction in Taiwan. Porous asphalt concrete employs features as water retention, cooling and promoting draining effect. However, with the increase of traffic volume and service duration, its draining function will decrease gradually, wherein porosity blocking is one of the major problems. The research aims at the analogue experiment on pervious concrete subject to dust blocking, which discusses the blocking status and changes in permeability due to natural dust fall and clump dust fall after rainfall. The experiment prepares 4 groups of mixing ratio. The aggregates are coarse and fine bottom ashes from the refuse incinerator. The proportion of cement is 130kg/m3 and 200kg/m3. The experiment simulates the influence and in-situ water permeability changes of specimens with different porosities been blocked by natural dust fall and then the dust been rushed into specimens by rainfall. Before the analogue experiment, the water permeability of 4 groups of specimens is 1399.75∼1412.91ml/15sec. The experiment adopts 2011 average monthly dust fall in Pingtung County and magnifies it by 10 to 20 times to simulate natural dust fall and clump dust fall on the pavement accordingly. It is known from the experimental results that due to the high porosity of pervious concrete, by ruling out other blocking factors, the natural dust fall has little influence on the water permeability of pervious concrete. While the simulation of clump dust fall is 15 times the natural dust fall, although water permeability the pavement is reduced sharply, it still meets the minimum 400ml/15sec of Japanese porous pavement technical indicator. It shows that the specimens have good permeability on future practical applications.

Scalable fabrication of anti-biofouling membranes through 2-aminoimidazole incorporation during polyamide casting

A proof-of-concept for the fabrication of novel anti-biofouling water purification membranes through the incorporation of a 2-aminoimidazole (2-AI) during membrane casting is presented. 2-AI molecules are known to inhibit biofouling through the disruption of biofilm formation mechanisms, not through the inactivation of bacteria. Three approaches to incorporation were evaluated, adding the 2-AI to either one of the two monomer solutions, (a) m-phenylene diamine or (b) trimesoyl chloride, that polymerize to make a polyamide active layer, or by (c) reacting the active layer with a post-polymerization-2-AI-soak solution. These methods of incorporation are directly translatable to current membrane fabrication practices without the addition of other chemicals aside from the 2-AIs themselves. Results showed that the 2-AI was incorporated into the active layer of the membranes at concentrations (0.16–0.93 M) orders of magnitude higher than what is required for biofilm inhibition (IC50 = 162–420 μM). The 2-AI membranes significantly (p = 0.002–0.04) inhibited Pseudomonas aeruginosa biofilms (49–90% on average) due to the presence and action of 2-AI, not physico-chemical changes. The 2-AI-soak approach produced membranes that had the most stable incorporation, with no loss of compound during use and cleaning, and the highest biofilm inhibition, at 90% inhibition on average. The incorporation of 2-AI into the membranes decreased water permeability by 26–44% and salt rejection by 1.2–4.3% points, as compared to control membranes. No attempt was made to optimize 2-AI membrane preparation toward minimization of changes in water permeability and salt rejection. Given the substantial biofilm formation inhibition exhibited by the 2-AI membranes, and the limited decrease observed in water permeability and salt rejection, the 2-AI membranes presented in this study support 2-AI incorporation into polyamide active layers as a promising avenue to enhance current water purification membranes.

Plasticity of skin water permeability and skin thickness in the amphibious mangrove rivulus Kryptolebias marmoratus.

The skin of amphibious fishes is a multipurpose organ, important for gas and ion exchange and nitrogen excretion when fish are out of water (emersed). We tested the hypothesis that skin permeability is altered to maintain water balance through changes in water permeability and skin thickness during salinity acclimation and/or when fish emerse, using the euryhaline, amphibious fish Kryptolebias marmoratus as a model. We first recorded the behaviour of fish out of water to determine which part of the cutaneous surface was in contact with the substrate. Fish spent about 70% of their time on their ventral surface when out of water. Osmotic permeability of the skin was assessed in fish acclimated to 0.3 or 45‰ using 3H2O fluxes in an in vitro micro-Ussing chamber setup. In freshwater-acclimated fish, 3H2O influx across the skin was significantly higher compared to hypersaline-acclimated fish, with no significant changes in efflux. Prolonged emersion (7 days) resulted in an increase in skin 3H2O influx, but not efflux in fish acclimated to a moist 45‰ substrate. In a separate experiment, dorsal epidermal skin thickness increased while the ventral dermis thickness decreased in fish emersed for over a week. However, there was no link between regional skin thickness and water flux in our experiments. Taken together, these findings suggest that K. marmoratus alter skin permeability to maximize water uptake while emersed in hypersaline conditions, adjustments that probably help them survive months of emersion during the dry season when drinking to replace water loss is not possible.

Changes observed in erythrocyte cells exposed to an alternating current.

Background and aimsAppliance of electric pulses induces red blood cells (RBCs) membrane poration, membrane aminophospholipid perturbation and alteration of the normal flip-flop process, resulting in various shape changes of the RBCs. We studied morphological and water permeability changes of RBCs bombarded with electrons in an alternating current circuit.MethodsWe used three venous blood samples of 100 mL and an alternating current device. The harvested blood was divided into four experimental sets to be used for various exposure times: 0 hours (control RBCs), 0.5h, 3h and 6h (electric-stimulated RBCs).Following the electric current each of the four sets were further divided into three samples: one for the assessment of the echinocytes/RBCs ratio, another for the electron microscopy study of ultrastructural changes induced by the alternating electrical current and a larger third one for determining water permeability of RCBs by 1H-NMR spectroscopy and morphological measurements.ResultsThere is a small but statistically significant effect of the RBC exposure to alternating electric current on cell diameters. Exposure to electric current is positively and strongly correlated with the percentage of echinocytes in a duration-dependent manner. There is a strong and statistically significant correlation between electric current exposure and permeability to water as measured by 1H-NMR spectroscopy.ConclusionFollowing interactions between electric current and RBC membrane, certain modifications were observed in the erythrocyte structure. We attribute the increased cell size to a higher permeability to water and a decreased tonicity. This leads to the transformation of the RBCs into echinocytes.

Barrier properties of polyamide 12/montmorillonite nanocomposites: Effect of clay structure and mixing conditions

Hybrid films, composed of a PA12 polyamide matrix filled with 5 wt% of clays were melt processed under different mixing conditions to classically obtain montmorillonite-filled microcomposites and organo-modified montmorillonite-filled nanocomposites. The change in mixing shear rates allowed to notably modulating the fragmentation level for montmorillonite and the exfoliation level for modified montmorillonite. Barrier properties to nitrogen and water were altered with a reduction in PA12 chain mobility by confinement effect and geometrical constraints. Tortuosity effects induced by fillers were also highlighted. The water permeability and diffusivity were significantly decreased with exfoliated clays, while an increase was measured with an increased water solubility in presence of clay aggregates, both counterbalanced tortuosity effects. This trend was amplified when using low shear rates. According to filler used and mixing conditions, water sorption measurement has successfully demonstrated an increase in water solubility, due to filler affinity, which was surprisingly inconsistent with the change of water permeability. The occurrence of water plasticization phenomenon was also pointed out through the non-constant diffusivity, reflecting an increased free volume with water activity. Again, a decrease in water diffusivity was unexpectedly obtained, explained by tortuosity effects and ascribed to local water retention at the vicinity of clays, which creates water aggregates in films. These findings were also confirmed by a mathematical modeling approach of sorption process, discussing about the sorbed water access.

Oxidative Stress and Nuclear Factor κB (NF-κB) Increase Peritoneal Filtration and Contribute to Ascites Formation in Nephrotic Syndrome

Water accumulation in the interstitium (edema) and the peritoneum (ascites) of nephrotic patients is classically thought to stem from the prevailing low plasma albumin concentration and the decreased transcapillary oncotic pressure gradient. However, several clinical and experimental observations suggest that it might also stem from changes in capillary permeability. We addressed this hypothesis by studying the peritoneum permeability of rats with puromycin aminonucleoside-induced nephrotic syndrome. The peritoneum of puromycin aminonucleoside rats displayed an increase in the water filtration coefficient of paracellular and transcellular pathways, and a decrease in the reflection coefficient to proteins. It also displayed oxidative stress and subsequent activation of NF-κB. Scavenging of reactive oxygen species and inhibition of NF-κB prevented the changes in the water permeability and reflection coefficient to proteins and reduced the volume of ascites by over 50%. Changes in water permeability were associated with the overexpression of the water channel aquaporin 1, which was prevented by reactive oxygen species scavenging and inhibition of NF-κB. In conclusion, nephrotic syndrome is associated with an increased filtration coefficient of the peritoneum and a decreased reflection coefficient to proteins. These changes, which account for over half of ascite volume, are triggered by oxidative stress and subsequent activation of NF-κB.

Water structure changes induced by ceramics can be detected by increased permeability through aquaporin

Aquporins are intrinsic membrane proteins that function as water channel to transport water and/or mineral nutrients across biological membranes. In this study, we aimed to clarify whether water structure can be changed by the presence of ceramics and whether such a change can be determined by aquaporin. First, we confirmed that ceramics could transform tap water into active tap water by increasing water permeability through aquaporin. We also found that this change in water permeability by treatment with ceramics occurred in distilled water. The distilled water was determined to exhibit the same aquaporin permeability as the original tap water. Our data indicate that the aquaporin permeability of water can be changed by severe physical shocks, such as slapping and sonication, which is consistent with the implication that the aquaporin permeability is closely related to the structure of the water. In this study, using aquaporins, we first reported that the treatment of water with ceramics can affect the structure of water, and the water can retain the structure for a given period under certain condition

Novel magneto-responsive membrane for remote control switchable molecular sieving.

Stimuli-responsive separation membranes with tunable molecular scale pore size, which are desirable for on-demand sieving of targeted macromolecules, have attracted increasing attention in recent years. In this study, novel magneto-hydrogel pore-filled composite membranes with excellent magneto-responsivity and tunability for molecular sieving have been developed. Such membranes comprising magnetic nanoparticles (MNPs) as localized heater which can be excited by high frequency alternating magnetic field (AMF), poly(N-isopropylacrylamide) (PNIPAAm) hydrogel network as the sieving medium and actuator, and polyethylene terephthalate (PET) track-etched membrane as robust support, have been prepared via in situ reactive pore-filling functionalization. Rheological study has been carried out first to investigate the influence of MNPs and initiation methods on gelation kinetics and microstructure of the MNP-PNIPAAm composite hydrogels, and to identify proper conditions for further pore-filling functionalization. Then AMF distribution of chosen field condition and its heating effectiveness for MNPs and MNP-PNIPAMm composite hydrogel were studied. Pre-functionalization of the PET membranes with linear polymer chains with different composition were compared with respect to their effects for achieving desired MNP loading and fixation of the hydrogel network in the pores. At last, in situ reactive pore-filling functionalization was carried out to immobilize robust magneto-hydrogel in the pores of the membranes. Conditions were investigated and optimized to obtain functionalized membranes with high MNP loading and suited PNIPAM network properties, i.e. good stimuli-responsivity and sieving in the ultrafiltration range. The excellent thermo- and magneto-responsivity of obtained pore-filled membranes was proved by its large and reversible change of water permeability in response to switching on and off the AMF. Finally, it was demonstrated by filtration of dextrans with different molecular weights that the membranes had ultrafiltration properties and that large changes of their molecular sieving performance could be obtained by "remote control" with the external AMF.

Investigation of the changes in microstructure and transport properties of leached cement pastes accounting for mix composition

Ca-leaching of cement-based materials induces detrimental effects on properties related to long-term durability. A better understanding of leaching degradation in terms of alterations in mineralogy, microstructure, and transport properties is important for long-term assessments of concrete and reinforced concrete structures used in nuclear waste disposal systems or in hydro structures. However, the decalcification process is not easy to study because it is extremely slow. In this study, an ammonium nitrate (NH4NO3) solution of 6mol/l was used to accelerate the leaching kinetics. The experiments were performed on cement paste samples with different water/powder (w/p) and limestone filler (LS) replacement ratios. Both the change of sample mass over time and the amount of calcium ion leached out were monitored during the test. Different post-analysis techniques including SEM/SEM-EDX, XRD/QXRD, MIP, ion chromatography, and N2-adsorption were used to characterize the microstructural and mineralogical changes. The effect of accelerated leaching on transport properties was studied by measuring the changes in water permeability and diffusivity of dissolved gases. Results showed that the square-root-time law of degradation was applicable under accelerated conditions. Both higher w/p ratios and LS replacements increased the rate of leaching propagation; the former had a more significant effect. The accelerated leaching significantly altered the microstructure of the cement paste to a material with a higher specific surface area, increased total porosity and a shift to larger pore sizes. Those changes led to a significant increase in water permeability (one to two orders of magnitude) and diffusivity (less than one order) depending on degradation state.

Evaluation of the transport parameters and physiochemical properties of forward osmosis membranes after treatment of produced water

The application of semipermeable membranes for dewatering of complex oil and gas wastewaters continues to be a topic of increasing interest. Several studies have explored the fouling propensity and contaminant rejection of osmotically driven membranes during forward osmosis (FO) treatment of produced waters; however, none have investigated changes in membrane transport and physiochemical properties after exposure to these feed streams. In this study we discuss the impacts of produced water exposure on the transport and active layer surface properties of cellulose triacetate (CTA) and polyamide thin-film composite (TFC) FO membranes. While produced water exposure yields some, albeit minor changes to the membrane performance and surface characteristics of the CTA and the traditional TFC membranes, close to 50% reduction in reverse salt flux and contaminant transport was observed for a surface-modified TFC FO membrane; only minimal changes in water permeability were recorded. Results of this study demonstrate the chemical and physical robustness of FO membranes for treatment of oil and gas wastewaters, and they highlight a knowledge gap that exists in membrane polymer selection and contaminant interactions with the membrane polymer matrix that should be further addressed in future membrane fouling studies.

Molecular dynamics simulations of the transport of reactive oxygen species by mammalian and plant aquaporins

BackgroundAquaporins are responsible for water transport across lipid membranes. They are also able to transport reactive oxygen species, playing an important role in redox signaling. Certain plant aquaporins have even the ability to be regulated by oxidative stress. However, the underlying mechanisms are still not fully understood. MethodsHere, molecular dynamics simulations were employed to determine the activation free energies related to the transport of reactive oxygen species through both mammalian and plant aquaporin models. Results and conclusionsBoth aquaporins may transport hydrogen peroxide (H2O2) and the protonated form of superoxide radicals (HO2). The solution-to-pore transfer free energies were low for small oxy-radicals, suggesting that even highly reactive hydroxyl radicals (HO) might have access to the pore interior and oxidize amino acids responsible for channel selectivity. In the plant aquaporin, no significant change in water permeability was observed upon oxidation of the solvent-exposed disulfide bonds at the extracellular region. During the simulated time scale, the existence of a direct oxidative gating mechanism involving these disulfide bonds could not be demonstrated. General significanceSimulation results may improve the understanding of redox signaling mechanisms and help in the interpretation of protein oxidative labeling experiments.

The Effects of Tillage on Soil Water Content in Dry Areas

Abstract Annual rainfall is less than 500 mm of rainfall in the dry farming regions in order to be stored in the soil processing. At the time, and is provided with a sufficient number of the version of weed control, leveling a good soil is obtained, the temperature of the soil evaporation will be blocked, and capillarity corruption prevented erosion. Some dry land farming areas is 7-8 times a year. As a result of the false and incorrect versions of the soil organic matter content decreases, due to the heavy traffic and rainfall feeds into and hardens. Also, the more time the soil impermeable layer consists of the processing of terrain plow deep, it's broken, you need to increase water permeability changes in the ground. Our country's (Turkiye) Southeastern Anatolia region, especially during the period of erroneous releases summer soil cultivation of pistachios to crack and evaporate the water accumulated in the profile. In this region, the soil is less to prevent evaporation and mulch practices are required to do. Usually in the winter and spring to gain ground in both the water and the soil is completely dry in order to struggle for and type weeds, cracks and prevent evaporation of water to close the land sliding. In our region the soil structure and the orchards slope, vegetation, depending on the year, to a loss of between 40-100 tons per hectare. Soil processing by lose ground is important for quantities of soil and water losses in every year. The importance of the land in agricultural production processing topics, manufacturers, increases productivity with timely and accurate processing of applications on soil. In addition to the increase in the efficiency of handling soil erosion by the soil protection and control of soil water contents are benefits such as to conservation. In this study, tillage, reduced tillage in dry farming areas, mulching and soil moisture content will rely upon.

Phosphorylation of rat aquaporin‐4 at Ser111 is not required for channel gating

Aquaporin 4 (AQP4) is the predominant water channel in the mammalian brain and is mainly expressed in the perivascular glial endfeet at the brain‐blood interface. AQP4 has been described as an important entry and exit site for water during formation of brain edema and regulation of AQP4 is therefore of therapeutic interest. Phosphorylation of some aquaporins has been proposed to regulate their water permeability via gating of the channel itself. Protein kinase (PK)‐dependent phosphorylation of Ser111 has been reported to increase the water permeability of AQP4 expressed in an astrocytic cell line. This possibility was, however, questioned based on the crystal structure of the human AQP4. Our study aimed to resolve if Ser111 was indeed a site involved in phosphorylation‐mediated gating of AQP4. The water permeability of AQP4‐expressing Xenopus oocytes was not altered by a range of activators and inhibitors of PKG and PKA. Mutation of Ser111 to alanine or aspartate (to prevent or mimic phosphorylation) did not change the water permeability of AQP4. PKG activation had no effect on the water permeability of AQP4 in primary cultures of rat astrocytes. Molecular dynamics simulations of a phosphorylation of AQP4.Ser111 recorded no phosphorylation‐induced change in water permeability. A phospho‐specific antibody, exclusively recognizing AQP4 when phosphorylated on Ser111, failed to detect phosphorylation in cell lysate of rat brain stimulated by conditions proposed to induce phosphorylation of this residue. Thus, our data indicate a lack of phosphorylation of Ser111 and of phosphorylation‐dependent gating of AQP4.

Neuromyelitis optica IgG does not alter aquaporin‐4 water permeability, plasma membrane M1/M23 isoform content, or supramolecular assembly

Neuromyelitis optica (NMO) is thought to be caused by immunoglobulin G autoantibodies (NMO-IgG) against astrocyte water channel aquaporin-4 (AQP4). A recent study (Hinson et al. (2012) Proc Natl Acad Sci USA 109:1245-1250) reported that NMO-IgG inhibits AQP4 water permeability directly and causes rapid cellular internalization of the M1 but not M23 isoform of AQP4, resulting in AQP4 clustering, enhanced complement-dependent cytotoxicity, and tissue swelling. Here, we report evidence challenging this proposed mechanism of NMO-IgG-mediated pathology. We measured osmotic water permeability by stopped-flow light scattering on plasma membrane vesicles isolated from AQP4-expressing CHO cells, an approach that can detect changes in water permeability as small as 5% and is not confounded by internalization effects. We found similar single-molecule water permeability for M1-AQP4 tetramers and M23-AQP4 clusters (orthogonal arrays of particles, OAPs). Exposure of AQP4 to high concentrations of NMO-IgG from six seropositive NMO patients, and to high-affinity recombinant monoclonal NMO antibodies, did not reduce AQP4 water permeability. Also, NMO-IgG did not reduce water permeability in AQP4-reconstituted proteoliposomes. In transfected cells expressing M1- or M23-AQP4 individually, NMO-IgG caused more rapid internalization of M23- than M1-AQP4. In cells coexpressing both isoforms, M1- and M23-AQP4 comingled in OAPs that were internalized together in response to NMO-IgG. Super-resolution imaging and native gel electrophoresis showed that the size of AQP4 OAPs was not altered by NMO sera or recombinant NMO antibodies. We conclude that NMO-IgG does not: (i) inhibit AQP4 water permeability, (ii) cause preferential internalization of M1-AQP4, or (iii) cause intramembrane AQP4 clustering.