Changes In Water Permeability Research Articles

Hydrophilic silica additives for disulfonated poly(arylene ether sulfone) random copolymer membranes

Hydrophilic silica (SiO 2) nanoparticles (average size = 7 nm), which act as inorganic acids at low pH (<2), were added together with a PEO–PPO–PEO triblock copolymer dispersant to a random disulfonated poly(arylene ether sulfone) copolymer in the potassium salt ( SO 3 −K +) form in order to control permeation and rejection characteristics of the homopolymer. The dispersants (shell) absorbed on the surface of SiO 2 nanoparticles (core) formed a distinctive core–shell structure. The PEO units located at the outside of the dispersant formed complexes with SO 3 −K + groups of BPS-20 via ion–dipole interactions. These interactions induced a compatible binary system following the Flory–Fox equation associated with glass transition temperature ( T g) depression and prevented extraction of the water-soluble dispersant even under aqueous conditions. The ion–dipole interaction, combined with hydrogen bonding between SiO 2 and the dispersant, caused SiO 2 nanoparticles to be well distributed within the BPS-20 matrix up to a limit of 1 wt.% of SiO 2 and minimized the formation of non-selective cavities within the matrix's hydrophilic water channels. The resulting BPS-20_SiO 2 nanocomposites showed improved salt rejection and reduced ionic conductivity. These trends are analogous to those of disulfonated copolymer systems, with polar groups creating hydrogen bonding or acid–base complexation with SO 3 −K + groups in BPS copolymers. Well dispersed SiO 2 nanoparticles in highly water-permeable desalination membranes are expected to result in an increase in salt rejection but very little change in water permeability. The addition of nanoparticles to desalination membranes may offset the permeability-selectivity tradeoff observed in polymer membranes. Above 1 wt.%, SiO 2 nanoparticles increased both the interchain distance between polymer chains and the water uptake. However, the increased hydrophilicity due to high SiO 2 content did not yield improved water permeation of the nanocomposite membranes. The SiO 2 nanoparticles acted as barriers, hindering water passage (restrictive diffusion) and lowering water permeability. Meanwhile, acidic hydroxyl groups (OH 2 +) on the SiO 2 surface in the sulfonate matrix led to improved ionic conductivity, but NaCl rejection capability decreased because the concentration of SO 3 −K + was diluted by highly absorbed water molecules, resulting in weakened Donnan exclusion. The mechanical properties and chlorine resistance of all BPS-20_SiO 2 nanocomposites were comparable to those of BPS-20.

Day/night regulation of aquaporins during the CAM cycle in Mesembryanthemum crystallinum

Mesembryanthemum crystallinum exhibits induction of Crassulacean acid metabolism (CAM) after a threshold stage of development, by exposure to long days with high light intensities or by water and salt stress. During the CAM cycle, fluctuations in carbon partitioning within the cell lead to transient drops in osmotic potential, which are likely stabilized/balanced by passive movement of water via aquaporins (AQPs). Protoplast swelling assays were used to detect changes in water permeability during the day/night cycle of CAM. To assess the role of AQPs during the same period, we followed transcript accumulation and protein abundance of four plasma membrane intrinsic proteins (PIPs) and one tonoplast intrinsic protein (TIP). CAM plants showed a persistent rhythm of specific AQP protein abundance changes throughout the day/night cycle, including changes in amount of McPIP2;1, McTIP1;2, McPIP1;4 and McPIP1;5, while the abundance of McPIP1;2 was unchanged. These protein changes did not appear to be coordinated with transcript levels for any of the AQPs analysed; however, they did occur in parrallel to alterations in water permeability, as well as variations in cell osmolarity, pinitol, glucose, fructose and phosphoenolpyruvate carboxylase (PEPc) levels measured throughout the day/night CAM cycle. Results suggest a role for AQPs in maintaining water balance during CAM and highlight the complexity of protein expression during the CAM cycle.

Early changes of water diffusional transfer in maize roots under the influence of water stress

The time dependent response of the hydrodynamic root system to PEG-induced water stress was studied in intact maize Zea mays L. seedlings at intervals varying from several seconds to 3 h by detecting diffusional water transfer with the use of pulsed NMR. In order to establish the contribution of water transfer through aquaporins in response to water stress, the transmembrane water transport in control roots and roots treated with aquaporin blocker was detected. Changes in diffusional water transfer under stress were shown to depend on the duration of osmotic treatment, and include the series of heterogeneous processes. A transient pulsed jump in diffusional water transfer detected several seconds after beginning the osmotic treatment is associated with the spread of the wave of hydraulic pressure along the root. It is proposed that early responses of the hydrodynamic system of maize roots to PEG-induced water stress lies in the unequal change in water permeability of the plasmalemma and tonoplast resulting from the changes in aquaporin activity and perhaps in the escalation of water transfer along the cell vacuome.

Ultrafiltration of humic acid solutions through unmodified and surface functionalized low-fouling polyethersulfone membranes – Effects of feed properties, molecular weight cut-off and membrane chemistry on fouling behavior and cleanability

In the present work, polyethersulfone (PES) ultrafiltration (UF) membranes with molecular weight cut-off (MWCO) from 5 to 300 kDa were analyzed with respect to fouling during filtration of humic acid (HA) model solution. The impact of MWCO and prefiltration of the feed solution on the fouling behavior of these membranes is presented. Moreover, an UV-initiated graft copolymerization of poly(ethylene glycol) methacrylate (PEGMA) onto PES membranes was performed and the effect of the applied modification was examined in terms of MWCO and water permeability changes as well as performance during filtration of HA. Moreover, the fouling behavior and principles during the filtration were compared. Membranes with higher MWCO exhibited stronger flux decline during UF but better cleanability. Prefiltration through 0.45 μm filter improved the membrane performance during filtration of HA but the efficiency of physical cleaning was deteriorated. The applied modification improved the membrane performance during ultrafiltration and facilitated the physical cleaning. This work contributes to a better understanding of the relationships between membrane MWCO, solute size and size distribution, membrane surface chemistry and membrane fouling.

Effects of drugs on water permeability of erythrocyte membranes

The method of NMR-relaxation with the manganese doping has been applied to study changes of water permeability of red blood cell membranes affected by various concentrations of chlorhexidine digluconate and dimephosphone. It is shown that both investigated substances suppress the water permeability of the red blood cell membrane in a dose-dependent manner. Half-maximum inhibitory effect of studied substances was reached at the concentrations of 9 μM of chlorhexidine and 400 μM of dimephosphone.

Vacuolar symplast formation is due to highly permeable gap junctions between the tonoplast and endoplasmic reticulum membrane

An NMR method with a pulsed magnetic field gradient was applied to study changes in water permeability of the vacuolar symplast in maize (Zea mays L.) seedling roots treated with various inhibitors of cell metabolism. The results were qualitatively analogous to literature data on conductivity changes of intercellular gap junctions in animal cells exposed to similar treatments. Electron microscopy examination of root cells provided evidence for the existence of membrane contacts between the endoplasmic reticulum and the tonoplast. It is supposed that vacuoles of neighboring plant cells are interconnected through highly dynamical gap junctions between the tonoplast and the endoplasmic reticulum membrane.

Adaptation of the sea-bass ( Dicentrarchus labrax) to fresh water: Role of aquaporins and Na +/K +-ATPases

Sea-bass ( Dicentrarchus labrax) grow under different salinity regimes, from the open sea to lagoons and even rivers, but some mortality has been recorded in juvenile stages when exposed to low salinity water. Changes in water permeability of different osmoregulatory tissues could be the cause of reduction in blood osmotic pressure and death in some fish in fresh water (FW). In order to explore this condition, we have studied the changes of aquaporins (AQP1 and AQP3), α1 and α4 Na +/K +-ATPase transcript levels in the digestive tract, kidney and gills after a long-term exposure of juvenile sea-bass to sea water (SW) and FW fish able to survive in SW and FW are called SW-adapted fish (SWS), FW successfully-adapted fish (FWS) respectively, while fish that die in FW are called FW unsuccessfully-adapted fish (FWU). AQP1 was highly expressed in SWS digestive tract and kidney, suggesting its involvement in water absorption. In FWU, AQP1 transcript levels in the digestive tract were higher than in FWS, suggesting higher water absorption. AQP3 transcript levels in gills were higher in FWS compared to SWS, suggesting a role in FW adaptation. AQP3 transcript levels in gills were higher in FWU than in FWS, suggesting an increase in gill water permeability or other solutes. Transfer to FW was followed in gills by an increase in α1 and α4 Na +/K +-ATPase levels in FWS and FWU, supporting the current model of ion absorption through the gills.

Differing Effects of Cilostazol and Aspirin on Thrombus Formation and Microvascular Permeability

Cilostazol is a unique antiplatelet drug as it has been shown to reduce the recurrence of vascular events without exacerbating a risk of bleeding complication, although mechanisms for such effects are unknown. We examined its effects on changes in formation of platelet thrombus and compared those with aspirin. Microhemorrhage was induced by laser ablation on a rat mesenteric venule to observe a spatiotemporal process of non‐occlusive thrombus formation. Platelet thrombi in both cilostazol‐ and aspirin‐treated rats were examined to choose the doses of reagents resulting in comparable anti‐platelet effects. Surprisingly, cilostazol, but not aspirin, was found to reduce erythrocyte extravasation under these conditions. To test if such an effect is attributed to modulation of endothelial barrier properties, we measured changes in water permeability (Lp) and reflection coefficient to albumin (σ) in single‐perfused venules. Cilostazol significantly abolished a transient increase in Lp and a decrease in σ when vessels were challenged by histamine. Furthermore the reagent attenuated baseline Lp under a control state. These results indicate that cilostazol not only acts on the platelet to reduce the size of developing thrombus, but also acts on endothelium to tighten up the endothelial barrier at least in part by inhibiting the cAMP‐degrading enzyme in the endothelium that differs from aspirin. Supported by MEXT.

Fluid transport phenomena in ocular epithelia

This article discusses three largely unrecognized aspects related to fluid movement in ocular tissues; namely, (a) the dynamic changes in water permeability observed in corneal and conjunctival epithelia under anisotonic conditions, (b) the indications that the fluid transport rate exhibited by the ciliary epithelium is insufficient to explain aqueous humor production, and (c) the evidence for fluid movement into and out of the lens during accommodation. We have studied each of these subjects in recent years and present an evaluation of our data within the context of the results of others who have also worked on electrolyte and fluid transport in ocular tissues. We propose that (1) the corneal and conjunctival epithelia, with apical aspects naturally exposed to variable tonicities, are capable of regulating their water permeabilities as part of the cell-volume regulatory process, (2) fluid may directly enter the anterior chamber of the eye across the anterior surface of the iris, thereby representing an additional entry pathway for aqueous humor production, and (3) changes in lens volume occur during accommodation, and such changes are best explained by a net influx and efflux of fluid.

Zinc Modulation of Water Permeability Reveals that Aquaporin 0 Functions as a Cooperative Tetramer

We previously showed that the water permeability of AQP0, the water channel of the lens, increases with acid pH and that His40 is required (Németh-Cahalan, K.L., and J.E. Hall. 2000. J. Biol. Chem. 275:6777–6782; Németh-Cahalan, K.L., K. Kalman, and J.E. Hall. 2004. J. Gen. Physiol. 123:573–580). We have now investigated the effect of zinc (and other transition metals) on the water permeability of AQP0 expressed in Xenopus oocytes and determined the amino acid residues that facilitate zinc modulation. Zinc (1 mM) increased AQP0 water permeability by a factor of two and prevented any additional increase induced by acid pH. Zinc had no effect on water permeability of AQP1, AQP4 or MIPfun (AQP0 from killifish), or on mutants of AQP1 and MIPfun with added external histidines. Nickel, but not copper, had the same effect on AQP0 water permeability as zinc. A fit of the concentration dependence of the zinc effect to the Hill equation gives a coefficient greater than three, suggesting that binding of more than one zinc ion is necessary to enhance water permeability. His40 and His122 are necessary for zinc modulation of AQP0 water permeability, implying structural constraints for zinc binding and functional modulation. The change in water permeability was highly sensitive to a coinjected zinc-insensitive mutant and a single insensitive monomer completely abolished zinc modulation. Our results suggest a model in which positive cooperativity among subunits of the AQP0 tetramer is required for zinc modulation, implying that the tetramer is the functional unit. The results also offer the possibility of a pharmacological approach to manipulate the water permeability and transparency of the lens.

Bilayer polarity and its thermal dependency in the ℓ o and ℓ d phases of binary phosphatidylcholine/cholesterol mixtures

Diverse variations in membrane properties are observed in binary phosphatidylcholine/cholesterol mixtures. These mixtures are nonideal, displaying single or phase coexistence, depending on chemical composition and other thermodynamic parameters. When compared with pure phospholipid bilayers, there are changes in water permeability, bilayer thickness and thermomechanical properties, molecular packing and conformational freedom of phospholipid acyl chains, in internal dipolar potential and in lipid lateral diffusion. Based on the phase diagrams for DMPC/cholesterol and DPPC/cholesterol, we compare the equivalent polarity of pure bilayers with specific compositions of these mixtures, by using the Py empirical scale of polarity. Besides the contrast between pure and mixed lipid bilayers, we find that liquid-ordered (ℓ o) and liquid-disordered (ℓ d) phases display significantly different polarities. Moreover, in the ℓ o phase, the polarities of bilayers and their thermal dependences vary with the chemical composition, showing noteworthy differences for cholesterol proportions at 35, 40, and 45 mol%. At 20 °C, for DMPC/cholesterol at 35 and 45 mol%, the equivalent dielectric constants are 21.8 and 23.8, respectively. Additionally, we illustrate potential implications of polarity in various membrane-based processes and reactions, proposing that for cholesterol containing bilayers, it may also go along with the occurrence of lateral heterogeneity in biological membranes.

Photografted Thin Polymer Hydrogel Layers on PES Ultrafiltration Membranes: Characterization, Stability, and Influence on Separation Performance

Highly fouling-resistant ultrafiltration (UF) membranes were synthesized by heterogeneous photograft copolymerization of two water-soluble monomers, poly(ethylene glycol) methacrylate (PEGMA) and N,N-dimethyl-N-(2-methacryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine (SPE), with and without cross-linker monomer N,N'-methylene bisacrylamide (MBAA), onto a polyethersulfone (PES) UF membrane. The characteristics, the stability, and the UF separation performance of the resulting composite membranes were evaluated in detail. The membranes were characterized with respect to membrane chemistry (by ATR-IR spectroscopy and elemental analysis), surface wettability (by contact angle), surface charge (by zeta potential), surface morphology (by scanning electron microscopy), and pure water permeability and rejection of macromolecular test substances (including the "cutoff" value). The surface chemistry and wettability of the composite membranes did not change after incubating in sodium hypochlorite solution (typically used for cleaning UF membranes) for a period of 8 days. Changes in water permeability after static contact with solutions of a model protein (myoglobin) were used as a measure of fouling resistance, and the results suggest that PEGMA- and SPE-based composite membranes at a sufficient degree of graft modification showed much higher adsorptive fouling resistance than unmodified PES membranes of similar or larger nominal cutoff. This was confirmed in UF experiments with myoglobin solutions. Similar results, namely, a very much improved fouling resistance due to the grafted thin polymer hydrogel layer, were also obtained in the UF evaluation using humic acid as another strong foulant. In some cases, the addition of the cross-linker during modification could improve both permeate flux and solute rejection during UF. Overall, composite membranes prepared with an "old generation" nonfouling material, PEGMA, showed better performance than composite membranes prepared with a "new generation" one, the zwitterionic SPE.

Effect of hypo- and hypersaline conditions on osmolality and Na+/K+-ATPase activity in juvenile shrimp (Litopenaeus vannamei) fed low- and high-HUFA diets

Fatty acid composition of cellular membranes can modify permeability and can modulate the activity of Na(+)/K(+)-ATPase. Although highly unsaturated fatty acids (HUFA) improve survival and osmoregulatory capacity to low salinities in penaeid shrimp, the possible mechanisms have not been established. For this purpose the influence of HUFA supplementation in diet (2.9 vs. 34% HUFA proportion to total fatty acids) on osmoregulatory responses of juvenile Litopenaeus vannamei submitted to an acute (15 h) or chronic exposure (21 days), to low (5 g L(-1)) and high salinities (50 g L(-1)) was analyzed. Shrimp fed the high-HUFA diet, had higher concentration of main HUFA (20:5n-3 and 22:6n-3) in polar lipids of gills. Osmotic pressure in hemolymph was significantly affected by salinity in acute (640, 751, 847 mOsm/kg for 5, 30 and 50 g L(-1), respectively), and chronic exposure (645, 713, 814 mOsm/kg), but variations between them were small compared to environmental salinity (206, 832, 1547 mOsm/kg), indicating that osmoregulation was achieved in a matter of hours. An increase in Na(+)/K(+)-ATPase activity was observed only after a chronic exposure to low salinity. Free amino acids (FAA), mainly alanine and arginine, were higher at 30 (control) and 50 g L(-1) in accordance to their role as organic osmolites. Neither osmotic pressure, Na(+)/K(+)-ATPase activity, nor FAA was affected by HUFA supplementation. However, higher water content in gills of shrimp exposed to low salinities was counteracted by increased HUFA content, which could be a result of changes in water permeability of gills. The osmoregulatory capacity of penaeid shrimp to low and high salinities was achieved within 15 h of acclimation and did not depend on HUFA supplementation in the diet.

Inability of the lone star tick, Amblyomma Americanum (L.), to resist desiccation and maintain water balance following application of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae (Deuteromycota)

We report that female lone star ticks (Amblyomma americanum) experience a rapid change in water permeability when treated with the entomopathogenic fungus Metarhizium anisopliae. The amount of water loss is nearly double the rate of control ticks not exposed to this fungus. As a result, ticks are prevented from stabilizing body water levels (water gain ≠ water loss) at hydrating atmospheres greater than the critical equilibrium activity (CEA) of 0.85a v-0.93av (a v = % RH/100) and reach their dehydration tolerance limit in less time. Thus, disruption of water balance is a pathogenic consequence of fungus infection. This served as a benchmark for evaluating effects on ticks of frequently encountered soil molds in nature (wild tick isolates), Aspergillus niger, Cladosporium cladosporioides, Penicillium glabrum and Scopulariopsis brevicaulis. In contrast to M. anisopliae treatment, no effect on tick water balance was noted with topical application of C. cladosporioides, but water loss rates of ticks following treatment with S. brevicaulis fell between both extremes. Water loss rates imply that P. glabrum may be a tick pathogen, whereas A. niger is apparently not able to use ticks as a substrate. Enhanced desiccation arising from these common molds shows the importance of local mycoflora as natural regulators of tick populations. Water loss rates also provide a tool to assess the pathogenicity of different fungal strains targeted for application in the biological control of ticks.

Influence of the growth at high osmolality on the lipid composition, water permeability and osmotic response of Lactobacillus bulgaricus

Changes in water permeability and membrane packing were measured in cells of Lactobacillus bulgaricus and in vesicles prepared with lipids extracted from them. The osmotic response of whole cells and vesicles is compared with the one of bacteria grown in a high osmolal medium. Both bacteria and vesicles, behave as osmometers. This means that the volume decrease is promoted by the outflow of water, driven by the NaCl concentration difference, arguing that neither Na + nor Cl − permeates the cell or the lipid membrane in these conditions. Therefore, the volume changes can be correlated with the rate of water permeation across the cell or the vesicle membranes. The permeation of water was analyzed as a function of the lipid species by measuring the volume changes and the saturation ratio of the lipids. To put into relevance the membrane processes, the permeation properties of lipid vesicles prepared with lipids extracted from bacteria grown in normal and high osmolality conditions were also analyzed. The permeation response was correlated with the physical properties of the membrane of whole cells and vesicles, by means of fluorescence anisotropy of diphenyl hexatriene (DPH). The modifications in membrane properties are related with the changes in the membrane composition triggered by the growth in a high osmolal medium. The changes appear related to an increase in the sugar content of the whole pool of lipids and in the saturated fatty acid residues.

Study on ice storing characteristics in dynamic-type ice storage system by using supercooled water.: Effects of the supplying conditions of ice-slurry at deployment to district heating and cooling system

For deploying the dynamic-type ice storage system to district heating and cooling system (DHC), the effects of ice content (ice packing factor, IPF) and mass flow rate of supplying ice-slurry on the ice storing characteristics in a tank were investigated both experimentally and analytically. By raising IPF and reducing mass flow rate of supplying ice-slurry, the ice-rich layer was hard spreading horizontally in the tank. The overall porosity of the ice-rich layer was converging to the value of 0.8–0.9 in the ice storing process. The analytical results of the shape of the ice-rich layer agreed fairly with the experimental results, by modeling the change of water permeability in the ice-rich layer in the tank. This analytical model is considered to be applicable to the design of ice storage tanks in DHC.

Cloning and characterization of ZmPIP1-5b, an aquaporin transporting water and urea

A cDNA, ZmPIP1-5b, isolated from a nitrate-treated maize roots cDNA library has 95.2% sequence identity to ZmPIP1-5. However, sequence divergences are not uniformly distributed, but are mainly observed in 3′ and 5′ non-coding regions (82.7 and 77.3%, respectively). The coding regions differ by two nucleotides over 864, but ZmPIP1-5b and ZmPIP1-5 encode identical proteins. The deduced ZmPIP1-5 protein is 288 amino acids in length, contains six putative transmembrane domains and the MIP signature NPA. ZmPIP1-5, like other proteins belonging to PIP1 subfamily, has a low aquaporin activity when expressed in Xenopus oocytes. However, a special feature of ZmPIP1-5, when compared with other plant PIPs, is its capacity to transport urea. ZmPIP1-5 is preferentially expressed in roots and addition of KNO 3 to previously nitrogen-starved maize plants induced the transcript level of this gene. Furthermore, ZmPIP1-5 expression oscillated during the day–night cycle. In situ hybridization showed that this regulation is tissue specific. Modulation of ZmPIP1-5 expression by KNO 3 and during the day–night cycle is discussed in regards to root water permeability changes.

Influence of coating system composition on moisture dynamic performance of coated wood

Model coatings with known composition were assessed for liquid water permeability both as single coat systems and combined as primers and topcoats to form regularly used coating systems—in total 38 different systems. The water permeability of the coatings, expressed as water absorption value, was measured by a method similar to the method that now is proposed as a European standard for the assessment of liquid water permeability. During artificial weathering, the samples were measured for a water absorption value, thus showing the change in water permeability as a function of weathering.

Peroxyl radicals promoted changes in water permeability through gramicidin channels in DPPC and lecithin-PC vesicles

Gramicidin incorporation to DPPC or lecithin-PC large unilamellar vesicles (LUVs) leads to pore formation that, under hyper-osmotic conditions, produces a noticeable increase in the rate of trans-membrane water flow. This pore formation is more efficient in the more fluid lecithin-PC LUVs. Exposure of these vesicles to peroxyl radicals generated in the aerobic thermolysis of 2,2′-azo-bis(2-amidinopropane) (AAPH), changes the physical properties of the bilayer (as sensed employing fluorescent probes), modifies gramicidin molecules (as sensed by the decrease in Trp fluorescence) and notably reduces the transbilayer rate of water outflow. In order to evaluate if this reduced water-transport capacity is due to changes in the membrane due to lipid-peroxidation and/or direct damage to gramicidin channels, results obtained in the oxidable vesicles (lecithin-PC) were compared to those obtained in DPPC vesicles. The data obtained show that most of the water transport efficiency loss can be ascribed to a direct disruption of gramicidin channels by AAPH derived peroxyl radicals.

Positive and negative regulation of water channel aquaporins in human small intestine by cholera toxin

Analysis of osmotic water permeability of aquaporin (AQP) 1, AQP3 and AQP4, which are expressed in human small intestine, in the presence or absence of cholera toxin (CT) was performed using a Xenopus oocyte expression system. When treated with CT, water permeability of AQP4 was facilitated while that of AQP3 was suppressed. AQP1 did not show any significant change of water permeability when treated with CT. An adenylyl cyclase accelerator forskolin showed similar effects as CT did, suggesting that changes of the water permeability of AQP4 and AQP3 were due to an increase of intracellular cAMP concentration. A possibility that these AQPs are responsible molecules for causing acute secretory diarrhoea as in cholera is considered.