Small Neutral Solutes Research Articles

Drugging aquaporins

Water is essential for all life because it is required for the proper functioning of the cells and tissues of all organisms. It crosses biological membranes down osmotic gradients through the pores of aquaporin membrane channels at rates of up to 3 billion molecules per second. In the twenty years since Peter Agre was awarded the 2003 Nobel Prize in Chemistry for the discovery of the aquaporin family, aquaporin structure and function have become established in the literature. As a consequence, we understand in fine detail the mechanism by which aquaporins facilitate membrane water flow while excluding protons. We also know that some aquaporins facilitate the permeation of other small neutral solutes, ions or even unexpected substrates across biological membranes. The thirteen aquaporins in the human body have been implicated in pathologies including oedema, epilepsy, cancer cell migration, tumour angiogenesis, metabolic disorders and inflammation. Surprisingly, however, there is no aquaporin-targeted drug in the clinic. Some scientists have therefore concluded that aquaporins are intrinsically non-druggable targets. Discovering medicines to treat disorders of water homeostasis is thus an enduring challenge for the aquaporin field. Success in this endeavour will meet the urgent clinical need of millions of patients suffering from a range of life-threatening conditions and for whom no pharmacological interventions are currently available.

Co-transport of water and p-xylene through carbon molecular sieve membranes

Carbon molecular sieve (CMS) materials are a potential candidate for scalable and high-performance reverse osmosis membranes due to their impressive chemical and thermal stabilities. Moreover, they have the potential to enable impressive rejections of small neutral solutes from water based on their known ability to separate small organic molecules. CMS has been extensively examined for gas and organic solvent separations, but the transport of organic and aqueous mixtures through CMS microstructures is poorly understood. In this work, we investigated the sorption, diffusion, and permeation behavior of organic compounds and water in poly(vinylidene fluoride)(PVDF)-derived CMS (PVDF-CMS). Experimental observations of diffusion, sorption, and permeation shows how the properties of penetrants such as polarity and molecular size affect the transport rates and selectivity. These basic transport and sorption parameters are utilized in sorption-diffusion models to permeation rates of water-organic mixtures in CMS membranes. The transport of water and p-xylene in CMS was experimentally confirmed to follow the sorption-diffusion mechanism. The sorption-diffusion model ideal permselectivity indicates that the CMS is p-xylene selective over water. Water/p-xylene mixture permeation experiments revealed an increased selectivity of p-xylene over water, thus providing tentative evidence for a competitive sorption-selective separation mechanism. This work suggests that CMS membranes exhibit organic-permeable separation properties in water/organic separations. The results presented here highlight the potential for the removal of dilute organics in water via CMS pervaporation membranes.

Aquaporins Are One of the Critical Factors in the Disruption of the Skin Barrier in Inflammatory Skin Diseases.

The skin is the largest organ of the human body, serving as an effective mechanical barrier between the internal milieu and the external environment. The skin is widely considered the first-line defence of the body, with an essential function in rejecting pathogens and preventing mechanical, chemical, and physical damages. Keratinocytes are the predominant cells of the outer skin layer, the epidermis, which acts as a mechanical and water-permeability barrier. The epidermis is a permanently renewed tissue where undifferentiated keratinocytes located at the basal layer proliferate and migrate to the overlying layers. During this migration process, keratinocytes undertake a differentiation program known as keratinization process. Dysregulation of this differentiation process can result in a series of skin disorders. In this context, aquaporins (AQPs), a family of membrane channel proteins allowing the movement of water and small neutral solutes, are emerging as important players in skin physiology and skin diseases. Here, we review the role of AQPs in skin keratinization, hydration, keratinocytes proliferation, water retention, barrier repair, wound healing, and immune response activation. We also discuss the dysregulated involvement of AQPs in some common inflammatory dermatological diseases characterised by skin barrier disruption.

The Role of Aquaporin 7 in the Movement of Water and Cryoprotectants in Bovine In Vitro Matured Oocytes.

Simple SummaryThe permeability of the plasma membrane to water and cryoprotectants is a critical factor in the effective vitrification of oocytes. The goal of this study is to better understand the pathways used to transport water and other cryoprotectants through the plasma membrane of bovine in vitro matured oocytes, with a focus on the role of aquaporin 7 (AQP7). We demonstrated that cryoprotectants stimulated AQP3 and AQP7 but not AQP9 expression in mature bovine oocytes. Dimethyl sulfoxide upregulates AQP3 expression, while ethylene glycol upregulates AQP7 expression in oocytes in a CPA-dependent fashion. We also demonstrated that exogenous expression of aquaglyceroporins such as AQP7 is possible in in vitro matured oocytes. When permeability values for membrane transport of dimethyl sulfoxide, ethylene glycol and sucrose were assessed, we observed that AQP7 overexpressed oocytes are more permeable to water in the presence of dimethyl sulfoxide solution. These biophysical characteristics, together with the use of membrane transport modeling, will allow re-evaluation and possibly improvement of previously described protocols for bovine oocyte cryopreservation.Aquaglyceroporins are known as channel proteins, and are able to transport water and small neutral solutes. In this study, we evaluate the effect of exposure of in vitro matured bovine oocytes to hyperosmotic solutions containing ethylene glycol (EG), dimethyl sulfoxide (Me2SO) or sucrose on the expression levels of AQP3, AQP7 and AQP9. Moreover, we studied whether artificial protein expression of AQP7 in bovine oocytes increases their permeability to water and cryoprotectants. Exposure to hyperosmotic solutions stimulated AQP3 and AQP7 but not AQP9 expression. Oocytes exposed to hyperosmotic Me2SO solution exhibited upregulated AQP3 expression, while AQP7 expression was upregulated by EG hyperosmotic exposure. Microinjection of oocytes at the germinal vesicle stage with enhanced green fluorescent protein (EGFP) or EGFP+AQP7 cRNAs resulted in the expression of the corresponding proteins in ≈86% of the metaphase-II stage oocytes. AQP7 facilitated water diffusion when bovine MII oocytes were in presence of Me2SO solution but not EG or sucrose solution. However, the overexpression of this aquaporin did not increase membrane permeability to Me2SO or EG. In summary, cryoprotectant-induced increase of AQP3 and AQP7 expression could be one of the mechanisms underlying oocyte tolerance to hyperosmotic stress. Water diffusion appears to be improved when AQP7 overexpressed oocytes are exposed to Me2SO, shortening the time required for oocytes to achieve osmotic balance with cryoprotectant solutions.

Signaling Mechanisms and Pharmacological Modulators Governing Diverse Aquaporin Functions in Human Health and Disease.

The aquaporins (AQPs) are a family of small integral membrane proteins that facilitate the bidirectional transport of water across biological membranes in response to osmotic pressure gradients as well as enable the transmembrane diffusion of small neutral solutes (such as urea, glycerol, and hydrogen peroxide) and ions. AQPs are expressed throughout the human body. Here, we review their key roles in fluid homeostasis, glandular secretions, signal transduction and sensation, barrier function, immunity and inflammation, cell migration, and angiogenesis. Evidence from a wide variety of studies now supports a view of the functions of AQPs being much more complex than simply mediating the passive flow of water across biological membranes. The discovery and development of small-molecule AQP inhibitors for research use and therapeutic development will lead to new insights into the basic biology of and novel treatments for the wide range of AQP-associated disorders.

Boron removal by water molecules inside covalent organic framework (COF) multilayers

Removal of small neutral solutes (SNSs) by reverse osmosis membranes is crucial but challenging. Common consideration of narrowing pore sizes works very little as SNSs have close sizes to the one of water molecules. The most serious drawback of narrowing pore sizes is the reduction of permeance, which dramatically enhances the energy input per volume of permeate water. In this work, an alternative strategy of driving water molecules to reject SNSs is proposed. Using non-equilibrium molecular dynamics simulations, we reveal that inside the nanopores of TpTG multilayers, stable imine-linked covalent organic frameworks, water molecules will preferentially adsorb via the hydrogen bonding interaction. In that way, water molecules in TpTG multilayers other than TpTG themselves can completely reject SNSs, e.g. boric acid. The permeance of TpTG multilayers is excellent as the nanopores are fulfilled with fluidic water. The findings in this work will inspire researchers with an alternative way to design the membranes for SNS removal.

Precise separation of small neutral solutes with mixed-diamine-based nanofiltration membranes and the impact of solvent activation

Mixed-diamine-based nanofilm composite membranes prepared with 1.0 wt% PIP and 0.1 wt% MPD on crosslinked polyimide (XP84) UF support show a seven times higher selectivity of ∼ 59.0 between glycerol and glucose than the conventional membranes (selectivity of ∼ 8.2). Membranes also show a ∼ 55.8% increase in pure water permeance (PWP) without altering Na 2 SO 4 rejection (from 99.27 % to 99.53%) and an increased selectivity between NaCl to Na 2 SO 4 (from 43.7 to 98.9) after solvent activation with DMF. Additionally, after solvent activation, mixed-diamine-based nanofilm composite membranes show a sharp and reduced molecular weight cut-off (MWCO) compared to the membranes prepared from semi-aromatic polyamide. • 1. Nanofilm membranes are made from mixed diamines via interfacial polymerization. • 2. Nanofilm membranes show a seven times higher selectivity between glycerol and glucose. • 3. Membranes show a ∼ 55.8% increase in pure water permeance upon DMF activation. • 4. Nanofilm membranes show a sharp and reduced MWCO (∼170 Da) upon DMF activation. • 5. The mean pore size is ∼ 13.0 Å with an enhancement of up to 22.6% after DMF activation. High permeance membranes selective towards small ions and solutes are required to produce high-quality product water. Conventional semi-aromatic polyamide thin-film composite (TFC) nanofiltration membranes prepared via interfacial polymerization of diamine, e.g., piperazine (PIP) and acid chloride, do not show the precise separation of small solutes (<200 Da). To achieve this, we introduced an aromatic diamine group, e.g., m -phenylenediamine (MPD), within the semi-aromatic polyamide structure to achieve selective separation between small solutes with enhanced permeation upon solvent activation. Herein, we report the fabrication of polyamide nanofilm composite membranes using a mixture of PIP and MPD as a diamine precursor and react with trimesoyl chloride (TMC) on top of the ultrafiltration (UF) supports. Nanofilm composite membranes prepared with 1.0 wt% PIP and 0.1 wt% MPD on crosslinked polyimide (XP84) UF support show a seven times higher selectivity of ∼ 59.0 between glycerol and glucose than the conventional nanofiltration membranes (selectivity of ∼ 8.2). Membranes also show a ∼ 55.8% increase in pure water permeance (PWP) with identical Na 2 SO 4 rejection (99.27% – 99.53%) and an increased selectivity between NaCl to Na 2 SO 4 (from 43.7 to 98.9) after solvent activation with DMF. Additionally, after solvent activation, mixed-diamine-based nanofilm composite membranes show a sharp and reduced molecular weight cut-off (MWCO ∼ 170 Da) compared to the nanofiltration membranes prepared from semi-aromatic polyamide. The permeation results conducted with small neutral solutes in the aqueous feed suggest the existence of pores of mean size ∼ 13.0 Å, with an enhancement of pore sizes ∼ 7 – 22.6% after DMF activation. The process of membrane fabrication is acceptable for large-scale manufacturing.

Aquaporins and their implications on seeds: A brief review

Aquaporins (AQPs) are water channel proteins. They play a key role in maintaining water balance and homeostasis in cells under stress conditions in living organisms. AQPs are pore forming transmembrane proteins that facilitate water movement and various small neutral solutes across cellular membranes. Aquaporin expression and transport functions are modulated by various phytohormones mediated signalling in plants. Transcriptome analysis revealed the role of aquaporins in regulating hydraulic conductance in plant roots and leaves. Different AQPs found in the seed system have individual functions that are more time and tissue specific, ultimately helping in the seed imbibition process to complete seed germination. Seed specific TIP3s aquaporin helps to maintain seed longevity under expressional control of ABI3 during seed maturation and heat shock proteins and late embryogenic abundant proteins. Under stress circumstances, the major significance of aquaporin expression in seeds is to maintain water influx and efflux rates, as well as protein modification, post translational alterations, nutritional acquisition and allocation, subcellular trafficking and CO2 transport. The present review mainly focused on aquaporin structure, classification, role and functional activity during solute transport, reproductive organs development, plant growth development, abiotic stress response and also various roles in seeds such as seed biology, seed development and maturation, seed dormancy, seed germination and longevity.

The pip1s Quintuple Mutants Demonstrate the Essential Roles of PIP1s in the Plant Growth and Development of Arabidopsis.

Plasma membrane intrinsic proteins (PIPs) transport water, CO2 and small neutral solutes across the plasma membranes. In this study, we used the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 system (CRISPR/Cas9) to mutate PIP1;4 and PIP1;5 in a pip1;1,2,3 triple mutant to generate a pip1;1,2,3,4,5 (pip1s−) quintuple mutant. Compared to the wild-type (WT) plant, the pip1s− mutants had smaller sized rosette leaves and flowers, less rosette leaf number, more undeveloped siliques, shorter silique and less seeds. The pollen germination rate of the pip1s− mutant was significantly lower than that of the WT and the outer wall of the pip1s− mutant’s pollen was deformed. The transcriptomic analysis showed significant alterations in the expression of many key genes and transcription factors (TFs) in the pip1s− mutant which involved in the development of leaf, flower and pollen, suggesting that the mutant of PIP1s not only directly affects hydraulics and carbon fixation, but also regulates the expression of related genes to affect plant growth and development.

Versatile Roles of Aquaporins in Plant Growth and Development.

Aquaporins (AQPs) are universal membrane integrated water channel proteins that selectively and reversibly facilitate the movement of water, gases, metalloids, and other small neutral solutes across cellular membranes in living organisms. Compared with other organisms, plants have the largest number of AQP members with diverse characteristics, subcellular localizations and substrate permeabilities. AQPs play important roles in plant water relations, cell turgor pressure maintenance, the hydraulic regulation of roots and leaves, and in leaf transpiration, root water uptake, and plant responses to multiple biotic and abiotic stresses. They are also required for plant growth and development. In this review, we comprehensively summarize the expression and roles of diverse AQPs in the growth and development of various vegetative and reproductive organs in plants. The functions of AQPs in the intracellular translocation of hydrogen peroxide are also discussed.

Plant water transport and aquaporins in oxygen-deprived environments

Oxygen deprivation commonly affects plants exposed to flooding and soil compaction. The resulting root hypoxia has an immediate effect on plant water relations and upsets water balance. Hypoxia inhibits root water transport and triggers stomatal closure. The processes contributing to the inhibition of root hydraulic conductivity and conductance (hydraulic conductivity of the whole root system) are complex and involve changes in root morphology and the functions of aquaporins. Aquaporins (AQPs) comprise a group of membrane intrinsic proteins that are responsible for the transport of water, as well as some small neutral solutes and ions. They respond to a wide range of environmental stresses including O2 deprivation, but the underlying functional mechanisms are still elusive. The aquaporin-mediated water transport is affected by the acidification of the cytoplasm and depletion of ATP that is required for aquaporin phosphorylation and membrane functions. Cytoplasmic pH, phosphorylation, and intracellular Ca2+ concentration directly control AQP gating, all of which are related to O2 deprivation. This review addresses the structural determinants that are essential for pore conformational changes in AQPs, to highlight the underlying mechanisms triggered by O2 deprivation stress. Gene expression of AQPs is modified in hypoxic plants, which may constitute an important, yet little explored, mechanism of hypoxia tolerance. In addition to water transport, AQPs may contribute to hypoxia tolerance by transporting O2, H2O2, and lactic acid. Responses of plants to O2 deprivation, and especially those that contribute to maintenance of water transport, are highly complex and entail the signals originating in roots and shoots that lead to and follow the stomatal closure. These complex responses may involve ethylene, abscisic acid, and possibly other hormonal factors and signaling molecules in ways that remain to be elucidated.

Electrochemical surface plasmon resonance as a probe of redox reactions at the ionic liquid|gold interface

Electrochemical surface plasmon resonance (ESPR) has been employed as a probe of redox reactions at the interface between gold (Au) and ionic liquid (IL). Two redox couples, ferrocene (Fc)/Fc+ and (ferrocenylmethyl)trimethylammonium (FTA+)/FTA2+, and two ILs, trioctylmethylammonium bis(trifluoromethanesulfonyl)amide ([TOMA+][C1C1N−]) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim+][C1C1N−]) have been studied. In the ESPR measurements, the shift of the SPR angle has been recorded simultaneously with cyclic voltammogram (CV). It has been revealed that the SPR angle shift reproduces CV when the former is semi-differentiated or the latter is semi-integrated, and, therefore, that the ESPR response probes the surface concentration of redox couples at the IL|Au interface. Among the four combination of the two redox couples and the two ILs, the case for Fc/Fc+ in [TOMA+][C1C1N−] shows significantly greater ESPR response than the other three cases. A model has been established for the relationship between the SPR angle shift and the surface concentration of redox species. The model predicts that the SPR angle shift becomes pronounced with increasing DR/DO, the diffusion coefficient ratio of the reduced (R) and oxidized (O) species when the reduced species is initially dissolved in the IL as is the case for the present study. Significantly greater DR/DO for Fc/Fc+ in [TOMA+][C1C1N−] than the three other cases has been confirmed from the DR and DO measurements by CV with a microdisk electrode. The trend of the measured DR and DO values agrees with recent findings by researchers that small neutral solutes in ILs composed of large ions diffuse fast beyond the prediction of the Stokes-Einstein relation.

Lipopolysaccharide Modifies Glycerol Permeability and Metabolism in 3T3-L1 Adipocytes.

Aquaglyceroporins—aquaporin membrane channels (AQP) that conduct glycerol and other small neutral solutes in addition to water—play major roles in obesity. In adipocytes, aquaglyceroporins mediate glycerol uptake and release across the plasma membrane, which are two key steps for triacylglycerols (TAGs) synthesis (lipogenesis) and hydrolysis (lipolysis). The aim of this study was to assess both glycerol permeability and metabolism in undifferentiated 3T3-L1 cells (UDCs) as well as in untreated (CTL-DCs) versus lipopolysaccharide (LPS-DCs)-treated differentiated 3T3-L1 adipocytes. Glycerol release, TAGs content and whole membrane glycerol permeability were significantly increased in DCs as compared to UDCs. Moreover, in DCs, LPS treatment significantly increased TAGs content and decreased glycerol permeability. In addition, a significant reduction in whole membrane glycerol permeability was observed in LPS-DCs as compared to CTL-DCs. The relative contributions of AQP3, AQP7 and AQP9 (facilitated diffusion), as well as that of the phospholipid bilayer (simple diffusion), to the whole membrane glycerol permeability, were estimated biophysically in UDCs, CTL-DCs and LPS-DCs, using selective AQP inhibitors. Further studies will be required to determine if modifications in either subcellular localization and/or activity of aquaglyceroporins could account for the data herein. Nevertheless, our findings provide novel insights in understanding the LPS-induced adipocyte hypertrophy that accompanies obesity.

Communication: Stiff and soft nano-environments and the "Octopus Effect" are the crux of ionic liquid structural and dynamical heterogeneity.

In a recent set of articles [J. C. Araque et al., J. Phys. Chem. B 119(23), 7015-7029 (2015) and J. C. Araque et al., J. Chem. Phys. 144, 204504 (2016)], we proposed the idea that for small neutral and charged solutes dissolved in ionic liquids, deviation from simple hydrodynamic predictions in translational and rotational dynamics can be explained in terms of diffusion through nano-environments that are stiff (high electrostriction, charge density, and number density) and others that are soft (charge depleted). The current article takes a purely solvent-centric approach in trying to provide molecular detail and intuitive visual understanding of time-dependent local mobility focusing on the most common case of an ionic liquid with well defined polar and apolar nano-domains. We find that at intermediate time scales, apolar regions are fluid, whereas the charge network is much less mobile. Because apolar domains and cationic heads must diffuse as single species, at long time the difference in mobility also necessarily dissipates.

Tamarix hispida aquaporin ThPIP2;5 confers salt and osmotic stress tolerance to transgenic Tamarix and Arabidopsis

Aquaporin (AQP) proteins constitute a large family of protein channels that facilitate the transport of water and small neutral solutes through biological membranes, which is important for plants to combat abiotic stress. However, the precise functions of AQP genes involved in abiotic stress are not completely understood in plants. In this study, ThPIP2;5, an AQP gene of the PIP2 subgroup, was cloned and characterized from Tamarix hispida. Cellular localization assays showed that ThPIP2;5 was localized to the plasma membrane. Transgenic Arabidopsis plants overexpressing ThPIP2;5 displayed improved seed germination rates and increased root growth and fresh weight gain under salt and osmotic stresses, indicating that ThPIP2;5 can improve abiotic stress tolerance. ThPIP2;5-overexpressing and RNAi-silencing T. hispida plants were generated using the transient transformation method and selected for gain- and loss-of ThPIP2;5 analyses, respectively. Overexpression of ThPIP2;5 in transgenic Tamarix and Arabidopsis plants increased ROS-scavenging capability, activities of antioxidant enzymes and proline contents; decreased malondialdehyde (MDA) and H2O2 contents; and reduced electrolyte leakage rates compared to equivalent controls under salt and osmotic stresses. Together, these data suggested that ThPIP2;5 plays an important physiological role in abiotic stress tolerance in transgenic plants by reducing ROS accumulation and membrane damage and increasing the activities of antioxidants.

Alkyl amine functional dextran macromonomer‐based thin film composite loose nanofiltration membranes for separation of charged and neutral solutes

ABSTRACTThin film composite (TFC) nanofiltration membranes with defined porous structure of the separation layer are desirable for the concentration of neutral solute and separation of salts from a mixture. Herein, we report the formation of TFC membranes composed of polyamide (PA) separation layer by the interfacial polymerization between new dextran‐butyl amine (Dex‐NH2) macromonomer and trimesoyl chloride on polysulfone support membrane. The membranes prepared with 1%–1.5% (wt/vol) of Dex‐NH2 exhibited water permeance of 110–116 L m−2 h−1 MPa−1 with 62%–71% rejection of Na2SO4 and 12%–14% rejection of MgCl2. The membranes also showed about 91% rejection of poly(ethylene glycol) of molecular weight 2000 g/mol and about 11% rejection of NaCl. A decrease in permeance and ions selectivity was observed with increasing concentration of Dex‐NH2. The dextran chains attached to the PA network restrict the diffusion of Dex‐NH2 toward the interfacial zone and thereby assist the formation of porous and thin PA layer compared to that when free amine (alkyl diamine) was used. These membranes are applicable for the separation of small molecular weight neutral solutes from mixture containing monovalent salts. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45301.

Single amino acid substitutions in the selectivity filter render NbXIP1;1\u03b1 aquaporin water permeable

BackgroundAquaporins (AQPs) are integral membrane proteins that facilitate transport of water and/or other small neutral solutes across membranes in all forms of life. The X Intrinsic Proteins (XIPs) are the most recently recognized and the least characterized aquaporin subfamily in higher plants. XIP1s have been shown to be impermeable to water but permeable to boric acid, glycerol, hydrogen peroxide and urea. However, uncertainty regarding the determinants for selectivity and lack of an activity that is easy to quantify have hindered functional investigations. In an effort to resolve these issues, we set out to introduce water permeability in Nicotiana benthamiana XIP1;1α (NbXIP1;1α), by exchanging amino acid residues of predicted alternative aromatic/arginine (ar/R) selectivity filters of NbXIP1;1α for residues constituting the water permeable ar/R selectivity filter of AtTIP2;1.ResultsHere, we present functional results regarding the amino acid substitutions in the putative filters as well as deletions in loops C and D of NbXIP1;1α. In addition, homology models were created based on the high resolution X-ray structure of AtTIP2;1 to rationalize the functional properties of wild-type and mutant NbXIP1;1α. Our results favour Thr 246 rather than Val 242 as the residue at the helix 5 position in the ar/R filter of NbXIP1;1α and indicate that the pore is not occluded by the loops when heterologously expressed in Pichia pastoris. Moreover, our results show that a single amino acid substitution in helix 1 (L79G) or in helix 2 (I102H) is sufficient to render NbXIP1;1α water permeable. Most of the functional results can be rationalized from the models based on a combination of aperture and hydrophobicity of the ar/R filter.ConclusionThe water permeable NbXIP1;1α mutants imply that the heterologously expressed proteins are correctly folded and offer means to explore the structural and functional properties of NbXIP1;1α. Our results support that Thr 246 is part of the ar/R filter. Furthermore, we suggest that a salt bridge to an acidic residue in helix 1, conserved among the XIPs in clade B, directs the orientation of the arginine in the ar/R selectivity filter and provides a novel approach to tune the selectivity of AQPs.

Transport Characteristics of Aquaporins.

Aquaporins (AQPs ) are a class of the integral membrane proteins, which are permeable to water , some small neutral solutes and certain gases across biological membranes. AQPs are considered as critical transport mediators that are involved in many physiological functions and pathological processes such as transepithelial fluid transport , cell migration, brain edema , neuro excitation and carcinoma. This chapter will provide information about the transport characteristics of AQPs .

All-Trans Retinoic Acid Increases Aquaporin 3 Expression in Human Vaginal Epithelial Cells.

IntroductionWater channel aquaporin 3 (AQP3) is an aquaglyceroporin that transports small neutral solutes and water. All-trans retinoic acid (ATRA), a member of the retinoid drug class, acts as a regulator in several biological processes.AimTo investigate the effect of ATRA on the expression of AQP3 in human vaginal epithelial cells.MethodsHuman vaginal mucosal epithelial cells (CRL2616) were treated with ATRA 0, 0.01, 0.1, and 1 μmol/L for 24 hours to examine the dose-dependent effects of ATRA and with ATRA 1 μmol/L for 0, 3, 6, 12, and 24 hours.Main Outcome MeasuresThe expression of AQP3 and retinoic acid receptor (RAR) was determined by western blot analysis and reverse transcription polymerase chain reaction.ResultsAQP3 was detected in the cell membrane of human vaginal epithelial cells. ATRA increased the protein expression and mRNA levels of AQP3 in a dose-dependent manner (P < .05). ATRA also increased the protein expression of RARα (P < .05). Treatment of CRL2616 cells with an RAR antagonist (Ro 41-5253) significantly decreased AQP3 protein expression (P < .05).ConclusionATRA mediated by RARα increased AQP3 gene and protein expression in human vaginal mucosal epithelial cells. These results imply that AQP3 regulated by ATRA could play an important role in the mechanism of vaginal lubrication.

The Roles of Aquaporins in Plant Stress Responses.

Aquaporins are membrane channel proteins ubiquitously present in all kingdoms of life. Although aquaporins were originally discovered as water channels, their roles in the transport of small neutral solutes, gasses, and metal ions are now well established. Plants contain the largest number and greatest diversity of aquaporin homologs with diverse subcellular localization patterns, gating properties, and solute specificity. The roles of aquaporins in physiological functions throughout plant growth and development are well known. As an integral regulator of plant–water relations, they are presumed to play an important role in plant defense responses against biotic and abiotic stressors. This review highlights involvement of various aquaporin homologs in plant stress responses against a variety of environmental stresses that disturb plant cell osmotic balance and nutrient homeostasis.