Membrane Channels Research Articles

Accelerating Ion Desolvation via Bioinspired Ion Channel Design in Nonconcentrated Aqueous Electrolytes.

In aqueous-based electrochemical energy storage devices, uncontrolled hydrolysis of water at the electrochemical interfaces limits the application of such aqueous batteries or supercapacitors in business. The "water-in-salt" design is a valid strategy to broaden the electrochemical stability window in aqueous electrolytes, but drawbacks such as high manufacturing cost, high electrolyte viscosity, etc., also hinder its development. Here, inspired by biological ion channels in cell membranes, we propose an effective approach to engineer the electrode surface, inducing the desolvation of hydrated ions at the electrochemical interface and inhibiting water decomposition in nonconcentrated electrolytes. The biological engineering strategy enables the induction of controlled desolvation and accelerates the transportation of hydrated ions, e.g., potassium. The subnanometer design (0.8 nm) forces the hydrated potassium ions to shed their solvation shell with a hydration number of only 0.3, while the electrostatic interactions between the pore groups and the potassium ions facilitate their transport. The Zn||Zn cells demonstrate a stable cycling lifespan of over 1000 h at 1 mA cm-2/10 mAh cm-2. This work sheds new light on regulating the electrochemical interfaces in low-concentration aqueous electrolytes for designing aqueous-based energy storage devices.

Kir5.1 regulates Kir4.2 expression and is a key component of the 50-pS inwardly rectifying potassium channel in basolateral membrane of mouse proximal tubules.

Kir5.1 encoded by Kcnj16 is an inwardly rectifying K+ channel subunit, and it possibly interacts with Kir4.2 subunit encoded by Kcnj15 for assembling a Kir4.2/Kir5.1 heterotetramer in the basolateral membrane of mouse proximal tubule. We now used patch clamp technique to examine basolateral K+ channels of mouse proximal tubule (PT) and an immunoblotting/immunofluorescence (IF) staining microscope to examine Kir4.2 expression in wild-type and Kir5.1-knockout mice. IF staining shows that Kir4.2 was exclusively expressed in the proximal tubule, whereas Kir5.1 was expressed in the proximal tubule and distal nephrons including distal convoluted tubule. Immunoblotting showed that the expression of Kir4.2 monomer was lower in Kir5.1-knockout mice than that in the wild-type mice. In contrast, Kir4.1 monomer expression was increased in Kir5.1 knockout mice. IF images further demonstrated that the basolateral membrane staining of Kir4.2 was significantly decreased in Kir5.1 knockout mice. This is in sharp contrast to Kir4.1, which also interacts with Kir5.1 in the distal nephron, and IF images show that Kir4.1 membrane expression was still visible and unchanged in Kir5.1 knockout mice. The single channel recording detected a 50-pS inwardly rectifying K+ channel, presumably a Kir4.2/Kir5.1 heterotetramer, in the basolateral membrane of the proximal tubule of Kir5.1 wild-type mice. However, this 50-pS K+ channel was completely absent in the basolateral membrane of the proximal tubule of Kir5.1 knockout mice. Moreover, the membrane potential of the proximal tubule was less negative in Kir5.1 knockout mice than wild-type mice. We conclude that Kir5.1 is essential for assembling basolateral 50-pS K+ channel in proximal tubule and that deletion of Kir5.1 decreased Kir4.2 expression in the proximal tubule thereby decreasing the basolateral K+ conductance and the membrane potentials.NEW & NOTEWORTHY Our studyprovides direct evidence for the notion that Kir5.1 is a key component of a 50-60 pS inwardly-rectifying-K+ channel, a main type K+ channel in the basolateral-membrane of PT. Also, we demonstrate that deletion of Kir5.1 decreased Kir4.2 protein expression including the basolateral-membrane in PT. Finally, depolarization ofPT-membrane- potential in Kir5.1-knockout mice suggests that Kir4.2 alone is not able to sustain basolateral K+ conductance of the PT in the absence of Kir5.1.

Prediction of Membrane Flux in Membrane Bioreactors through Dimensionless Analysis and Correlations

Membrane flux (J, m3/m2·s) is a key design and operation parameter of membrane bioreactor (MBR) wastewater treatment plants. In this study, the impact of mixed liquor properties (mixed liquor density (ρ, kg/m3), mixed liquor dynamic viscosity (μs, kg/m.s)), hydrodynamic conditions (mixed liquor cross-flow velocity Vm in tubular MBRs or air-mixed liquor two-phase cross-low velocity Vam in the riser zone of the filtration tank of submerged MBRs, generalized as V (m/s)), trans-membrane pressure ΔP (Pa), membrane module geometry (tubular membrane channel diameter (Dt) or the hydraulic diameter (Ds) of the submerged bioreactor filtration riser zone, generalized as D (m)), and membrane filtration characteristics (total membrane filtration resistance (Rt, 1/m)) on membrane flux J in MBRs was analyzed and investigated using the dimensionless analysis and correlation approach. Four dimensionless groups, the ratio of membrane flux J to mixed liquor or air-mixed liquor generalized cross-flow velocity V (J/V), Reynolds number of mixed liquor (ρVD/μs), Euler number of mixed liquor (ΔP/(ρV2), and a new dimensionless group, fouling number of mixed liquor, (μsRt/(ρV)), were derived to correlate the impact of these parameters on membrane flux J in MBRs as seen in Equation (i):Based on experimental data of MBRs from the literature, the coefficients (m, a, b, c) in Equation (i) were calibrated. The J/V values predicted using Equation (i) are in reasonably good agreement with the experimental J/V values from the literature with a typical relative error smaller than 20% in most cases. Sensitivity analysis showed that trans-membrane pressure, ΔP, and total membrane filtration resistance, Rt, are the two most important parameters affecting the prediction of the derived dimensionless correlations (J/V) for both side-stream tubular MBRs and submerged MBRs. These new dimensionless group correlations provide a new mathematical tool for representing in-depth insights of how mixed liquor properties, hydrodynamic conditions, membrane module geometry, and total membrane filtration characteristics affect membrane flux J in MBRs. They can then be used to predict the membrane performance and to guide the optimal design and operation of MBR plants.

Dual Relaxant Effect of Coumarin-3-carboxamides Through the NO/cGMP Pathway and Ca2+ Channels Blockade.

We aimed to determine the relaxant pathway of seventeen synthetic compounds derived from coumarin-3-carboxamide. An isolated rat aorta assay was used. To determine the vasorelaxant mode of action, receptor blockers and specific enzyme inhibitors involved in endothelial and smooth muscle signaling pathways were used. The compounds 2, 4, and 5 showed higher activity than the other compounds. N-nitro-L-arginine methyl ester (L-NAME; 10 µM) and methylene blue (MB; 10 µM) significantly inhibited the relaxant effect of the compounds 2, 4, and 5 (P ≤ 0.05), but not tetraethylammonium (TEA, 5 mM), indomethacin (10 µM), or atropine (1 µM). The compounds 2, 4, and 5 abated the contraction induced by CaCl2. The compounds 2, 4, and 5 exert a relaxing effect through the NO/cGMP pathway activation and by blocking Ca2+ channels of the cell membrane. These findings propose coumarin-3-carboxamides as new drug entities with potential to develop non-clinical and clinical.

Chemiluminescence Resonance Energy Transfer for Targeted Photoactivation of Ion Channels in Living Cells.

The regulation of oxidative stress in living cells is essential for maintaining cellular processes and signal transduction. However, developing straightforward strategies to activate oxidative stress-sensitive membrane channels in situ poses significant challenges. In this study, we presented a chemiluminescence resonance energy transfer (CRET) system based on a conjugated oligomer, oligo(p-phenylenevinylene)-imidazole (OPV-Im), designed for the activation of transient receptor potential melastatin 2 (TRPM2) calcium channels in situ by superoxide anion (O2•-) without requiring external light sources. The OPV-Im oligomer, which targeted the cell membrane efficiently, leading to the activation of TRPM2 channels in situ by CRET process and subsequent intracellular calcium overload. This cascade resulted in mitochondrial damage and inhibition of autophagy, ultimately inducing cell apoptosis. Additionally, this strategy can be applied for the selective killing of tumor cells that overexpress TRPM2 ion channels and for inhibiting the growth of three-dimensional tumor cell spheroids. Compared to optogenetics and photodynamic therapy, our system offers a novel approach for regulating ion channel activity and oxidative stress in living cells.

Naltriben promotes tumor growth by activating the TRPM7-mediated development of the anti-inflammatory M2 phenotype

Macrophage plasticity is critical for maintaining immune function and developing solid tumors; however, the macrophage polarization mechanism remains incompletely understood. Our findings reveal that Mg2+ entry through distinct plasma membrane channels is critical to macrophage plasticity. Naïve macrophages displayed a previously unidentified Mg2+ dependent current, and TRPM7-like activity, which modulates its survival. Significantly, in M1 macrophages, Mg2+ entry is facilitated by a novel Mg²-dependent current that relies on extracellular Mg2+, which was crucial for activating iNOS/NFκB pathways and cellular bioenergetics, which drives pro-inflammatory cytokines. Conversely, in M2 macrophages, Mg2+ entry occurs primarily through TRPM7 channels, pivotal for IL-4 and IL-10-mediated anti-inflammatory cytokine secretion. Notably, the Mg2+ deficient diet or addition of TRPM7 agonist Naltriben suppresses the M1 phenotype while promoting angiogenic factors and fostering tumor growth. These findings suggest that Mg2+ flux via specific channels is indispensable for macrophage polarization, with its dysregulation playing a pivotal role in tumor progression.

Quasi-vertically asymmetric channels of graphene oxide membrane for ultrafast ion sieving

The high performance of two-dimensional (2D) channel membranes is generally achieved by preparing ultrathin or forming short channels with less tortuous transport through self-assembly of small flakes, demonstrating potential for highly efficient water desalination and purification, gas and ion separation, and organic solvent waste treatment. Here, we report the construction of vertical channels in graphene oxide (GO) membrane based on a substrate template with asymmetric pores. The membranes achieved water permeance of 2647 L m−2 h−1 bar−1 while still maintaining an ultrahigh rejection rate of 99.9% for heavy metal ions, which is superior to the state-of-the-art 2D membranes reported. Furthermore, the membranes exhibited excellent stability during long-term filtration experiments for at least 48 h, as well as resistance to ultrasonic treatment for over 100 minutes. The vertical channels possess very short pathway for almost direct water transport and a highly effective channel area, meanwhile the asymmetric porous template enhances the packing of the inserted GO nanosheets to avoid the swelling effect of membrane. Our work provides a simple way to fabricate vertical channels of 2D nanofiltration membranes with high water purification performance.

Role of astrocytes connexins - pannexins in acute brain injury.

Acute brain injuries (ABIs) encompass a broad spectrum of primary injuries such as ischemia, hypoxia, trauma, and hemorrhage that converge into secondary injury where some mechanisms show common determinants. In this regard, astroglial connexin and pannexin channels have been shown to play an important role. These channels are transmembrane proteins sharing similar topology and form gateways between adjacent cells named gap junctions (GJs) and pores into unopposed membranes named hemichannels (HCs). In astrocytes, GJs and HCs enable intercellular communication and have active participation in normal brain physiological processes, such as calcium waves, synapsis modulation, regional blood flow regulation, and homeostatic control of the extracellular environment, among others. However, after acute brain injury, astrocytes can change their phenotype and modify the activity of both channels and hemichannels, which can result in the amplification of danger signals, increased mediators of inflammation, and neuronal death, contributing to the expansion of brain damage and neurological deterioration. This is known as secondary brain damage. In this review, we discussed the main biological mechanism of secondary brain damage with a particular focus on astroglial connexin and pannexin participation during acute brain injuries.

Morphology remodelling and membrane channel formation in synthetic cells via reconfigurable DNA nanorafts

The shape of biological matter is central to cell function at different length scales and determines how cellular components recognize, interact and respond to one another. However, their shapes are often transient and hard to reprogramme. Here we construct a synthetic cell model composed of signal-responsive DNA nanorafts, biogenic pores and giant unilamellar vesicles (GUVs). We demonstrate that reshaping of DNA rafts at the nanoscale can be coupled to reshaping of GUVs at the microscale. The nanorafts collectively undergo reversible transitions between isotropic and short-range local order on the lipid membrane, programmably remodelling the GUV shape. Assisted by the biogenic pores, during GUV shape recovery the locally ordered DNA rafts perforate the membrane, forming sealable synthetic channels for large cargo transport. Our work outlines a versatile platform for interfacing reconfigurable DNA nanostructures with synthetic cells, expanding the potential of DNA nanotechnology in synthetic biology.

Mitochondrial Porin Is Required for Versatile Biocontrol Trait-Involved Biological Processes in a Filamentous Insect Pathogenic Fungus.

The mitochondrial voltage-dependent anion channel (VDAC) is the major channel in the mitochondrial outer membrane for metabolites and ions. VDACs also regulate a variety of biological processes, which vary in the number of VDAC isoforms across different eukaryotes. However, little is known about VDAC-mediated biocontrol traits in biocontrol fungi. Here, the only VDAC isoform (BbOmm1) in the filamentous insect pathogenic fungus Beauveria bassiana was characterized, which was crucial for maintenance of mitochondrial homeostasis and function and important biocontrol traits. Besides serious impairment of fungal growth, conidiation, and germination, inactivation of BbOmm1 led to increased sensitivity/tolerance to oxidative and osmotic stresses and production of oosporein and other secondary metabolites, which corresponded to the mitochondrial damage, downregulation of membrane lipid and cell wall homeostasis-involved genes, and upregulation of detoxification genes and biosynthesis gene clusters of those metabolites. These results enrich our understanding of VDAC-mediated biocontrol traits in insect fungal pathogens.

Flux through membrane channel: linear transport vs. single-molecule approaches.

One of the most subtle steps in the single-molecule approach to the flux through the membrane channel, which uses the one-dimensional Smoluchowski equation, is to describe the molecule's "behavior" at the contacts between the channel openings and the bulk. Earlier, to handle this issue, we introduced the so-called "radiation boundary conditions" that account for the interplay between the two types of trajectories of the molecules starting at the openings, specifically, the ones that eventually return to the channel and the ones that escape to infinity. The latter trajectories represent the true translocation events on the condition that initially the molecule entered the channel from the opposite side. Here, we demonstrate that the single molecule approach based on the one-dimensional Smoluchowski equation with radiation boundary conditions leads to the same expression for the flux through the channel as the conventional approach based on the linear transport theory.

Imine-Linked 3D Covalent Organic Framework Membrane Featuring Highly Charged Sub-1nm Channels for Exceptional Lithium-Ion Sieving.

Coupling ion exclusion and interaction screening within sub-nanoconfinement channels in novel porous material membranes hold great potential to realize highly efficient ion sieving, particularly for high-performance lithium-ion extraction. Diverse kinds of advanced membranes have been previously reported to realize this goal but with moderate performance and complex operations gained. Herein, these issues are circumvented by preparing the consecutive and intact imine-linked three-dimensional covalent organic framework(i.e., COF-300) membranes via a simple solvothermal approach and employing the intrinsically interconnected sub-1nm one-dimensional channels for exceptional lithium-ion sieving. The synthesized membranes with highly charged angstrom scale channels of ≈0.78nm achieve an excellent Li+ permeance (0.123mol m-2 h-1) with an ultrahigh Li+/Mg2+ of 36 in the binary system. The experimental measurement and theoretical calculation reveal that a channel size right exactly between Li+ and Mg2+ enables restricted Mg2+ penetration. Meanwhile, the ion affinity interaction screening with imine groups further strengthens the fast Li+ permeability but severely suppresses the Mg2+ passage. In particular, the synthesized three-dimensional covalent organic framwork membranes also have a remarkable separation performance during a long-term operation test without sacrificing trade-off, demonstrating chemistry stability and mechanical integrity under the high-salinity aqueous environment.

Filamin A C-terminal fragment modulates Orai1 expression by inhibition of protein degradation.

Filamin A (FLNA) is an actin-binding protein that has been reported to interact with STIM1 modulating the activation of Orai1 channels. Cleaving of FLNA by calpain leads to a C-terminal fragment that is involved in a variety of functional and pathological events, including pro-oncogenic activity in different types of cancer. Here, we show that full-length FLNA is downregulated in samples from patients with colon cancer as well as in the adenocarcinoma cell line HT-29. This is consistent with an increased calpain-dependent FLNA cleaving with enhanced expression of the C-terminal FLNA fragment accompanied by enhanced expression of Orai1 and STIM1, as well as store-operated Ca2+ entry (SOCE). To further explore the mechanism underlying the enhancement of SOCE by the C-terminal FLNA fragment, we expressed in HEK-293 cells the C-terminal FLNA region encompassing repeats 16-24 (FLNA16-24 fragment), which enhanced both Orai1 and STIM1 as well as SOCE. Transfection of the FLNA16-24 fragment attenuates Orai1 and STIM1 protein degradation, and, specifically, abrogates Orai1α lysosomal degradation and retains this channel in the plasma membrane. However, the C-terminal FLNA fragment did not induce a detectable modification in Orai1β degradation. Due to the relevance of SOCE in cell physiology, our results provide evidence of a novel mechanism for the regulation of Ca2+ influx with relevant pathophysiological implications.NOTE & NOTEWORTHY FLNA cleaving by calpain has been observed in a variety of tumoral, including prostate and colorectal cancer cells, as well as in nontumoral cells, leading to a C-terminal fragment encompassing repeats 16-24. Expression of the FLNA16-24 fragment in HEK-293 cells enhances Orai1 and STIM1 expression, as well as SOCE, a mechanism mediated by attenuation of Orai1α and STIM1 degradation, providing evidence for a novel mechanism for the regulation of SOCE in normal and malignant cells.

Mitochondrial YME1L1 governs unoccupied protein translocase channels.

Mitochondrial protein import through the outer and inner membranes is key to mitochondrial biogenesis. Recent studies have explored how cells respond when import is impaired by a variety of different insults. Here, we developed a mammalian import blocking system using dihydrofolate reductase fused to the N terminus of the inner membrane protein MIC60. While stabilization of the dihydrofolate reductase domain by methotrexate inhibited endogenous mitochondrial protein import, it neither activated the transcription factor ATF4, nor was affected by ATAD1 expression or by VCP/p97 inhibition. On the other hand, notably, plugging the channel of translocase of the outer membrane) induced YME1L1, an ATP-dependent protease, to eliminate translocase of the inner membrane (TIM23) channel components TIMM17A and TIMM23. The data suggest that unoccupied TIM23 complexes expose a C-terminal degron on TIMM17A to YME1L1 for degradation. Import plugging caused a cell growth defect and loss of YME1L1 exacerbated the growth inhibition, showing the protective effect of YME1L1 activity. YME1L1 seems to play a crucial role in mitochondrial quality control to counteract precursor stalling in the translocase of the outer membrane complex and unoccupied TIM23 channels.

A Chiral COFs Membrane for Enantioselective Amino Acid Separation

AbstractIncorporating chiral molecules in the covalent organic frameworks (COFs) with uniformly ordered pores results in chiral COFs, which have been highly promising candidates for enantioseparation. Herein, a homochiral COF nanochannel membrane is reported by introducing chiral centers (L‐phenylalanine methyl ester) into one of the organic ligands for the enantioseparation of chiral amino acids. The separation results show that the D‐isomer is preferentially transported through the porous membrane channel. This composite membrane exhibits excellent selectivity for racemic phenylalanine with the highest enantiomeric excess value of up to 99.4 %. The adsorption and molecular modeling studies substantiate the experiment results by showing higher bonding affinity towards D‐isomer over L‐isomer. The excellent enantioselective gating performance unveils the porous COF skeleton with chiral selectors and the size‐matching synergy for stereoselective interactions with chiral isomers.

Engineering Interference-Removal and Target-Response Cascade Zones on Wood Channels for Straightforward Detection of Uric Acid in Saliva

The detection of biomarkers is crucial for assessing disease status and progression. Uric acid (UA), a common biomarker in body fluids, plays an important role in the diagnosis and monitoring of conditions such as hyperuricemia, chronic kidney disease, and cardiovascular disease. However, the low concentration of UA in non-invasive body fluids, combined with numerous interfering substances, makes its detection challenging. Therefore, there is a pressing need to develop advanced sensor platforms that exhibit both high sensitivity and excellent specificity for accurate monitoring of UA levels in various body fluids. In this study, an electrochemical sensing system is developed by integrating a cascade interference-removal zone and a target-response zone on a wooden channel membrane (CM) for the pretreatment-free detection of UA in body fluids. In this design, cysteine-doped ZIF-67(Co) nanocrystals, a mimic with multi-enzyme activity, are modified in the interference-removal zone. The target-response zone on the other side of the CM is contacted with a solution containing Fe3+ and [Fe(CN)6]3- ions. Using saliva as a proof-of-concept, the interference species, including ascorbic acid (AA), dopamine (DA), and glutathione (GSH), are oxidized and removed when passing through the interference-removal zone, while UA reaches the target-response zone and triggers the growth of Prussian blue (PB) on site. Utilizing the peroxidase-like activity of PB, UA concentration is directly determined based on changes in transmembrane ion currents. The resulting sensing system exhibits higher sensitivity than commercial UA meters and demonstrates straightforward, continuous, and non-invasive monitoring of UA in saliva after consuming purine-rich foods. The technology provides a simple, reliable and low-cost device for sensing UA in complex biological matrices. Moreover, the CM based sensing device also provides the benefit of being incineratable and biodegradable, reducing medical and electronic waste, making it eco-friendly for daily diagnostics.

Ion Transport and Membrane Channel Formation Using a Peptidomimetic in Droplet Interface Bilayers

Herein, we present a synthetic peptidomimetic, TBP2, which forms artificial membrane channels within Droplet Interface Bilayers (DIBs). Through real-time electrophysiology, TIRF microscopy, and single-channel recordings, we demonstrate the ability of...

Design and synthesis of cyclic lipidated peptides derived from the C-terminus of Cx43 for hemichannel inhibition and cardiac endothelium targeting.

A peptide segment that is 10 residues long at the C-terminal (CT) region of Cx43 is known to be involved in interactions, both with the Cx43 protein itself and with other proteins, that result in hemichannel (HC) activity regulation. Previously reported mimetic peptides based on this region (e.g., αCT1, CT10) have been revealed to be promising therapeutic agents in the context of cardiovascular diseases. In this work, novel approaches, such as C- and N-terminal modification and cyclization, to improve the proteolytic stability and bioavailability of the CT10 peptide are presented. These efforts resulted in a set of unprecedented potent cyclic inhibitors of HC-mediated ATP release with a half-life largely exceeding 24 hours. Additionally, the introduction of a lipophilic moiety with different solubilizing linkers led to the generation of a novel series of water-soluble and lipidated peptides that exhibited high inhibitory capacity in in vitro assays at submicromolar concentrations. A cardiac endothelium targeting strategy was also adopted, exploiting the ability of the CRPPR peptide to selectively deliver the peptides to endothelial cells.

Cascade charged channels in monovalent selective cation exchange membranes enable highly efficient separation

Cascade charged channels in monovalent selective cation exchange membranes enable highly efficient separation

Construction of proton exchange membrane with high proton conductivity based on 3D self-assembly structures as multiple proton transport channels

Proton exchange membranes are currently of a great interest due to their tunable proton transport channels in design. However, the construction of proton transport channels in composite membranes still encounters enormous challenges. In this study, a series of composite membranes composed of nanocomposites reinforced with electrostatically self-assembly of zirconium phosphate (ZrP) and poly(diallyldimethylammonium chloride) (PDDA)modified sulfonated halloysite (PSHNT) were designed and prepared. Further, long-range ordered proton transport channels were constructed in the membrane owing to synergistic effect of ZrP and PSHNT. It is revealed that acidic groups of ZrP nanoparticles and PSHNT yield more acidic sites for effective proton transport, and hollow tubular halloysite creates a fast channel for proton transport via a vehicle-type mechanism. The excellent hydrophilicity of ZrP/PSHNT and their good dispersion in polymer matrices result in a much higher water absorption of 45.5% and a lower swelling rate of 6.4% at 80⁰C. More impressively, SPI-ZrP/PSHNT-6 exhibits a remarkable proton conductivity of 288.2 mS cm-1 at 80°C under hydrated conditions. In addition, due to its excellent proton conductivity, a high peak power density up to 230.2 mW cm-2 has been achieved in H2-Air fuel cell. The excellent material performance of such proton exchange membranes in this study paves a new way towards the commercialization of high-performance proton exchange membranes in future applications for hydrogen fuel cell.