Anion Conductance Research Articles

CFTR‐mediated transepithelial bicarbonate conductance is affected differently than chloride conductance by CFTR correctors and potentiators

The advent of targeted CFTR therapeutics allows us to assess differences in epithelial Cl− and HCO3− conductances that might be attributed to unique combinations of CFTR variants (mutations), CFTR modulators (corrector(s) and potentiators) as well as secretory agonists. To address these questions, Fisher rat thyroid cells expressing wt or mutant CFTR were cultured on permeable supports for the measurement of transepithelial conductance (Gt) in defined ionic conditions. Initial experiments demonstrated stepwise reduction in the forskolin (Forsk)+ivacaftor (VX770)‐stimulated change in Gt as bath NaCl was partially replaced isosmotically with mannitol. Subsequent experiments were conducted in buffers containing 100 mEq/l Cl− with the addition of either 25 mM alternative anions (Na+ salts) or 50 mM mannitol. Outcomes showed forskolin‐induced Gt changes consistent with reported CFTR permselectivity: Cl− > NO3− ≥ Br− > isethionate ≥ gluconate > mannitol. All subsequent experiments were conducted to assess Gt with 100 mEq/l Cl− plus either 25 mEq/l HCO3−, 50 mM mannitol or 25 mEq/l Cl−, in a 5% CO2 atmosphere. Epithelia expressing wtCFTR respond to forskolin with a substantial increase in Gt. The response in HCO3− was ~75% of that observed with Cl−. Exposure to VX770 increased conductance, but a disproportionately lesser change was observed in HCO3− (vs. Cl−), providing an initial suggestion that VX770 promotes differential ion selectivity.Exposure of cells expressing F508del CFTR to correctors, either C17 or C18, allowed for forskolin‐induced stimulation of Gt with a modest increment of HCO3− conductance. In these conditions, VX770 induced additional Cl− conductance, but no enhancement of HCO3− conductance could be detected. Alternatively, cells exposed to the corrector combination (C17+C18) showed a substantial forskolin‐stimulated increase in anion conductance and a modest increase in CFTR‐associated HCO3− conductance. Thus, the combination of C17 and C18 gives a different outcome regarding F508del‐CFTR HCO3− conductance than either corrector alone.Cells expressing G551D CFTR exhibited little response to forskolin, but substantial responses to VX770. Responses to VX770 in HCO3− approached the magnitude of the responses observed in Cl−.Taken together, the results suggest that CFTR correctors and potentiators can enhance CFTR‐mediated anion conductance, but that significant differences in the conductances of HCO3− relative to Cl− are observed between CFTR variants and that responses can be influenced by the correctors employed. Ultimately, these results suggest that CFTR‐associated pH regulation will be impacted by both the patient’s mutation and the CFTR modulator treatment. Furthermore, additional studies are required to evaluate the CFTR modulators for their effects on Cl− and HCO3− conductances on the many CF causing CFTR variants.Support or Funding InformationCFF BRIDGE18XX0; K‐State CVM SMILE

Synthesizing spindle-shaped anion exchange membranes to improve conductivity and stability

High ionic conductivity and excellent alkaline stability are very important for solid electrolyte. Therefore, spindle-shaped anion exchange membranes (AEMs) based on poly (arylene ether ketone) and 1-Bromo-N,N,N-trimethylhexane-6-aminium bromide (Br-QA) have been prepared. The obtained Br-QA can be grafted with poly (arylene ether ketone) main chains to form micro-phase separation structure enhancing the ionic conductivity. Especially, the grafting quaternary ammonium (QA) cation groups are separated by alkyl bromine endows the AEMs with alkaline stability features. Simultaneously, the OH− conductivity of the QA-PAEK-0.6 obtained membranes is 0.046 S/cm under fully hydrated conditions at 60 °C. After immersing into 1 M NaOH alkaline solution for 15 days at 60 °C, the anionic conductivity still high to 0.03 S/cm. Meanwhile, the poly (arylene ether ketone) backbones provide excellent mechanical properties and the Br-QA cation groups also possess good thermal stability, which satisfy the requirement of wide applications.

Enhanced conductivity and stability of anion exchange membranes depending on chain lengths with crosslinking based on poly(phenylene oxide)

Quaternized polymer electrolytes (QPXs) with various lengths of side chains terminating in quaternary ammonium groups are synthesized, with the aim of enhancing anion conductivity. When chain lengths are equal, the crosslinked membranes have better alkaline stabilities than non-crosslinked membranes. cQPH, which has a hexyl acyl chain and a crosslinked structure shows the best anion conductivity (105 mS/cm at 80 °C) owing to a good phase separation. In addition, it has superior alkaline stability, retaining up to 88% of its conductivity after immersion in 1 M NaOH at 80 °C for 16 days. Moreover, QPXs and cQPXs show enough thermal stability over 200 °C to operate in alkaline fuel cell systems. The dimensional stabilities of the membranes are measured, showing that water is absorbed while the strength is maintained. These results imply that cQPXs can be promising materials for use in alkaline fuel cells.

Assessment of the FAA3-50 polymer electrolyte in combination with a NiMn2O4 anode catalyst for anion exchange membrane water electrolysis

A commercial FAA3-50 membrane was investigated as a solid polymer electrolyte in an alkaline water electrolysis. An improved chemical treatment based on alkaline KOH solution was carried out. A limited degradation of the functional groups was observed allowing to maintain a good anion conductivity approaching 55 mS cm-1 at 100 °C. Thermal stability up to 200 °C was assessed by thermal analysis.A specific membrane-electrodes assembly based on FAA3-50 anionic membrane and NiMn2O4 anode catalyst was developed and investigated in a single cell for water electrolysis at a moderate temperature (50 °C).Performance stability was assessed by a potential cycling-based durability test for 1000 h by varying the cell potential between 1 and 1.8 V for the FAA3-50 and NiMn2O4 based-MEA.According to this evaluation, both the FAA3-50 membrane and the NiMn2O4 catalyst appear sufficiently stable for electrolysis operation under mild operating temperatures.

Stepwise Dissociation of an Inner Gate Controls Pore Opening in the Calcium-activated Chloride Channel TMEM16A

TMEM16A is a Ca2+-activated Cl- channel that plays key roles in diverse physiological processes. This channel functions as a homodimer with each subunit containing an independent pore and closely apposed Ca2+ binding sites. Recent cryo-electron microscopy structures of TMEM16A have revealed a conformational change involving the rearrangement of a pore-lining helix (α6) upon Ca2+ binding in a process that precedes pore activation. We have further shown that an electrostatic gating mechanism operates in TMEM16A where bound Ca2+ ions lower the energy barriers for anion conduction via direct Coulombic interactions. However, despite the described advances, the location of the gate that prevents ion conduction in the close conformation has remained elusive. Here, we investigated conformational gating of TMEM16A using electrophysiology and spectral analysis. Systematic mutagenesis of pore-lining helices identifies a specific cluster of hydrophobic residues at the inner pore that closes the anion conduction path in the closed state. The stability of the cluster increases with hydrophobic volume but correlates inversely with increasing hydrophilicity, consistent with a gate region where water and ions are excluded when closed. We analysed the power spectra of alanine mutants at the constriction and found that the loss of hydrophobic volume results in enhanced pore opening at equilibrium. The presence of three Lorentzian components in the spectra suggests an intermediate gating step that relays α6 activation to the opening of the pore. Combined with analysis of multiple double-mutant cycles, our results reveal a pore opening mechanism that involves stepwise dissociation of the inner hydrophobic gate and the pairwise interactions underlying these conformational transitions.

Three-Layered Membranes for Planar Solid Oxide Fuel Cells of the Electrolyte-Supported Design: Characteristics and Applications

Three-layered ceramic membranes based on stabilized zirconia for planar solid-oxide fuel cell (SOFC) are prepared by the tape casting method. The outer layers containing 94 mol % ZrO2???6 mol % Sc2O3 provide the enhanced mechanical stability; the inner layer has the composition of 89 mol % ZrO2???10 mol % Sc2O3???1 mol % Y2O3 which has the highest anionic conductivity in the series of solid solutions ZrO2???Y2O3???Sc2O3. Studying the mechanical characteristics shows that the ultimate strength (bending strength) of these membranes much exceeds the value typical of single-layered samples. The anionic conductivity of three-layered ceramics is studied by the impedance spectroscopy in the frequency range from 1Hz to 1 MHz. Membrane-electrode assemblies for SOFCs are fabricated and their electrochemical properties are studied under the conditions of fuel cell operation.

Layered Solid-Electrolyte Membranes Based on Zirconia: Production Technology

A solid electrolyte membrane is a key part of a solid oxide fuel cell (SOFC). This paper presents the results of our study of the effects of particle size of the starting powders, composition of organic additives in suspension, and process parameters on the quality of three-layer ceramic sheets of solid electrolyte with dimensions of 100 × 100 mm and a thickness of 0.15 mm, made by casting on a moving tape. The inner layer was 10Sc1YSZ (10 mol % Sc2O3, 1 mol % Y2O3, 89 mol % ZrO2)—a material with the highest oxygen ion conductivity among zirconia-based solid solutions. 6ScSZ was chosen for the outer layers (6 mol % Sc2O3, 94 mol % ZrO2). The three-layer architecture of the solid electrolyte membranes allows the improvement of the mechanical characteristics while maintaining the required functional properties (primarily, anion conductivity). This study is devoted to optimization of the production technology of these layered membranes by tape casting.

Development of Polymeric Membranes Based on Quaternized Polysulfones for AMFC Applications.

A series of quaternary ammonium-functionalized polysulfones were successfully synthesized using a chloromethylation two-step method. In particular, triethylammonium and trimethylammonium polysulfone derivatives with different functionalization degrees from 60% to 150% were investigated. NMR spectroscopic techniques were used to determine the degree of functionalization of the polymers. The possibility to predict the functionalization degree by a reaction tool based on a linear regression was highlighted. Anionic membranes with a good homogeneity of thickness were prepared using a doctor-blade casting method of functionalized polymers. The chemical–physical data showed that ion exchange capacity, water content, and wettability increase with the increase of functionalization degree. A higher wettability was found for membranes prepared by the trimethylamine (TMA) quaternary ammonium group. A degree of functionalization of 100% was chosen for an electrochemical test as the best compromise between chemical–physical properties and mechanical stability. From anionic conductivity measurement a better stability was found for the triethylamine (TEA)-based membrane due to a lower swelling effect. A power density of about 300 mW/cm2 for the TEA-based sample at 60 °C in a H2/O2 fuel cell was found.

Molecular Dynamics Simulation of Transmembrane Transport of Chloride Ions in Mutants of Channelrhodopsin.

Channelrhodopsins (ChRs) are light-gated transmembrane cation channels which are widely used for optogenetic technology. Replacing glutamate located at the central gate of the ion channel with positively charged amino acid residues will reverse ion selectivity and allow anion conduction. The structures and properties of the ion channel, the transport of chloride, and potential of mean force (PMF) of the chimera protein (C1C2) and its mutants, EK-TC, ER-TC and iChloC, were investigated by molecular dynamics simulation. The results show that the five-fold mutation in E122Q-E129R-E140S-D195N-T198C (iChloC) increases the flexibility of the transmembrane channel protein better than the double mutations in EK-TC and ER-TC, and results in an expanded ion channel pore size and decreased steric resistance. The iChloC mutant was also found to have a higher affinity for chloride ions and, based on surface electrostatic potential analysis, provides a favorable electrostatic environment for anion conduction. The PMF free energy curves revealed that high affinity Cl− binding sites are generated near the central gate of the three mutant proteins. The energy barriers for the EK-TC and ER-TC were found to be much higher than that of iChloC. The results suggest that the transmembrane ion channel of iChloC protein is better at facilitating the capture and transport of chloride ions.

Bacteriophage M13 Aggregation on a Microhole Poly(ethylene terephthalate) Substrate Produces an Anionic Current Rectifier: Sensitivity toward Anionic versus Cationic Guests.

Bacteriophage material (M13, wild-type) deposited as a film onto a poly(ethylene terephthalate) (PET) substrate (6 μm thick with a 20 μm diameter laser-drilled microhole) has been investigated for ion conductivity and ionic current rectification effects for potential applications in membranes. The M13 aggregate membrane forms under acidic conditions (in aqueous 10 mM acids) and behaves like a microporous anion conductor with micropores defined by the packing of cylindrical virus particles. Asymmetric deposition on the PET film substrate in conjunction with semipermeability leads to anionic diode behavior. Typical rectification ratio values are around 10 (determined at ±1 V) in aqueous 10 mM acids. Cationic guest species (aqueous Cu2+, Co2+, Ag+) consistently lead to a rectification minimum at 0.5 mM guest concentration. In contrast, anionic guest species (indigo carmine) lead to a similar rectification minimum already at 5 μM concentration. The behavior is proposed to be associated with cation exclusion effects on transport.

Structure-transport relationships of poly(aryl piperidinium) anion-exchange membranes: Eeffect of anions and hydration

Hydroxide-exchange membrane (HEM) fuel cells are emerging energy conversion technologies. A significant effort has been expended to develop new HEMs with enhanced transport functionality, which has driven the need for understanding how transport of hydroxide and other anions in these membranes is related to hydration and nano-morphology. In this work, we report the results of a systematic study on poly(aryl piperidinium)-based on terphenyl (PAP-TP-85), a HEM that previously showed promising fuel cell performance and durability. Membrane water uptake and anion conductivity in liquid and vapor water, as well as the impact of counter-anion forms on these properties, are investigated and compared with a commercial anion exchange membrane (AEM), Fumasep FAA3, and proton-exchange membranes (PEMs), Nafion and sPEEK. Different water uptake in liquid vs. saturated vapor is observed for both AEMs (i.e., PAP and FAA3), indicating Schroeder's paradox, regardless of anion form. Morphology of AEMs examined via small-angle X-ray scattering (SAXS) shows weak phase-separation, regardless of hydration level and anion type, which is attributed to the reduced chemical dissimilarity between the backbone and ionic moieties. Despite both AEMs' amorphous nanostructure, PAP-AEM has a higher ion conductivity than FAA3. Water content plays a more significant role than does temperature in controlling the anion conductivity in water vapor. In liquid water, normalized conductivity shows a universal dependence on hydration, regardless of the anion form. Moreover, in water vapor, conductivity is influenced more by ion mobility than ion concentration, and depends mainly on hydration. Thus, ion transport in disordered AEMs is governed primarily by hydration, in contrast to phase-separated ionomers, where ion transport is governed by nanostructure-hydration interplay. This study demonstrates the importance of hydration level and ion mobility for anion transport in amorphous AEMs and provides an understanding of parameters governing their transport properties.

Chloride Conductance, Nasal Potential Difference and Cystic Fibrosis Pathophysiology.

Cystic fibrosis (CF) is a multisystem genetic disease caused by dysfunction of the epithelial anionic channel Cystic Fibrosis Transmembrane conductance Regulator (CFTR). Decreased mucociliary clearance because of thickened mucus is part of the pulmonary disease pathophysiology. It is controversial if the thickenedairway surface liquid (ASL) is caused by the deficient chloride secretion and excessive sodium (through ENaC) and water hyperabsorption from the periciliar fluid or by the lack of bicarbonate secretion with relative acidification of the ASL. Correlations between the magnitude of in vivo chloride conductance with phenotypic characteristics and CF genotype can help to elucidate these mechanisms and direct to new treatments. Nasal potential difference was measured in 28 CF patients (age from 0.3 to 28year) and correlated with pulmonary function, pancreatic phenotype, pulmonary colonization and genotype severity. The CFTR-chloride conductance was better in older patients (r = 0.40; P = 0.03), in patients with better pulmonary function (r = 0.48; P = 0.01), and was associated with genotype severity. Higher chloride diffusion in the presence of a favorable chemical gradient was associated with Pseudomonas aeruginosa negativity (P < 0.05). More negative NPDmax was associated with pancreatic insufficiency (P < 0.01) as well with genotype severity, but not with the pulmonary function. The anion permeability through CFTR, mainly chloride, but bicarbonate as well, is the most critical factor in CF airway pathophysiology. Treatments primarily directed to correct CFTR function and/or airway acidity are clearly a priority.

Poly(terphenylene) anion exchange membranes with high conductivity and low vanadium permeability for vanadium redox flow batteries (VRFBs)

In this study, we demonstrate a new class of poly(terphenylene) based anion exchange membranes (AEMs) with improved chemical stability and anion conductivity in vanadium redox flow batteries (VRFBs). A series of terphenyl- and biphenyl-based polymers with pendant quaternary ammonium alkyl groups were synthesized and characterized for VRFB applications. When the arrangement of the polymer backbone and cation-tethered alkyl chains was varied, the prepared AEM membranes exhibited extremely low vanadium permeance while maintaining high conductivity. These properties further provided a high coulombic efficiency close to 100% at all current densities as well as high voltage efficiency. The single cell VRFB performance with the poly(terphenylene) based AEMs showed 2–5% higher coulombic efficiency than those of commercial AEMs and similar voltage efficiency to those of commercial PEMs (Nafion® 212). The highest EE value of 93.64% was achieved at the current density of 20 mA/cm2 (vs. 72% EE for Nafion212). In addition, poly(terphenylene) based AEMs showed superior cycle stability and high capacity retention, thus demonstrating their high performance as promising IEMs for VRFB application.

Comparison of in-situ Raman studies of SOFC with thick single-crystal and thin-film magnetron sputtered membranes

In current work, we conducted comparative studies of electrolyte-supported and anode-supported solid oxide fuel cells by means of electrochemical techniques (studies of I-V curves and impedance spectroscopy) as well as using Raman spectroscopy from the inner interface of the anode electrode and solid electrolyte. Electrolyte-supported (ESC) SOFCs were based on thick single-crystalline 8YSZ anion conductor membrane and had multilayered composite electrodes. Anode-supported cells (ASC) were based on thick two-layered commercially available anode supports, the thin-film electrolyte was deposited using a magnetron sputtering technique. Comparative studies showed a significant dependence of 460 cm−1 Raman peak both on fuel mixture composition and current load applied to the cell. Linear dependences of OCV on normalized peak area gave an opportunity to estimate local anodic overpotential on the current load applied for both SOFC structures. Application of ASC model cells gave an opportunity to significantly extend a range of current loads applied. Analysis of impedance spectra gave the opportunity to study the structure of complex resistance as well as the structure of local anodic overpotential obtained.

Synergistic role of graphene oxide-magnetite nanofillers contribution on ionic conductivity and permeability for polybenzimidazole membrane electrolytes

Efficient nanofillers within polymeric electrolytes are an interesting design for constructing high-performance membranes for direct methanol alkaline fuel cells. In this work magnetite (Fe3O4) particles are synthesized onto graphene oxide (GO) nanofillers and incorporating into a polybenzimidazole (PBI) matrix for membrane formation. The Fe3O4 nanoparticles are simultaneously anchored onto GO carbon basal planes to form GO-Fe3O4 via the solvothermal process. The pristine PBI, PBI/GO, PBI/Fe3O4, and PBI/GO-Fe3O4 composites are formulated and doped with potassium hydroxide solution to form ionic conductors. GO nanofillers suppress the methanol permeation rate in PBI/GO-Fe3O4 composite membranes while the anchored Fe3O4 nanoparticles result in a bumpy surface, reducing chain packing and promoting anionic conductivity via the loose polymeric free volume. Therefore, the conductivity-to-permeability selectivity of PBI/GO-Fe3O4 composite membrane is improved three times than other samples. The maximum peak power density (Pmax) of a fuel cell employing the PBI/GO-Fe3O4 composite membrane achieves 233 mW cm−2 at 80 °C. The superior power output is attributed to the combined effect of the enhanced anionic conduction resulting from anchored GO-Fe3O4 particles' steric hindrance on polymer chains to enlarged ion diffusion pathways, and the reduced methanol cross-over from the GO's high aspect ratio to retard molecular permeation in the composite membrane.

Manisa Yöresi Sulama Suyu Kaynaklarının Toprak, Bitki ve Damla Sulama Sistemi Yönünden Değerlendirilmesi

Manisa ilinde tarımsal sulamada yaygın olarak kullanılan 5 yer üstü ve 30 yer altı suyu kaynağının kimyasal kalite analiz sonuçları değerlendirilerek toprağa, bitkiye ve damla sulama sistemine olası etkileri belirlenmiştir. Bu kapsamda su kaynaklarının katyon (Ca, Mg, Na, K), anyon (CO3, HCO3, CI, SO4), Fe, B içerikleri ile pH ve elektriksel iletkenlik değerleri yanında hesaplamayla belirlenen Yüzde Sodyum, Sodyum Adsorpsiyon Oranı, Düzeltilmiş Sodyum Adsorpsiyon Oranı, Kalıcı Sodyum Karbonat, Langelier Saturasyon İndeksi, Potansiyel Tuzluluk, Permeabilite İndeksi ve Sertlik parametrelerine ait değerler kullanılmıştır. Sonuçlar, yer üstü su kaynaklarının sorun yaratma potansiyelinin yer altı sularına göre daha fazla olduğunu göstermiştir. Salihli-Köseali ve Necati bey çiftlik ile Alaşehir-Kasaplı yer altı su kaynaklarının kullanıldığı yerlerde de diğer yer altı su kaynaklarına göre daha ciddi sorunlar yaşanacağı belirlenmiştir. Oluşabilecek sorunun türüne göre yıkama, tuza dayanıklı bitki yetiştirme, organik madde ve doğal Ca kaynakları ilavesi ile seyreltik asit uygulamasını içeren bir dizi önlemler konusunda önerilerde bulunulmuştur.

Chloromethylation and Quaternization of Poly(aryl ether ketone sulfone)s with Clustered Electron-rich Phenyl Groups for Anion Exchange Membranes

Ion segregation is critically important for achieving high ion conductivity for anion exchange membranes (AEMs). Herein, a new bisphenol monomer bearing ten electron-rich phenyl groups was designed and polymerized with various amounts of electron-deficient 4,4′-dihydroxydiphenylsulfone and 4,4′-difluorobenzophenone to yield dense and selective reaction sites for chloromethylation and quaternization. As the most challenging step, chloromethylation was optimized by tuning the reaction temperature, reaction time, and reactant ratios. Ion exchange capacity, water uptake, anion conductivity, mechanical stability, and alkaline stability of the resulting AEMs were characterized in detail. It is found that chloromethylation reaction needed to be carried out at low equivalent of chloromethylation agents to avoid undesirable crosslinking. The QA-PAEKS-20 sample with an IEC of 1.19 mmol·g−1 exhibited a Cl– conductivity of 11.2 mS·cm−1 and a water uptake of 30.2% at 80 °C, which are promising for AEM applications.

Hydrogen production by electrochemical methanol reformation using alkaline anion exchange membrane based cell

Electrochemical methanol reformation (ECMR) is an alternative promising technology for producing hydrogen at low energy consumption compared to water electrolysis. In this process, solid polymer electrolyte Nafion® is widely employed, due to its superior proton conductivity. However, major limitations are the utilisation of expensive platinum based catalysts, high cost of the above membrane and the crossover of methanol through the polymer electrolyte membrane. In the present work, attempt has been to made to use low cost polymer electrolyte membrane and less noble electro catalyst. A series of Anion Exchange Membranes (AEM) are synthesized from Poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) for its application in ECMR. PPO is successfully made into anion conducting by chloromethylation followed by quaternization. Two AEM's are synthesized by optimizing chloromethylation reaction time to 5 h and quaternization time to 5 and 8 h and are labelled as QPPO (C5, Q5) and QPPO (C5, Q8) respectively. Further, with the view to improve the anion conductivity further, composite AEMs are prepared by incorporating inorganic anion conducting quaternized graphene oxide particles in the matrix of PPO and QPPO (C5, Q8) polymers separately to obtain two polymers PPO/QGO and QPPO/QGO. The anionic conductivity of PPO/QGO and QPPO/QGO polymer is 1.2 × 10−4 and 1.5 × 10−4 S cm−1 respectively. Both the membranes are subjected as electrolyte for ECMR application using membrane electrode assembly made by with in house synthesized nitrogen doped graphene supported Pd catalyst (Pd/NG) as anode catalyst and commercial Pt/C as cathode catalyst. The performance of composite membrane was compared with the commercial Fumasep® FAA anion exchange membrane. The polarization studies of ECMR cell with composite membrane shows comparable performance with that of commercial Fumasep® FAA-2 FAA membrane. The durability of the membrane(s) in the electrolysis environment was tested for about 20 h.

Functional identification of Ammopiptanthus mongolicus anion channel AmSLAC1 involved in drought induced stomata closure

Drought, one of the most acute abiotic stressors plants encountered, can adversely affect plants growth and development. The fast adjustment of stomatal aperture is necessary for effective drought tolerance in plants. Anion channels were identified as important controllers of stomatal closing via mediating anion efflux. The present study reports the isolation and identification of a SLAC (SLOW ANION CHANNEL-ASSOCIATED 1) ortholog from an ancient desert shrub Ammopiptanthus mongolicus (Maxim.) Cheng f. (AmSLAC1), which is functionally conserved for ABA and drought induced stomata closure. AmSLAC1 was primarily expressed in shoots, especially in guard cells. The transcription of AmSLAC1 was induced in response to ABA and PEG treatments, implying the potential involvement in ABA-induced drought stress responses. Fluorescence observation suggested that AmSLAC1 was localized in the plasma membrane. BiFC asssays demonstrated an interaction between AmSLAC1 and the typical calcium-dependent protein kinases AmCPK6. Ectopic expression of AmSLAC1 restores a slac1-defective phenotype in Arabidopsis. Furthermore, anion conductance mediated by AmSLAC1 can be activated by AmCPK6 in Xenopus oocytes. Taken together, these results demonstrate that the expression of AmSLAC1 enables the complement of the phenotypes of Arabidopsis slac1 mutants, indicating that AmSLAC1, as an anion channel and regulated by AmCPK6, is functionally conserved for ABA and drought induced stomata closure.

Early Extracellular ATP Signaling in Arabidopsis Root Epidermis: A Multi-Conductance Process.

Adenosine 5′-triphosphate (ATP) is an important extracellular signaling agent, operating in growth regulation, stomatal conductance, and wound response. With the first receptor for extracellular ATP now identified in plants (P2K1/DORN1) and a plasma membrane NADPH oxidase revealed as its target, the search continues for the components of the signaling cascades they command. The Arabidopsis root elongation zone epidermal plasma membrane has recently been shown to contain cation transport pathways (channel conductances) that operate downstream of P2K1 and could contribute to extracellular ATP (eATP) signaling. Here, patch clamp electrophysiology has been used to delineate two further conductances from the root elongation zone epidermal plasma membrane that respond to eATP, including one that would permit chloride transport. This perspective addresses how these conductances compare to those previously characterized in roots and how they might operate together to enable early events in eATP signaling, including elevation of cytosolic-free calcium as a second messenger. The role of the reactive oxygen species (ROS) that could arise from eATP’s activation of NADPH oxidases is considered in a qualitative model that also considers the regulation of plasma membrane potential by the concerted action of the various cation and anion conductances. The molecular identities of the channel conductances in eATP signaling remain enigmatic but may yet be found in the multigene families of glutamate receptor-like channels, cyclic nucleotide-gated channels, annexins, and aluminum-activated malate transporters.