Membrane Ion Transport Research Articles

Ion Transport in Hybrid Membranes Based on Perfluorosulfonic Polymers

A comparative study of the transport characteristics of Nafion and Aquivion perfluorinated membranes and hybrid membranes on their basis has been carried out. It has been shown that the modification of membranes of both types with acid salts of heteropoly acids and silica significantly increases their proton conductivity. In the case of high humidity, the best conductivity is achieved when they are doped with salts of heteropoly acids. The highest improvement in the membrane conductivity is achieved at low humidity for membranes doped with SiO2; in this case, the conductivity is increased by almost an order of magnitude.

Role of Surface Chemistry on Nanoparticle Dispersion and Vanadium Ion Crossover in Nafion Nanocomposite Membranes.

While the introduction of nanoparticles into Nafion membranes has proven to be a viable method to tune the ion selectivity in energy storage technologies such as the vanadium redox flow battery, there still remains a limited understanding of the fundamental mechanism by which the nanoparticles selectively restrict ion crossover. Herein, the surface chemistry and loading of SiO2 nanoparticles (SiNPs) were systematically varied to elucidate the relationship between nanoparticle dispersion (or dispersion state) and vanadium ion permeability in Nafion nanocomposite membranes. Specifically, nanoparticle surface functionalization was altered to achieve both attractive (amine-functionalized) and repulsive (unfunctionalized and sulfonic acid-functionalized) electrostatic interactions between the SiNPs and the ionic groups of Nafion. At a nanoparticle loading of 5 wt %, membranes containing unfunctionalized and amine-functionalized SiNPs demonstrated ∼25% reduction in vanadium ion permeability as compared to unmodified Nafion. Drastically different dispersion states were observed in the electron microscopy images of each nanocomposite membrane, where most notably, aggregates on the order of 500 nm were observed for membranes containing amine-functionalized SiNPs (at all nanoparticle loadings). Results from this work indicate that both dispersion state and surface chemistry of the SiNPs play a critical role in governing the vanadium ion transport in these ionomer nanocomposite membranes.

The importance of antioxidants and plasma membrane ion transporters which play role in cellular response against salt induced oxidative stress

Abstract Salt-induced oxidative stress accounts for redox imbalance and cell death in the food spoilage yeasts. However, the physiological mechanisms underlying this imbalance and succeeding effective tolerance are still poorly understood. To elucidate this cellular protective mechanism governing in moderately halotolerant yeasts, Zygosaccharomyces bisporus was analyzed under sub-lethal conditions of sodium salt. For most stress intervals; high activity of enzymic antioxidants suggested their broad panorama in rescuing salt prompted apoptosis, attenuating intracellular degenerative reactive species with simultaneous reversal of characteristic apoptotic changes as nuclear fragmentation and chromatin condensation. In addition, the synergistic role of cell membrane cation transporters; plasma membrane ATPase and Na+/H+ like antiporter have been investigated by quantifying the external pH of the medium under stress, with the aid of specific ion transporter inhibitors like N,N'-Dicyclohexylcarbodiimide, sodium azide, and amiloride respectively. Taken together, the major outcomes from this study provide the evidence of salt imposed cell death by triggering unbalanced redox status via several key mitochondrial reactive species, allied with yeast defensive pleiotropic manipulations like antioxidants, expulsion of toxic Na+ by Nha transporters and re-establishing the optimal growth pH in alliance with PM-ATPase as a stress response resulting redox homeostasis restoration and osmoregulation. This study critically claims a proteostatic crosstalk mechanism between mitochondria and the cytosol, thus plays an important role in cell survival and advance halo-tolerance. Thereby, this inter-relationship can be further exploited for biotechnological and industrial applications in spoilage yeasts.

Study of the Transport of Ions through an Anion-Exchange Membrane By Electrochemical Methods

Studies of the ionic transport through ion exchange membranes and in their adjacent electrolyte films have become a topic of great importance, due to their different applications in environmental problems [1]. A better understanding of the phenomena and processes involved in the mass transport in devices with ion exchange membranes allows designing cells with higher performance and lower energy consumption. There are few studies about of transport of ions in membranes, Wang et al. (1990) studied the mass transport of monovalent cations across a polypyrrole membrane [2], Oulmi, (2012) [3] analyzed the transport of Na+ in cation-exchange membrane (CEM), in both previous work CEM are used, studies on anion-exchange membrane (AEM) are scarce, and the transport mechanism may be different from the one observed in a CEM. Therefore, in the present work, the transport of HSO4 - through AEM is studied. The system used consists of a cell of four electrodes, where anode and cathode are separated by an anionic-exchange membrane (Selemion) with an exposed area of 0.28 cm2 on each side. Two platinized titanium plates with an area exposed to the 10.8 cm2 are used as anode and cathode; two saturated calomel with Luggin capillaries were used as reference electrodes. The electrochemical studies were: open circuit potential, chronoamperometry of sampled current and cyclic voltammetry at different scan rate, H2SO4 concentration and different potential range. The cyclic voltammograms at different H2SO4 concentrations are shown in the Figure 1. It exhibits that HSO4 - can transfer across the Selemion membrane due to a peak current. The peak current increases as the HSO4 - concentration increases, but when the species HSO4 - is depleted at the interface of the membrane, the intensity of current decreases until a limiting current is reached, similar to the phenomenon that occurs when a species depletes at the interface of an electrode/electrolyte [2]. By continuing to increase the potential, the current intensity begins to increase. The water splitting supplying new current carriers and giving rise to the so-called exaltation effect [4]. This phenomenon appears at all the HSO4 - concentration. On the other hand, electrochemical studies show that the transfer of the anions in the anion-exchange membrane (Selemion) is through a migration process and the adjacent films by migration and diffusion. Figure 1

Influence of the Supporting Electrolyte on the Structure-Transport Properties of PFSA Membranes for Redox Flow Batteries

Redox flow batteries (RFBs) are poised at becoming one of the most promising technologies that are being explored for grid-scale energy storage from discontinuous power sources such as wind and solar.[1] This has resulted in a need for continued development and understanding of new redox couples and their supporting electrolyte counterparts, as well as improving membranes for RFB operation while reducing cost. Membranes employed in RFB technology are largely comprised of the perfluorosulfonic acid (PFSA) family (e.g. Nafion, Aquivion, and 3M PFSA) which exhibit different material properties depending on the surrounding environment, such as transport properties.[2] The structure-property relationships of PFSAs are well-known and studied,[3] providing the initial framework for our understanding; however, much of this work has been performed in either vapor or liquid water. Thus, it is of interest to elucidate how the structure and transport properties of PFSAs change in various electrolytes used in RFBs. In this work, we discuss our progress in linking the electrolyte concentration-dependent nanostructure to the transport of ions in PFSA membranes. Sulfuric acid and hydrochloric acid represent the majority of supporting electrolytes used in RFB applications and are therefore the primary focus of this study. The polymer’s nanostructure in electrolytes is analyzed using small angle X-ray scattering (SAXS) in-situ, in order to understand the influence of the type and concentration of the supporting electrolytes on the characteristic morphological features of the membrane. Then, nanostructural information is linked to the ion transport through the membrane, via conductivity. Linking the conductivity and polymer morphology provides a better understanding of the structure-transport relationships of PFSAs in electrolytes, and their implications for membrane performance in a RFB cell. Perry, M.L. and A.Z. Weber, Advanced Redox-Flow Batteries: A Perspective. Journal of the Electrochemical Society, 2016. 163(1): p. A5064-A5067.Tang, Z., et al., Composition and Conductivity of Membranes Equilibrated with Solutions of Sulfuric Acid and Vanadyl Sulfate. Journal of the Electrochemical Society, 2013. 160(9): p. F1040-F1047.Kusoglu, A. and A.Z. Weber, New Insights into Perfluorinated Sulfonic-Acid Ionomers. Chem Rev, 2017. 117(3): p. 987-1104.

Impact of Solution Composition on the Resistance of Ion Exchange Membranes

Introduction: Resistance to ion transport in ion exchange membranes (IEMs) is detrimental to the performance of IEM-based processes such as electrodialysis (ED) and reverse electrodialysis (RED). IEM resistance depends on solution composition. However, such understanding is currently limited and of a qualitative nature (e.g., IEM resistance decreases with salt concentration in solution, multivalent ions increase IEM resistance). Therefore, a quantitative understanding of this dependency is needed to predict ED/RED performance. Accordingly, we measured the resistance of representative IEMs in single-solute solutions and used our results to draw quantitative and mechanistic conclusions. Methods: IEM resistance values were obtained using electrochemical impedance spectroscopy with the membrane mounted in a diffusion cell. The resistance of one representative cation (CEM) and one anion (AEM) exchange membrane was investigated in 15 single-solute solutions. Results: In general, membrane resistance for both the CEM and AEM decreased with increasing solution concentration. Membrane resistance was on the order of tens to hundreds of ohm.cm2 in dilute (<0.01M) solutions and a few to tens of ohm.cm2 in concentrated (>0.1M) solutions. The primary findings include: -Membrane resistance was sensitive to salt identity only in the case of the CEM, for which it depended on the counter-ion identity. -Membrane resistance increased with increasing hydration free energy of the counter-ion in bulk solution, indicating that steric effects are important determinants of membrane ionic resistance. -Membrane resistance had a strong inverse correlation with solution concentration below 0.1 M, and remained approximately constant at higher concentrations. -The dependence of membrane resistance on salt concentration in bulk solution was fitted well by a semi-empirical expression containing a concentration-independent term and a concentration-dependent term; the latter followed a non-linear dependence on bulk solution concentration. The non-linear dependence on bulk solution concentration suggests that the interconnectedness of the structural domains within the membrane that contribute to ionic resistance has a certain level of randomness. Future studies are required to fully understand the dependence of membrane ionic resistance on bulk solution concentration at low salt concentrations, including why membrane resistance depends on the co-ion identity only at relatively low salt concentrations (0.001-0.05 M). Conclusions: Overall, our analysis produced a quantitative understanding of the dependence of IEM resistance on the identity and properties of single-salt solutions, and contribute necessary information towards the development of a complete theory for IEM resistance. Specifically, we found that steric effects are a primary determinant of membrane resistance and that the structural domains are arranged randomly (as opposed to in series or parallel). Thus, future work to develop a complete IEM resistance theory should include (i) understanding how the hydration free energy of ions relates to their interactions with water and the membrane, (ii) elucidating how these interactions relate to ion mobility, and (iii) developing a mathematical model describing the random interconnectedness of structural membrane domains. Figure 1

WNK1 regulates skeletal muscle cell hypertrophy by modulating the nuclear localization and transcriptional activity of FOXO4

With-no-lysine (K) (WNK) kinases, which are mutated in the inherited form of hypertension pseudohypoaldosteronism type II, are essential regulators of membrane ion transporters. Here, we report that WNK1 positively regulates skeletal muscle cell hypertrophy via mediating the function of the pro-longevity transcription factor forkhead box protein O4 (FOXO4) independent of the conventional WNK signaling pathway linking SPS/STE20-related proline-alanine–rich kinase (SPAK)/oxidative stress response kinase 1 (OSR1) to downstream effector ion transporters. Small interfering RNA (siRNA)-mediated silencing of WNK1, but not SPAK/OSR1 kinases, induced myotube atrophy and remarkable increases in the mRNA expression of the muscle atrophy ubiquitin ligases MAFbx and MuRF1 in C2C12 mouse skeletal muscle cells. WNK1 silencing also increased FOXO4 nuclear localization, and co-transfection of Foxo4-targeted siRNA completely reversed the myotube atrophy and upregulation of atrogene transcription induced by WNK1 silencing. We further illustrated that WNK1 protein abundance in skeletal muscle was increased by chronic voluntary wheel running exercise (hypertrophic stimulus) and markedly decreased by adenine-induced chronic kidney disease (atrophic stimulus) in mice. These findings suggest that WNK1 is involved in the physiological regulation of mammalian skeletal muscle hypertrophy and atrophy via interactions with FOXO4. The WNK1-FOXO4 axis may be a potential therapeutic target in human diseases causing sarcopenia.

Effect of Electric Field on Ion Transport in Nanoporous Membranes with Conductive Surface

The effect of an external electric field on the ionic conductivity and selective properties of ceramic membranes based on alumina nanofibers coated with a conductive carbon layer has been studied. It has been shown that the membranes are ideally polarizable in the polarizing voltage range of −500 to +500 mV and, therefore, can be used for implementing switchable ionic selectivity. Experiments have revealed that the membrane resistance decreases with a change in the applied potential from 0 to ±500 mV. It has been shown that the membrane selectivity can be switched from anion to cation by varying the external potential. The surface charge density of the membranes has been determined in terms of the Teorell–Meyer–Sievers model according to the experimental measurements of the membrane potential.

Na/K-ATPase signaling mediates miR-29b-3p regulation and cardiac fibrosis formation in mice with chronic kidney disease.

The Na/K-ATPase is an important membrane ion transporter and a signaling receptor that is essential for maintaining normal cell function. The current study examined the role of Na/K-ATPase signaling in regulating miR-29b-3p, an anti-fibrotic microRNA, in a mouse chronic kidney disease (CKD) model (5/6th partial nephrectomy or PNx). The results showed that CKD induced significant reduction of miR-29b-3p expression in the heart tissue by activation of Src and NFκB signaling in these animals. To demonstrate the role of Na/K-ATPase signaling, we also performed the PNx surgery on Na/K-ATPase α1 heterozygous (α1+/-) mice, which expresses ~40% less Na/K-ATPase α1 compared to their wild type littermates (WT) and exhibits deficiency in Na/K-ATPase signaling. We found that CKD did not significantly change the miR-29b-3p expression in heart tissue from the α1+/- animals. We also found that CKD failed to activate Src and NFκB signaling in these animals. Using isolated cardiac fibroblasts from α1+/- mice and their WT littermates, we showed that ouabain, a specific Na/K-ATPase ligand, induces decreased miR-29b-3p expression in fibroblasts isolated from WT mice, but had no effect in cells from α1+/- mice. Inhibition of NFκB by Bay11-7082 prevented ouabain-induced miR-29b-3p reduction in WT fibroblasts. To further confirm the in vivo effect of Na/K-ATPase signaling in regulation of miR-29b-3p and cardiac fibrosis in CKD animals, we used pNaKtide, a Src inhibiting peptide derived from the sequence of Na/K-ATPase, to block the activation of Na/K-ATPase signaling. The result showed that pNaKtide injection significantly increased miR-29b-3p expression and mitigated the CKD-induced cardiac fibrosis in these animals. These results clearly demonstrated that Na/K-ATPase signaling is an important mediator in CKD that regulates miR-29b-3p expression and cardiac fibrosis, which provides a novel target for regulation of miR-29b-3p in CKD. We also demonstrate that antagonizing Na/K-ATPase signaling by pNaKtide can reduce organ fibrosis through the stimulation of tissue miR-29b-3p expression.

Analysis of the genomic basis of functional diversity in dinoflagellates using a transcriptome-based sequence similarity network.

Dinoflagellates are one of the most abundant and functionally diverse groups of eukaryotes. Despite an overall scarcity of genomic information for dinoflagellates, constantly emerging high-throughput sequencing resources can be used to characterize and compare these organisms. We assembled de novo and processed 46 dinoflagellate transcriptomes and used a sequence similarity network (SSN) to compare the underlying genomic basis of functional features within the group. This approach constitutes the most comprehensive picture to date of the genomic potential of dinoflagellates. A core-predicted proteome composed of 252 connected components (CCs) of putative conserved protein domains (pCDs) was identified. Of these, 206 were novel and 16 lacked any functional annotation in public databases. Integration of functional information in our network analyses allowed investigation of pCDs specifically associated with functional traits. With respect to toxicity, sequences homologous to those of proteins found in species with toxicity potential (e.g., sxtA4 and sxtG) were not specific to known toxin-producing species. Although not fully specific to symbiosis, the most represented functions associated with proteins involved in the symbiotic trait were related to membrane processes and ion transport. Overall, our SSN approach led to identification of 45,207 and 90,794 specific and constitutive pCDs of, respectively, the toxic and symbiotic species represented in our analyses. Of these, 56% and 57%, respectively (i.e., 25,393 and 52,193 pCDs), completely lacked annotation in public databases. This stresses the extent of our lack of knowledge, while emphasizing the potential of SSNs to identify candidate pCDs for further functional genomic characterization.

Determining Electro-Osmotic Drag of Water in Anion Exchange Membrane Fuel Cells

In an effort to reduce the cost of proton exchange membrane fuel cells (PEMFCs), a significant amount of research into non-precious metal (NPM) oxygen reduction catalysts has been conducted in recent decades. Despite this effort, platinum remains the only material with suitable stability and activity for use in the harsh environment of PEMFCs. Anion exchange membrane fuel cells (AEMFCs) have been gaining increased attention in recent years, providing advantages of higher stability and activity of NPM catalysts in alkaline environments. Unfortunately, the relevant properties, e.g. conductivity and mechanical & chemical stability, of anion exchange membranes (AEMs) are inferior to their proton conducting counterparts. Many studies have been conducted which focus on improving membrane properties such as swelling ratio, conductivity, and stability. In comparison, relatively little attention has been paid to studying ion and water transport in anion exchange membranes. Previous work conducted in our group has indicated that the majority of AEMFC polarization arises from the anode. The performance is relatively insensitive to catalyst loading and initial results indicate that electrode flooding is the primary cause of poor performance. To improve the performance of AEMFCs and better design AEMs, it is therefore important to study the transport of water and ions within AEMs. One key parameter which has received very little attention in the literature is the electro-osmotic transport of water due to the conduction of anions from the cathode to the anode. In this work, we study the electro-osmotic drag (EOD) in anion exchange membranes. The cell design and concept for electro-osmotic drag coefficient (ε) measurements in this work follow from the work of Fuller and Newman as adapted by others1–3. Analysis is conducted on the membranes in pure hydroxide form and carbonate form. The conductivity, water uptake and water mobility of the membranes is also studied over a wide range of relative humidities and temperatures. Better understanding of the transport of water and ions within anion exchange membranes will facilitate the development of models for AEMFC behavior and offer insight for future AEM production. Figure 1: Effect of water activity on the EOD coefficient (ε) and water content (λ) in Tokuyama A201. T. F. Fuller and J. Newman, J. Electrochem. Soc., 139, 1332–1337 (1992).T. A. Zawodzinski, J. Davey, J. A. Valerio, and S. Gottesfeld, Electrochim. Acta, 40, 297–302 (1995).X. Wang, J. P. Mcclure, and P. S. Fedkiw, Electrochim. Acta, 79, 126–132 (2012) http://dx.doi.org/10.1016/j.electacta.2012.06.098. Figure 1

Tuning the ion selectivity of porous poly(2,5-benzimidazole) membranes by phase separation for all vanadium redox flow batteries

Porous polybenzimidazole membranes have been suggested by far as the most promising candidate to replace perfluorinated ionomer membranes in all vanadium redox flow batteries (VRFB). These porous membranes can simply be prepared from a phase separation process induced by water vapor. In this work, the influence of the material properties of poly(2,5-benzimidazole) (ABPBI) on the membrane structure formation and ion transport characteristics is systematically investigated. Two batches of ABPBI polymers (intrinsic viscosity 2.0 and 1.4 dL g−1) are used; concentrations of polymer solution, the water vapor activity (temperature and relative humidity), and the exposure time of polymer solution to the water vapor are varied. It is found that high viscosity of ABPBI solution, among other factors, is essential in obtaining membranes with very low interconnectivity between macropores in the membrane bulk, therefore very low vanadium ion permeability suitable for VRFB applications. The porous ABPBI membranes in dry state have a low amount of pores ranging from 1 to ~ 200 nm. Due to the benzimidazole moieties in ABPBI polymers, the acid in vanadium electrolytes has two positive effects on ABPBI membranes: fixed positive charges, and absorption of acid in the membranes. The ion exchange capacity of ABPBI membranes increases with the increase in solution acid concentration, and reaches striking values as high as 8 mequ g−1 in 4.0 M H2SO4. This makes the Donnan exclusion towards positively charged vanadium ions very profound. The macropores in the porous membranes increase the absorption amount of free acid, therefore significantly increase the membrane ionic conductivity. These properties make porous ABPBI membranes very efficient separators for VRFB applications.

An equivalent 1D nanochannel model to describe ion transport in multilayered graphene membranes

Multilayered graphene-based membranes are promising for a variety of applications related to ion or molecule transport, such as energy storage and water treatment. However, the complex three-dimensional cascading nanoslit-like structure embedded in the membrane makes it difficult to interpret and rationalize experimental results, quantitatively compare with the traditional membrane systems, and quantitatively design new membrane structures. In this paper, systematic numerical simulations were performed to establish an equivalent one-dimensional (1D) nanochannel model to represent the structure of multilayered graphene membranes. We have established a quantitative relationship between effective diffusion length Leff and cross-section area Aeff of the 1D model and our recently developed two dimensional (2D) representative microstructure for graphene membranes. We find that only in the cases of a relatively large lateral size L (> ~100 nm) and a small slit size h (< 2 nm), the effective diffusion length Leff and Aeff can be calculated by an over-simplified but often used model. Otherwise, they show complex dependence on all three structural parameters of the 2D structural model. Our equivalent 1D nano-channel model can reproduce experimental results very well except for h < 0.5 nm. The discrepancy could be attributed to the anomalous behaviour of molecules under nano-confinement that is not considered in our simulations. This model can also be extended to multilayered membranes assembled by other 2D materials.

Roles of Chloroplast Retrograde Signals and Ion Transport in Plant Drought Tolerance.

Worldwide, drought affects crop yields; therefore, understanding plants’ strategies to adapt to drought is critical. Chloroplasts are key regulators of plant responses, and signals from chloroplasts also regulate nuclear gene expression during drought. However, the interactions between chloroplast-initiated retrograde signals and ion channels under stress are still not clear. In this review, we summarise the retrograde signals that participate in regulating plant stress tolerance. We compare chloroplastic transporters that modulate retrograde signalling through retrograde biosynthesis or as critical components in retrograde signalling. We also discuss the roles of important plasma membrane and tonoplast ion transporters that are involved in regulating stomatal movement. We propose how retrograde signals interact with ion transporters under stress.

Electrokinetic ion transport in nanofluidics and membranes with applications in bioanalysis and beyond.

Electrokinetic transport of ions between electrolyte solutions and ion permselective solid media governs a variety of applications, such as molecular separation, biological detection, and bioelectronics. These applications rely on a unique class of materials and devices to interface the ionic and electronic systems. The devices built on ion permselective materials or micro-/nanofluidic channels are arranged to work with aqueous environments capable of either manipulating charged species through applied electric fields or transducing biological responses into electronic signals. In this review, we focus on recent advances in the application of electrokinetic ion transport using nanofluidic and membrane technologies. We start with an introduction into the theoretical basis of ion transport kinetics and their analogy to the charge transport in electronic systems. We continue with discussions of the materials and nanofabrication technologies developed to create ion permselective membranes and nanofluidic devices. Accomplishments from various applications are highlighted, including biosensing, molecular separation, energy conversion, and bio-electronic interfaces. We also briefly outline potential applications and challenges in this field.

Theory of Ion and Water Transport in Reverse-Osmosis Membranes

We present theory for ion and water transport through reverse osmosis membranes based on a Maxwell-Stefan framework combined with hydrodynamic theory for the reduced motion of particles in thin pores. We include all driving forces and frictions both on the fluid (water), and on the ions, including ion-fluid friction as well as ion-wall friction. By including the acid-base character of the carbonic acid system, the boric acid system, H$_3$O$^+$/OH$^-$, and the membrane charge, we locally determine pH and thus the effective charge of the membrane as well as the dissociation degree of boric acid. We present calculation results for a dead end experiment with fixed feed concentration, where effluent composition is a self-consistent function of fluxes through the membrane. Comparison with experimental results from literature for fluid flow vs. pressure, and for salt and boron rejection, shows that theory agrees well with data. Our model is based on realistic assumptions for the effective sizes of the ions and for the diameter of the RO membrane pore in the polyamide toplayer ($\sim$0.75 nm).

Impact of solution composition on the resistance of ion exchange membranes

Resistance to ion transport in ion exchange membranes (IEMs) is detrimental to the performance of IEM-based processes. In this work we measured the resistance of representative IEMs, i.e. one cation (CEM) and one anion (AEM) exchange membrane, in 15 single-salt solutions using electrochemical impedance spectroscopy. Resistance was sensitive to solute identity only in the case of the CEM for which it depended on the counter-ion identity; the resistance of the CEM was mostly insensitive to the co-ion identity, and the resistance of the AEM was mostly insensitive to both the counter-ion and co-ion identity. For all solutes, membrane resistance decreased sharply with increasing solution concentration below 0.1 M, and remained approximately constant above 0.1 M. An empirical mathematical model comprising a concentration-dependent term and a concentration-independent term successfully described membrane resistance as a function of solution concentration. The model builds on that previously proposed by Galama et al. (JMS 467 (2014), 279–291). We found that for both membranes, the concentration-dependent and concentration-independent terms of the resistance increased with increasing counter-ion hydration free energy. This was rationalized as the energy barrier to counter-ions having to shed/reorient water molecules of hydration, due to steric effects, when permeating the membranes. Also for both membranes, the concentration-dependent term of the resistance generally had a non-linear relationship with salt concentration. This result suggests that the concentration-dependent term is not attributable to bulk solution, and that there is a degree of randomness to the interconnectedness between the different membrane regions that contribute to ionic resistance. Our findings improve the understanding of the relationships between electrolyte properties and IEM resistance, and provide tools for assessing IEM resistance. This improved understanding is critical to establishing a complete IEM resistance theory and to evaluating new applications for IEMs.

Quantitative Proteomics of Synaptosomal Fractions in a Rat Overexpressing Human DISC1 Gene Indicates Profound Synaptic Dysregulation in the Dorsal Striatum.

Disrupted-in-schizophrenia 1 (DISC1) is a key protein involved in behavioral processes and various mental disorders, including schizophrenia and major depression. A transgenic rat overexpressing non-mutant human DISC1, modeling aberrant proteostasis of the DISC1 protein, displays behavioral, biochemical and anatomical deficits consistent with aspects of mental disorders, including changes in the dorsal striatum, an anatomical region critical in the development of behavioral disorders. Herein, dorsal striatum of 10 transgenic DISC1 (tgDISC1) and 10 wild type (WT) littermate control rats was used for synaptosomal preparations and for performing liquid chromatography-tandem mass spectrometry (LC-MS)-based quantitative proteomics, using isobaric labeling (TMT10plex). Functional enrichment analysis was generated from proteins with level changes. The increase in DISC1 expression leads to changes in proteins and synaptic-associated processes including membrane trafficking, ion transport, synaptic organization and neurodevelopment. Canonical pathway analysis assigned proteins with level changes to actin cytoskeleton, Gαq, Rho family GTPase and Rho GDI, axonal guidance, ephrin receptor and dopamine-DARPP32 feedback in cAMP signaling. DISC1-regulated proteins proposed in the current study are also highly associated with neurodevelopmental and mental disorders. Bioinformatics analyses from the current study predicted that the following biological processes may be activated by overexpression of DISC1, i.e., regulation of cell quantities, neuronal and axonal extension and long term potentiation. Our findings demonstrate that the effects of overexpression of non-mutant DISC1 or its misassembly has profound consequences on protein networks essential for behavioral control. These results are also relevant for the interpretation of previous as well as for the design of future studies on DISC1.

Free-Standing Lipid Bilayers: A Versatile Platform for the Mechanistic Studies of Voltage Sensitive Dyes and Membrane Ion Transport

Free-Standing Lipid Bilayers: A Versatile Platform for the Mechanistic Studies of Voltage Sensitive Dyes and Membrane Ion Transport

Microstructural and Functional Imaging of the Intact Sinoatrial Node Detects Heterogenous Ca2+-Driven Intra and Intercellular Communications that Lead to Pacing Perfection

Cells within the sinoatrial node (SAN), the primary pacemaker of the heart, are extremely heterogeneous in size, morphology and electrophysiological characteristics. A coupled-clock theory suggests that rhythmic action potential (AP) firing is generated by tight interactions of rhythmic local Ca releases with cell surface membrane ion channels and transporters. This mechanism was reported in single cells, but has not been systematically explored within cells residing in intact SAN tissue. We developed novel Ca imaging techniques to visualize the spread of the impulse across the entire network of SAN cells and local Ca release dynamics within individual cells. Immunolabeling of Connexin-43 and HCN4 was employed to correlate cytoarchitecture with Ca activity. Rhythmic AP-induced Ca transients (APCTs), which correlated with APs recorded simultaneously using sharp microelectrode, were employed to monitor the impulse conduction across the SAN. The site at which the earliest APCTs occurred, identified by phase shift analysis, was between crista terminalis and superior vena cava. The APCT travels from this area across the entire SAN along curvilinear bundles of striated SAN cells rich in Connexion-43 and weak in HCN4 immunolabeling. LCRs were observed in all areas of SAN, including cells within the conduction bundles. Cells close to the APCT initiation site generated only rhythmic LCRs (without APCTs) and these LCRs preceded APCTs in the cells of the APCT-initiation area. Cells close to APCT initiation site were rich in HCN4, but essentially devoid of Connexin-43 and striations. Our results are consistent with the hypothesis that a coupled-clock system operates both within and among cells comprising the SAN network: some specialized cells generate only rhythmic LCRs that ignite adjacent cells to initiate the impulse that propagates throughout the SAN cell network.