Sodium Influx Research Articles

Electrochemical characterization of mixed matrix electrodialysis cation exchange membrane incorporated with carbon nanofibers for desalination

A new type of electrodialysis mixed matrix (MM) cation exchange membrane was prepared by incorporating carbon nanofibers (CNFs) into membrane matrix. The microscopy images showed uniform surface for the membrane relatively. The use of CNFs into membrane body enhanced membrane surface hydrophilicity, potential, transport number, permselectivity, and ionic conductivity obviously, while water uptake decreased. The sodium flux was also enhanced by incorporation of CNFs into membrane matrix from 0 to 0.5%wt and 2 to 8%wt, while declined for the samples in the range of 0.5 to 2%wt CNF ratios. Compared to pristine membrane, a smoother surface was observed for PVC-CNF membrane. Electrodialysis showed the (K+/Na+) flux ratio about 2.14. The transport mechanism of K+ and Na+ ions through the membranes discussed by considering ionic and hydrated radius, hydration potential, hydration free energy, entropy of hydration, and the Jones-Dole coefficient. Optimal performance was achieved for PVC-0.5%wt CNF membrane.

The role of vacuolar ion channels in salt stress tolerance in the liverwort Conocephalum conicum

Liverworts are pioneer plants that colonized lands. They had to cope with frequent sea water flooding causing salt stress. The role of vacuoles and in particular slow-activating (SV) channels in the salt stress tolerance was addressed in the present study. A patch-clamp method was used to study sodium fluxes through the tonoplast of the liverwort Conocephalum conicum. The whole-vacuole measurements carried out in a symmetrical Na+ concentration allowed recording of slowly activated outward currents typical for SV channels. In a Na+ gradient promoting an efflux of Na+ from the vacuole, the outward rectifying properties of SV channels were reduced and inward Na+ currents with different inactivation rates were recorded. Single channel analysis proved that a decrease in cytoplasmic Na+ concentration evoked an increase in the open probability of the channels and shifted the activation voltages towards negative values. The number of SV channels recorded at negative voltages was dependent on the vacuolar calcium and decreased at the high concentration of this ion in the vacuole. In some of the tested patches, the channels exhibited a flickering type of activity and two different conductance levels. The role of SV channels in Na+ accumulation during salt stress and its removal after periods of flooding is discussed in the present paper.

Geothermal steam condition performance monitoring

Turbine scaling from poor purity steam is a major problem in geothermal power stations. The “true” purity and quality of steam going into geothermal turbines can’t easily be measured in stations equipped with direct-contact condensers. Field testing has also shown that wet steam line samples are generally not representative of steam purity. Measuring sodium flux or chemical tracer injected upstream of the separators in drainpot condensate discharges can be used to determine the steam condition. However, the best measurement method seems to be the measuring of sodium flux.Tracers injected upstream of separators can take a long time to stabilise. The results of tracer studies need to be treated with caution and if they are used for a short interval test, they can give misleadingly optimistic results.Even with reliable representative data, there are very few changes that can be made to improve steam purity or quality without either major capital expenditure or significant load loss. This means that the design of a steam delivery system capable of providing clean dry steam is of vital importance in power station design. Results from existing stations’ performance shows that the design of steam delivery systems is currently being poorly done.

Magnetic cation exchange membrane incorporated with cobalt ferrite nanoparticles for chromium ions removal via electrodialysis

A new type of magnetic mixed matrix cation exchange membrane was prepared by incorporating cobalt ferrite nanoparticles for chromium ions removal via electrodialysis. The CoFe2O4 nanoparticles were synthesized via a simple chemical precipitation method. The synthesized nanoparticles and mixed matrix lab-made membranes were characterized by XRD, FT-IR, EDX, SEM and SOM. The images showed a uniform particle distribution and a relatively uniform surface for the prepared membranes. Utilizing CoFe2O4 nanoparticles in the membrane matrix led to increase of the membrane electrical conductivity and surface hyrophilicity. The membrane potential, charge density, permselectivity, transport number, ion exchange capacity and water content in the membrane were enhanced by using CoFe2O4 nanoparticles loading ratios up to 2 wt% and then decreased again for concentrations above 2 wt%. The sodium flux was also increased sharply by using cobalt ferrite nanoparticles in the membrane matrix. The magnetic PVC-CoFe2O4 membrane showed more dialytic rate in chromium ions removal compared to pristine PVC membrane which could be linked to strong affinity of magnetic nanoparticles in heavy metal ions adsorption.

Teamwork: Ion channels and transporters join forces in the brain

Voltage-gated potassium (Kv) channels open in response to changes in membrane potential to permit passage of K+ ions across the cell membrane, down their electrochemical gradient. Sodium-coupled solute transporters utilize the downhill sodium gradient to co-transport solutes, ranging from ions to sugars to neurotransmitters, into the cell. A variety of recent studies have uncovered cooperation between these two structurally and functionally unrelated classes of protein, revealing previously unnoticed functional crosstalk and in many cases physical interaction to form channel-transporter (chansporter) complexes. Adding to this field, Bartolomé-Martín and colleagues now report that the heteromeric KCNQ2/KCNQ3 (Kv7.2/7.3) potassium channel – the primary molecular correlate of the neuronal M-current – can physically interact with two sodium-coupled neurotransmitter transporters expressed in the brain, DAT and GLT1 (dopamine and glutamate transporters, respectively). The authors provide evidence that the interactions may enhance transporter activity while dampening the depolarizing effects of sodium influx. Cumulative evidence discussed here suggests that chansporter complexes represent a widespread form of cellular signaling hub, in the CNS and other tissues.This article is part of the issue entitled ‘Special Issue on Neurotransmitter Transporters’.

Epithelial Modelling Platform: A Tool for Investigating Hypothesis through Discovery and Assembly of Computational Models of Epithelial Transport

Scientists often leverage computational models of biological systems to investigate hypotheses which are difficult or prohibitively expensive to achieve experimentally. Such investigations are best achieved by utilizing suitable computational models, reusing existing validated models where possible and creating novel models consistently as needed. This requires tools which enable the discovery and exploration of existing models matched with assistance in constructing and testing new models. Enabling scientists or clinicians to use such a tool by describing their requirements in a manner familiar to themselves greatly improves the accessibility of the tool. We have developed a web-based tool, the Epithelial Modelling Platform, for scientists and clinicians to discover relevant models and then assemble these into a novel model customized for investigating their hypotheses. While our tool specifically focuses on epithelial transport, by utilizing relevant community standards and publicly accessible knowledge repositories, it is extensible to other areas of application. The platform abstracts underlying mathematics of the computational models and provides a visual environment which mimics biological phenomena of an epithelial cell. Beyond the mathematical models, we have implemented a feature to discover existing simulation experiments which match the features of the novel models users create. By executing these simulation experiments with the novel models and comparing to previous model predictions and/or experimental or clinical observations we are able to provide the user with some measure of verification that their model matches, or doesn't match, existing knowledge captured in the various repositories utilized. Support or Funding Information Supported by the Medical Technologies Center of Research Excellence (MedTech CoRE), the Aotearoa Foundation, and the Auckland Bioengineering Institute Model discovery interface to search for models in the Physiome Model Repository (PMR) which are relevant to the query “flux of sodium”. By querying the biological knowledge stored in PMR the Epithelial Modelling Paltform retrieves components from the weinstein, mackenzie, and chang fujita models. Illustrating a similarity between weinstein and mackenzie model. In this case both models have similar compartment labeled with a unique color. An instance of the Epithelial Modelling Platform. It consists of five compartments and three membranes. Biological processes have been represented with various shapes: fluxes with circles; channels with polygons; and diffusive fluxes with a text, a line, and an arrow. On the right, check boxes have been generated for the visualized shapes on the membranes to allow the user to drag and drop. Concentration of the biological description of CellML variables float in the respective compartments. A suggestion window based on the biological description in the Physiome Model Repository when a circle, represented as flux of Na+ in the weinstein model, is moved from apical to basolateral membrane. A model verification instance for testing components of an assembled epithelial model reproduce the same simulation experiment. A model verification instance for testing components of an assembled epithelial model reproduce the same simulation experiment. A spider chart to find similarity of models with respect to an assembled epithelial model. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Development of a high-throughput fluorescent no-wash sodium influx assay.

Voltage-gated sodium channels (NaVs) are key therapeutic targets for pain, epilepsy and cardiac arrhythmias. Here we describe the development of a no-wash fluorescent sodium influx assay suitable for high-throughput screening and characterization of novel drug leads. Addition of red-violet food dyes (peak absorbance range 495–575 nm) to assays in HEK293 cells heterologously expressing hNaV1.1–1.8 effectively quenched background fluorescence of the sodium indicator dye Asante NaTRIUM Green-2 (ANG-2; peak emission 540 nm), negating the need for a wash step. Ponceau 4R (1 mM) was identified as a suitable quencher, which had no direct effect on NaV channels as assessed by patch-clamp experiments, and did not alter the pharmacology of the NaV1.1–1.7 activator veratridine (EC50 10–29 μM) or the NaV1.1–1.8 inhibitor tetracaine (IC50’s 6–66 μM). In addition, we also identified that the food dyes Ponceau 4R, Brilliant Black BN, Allura Red and Amaranth are effective at quenching the background fluorescence of the calcium indicator dyes fluo-4, fura-2 and fura-5F, identifying them as potential inexpensive alternatives to no-wash calcium ion indicator kits. In summary, we have developed a no-wash fluorescent sodium influx assay suitable for high-throughput screening based on the sodium indicator dye ANG-2 and the quencher Ponceau 4R.

Desalination and heavy metal ion removal from water by new ion exchange membrane modified by synthesized NiFe2O4/HAMPS nanocomposite

Magnetic nickel ferrite (NiFe2O4) nanoparticles were synthesized and then modified by a novel hydrogel based on 2-acrylamido-2-methyl propane sulfonic acid (HAMPS). Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) analyses were conducted to prove the NiFe2O4/HAMPS nanocomposite formation decisively. The effect of NiFe2O4/HAMPS in the matrix of the heterogeneous cation exchange membrane on separation performance was studied. Adding of NiFe2O4/HAMPS into the membrane body up to 1%wt resulted in an increase of sodium flux obviously. The sodium flux showed a decreased trend at higher nanocomposite ratios slightly. Membrane potential, permselectivity, and transport numbers also showed improving trends. Results exhibited more value for Na+ dynamic transport numbers compared to static ones. Membrane water content and porosity increased from 13.07 to 27.7% and 9.6 to 20.2% by utilizing NiFe2O4/HAMPS, respectively. By adding NiFe2O4-HAMPS into the membrane structure a pronounced improvement in membrane mechanical resistance (~ 94%) and chemical stability was observed. Modified membrane containing 1.0%wt NiFe2O4-HAMPS showed effective separation in Pb2+ (~ 98%), Cu2+ (~ 48%), and Ni2+ (~ 34%) removal. This sample also showed highest current efficiency (78.9%) in Pb2+ removal and lowest energy consumption (6.97 W/mol) compared to others.

Electrodialysis of concentrated brines: Effects of multivalent cations

Electrodialysis is an electrochemically driven membrane technology usually used for treating feed water containing several thousand mg/l total dissolved solids (TDS). This research investigated the use of conventional ED for the treatment of flowback water from shale gas hydraulic fracturing that contains up to tens of thousands of mg/l TDS and contain a mixture of multivalent cations. This paper discusses efforts to treat concentrated brines with electrodialysis and focuses on the mitigation of the detrimental effects of multivalent cations such as calcium, magnesium, barium, iron, and in the feedstock. A previous paper detailed the effects of calcium under defined lab conditions. The apparent calcium fouling (in and around) the electrode cells was mitigated by changing the single cathode chamber boundary membrane to a (CMX-S) that was more selective for monovalent cations. This paper covers efforts undertaken to mitigate problems associated with high concentrations of calcium, barium, iron, and magnesium. Four field samples of produced water from oil and gas operations in from the Marcellus shale formation (generally Pennsylvania, USA) and the Barnett shale formation (generally north central Texas, USA) were also tested. These results from field samples were similar to the results from lab defined tests. Mechanisms of process interference by the different multivalent cations appear different for each species. Calcium, magnesium, barium, and iron were preferentially transported from the diluate to the concentrate compared to sodium by a factor of about 1.4:1 on a charge basis resulting in a suppression of the flux of sodium to the concentrate. A single CMX-S membrane selective for monovalent cations was placed at the cathode barrier resulting in a reduced flux of calcium, magnesium and barium into the electrode rinse. However total ion flux was inhibited caused by apparent blockage of the cation transfer sites on the CMX-S membrane by the stagnant multivalent cations. A series of tests with periodic pulse polarity-reversal (anode and cathode reversed for a brief time) indicted the blockage by calcium and barium was immediately reversable, however, iron was more problematic and may have precipitated on membrane surfaces other than the cathode barrier.

Heterogeneity of Activity-Induced Sodium Transients between Astrocytes of the Mouse Hippocampus and Neocortex: Mechanisms and Consequences.

Activity-related sodium transients induced by glutamate uptake represent a special form of astrocyte excitability. Astrocytes of the neocortex, as opposed to the hippocampus proper, also express ionotropic glutamate receptors, which might provide additional sodium influx. We compared glutamate-related sodium transients in astrocytes and neurons in slices of the neocortex and hippocampus of juvenile mice of both sexes, using widefield and multiphoton imaging. Stimulation of glutamatergic afferents or glutamate application induced sodium transients that were twice as large in neocortical as in hippocampal astrocytes, despite similar neuronal responses. Astrocyte sodium transients were reduced by ∼50% upon blocking NMDA receptors in the neocortex, but not hippocampus. Neocortical, but not hippocampal, astrocytes exhibited marked sodium increases in response to NMDA. These key differences in sodium signaling were also observed in neonates and in adults. NMDA application evoked local calcium transients in processes of neocortical astrocytes, which were dampened upon blocking sodium/calcium exchange (NCX) with KB-R7943 or SEA0400. Mathematical computation based on our data predict that NMDA-induced sodium increases drive the NCX into reverse mode, resulting in calcium influx. Together, our study reveals a considerable regional heterogeneity in astrocyte sodium transients, which persists throughout postnatal development. Neocortical astrocytes respond with much larger sodium elevations to glutamatergic activity than hippocampal astrocytes. Moreover, neocortical astrocytes experience NMDA-receptor-mediated sodium influx, which hippocampal astrocytes lack, and which drives calcium import through reverse NCX. This pathway thereby links sodium to calcium signaling and represents a new mechanism for the generation of local calcium influx in neocortical astrocytes.SIGNIFICANCE STATEMENT Astrocyte calcium signals play a central role in neuron-glia interaction. Moreover, activity-related sodium transients may represent a new form of astrocyte excitability. Here we show that activation of NMDA receptors results in prominent sodium transients in neocortical, but not hippocampal, astrocytes in the mouse brain. NMDA receptor activation is accompanied by local calcium signaling in processes of neocortical astrocytes, which is augmented by sodium-driven reversal of the sodium/calcium exchanger. Our data demonstrate a significant regional heterogeneity in the magnitude and mechanisms of astrocyte sodium transients. They also suggest a close interrelation between NMDA-receptor-mediated sodium influx and calcium signaling through the reversal of sodium/calcium exchanger, thereby establishing a new pathway for the generation of local calcium signaling in astrocyte processes.

Effect of reverse sodium flux and pH on ammoniacal nitrogen transport through biomimetic membranes

Forward osmosis can be used to treat wastewater using seawater as the draw solution. This has been done for both water purification and nutrient concentration. However, the loss of ammoniacal nitrogen to the draw solution may be a key issue, reducing nutrient recovery and preventing the discharge of untreated seawater draw solution – a cost-saving strategy for the industrialisation of forward osmosis for wastewater treatment. In this study, forward ammoniacal nitrogen flux was studied using digester centrate from a wastewater treatment plant as the feed solution. The draw solution contained various NaCl concentrations in order to determine the effect of reverse sodium flux on forward ammoniacal nitrogen flux. The forward ammoniacal nitrogen flux was measured to be 1.5 × 10–6–8.0 × 10–5 mol m−2 s−1, and increased with pH and sodium concentration in the draw solution. The forward ammonium flux increased with draw solution reverse salt flux below pH = 9, whereas it was unaffected by this flux above pH = 9. Therefore, the reverse flux of sodium ions facilitates the forward transport of ammonium ions at low pH. The transport of the positively charged ammonium was lower than that of the neutral ammonia due to its higher hydrodynamic radius.

Investigation of TRPM4 in Prostate Cancer Cells with Novel Small Molecule Inhibitors

Transient receptor potential melastatin 4 (TRPM4) is a monovalent cation channel, mainly conducting Na+ and K+. TRPM4 is widely expressed, although its expression is most prominent in prostate and colon. TRPM4 protein and RNA expression levels are increased in prostate cancer compared to normal prostate tissue and TRPM4 was recently identified as a cancer driver gene in androgen-insensitive prostate cancer. TRPM4 is activated by Ca2+ and plays an important role in intracellular Ca2+ signaling through the initiation of an important negative feedback mechanism of store-operated calcium entry (SOCE). As a universal second messenger calcium is regulating multiple biological processes. Therefore, it is important that calcium homeostasis is tightly regulated. However, in several cancers, SOCE and its signaling components are dysregulated, contributing to several cancer hallmarks such as increased proliferation and enhanced migration. Sodium influx via TRPM4 depolarizes the membrane and by that reduces the driving force for further calcium influx. We hypothesize that TRPM4, as negative regulator of SOCE, plays a role in migration and proliferation of prostate cancer cells. We recently successfully evaluated a new TRPM4 blocker, 4-Chloro-2-(2-(2-chlorophenoxy) acetamido) benzoic acid (CBA), as a potent inhibitor of TRPM4 current. CBA blocks endogenous TRPM4 currents in LNCaP cells in a low micromolar range. Furthermore, LNCaP cells treated with CBA showed decreased viability. Additionally, two additional small molecule inhibitors were tested on the same cell line whereof one showed strong negative effect on the viability of LNCaP cells. Furthermore, DU145 cells treated with CBA demonstrated slight decrease in migration compared to vehicle treated cells. Stable TRPM4-K.O. cells were used to further study the role of TRPM4 in prostate cancer migration and proliferation. In line with our previous data using the blockers, DU145 TRPM4-K.O. cells displayed decreased migration and proliferation.

Non-Genomic Effects of Aldosterone.

Encouraging changes in the steroid hormone receptor field from initially questioning the role of non-genomic actions of steroid hormones to acceptance of the concept that the acute, membrane-centric actions are linked and/or regulate the nuclear actions. The focus of this chapter is how the non-genomic effects are linked to the longer lasting, genomic actions of aldosterone. By non-genomic we refer to the rapid actions that occur within minutes do not require transcription or translation and occur in both classical MR target organs (kidney and colon) and non-epithelial tissues (blood vessels, heart, and adipose). The mechanism of rapid non-genomic actions of aldosterone varies between tissues. As a result, this chapter is viewed through the lens of how the non-genomic and genomic actions of aldosterone are linked in cardiovascular disease. Specifically, regulation of sodium flux in the myocardium has an important role in pathogenesis of cardiac arrhythmia. Since there are now recognized gender differences in cardiovascular disease, we also include preliminary studies to investigate the interaction of sex steroid hormones with the ligand binding pocket of the mineralocorticoid receptor. Overall, we aim to showcase how the non-genomic effects of aldosterone potentially modulate the genomic effects and represent additional targets for intervention.

A new SCN5A mutation responsible for Multifocal Ectopic Purkinje-Related Premature Contractions

Recently, SCN5A mutations have been associated with Multifocal Ectopic Purkinje-Related Premature Contractions (MEPPC), a cardiac syndrome associating polymorphic ventricular arrhythmia with dilated cardiomyopathy. A new SCN5A mutation was identified in a young woman presenting with polymorphic PVCs and dilated cardiomyopathy since the age of 12. Radiofrequency catheter ablation showed at least three exit sites of purkinje-PVCs. A treatment by hydroquinidine was tried, leading to an immediate and spectacular disappearance of all PVCs. A new heterozygous missense mutation was identified in exon 5 of SCN5A (c.611C > A, pAla204Glu) in the DI-S3 domain. We investigated the functional consequences of NaV1.5-A204E expressed in HEK cells by recording the sodium current using the whole-cell configuration of the patch clamp technique. The NaV1.5-A204E mutant channels exhibited a significant leftward shift of the activation curve of 8 mV (V0.5 of activation = −42.9 ± 1.3 mV in A204E transfected cells ( n = 24) compared to −34.8 ± 1.9 mV in cells transfected with the wild-type (WT) channel ( n = 20), P < 0.001), leading to a large, hyperpolarized window current that predicts aberrant sodium influx at potentials near the cardiomyocyte resting membrane potential. We did not observe any difference in the sodium current density, nor persistent sodium current in NaV1.5-A204E transfected cells, when compared to WT cells. This profile of channel dysfunction shares features with other MEPCC-associated SCN5A mutations and overlapped that of congenital long QT syndrome LQT3. The functional consequences of this new SCN5A mutation associated with MEPPC revealed a pattern of abnormal voltage dependence of activation leading to a larger hyperpolarized window current as a shared biophysical mechanism of the syndrome. These features of the mutant sodium channel are likely to be responsible for hyperexcitability of the fascicular-Purkinje system.

Investigation of oxygen and other impurities and their effect on the transparency of a Na flux grown GaN crystal

In this study, we investigate several impurities in bulk GaN crystals grown by the sodium flux technique. In our system, black GaN is in general associated with oxygen, sodium, and molybdenum concentrations in excess of 1019 atoms/cm3. Here, we report on the correlation of high levels of oxygen with opaque crystals. Samples that contain oxygen concentrations above 1019 atoms/cm3 are highly absorbing regardless of the presence of other impurities. Experiments with partially submerged seeds indicated material grown mainly above the nominal liquid surface was more transparent and had a generally lower impurity concentration, especially oxygen. In optically transparent regions, concentrations of oxygen, sodium, and carbon were as low as 7 × 1016, 2 × 1016, and 5 × 1016 atoms/cm3, respectively, while the concentration of molybdenum was below the detection limit.

Effect of Flux Salts on the Recovery Extent and Quality of Metal Values from Spent Rechargeable Lead Batteries

Lead–calcium alloy containing up to 0.10% calcium was recovered from spent rechargeable sealed acid–lead batteries. Two techniques were investigated to explore the effect of flux salts on the extent and quality of the recovered alloy: pyrometallurgical and electrochemical methods. About 10 kg of the spent batteries were collected for testing. The sample was washed with hot water and dried. The plastic cases of the batteries were mechanically cut, the contents were dismantled manually, and the plastic containers were shredded for recycling. The electrode plates were freed from the loose powder and placed in SiC crucible and covered with alkali chloride salts. The loaded crucible was heated in an electronically controlled chamber furnace-type NaberthermC3 at temperatures up to 800 °C. The obtained metals were analyzed. The effect of temperature, rate of heating, atmospheric conditions, composition of the flux salts on the extent and quality of the recovered lead–calcium alloy were studied. Results revealed that the spent rechargeable batteries contain three groups of three plates of Pb–Ca grids, each packed with lead oxides. Direct heating of these plates in a silicon carbide crucible under ambient conditions produces lead metal poor in calcium content (0.07%) due to partial oxidation of the alloying calcium element. Rate of temperature increase has a considerable effect on the yield of the lead alloy composition. Thermodynamically, the activation energy of the alloying process amounts to 5366 kJ/mol. Flux sodium salts benefit the recovery process. Sodium salts are more powerful as compared to potassium salts. Lead calcium alloy meeting the standard specification has been successfully recovered from the spent rechargeable acid–lead batteries with a very competitive cost to that of the same alloy prepared from primary resources.

Experimental Evidence for Opposite Fluxes of Sodium, Potassium, and CO2 during Glaucophane Schist Interaction with Harzburgite and Websterite in Subduction Zones

This paper reports the results of high-pressure experimental modeling of interaction between glaucophane schist and harzburgite or websterite for the evaluation of the influence of mantle material on the input–output of components and character of metasomatic transformations at the crust–mantle boundary in the subduction zone. In all experiments, glaucophane schist (proxy for oceanic crust) containing volatile components (H2O and CO2) incorporated in hydrous minerals (amphiboles, phengite, and epidote) and calcite was loaded into the bottom of each capsule and overlain by mantle material. During the experiments at a temperature of 800°C and a pressure of 2.9 GPa, which correspond to the conditions of a hot subduction zone, the schist underwent partial (up to 10%) eclogitization with the formation of the anhydrous assemblage omphacite + garnet + quartz ± magnesite ± potassic phase. Carbonate and a potassic phase were formed only in the experiments with websterite in the upper layer. A reaction zone was formed at the base of the websterite layer, where newly formed omphacite, quartz, and orthopyroxene replaced in part initial pyroxenes. Orthopyroxene and phlogopite (or an unidentified potassic phase) were formed in the reaction zone at the base of the harzburgite layer; among the initial minerals, only orthopyroxene relicts were preserved. Above the reaction zones produced by diffusion metasomatism, new phases developed locally, mainly at grain boundaries: newly formed orthopyroxene and magnesite were observed in harzburgite, and omphacite and quartz, in websterite. Alterations along grain boundaries extended much further than the reaction zones, which indicates that fluid infiltration dominated over diffusion in the experiments. The experiments demonstrated that the H2O–CO2 fluid with dissolved major components released from the glaucophane schist can produce mineral assemblages of different chemical compositions in mantle materials: Na-bearing in websterite and K-bearing in harzburgite. The complementary components, K2O and CO2 for the websterite layer and Na2O for the harzburgite layer, are fixed in the initial glaucophane schist layer. The distinguished separation of alkalis and CO2 at the crust–mantle boundary can affect the character of metasomatism in the mantle wedge, primary magma compositions, and the chemical evolution of the rocks of the subducting slab.

Activity changes in gill ion transporter enzymes in response to salinity and temperature in fathead minnows (Pimephales promelas)

Fathead minnows, Pimephales promelas, are found throughout the continental United States in waters in which salinity can change with tides and temperatures vary seasonally. They have been used extensively in studies of environmental toxicology and are commercially important. In a very recent study in our labs RNA Seq was used to assemble transcriptomes from the gills of fatheads acclimated to either 5° or 22 °C. By comparison with published genomes, transcripts were identified for a number of ion transporters, ion channels, and signal molecule receptors, as well as enzymes that generate ammonia. H-ATPase and Na/K-ATPase activities were measured in supernatants of gill homogenates from fish acclimated to water sodium concentrations of 1.6, 3.1 or 124 mM sodium. As the water sodium concentration increased, in vitro activities of Na/K-ATPase activity and gill glutamate dehydrogenase activity decreased while H-ATPase activity increased. In a second series of experiments minnows were acclimated to 5 °C, 12.5 °C or 22 °C. In vitro activity of Na/K-ATPase decreased but activities of H-ATPase and glutamate dehydrogenase increased as temperature increased in gill membranes. These data do not support a primary role for apical H-ATPase in sodium influx under all conditions but do suggest a role for glutamate dehydrogenase production of ammonium to act as a counter-ion for sodium uptake by NHE-3.

Imaging Sodium Flux during Action Potentials in Neurons with Fluorescent Nanosensors and Transparent Microelectrodes.

Sodium flux plays a pivotal role in neurobiological processes including initiation of action potentials and regulation of neuronal cell excitability. However, unlike the wide range of fluorescent calcium indicators used extensively for cellular studies, the choice of sodium probes remains limited. We have previously demonstrated optode-based nanosensors (OBNs) for detecting sodium ions with advantageous modular properties such as tunable physiological sensing range, full reversibility, and superb selectivity against key physiological interfering ion potassium. (1) Motivated by bridging the gap between the great interest in sodium imaging of neuronal cell activity as an alternative to patch clamp and limited choices of optical sodium indicators, in this Letter we report the application of nanosensors capable of detecting intracellular sodium flux in isolated rat dorsal root ganglion neurons during electrical stimulation using transparent microelectrodes. Taking advantage of the ratiometric detection scheme offered by this fluorescent modular sensing platform, we performed dual color imaging of the sensor to monitor the intracellular sodium currents underlying trains of action potentials in real time. The combination of nanosensors and microelectrodes for monitoring neuronal sodium dynamics is a novel tool for investigating the regulatory role of sodium ions involved during neural activities.

Dialysate sodium concentration: The forgotten salt shaker.

The concentration of sodium in dialysis fluid, a major determinant of extracellular fluid volume and blood pressure, plays a major role in the sodium balance in end-stage renal disease patients. A low dialysate sodium concentration (DNa) reduces interdialytic weight gain (IDWG) and blood pressure and might help ameliorate endothelial dysfunction and inflammation. However, low DNa can also increase the incidence of hypotensive episodes and muscle cramps. Sodium profiling, as typically prescribed in which the DNa is ramped up from above 140mEq/L to nonphysiological levels, might reduce hypotension in patients with hemodynamic instability but at the cost of the consequences of hypernatremia. Serum sodium concentrations of individual patients fall within a narrow range around a "sodium setpoint." The sodium gradient, the difference between the sodium set point and the DNa, is associated more robustly with clinical outcomes than DNa itself. Sodium concentration presents several issues: the influence of the net negative charge of plasma proteins on sodium flux across the dialysis membrane (Donnan equilibrium); and the clinically important problems in measuring sodium levels. This article presents a review of the clinical effects of DNa and of basic aspects of sodium balance in hemodialysis patients.