Reversal Potential Research Articles

Lithium (Poly)sulfide Phase Conversion in Working Lithium–Sulfur Batteries: The Insight from the Equilibrium Potential Model

The commercialization of lithium–sulfur (Li–S) batteries is currently hindered by the electrochemical instability and capacity loss, due to the ultracomplex phase conversion of lithium polysulfides (LPSs) and lithium sulfide (Li2S). Revealing the mechanism is critical to rational regulation of the cathode reaction process so as to improve the cycling stability and capacity retention. Herein, we develop an equilibrium potential model to reveal the two conversion pathways under different electrolyte/sulfur ratios of working Li–S batteries. The model predicts that the supersaturation of Li2S and the precipitation of LPSs are responsible for the potential drop at the onset of the second plateau and the emergence of the third plateau, respectively, deviating from the typical discharge profiles. Furthermore, quantitative guidance for electrolyte screening and battery assembling is presented to selectively control LPS precipitation. The description of equilibrium potential could be used as a foundation for mechanism study and battery monitoring system development.

Promote electroreduction of CO2 via catalyst valence state manipulation by surface-capping ligand

Electrochemical CO2 reduction provides a potential means for synthesizing value-added chemicals over the near equilibrium potential regime, i.e., formate production on Pd-based catalysts. However, the activity of Pd catalysts has been largely plagued by the potential-depended deactivation pathways (e.g., [Formula: see text]-PdH to [Formula: see text]-PdH phase transition, CO poisoning), limiting the formate production to a narrow potential window of 0V to -0.25V vs. reversible hydrogen electrode (RHE). Herein, we discovered that the Pd surface capped with polyvinylpyrrolidone (PVP) ligand exhibits effective resistance to the potential-depended deactivations and can catalyze formate production at a much extended potential window (beyond -0.7V vs. RHE) with significantly improved activity (~14-times enhancement at -0.4V vs. RHE) compared to that of the pristine Pd surface. Combined results from physical and electrochemical characterizations, kinetic analysis, and first-principle simulations suggest that the PVP capping ligand can effectively stabilize the high-valence-state Pd species (Pdδ+) resulted from the catalyst synthesis and pretreatments, and these Pdδ+species are responsible for the inhibited phase transition from [Formula: see text]-PdH to [Formula: see text]-PdH, and the suppression of CO and H2 formation. The present study confers a desired catalyst design principle, introducing positive charges into Pd-based electrocatalyst to enable efficient and stable CO2 to formate conversion.

Electrochemical Behaviors and Extraction of Ln(III) (Ln = La, Ce, Nd) Ions in LiCl–KCl–CsCl Eutectic Salts at Low Temperatures

The LiCl–KCl–CsCl eutectic salt is expected to be used as a melt medium for the pyrochemical process of spent fuels because of its low melting point properties that reduce the temperature resistance requirements of the equipment. In this work, the electrochemical behaviors of La(III), Ce(III), and Nd(III) ions in the LiCl–KCl–CsCl eutectic salt in the range of 563–683 K were investigated, and it was found that the difficulty of cathodic passivation was in the order of La(III) < Ce(III) < Nd(III). Cyclic voltammetry (CV) and chronopotentiometry (CP) methods were conducted to determine the diffusion coefficients of La(III), Ce(III), and Nd(III). The corresponding diffusion activation energies were also calculated. It was also found that the passivation phenomenon does not affect the equilibrium potentials of La(III), Ce(III), and Nd(III), so we determined the apparent electrode potentials of La(III) and Ce (III) in the range of 563–683 K and Nd(III) in the range of 623–683 K by the galvanostatic voltammetry (GV) method. Finally, Ce and Nd metals were successfully extracted by potentiostatic electrolysis at 563 K for 4 h.

Ab-initio Study of the Strain Tuning Method for Improving Li Diffusion Performance of the LiCoO2 Cathode Material in Lithium-ion Batteries

The charging speed of lithium-ion batteries can be enhanced by improving the diffusion performance of Li ions inside and at the interface of their cathodes. In this study, we applied strain to LiCoO2 (LCO) cathode materials to elongate their lattices, and the relationship between the lattice strain and energy required for Li deintercalation, referred to as "Li vacancy formation energy," was estimated by ab-initio calculations to determine the optimal strain. The results suggest that the charging speed can be improved by adding a strain of less than 5% while retaining its high mechanical properties and equilibrium potential. Furthermore, we found that applying approximately 10% strain in the c-axis direction significantly reduces the Li vacancy formation energy of the LCO cathode. We applied strain to LiCoO2 cathodes to elongate their lattices, and the relationship between the lattice strain and energy required for Li deintercalation was estimated by ab-initio calculations. We found that the charging speed can be improved by adding a strain of less than 5% while retaining its high mechanical properties and equilibrium potential.

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

The Nernst equilibrium potential calculates the theoretical OCV, which estimates the best performance achievable by an electrochemical cell. When multiple semi-reactions (or multiple ionic species) are active in one of the electrodes, the calculation of the theoretical OCV is not straightforward, since different Nernst potentials are associated to each semi-reaction. In this paper, analytical equations for calculation of the theoretical OCV are developed, using the mixed potential theory. The case of H2 and CO co-oxidation (or H2O and CO2 co-reduction) in solid oxide cells is used as a reference case, but similar conclusions can be drawn for other equivalent cases. OCV data from literature are used to calibrate and validate the model. The relative reaction rate of H2 and CO semi-reactions is estimated within the calibration process, and the result is in line with assumptions and suggestions given by other authors. The validation procedure shows predicted OCV values in line with experimental literature data, except for mixtures with relatively large CH4 concentration (e.g., 8%), for which the OCV is significantly underestimated. This is expected when thermochemical reactions, in parallel to electrochemical reactions occur, since the additional H2 produced by internal steam methane reforming is not accounted within the local mixed potential model. A fuel cell polarization model is developed based on the results from the calibration procedure, and it is used to predict the polarization behavior of an SOFC fed with a H2-H2O-CO-CO2 fuel mixture. It is found that either H2 or CO may be reduced rather than oxidized via an equivalent electrochemical water-gas-shift reaction.

Raloxifene and bazedoxifene as selective ALDH1A1 inhibitors to ameliorate cyclophosphamide resistance: A drug repurposing approach

Cyclophosphamide (CP) is one of the most widely used anticancer drugs for various malignancies. However, its long-term use leads to ALDH1A1-mediated inactivation and subsequent resistance which necessitates the development of potential ALDH1A1 inhibitors. Currently, ALDH1A1 inhibitors from different chemical classes have been reported, but these failed to reach the market due to safety and efficacy problems. Developing a new treatment from the ground requires a huge amount of time, effort, and money, therefore it is worthwhile to improve CP efficacy by proposing better adjuvants as ALDH1A1 inhibitors. Herein, the database constituting the FDA-approved drugs with well-established safety and toxicity profiles was screened through already reported machine learning models by our research group. This model is validated for discriminating the ALDH1A1 inhibitors and non-inhibitors. Virtual screening protocol (VS) from this model identified four FDA-approved drugs, raloxifene, bazedoxifene, avanafil, and betrixaban as selective ALDH1A1 inhibitors. The molecular docking, dynamics, and water swap analysis also suggested these drugs to be promising ALDH1A1 inhibitors which were further validated for their CP resistance reversal potential by in-vitro analysis. The in-vitro enzymatic assay results indicated that raloxifene and bazedoxifene selectively inhibited the ALDH1A1 enzyme with IC50 values of 2.35 and 4.41 μM respectively, whereas IC50 values of both the drugs against ALDH2 and ALDH3A1 was >100 μM. Additional in-vitro studies with well-reported ALDH1A1 overexpressing A549 and MIA paCa-2 cell lines suggested that mafosfamide sensitivity was further ameliorated by the combination of both raloxifene and bazedoxifene. Collectively, in-silico and in-vitro studies indicate raloxifene and bazedoxifene act as promising adjuvants with CP that may improve the quality of treatment for cancer patients with minimal toxicities.

Electrochemical Pressure Impedance Spectroscopy for Polymer Electrolyte Membrane Fuel Cells: Signal Interpretation

Electrochemical pressure impedance spectroscopy (EPIS) is an emerging tool for the diagnosis of polymer electrolyte membrane fuel cells (PEMFC). It is based on analyzing the frequency response of the cell voltage with respect to an excitation of the gas-phase pressure. Several experimental studies in the past decade have shown the complexity of EPIS signals, and so far there is no agreement on the interpretation of EPIS features. The present study contributes to shed light into the physicochemical origin of EPIS features, by using a combination of pseudo-two-dimensional modeling and analytical interpretation. Using static simulations, the contributions of cathode equilibrium potential, cathode overpotential, and membrane resistance on the quasi-static EPIS response are quantified. Using model reduction, the EPIS responses of individual dynamic processes are predicted and compared to the response of the full model. We show that the EPIS signal of the PEMFC studied here is dominated by the humidifier. The signal is further analyzed by using transfer functions between various internal cell states and the outlet pressure excitation. We show that the EPIS response of the humidifier is caused by an oscillating oxygen molar fraction due to an oscillating mass flow rate.

NMDA Receptors at Primary Afferent-Excitatory Neuron Synapses Differentially Sustain Chemotherapy- and Nerve Trauma-Induced Chronic Pain.

The spinal dorsal horn contains vesicular glutamate transporter-2 (VGluT2)-expressing excitatory neurons and vesicular GABA transporter (VGAT)-expressing inhibitory neurons, which normally have different roles in nociceptive transmission. Spinal glutamate NMDAR hyperactivity is a crucial mechanism of chronic neuropathic pain. However, it is unclear how NMDARs regulate primary afferent input to spinal excitatory and inhibitory neurons in neuropathic pain. Also, the functional significance of presynaptic NMDARs in neuropathic pain has not been defined explicitly. Here we showed that paclitaxel treatment or spared nerve injury (SNI) similarly increased the NMDAR-mediated mEPSC frequency and dorsal root-evoked EPSCs in VGluT2 dorsal horn neurons in male and female mice. By contrast, neither paclitaxel nor SNI had any effect on mEPSCs or evoked EPSCs in VGAT neurons. In mice with conditional Grin1 (gene encoding GluN1) KO in primary sensory neurons (Grin1-cKO), paclitaxel treatment failed to induce pain hypersensitivity. Unexpectedly, SNI still caused long-lasting pain hypersensitivity in Grin1-cKO mice. SNI increased the amplitude of puff NMDA currents in VGluT2 neurons and caused similar depolarizing shifts in GABA reversal potentials in WT and Grin1-cKO mice. Concordantly, spinal Grin1 knockdown diminished SNI-induced pain hypersensitivity. Thus, presynaptic NMDARs preferentially amplify primary afferent input to spinal excitatory neurons in neuropathic pain. Although presynaptic NMDARs are required for chemotherapy-induced pain hypersensitivity, postsynaptic NMDARs in spinal excitatory neurons play a dominant role in traumatic nerve injury-induced chronic pain. Our findings reveal the divergent synaptic connectivity and functional significance of spinal presynaptic and postsynaptic NMDARs in regulating cell type-specific nociceptive input in neuropathic pain with different etiologies.SIGNIFICANCE STATEMENT Spinal excitatory neurons relay input from nociceptors, whereas inhibitory neurons repress spinal nociceptive transmission. Chronic nerve pain is associated with aberrant NMDAR activity in the spinal dorsal horn. This study demonstrates, for the first time, that chemotherapy and traumatic nerve injury preferentially enhance the NMDAR activity at primary afferent-excitatory neuron synapses but have no effect on primary afferent input to spinal inhibitory neurons. NMDARs in primary sensory neurons are essential for chemotherapy-induced chronic pain, whereas nerve trauma causes pain hypersensitivity predominantly via postsynaptic NMDARs in spinal excitatory neurons. Thus, presynaptic and postsynaptic NMDARs at primary afferent-excitatory neuron synapses are differentially engaged in chemotherapy- and nerve injury-induced chronic pain and could be targeted respectively for treating these painful conditions.

Synergistic Interaction of Glycyrrhizin with Norfloxacin Displays ROS-Induced Bactericidal Activity against Multidrug-Resistant Staphylococcus aureus

Acquired bacterial resistance against several antibiotics has severely impaired the drug treatment regime. Multidrug-resistant Staphylococcus aureus (MDRSA) causes several life-threatening human pathologies. The introduction of novel antibiotics is a tedious process. Therefore, we have introduced glycyrrhizin (Gly) as a bioenhancer of norfloxacin (Nor), which showed synergistic interactions and a robust drug response. The drug resistance reversal potential of Gly against MDRSA was monitored. Gly and GlyNor (glycyrrhizin + norfloxacin) were used for spectrofluorometer and flow cytometry analysis for the measurement of free radicals and its effect upon cell membranes and macromolecules. Morphological analysis was carried out with the help of SEM. qRT-PCR analysis was conducted for gene regulation. Gly was observed to lower the MIC (minimum inhibitory concentration) of different groups of antibiotics up to 64-fold against MDRSA. GlyNor exerted oxidative stress, as evidenced by the measurement of reactive oxygen species (ROS) and their effect upon cell components. Gly and GlyNor showed membrane damage potential. The expression analysis of oxidative-related and MDR genes showed the up- and downregulation of these genes, respectively. GlyNor significantly lengthened post-antibiotic effects (PAE) and showed reduced mutation frequency rate (MFR). The synergistic bioenhancer properties of Gly with Nor and their enhanced ROS generation against MDRSA are reported for the first time in this study. Severe oxidative stress caused membrane damage, DNA fragmentation, transcriptional changes, and bacterial cell death. We strongly believe this could be a potential measure against rapidly evolving MDRSA.

Hydrogen Radical-Induced Electrocatalytic N2 Reduction at a Low Potential.

Realizing efficient hydrogenation of N2 molecules in the electrocatalytic nitrogen reduction reaction (NRR) is crucial in achieving high activity at a low potential because it theoretically requires a higher equilibrium potential than other steps. Analogous to metal hydride complexes for N2 reduction, achieving this step by chemical hydrogenation can weaken the potential dependence of the initial hydrogenation process. However, this strategy is rarely reported in the electrocatalytic NRR, and the catalytic mechanism remains ambiguous and lacks experimental evidence. Here, we show a highly efficient electrocatalyst (ruthenium single atoms anchored on graphdiyne/graphene sandwich structures) with a hydrogen radical-transferring mechanism, in which graphdiyne (GDY) generates hydrogen radicals (H•), which can effectively activate N2 to generate NNH radicals (•NNH). A dual-active site is constructed to suppress competing hydrogen evolution, where hydrogen preferentially adsorbs on GDY and Ru single atoms serve as the adsorption site of •NNH to promote further hydrogenation of NH3 synthesis. As a result, high activity and selectivity are obtained simultaneously at -0.1 V versus a reversible hydrogen electrode. Our findings illustrate a novel hydrogen transfer mechanism that can greatly reduce the potential and maintain the high activity and selectivity in NRR and provide powerful guidelines for the design concept of electrocatalysts.

Conditional deletion of KCC2 impairs synaptic plasticity and both spatial and nonspatial memory.

The postsynaptic inhibition through GABAA receptors (GABAAR) relies on two mechanisms, a shunting effect due to an increase in the postsynaptic membrane conductance and, in mature neurons, a hyperpolarization effect due to an entry of chloride into postsynaptic neurons. The second effect requires the action of the K+-Cl- cotransporter KCC2 which extrudes Cl- from the cell and maintains its cytosolic concentration very low. Neuronal chloride equilibrium seems to be dysregulated in several neurological and psychiatric conditions such as epilepsy, anxiety, schizophrenia, Down syndrome, or Alzheimer's disease. In the present study, we used the KCC2 Cre-lox knockdown system to investigate the role of KCC2 in synaptic plasticity and memory formation in adult mice. Tamoxifen-induced conditional deletion of KCC2 in glutamatergic neurons of the forebrain was performed at 3 months of age and resulted in spatial and nonspatial learning impairment. On brain slices, the stimulation of Schaffer collaterals by a theta burst induced long-term potentiation (LTP). The lack of KCC2 did not affect potentiation of field excitatory postsynaptic potentials (fEPSP) measured in the stratum radiatum (dendrites) but increased population spike (PS) amplitudes measured in the CA1 somatic layer, suggesting a reinforcement of the EPSP-PS potentiation, i.e., an increased ability of EPSPs to generate action potentials. At the cellular level, KCC2 deletion induced a positive shift in the reversal potential of GABAAR-driven Cl- currents (EGABA), suggesting an intracellular accumulation of chloride subsequent to the downregulation of KCC2. After treatment with bumetanide, an antagonist of the Na+-K+-Cl- cotransporter NKCC1, spatial memory impairment, chloride accumulation, and EPSP-PS potentiation were rescued in mice lacking KCC2. The presented results emphasize the importance of chloride equilibrium and GABA-inhibiting ability in synaptic plasticity and memory formation.

Cardiac PDGFRα+ interstitial cells generate spontaneous inward currents that contribute to excitability in the heart.

The cell types and conductance that contribute to normal cardiac functions remain under investigation. We used mice that express an enhanced green fluorescent protein (eGFP)-histone 2B fusion protein driven off the cell-specific endogenous promoter for Pdgfra to investigate the distribution and functional role of PDGFRα+ cells in the heart. Cardiac PDGFRα+ cells were widely distributed within the endomysium of atria, ventricle, and sino-atrial node (SAN) tissues. PDGFRα+ cells formed a discrete network of cells, lying in close apposition to neighboring cardiac myocytes in mouse and Cynomolgus monkey (Macaca fascicularis) hearts. Expression of eGFP in nuclei allowed unequivocal identification of these cells following enzymatic dispersion of muscle tissues. FACS purification of PDGFRα+ cells from the SAN and analysis of gene transcripts by qPCR revealed that they were a distinct population of cells that expressed gap junction transcripts, Gja1 and Gjc1. Cardiac PDGFRα+ cells generated spontaneous transient inward currents (STICs) and spontaneous transient depolarizations (STDs) that reversed at 0 mV. Reversal potential was maintained when ECl = -40 mV. [Na+ ]o replacement and FTY720 abolished STICs, suggesting they were due to a non-selective cation conductance (NSCC) carried by TRPM7. PDGFRα+ cells also express β2 -adrenoceptor gene transcripts, Adrb2. Zinterol, a selective β2 -receptor agonist, increased the amplitude and frequency of STICs, suggesting these cells could contribute to adrenergic regulation of cardiac excitability. PDGFRα+ cells in cardiac muscles generate inward currents via an NSCC. STICs generated by these cells may contribute to the integrated membrane potentials of cardiac muscles, possibly affecting the frequency of pacemaker activity.

Responses in fast-spiking interneuron firing rates to parameter variations associated with degradation of perineuronal nets

The perineuronal nets (PNNs) are sugar coated protein structures that encapsulate certain neurons in the brain, such as parvalbumin positive (PV) inhibitory neurons. As PNNs are theorized to act as a barrier to ion transport, they may effectively increase the membrane charge-separation distance, thereby affecting the membrane capacitance. Tewari et al. (2018) found that degradation of PNNs induced a 25%-50% increase in membrane capacitance c_text {m} and a reduction in the firing rates of PV-cells. In the current work, we explore how changes in c_text {m} affects the firing rate in a selection of computational neuron models, ranging in complexity from a single compartment Hodgkin-Huxley model to morphologically detailed PV-neuron models. In all models, an increased c_text {m} lead to reduced firing, but the experimentally reported increase in c_text {m} was not alone sufficient to explain the experimentally reported reduction in firing rate. We therefore hypothesized that PNN degradation in the experiments affected not only c_text {m}, but also ionic reversal potentials and ion channel conductances. In simulations, we explored how various model parameters affected the firing rate of the model neurons, and identified which parameter variations in addition to c_text {m} that are most likely candidates for explaining the experimentally reported reduction in firing rate.

Abstract LB275: Transcriptomic reversal analysis yields cytokines and drugs mediating tumor microenvironmental reprogramming during cancer progression and therapy response

Abstract Recent computational work links therapy response to a drug based on the drug’s ability to reverse a tumor’s transcriptome towards a healthy state. This idea of reversal has been used to mine databases of cell-line transcriptional responses against drug libraries to prioritize anti-cancer drugs. However, there are two key shortcomings in these approaches: (1) though cytokines and their receptors are proposed as modulators of therapy response, there is no reversal-based method to prioritize cytokines as potential drugs or targets, and (2) responses of microenvironmental cell types to drugs, which dictate therapy response, have not been considered. We address these limitations by exploiting recent databases of cytokine transcriptional response and single-cell RNA-seq datasets of patient responses to cancer therapies. We first used a novel approach to derive drug response signatures from LINCS data that retained the coordinated nature of gene expression changes occurring during treatment. We then used these signatures to compute a transcriptional reversal score that ranks drugs by their ability to reverse TCGA RNA-seq profiles of a tumor towards its corresponding normal in GTEx. We found that FDA-approved drugs in prostate, lung, colorectal and breast adenocarcinomas have a significantly higher reversal potential than unapproved drugs, and that these drugs are more effective at in vitro cell killing amongst CTRP and GDSC cell viability measurements. Next, we extended our signature derivation and reversal computation approach to find cytokines in the CytoSig database that can reverse TCGA RNA-seq profiles. We found that the higher the reversal potential of a cytokine, the greater its association with better overall patient survival. In particular, our approach revealed the IL10 family and IL24 as potentially therapeutic cytokines based on their predicted ability to reverse cell states across tumor types and indeed found them to be associated with better overall and progression-free survival in the TCGA cohort. Finally, in two clinical cohorts where RNA-seq was carried out on breast cancer and multiple myeloma patients before and after therapy, cell types within the tumor microenvironment of responders showed a stronger reversal towards a healthy state compared to non-responders. Altogether, our work establishes the importance of transcriptional reversal in therapy response, particularly the role of microenvironmental transcriptional alterations. This allows us to refine the reversal principle based on pan-cell type transcriptional effects and to identify cytokines that mediate patient survival as a new class of drugs and drug targets. This research was supported by the Intramural Research Program of the NIH, Citation Format: Vishaka Gopalan, Sridhar Hannenhalli. Transcriptomic reversal analysis yields cytokines and drugs mediating tumor microenvironmental reprogramming during cancer progression and therapy response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB275.

Acceleration of GABA-switch after early life stress changes mouse prefrontal glutamatergic transmission

Early life stress (ELS) alters the excitation-inhibition-balance (EI-balance) in various rodent brain areas and may be responsible for behavioral impairment later in life. The EI-balance is (amongst others) influenced by the switch of GABAergic transmission from excitatory to inhibitory, the so-called “GABA-switch”.Here, we investigated how ELS affects the GABA-switch in mouse infralimbic Prefrontal Cortex layer 2/3 neurons, using the limited-nesting-and-bedding model. In ELS mice, the GABA-switch occurred already between postnatal day (P) 6 and P9, as opposed to P15–P21 in controls. This was associated with increased expression of the inward chloride transporter NKCC1, compared to the outward chloride transporter KCC2, both of which are important for the intracellular chloride concentration and, hence, the GABA reversal potential (Erev). Chloride transporters are not only important for regulating chloride concentration postsynaptically, but also presynaptically. Depending on the Erev of GABA, presynaptic GABAA receptor stimulation causes a depolarization or hyperpolarization, and thereby enhanced or reduced fusion of glutamate vesicles respectively, in turn changing the frequency of miniature postsynaptic currents (mEPSCs). In accordance, bumetanide, a blocker of NKCC1, shifted the Erev GABA towards more hyperpolarized levels in P9 control mice and reduced the mEPSC frequency. Other modulators of chloride transporters, e.g. VU0463271 (a KCC2 antagonist) and aldosterone -which increases NKCC1 expression-did not affect postsynaptic Erev in ELS P9 mice, but did increase the mEPSC frequency. We conclude that the mouse GABA-switch is accelerated after ELS, affecting both the pre- and postsynaptic chloride homeostasis, the former altering glutamatergic transmission. This may considerably affect brain development.

High calcium transport by Polycystin-2 (TRPP2) induces channel clustering and oscillatory currents

The regulation by Ca2+ of Ca2+-permeable ion channels represents an important mechanism in the control of cell function. Polycystin-2 (PC2, TRPP2), a member of the TRP channel family (Transient Potential Receptor), is a Ca2+ permeable non-selective cation channel. Previous studies from our laboratory demonstrated that physiological concentrations of Ca2+ do not regulate in vitro translated PC2 (PC2iv) channel activity. However, the issue as to PC2′s Ca2+ permeability and regulation remain ill-defined, in particular because Ca2+ transport is usually observed in the presence of other ionic gradients. In this study, we assessed Ca2+ transport by PC2iv in a lipid bilayer reconstitution system in a high Ca2+ gradient (CaCl2 100 mM cis, CaCl2 10 mM trans) in the presence of either 3:7 or 7:3 1-palmitoyl-2-oleoyl-choline and ethanolamine lipid mixtures. Reconstituted PC2iv showed spontaneous Ca2+ currents in both lipid mixtures, with a maximum conductance of 63 ± 13 pS (n = 19) and 105 pS ± 9.8 (n = 9), respectively. In both cases, we best fitted the experimental data with the Goldman-Hodgkin-Katz equation, observing a reversal potential (Vrev ∼ −27 mV) consistent with strict Ca2+ selectivity. The R742X mutated PC2 (PC2R742X), lacking the carboxy terminal domain of the channel showed no differences with wild type PC2. Interestingly, we also observed the onset of spontaneous Ca2+ current oscillations whenever PC2-containing samples were reconstituted in the 3:7, but not 7:3 POPC:POPE lipid mixture. The amplitude and frequency of the ionic oscillations were highly dependent on the applied voltage, the imposed Ca2+ gradient, and the presence of high Ca2+, which induced PC2 channel clustering as observed by atomic force microscopy (AFM). We also used the QuB suite to kinetically model the PC2 channel Ca2+ oscillations based on the presence of subconductance states in the channel. The encompassed evidence supports a high Ca2+ permeability by PC2, and a novel oscillatory mechanism dependent on the presence of Ca2+ and phospholipids that provides the first evidence for the relation between stochasticity and deterministic processes mediated by ion channels.

A Mean-Field Firing-Rate Model for the Suprachiasmatic Nucleus

We present a mean-field formalism for modeling firing-rate statistics of brain regions whose neurons exhibit atypical firing patterns and heterogeneous electrophysiological properties. We apply the formalism to the suprachiasmatic nucleus (SCN)—the human circadian pacemaker—whose neurons can intrinsically exhibit depolarized low-amplitude membrane oscillations (DLAMOs), depolarization block (DB), and standard action potential firing at different times of day. Further, gamma-aminobutyric acid reversal potentials and molecular circadian phases of SCN neurons, among other properties, vary across the network and/or slowly over time. Our formalism consists of a system of integro-differential equations describing the time evolution of the mean and standard deviation of synaptic conductances across the network. Electrophysiological properties of SCN neurons are incorporated by computing responses to synaptic conductance inputs of a Hodgkin–Huxley-type SCN neuron model that exhibits DLAMOs and DB. Such responses are then averaged over distributions of relevant quantities and included in the differential equations. Results suggest mechanisms by which physiologically relevant changes to firing activities may arise, highlighting means by which the amplitude of firing rates may shrink, the standard deviation of firing rates may grow, and by which a mid-day dip in firing rates may appear. For instance, results show that a large spread in circadian phases across SCN neurons reduces the size of oscillations in SCN network firing activity across the 24-hour day, identifying a mechanism by which heterogeneities in neuron electrophysiology could influence circadian rhythms.

Ion exclusion, osmoregulation and management of oxidative stress improve salt tolerance in rice at seedling stage

Excess ion accumulation disturbs ionic homeostasis, creates an osmotic imbalance, and generates oxidative stress in plants under salinity stress. In the present experiment, the effect of salt stress at the seedling stage on the osmotic equilibrium and ROS scavenging potential was evaluated in ten differentially salt-sensitive rice genotypes. For this, the plants were grown hydroponically and salt stress equivalent to 12 dS m-1 was imposed at 3-4 leaf stages. The results showed that a few genotypes like FL478, AC41585, and AC39416A were able to maintain a lower Na+/K+ ratio in the leaf and thus proved more tolerant to salt stress than others. Additionally, these genotypes produced greater organic osmolytes (proline, glycine betaine, trehalose) and also had higher activities of key antioxidant enzymes (superoxide dismutase, catalase, peroxidase). On the contrary, Rashpanjor and CSR27 showed lesser ionic discrimination (higher leaf Na+/K+ ratio) but a moderate degree of salt tolerance, perhaps using Na+ effectively as an inorganic osmoticum to overcome stress. The susceptible genotypes like IR29 and Sabita were found extremely poor in restricting the upward movement of Na+, as well as the management of oxidative stress under saline conditions. From this study, we conclude that an efficient reactive oxygen species scavenging system along with greater osmotolerance helps to render salt tolerance at the seedling stage in rice.

Activation of mouse Otop3 proton channels by Zn2+

Otopetrins (Otop1-Otop3) belong to a newly identified family of proton (H+) channels activated by extracellular acidification. Here, we found that Zn2+ activates the mouse Otop3 (mOtop3) proton channels by using electrophysiological patch-clamp techniques. In mOtop3-expressing human embryonic kidney HEK293T cells, a biphasic inward mOtop3 H+ current comprising a fast transient current followed by a sustained current was observed upon extracellular acidification at pH 5.0. No significant activation of the mOtop3 channel was observed at pH 6.5 and 7.4, but interestingly, Zn2+ dose-dependently induced a sustained activation of mOtop3 under these pH conditions. Increasing the Zn2+ concentration had no effect on the reversal potential of the channel currents, suggesting that Zn2+ does not permeate through the mOtop3. The activation of the mOtop3 channel was specific to Zn2+ among divalent metal cations. Our findings reveal a novel modulatory mechanism of mOtop3 proton channels by Zn2+.

Bumetanide increases postsynaptic inhibition after chronic SCI and decreases presynaptic inhibition with step-training.

Current anti-spastic medication significantly compromises motor recovery after spinal cord injury (SCI), indicating a critical need for alternative interventions. Because a shift in chloride homeostasis decreases spinal inhibition and contributes to hyperreflexia after SCI, we investigated the effect of bumetanide, an FDA-approved sodium-potassium-chloride intruder (NKCC1) antagonist, on presynaptic and postsynaptic inhibition. We compared its effect with step-training as it is known to improve spinal inhibition by restoring chloride homeostasis. In SCI rats, a prolonged bumetanide treatment increased postynaptic inhibition but not presynaptic inhibition of the plantar H-reflex evoked by posterior biceps and semitendinosus (PBSt) group I afferents. By using in vivo intracellular recordings of motoneurons, we further show that a prolonged bumetanide increased postsynaptic inhibition by hyperpolarizing the reversal potential for inhibitory postsynaptic potentials (IPSPs) after SCI. However, in step-trained SCI rats an acute delivery of bumetanide decreased presynaptic inhibition of the H-reflex, but not postsynaptic inhibition. These results suggest that bumetanide might be a viable option to improve postsynaptic inhibition after SCI, but it also decreases the recovery of presynaptic inhibition with step-training. We discuss whether the effects of bumetanide are mediated by NKCC1 or by off-target effects. KEY POINTS: After spinal cord injury (SCI), chloride homeostasis is dysregulated over time in parallel with the decrease in presynaptic inhibition of Ia afferents and postsynaptic inhibition of motoneurons, and the development of spasticity. While step-training counteracts these effects, it cannot always be implemented in the clinic because of comorbidities. An alternative intervention is to use pharmacological strategies to decrease spasticity without hindering the recovery of motor function with step-training. Here we found that, after SCI, a prolonged bumetanide (an FDA-approved antagonist of the sodium-potassium-chloride intruder, NKCC1) treatment increases postsynaptic inhibition of the H-reflex, and it hyperpolarizes the reversal potential for inhibitory postsynaptic potentials in motoneurons. However, in step-trained SCI, an acute delivery of bumetanide decreases presynaptic inhibition of the H-reflex, but not postsynaptic inhibition. Our results suggest that bumetanide has the potential to decrease spastic symptoms related to a decrease in postsynaptic but not presynaptic inhibition after SCI.