Dependence Of Membrane Potential Research Articles

Dependence of cell's membrane potential on extracellular voltage observed in Chara globularis

The membrane potential (Vm) of a cell results from the selective movement of ions across the cell membrane. Recent studies have revealed the presence of a gradient of voltage within a few nanometers adjacent to erythrocytes. Very notably this voltage is modified in response to changes in cell's membrane potential thus effectively extending the potential beyond the membrane and into the solution. In this study, using the microelectrode technique, we provide experimental evidence for the existence of a gradient of negative extracellular voltage (Vz) in a wide zone close to the cell wall of algal cells, extending over several micrometers. Modulating the ionic concentration of the extracellular solution with CO2 alters the extracellular voltage and causes an immediate change in Vm. Elevated extracellular CO2 levels depolarize the cell and hyperpolarize the zone of extracellular voltage (ZEV) by the same magnitude. This observation strongly suggests a coupling effect between Vz and Vm. An increase in the level of intracellular CO2 (dark respiration) leads to hyperpolarization of the cell without any immediate effect on the extracellular voltage. Therefore, the metabolic activity of a cell can proceed without inducing changes in Vz. Conversely, Vz can be modified by external stimulation without metabolic input from the cell. The evolution of the ZEV, particularly around spines and wounded cells, where ion exchange is enhanced, suggests that the formation of the ZEV may be attributed to the exchange of ions across the cell wall and cell membrane. By comparing the changes in Vm in response to external stimuli, as measured by electrodes and observed using a potential-sensitive dye, we provide experimental evidence demonstrating the significance of extracellular voltage in determining the cell's membrane potential. This may have implications for our understanding of cell membrane potential generation beyond the activities of ion channels.

Super-Resolution Imaging of Voltages in the Interior of Individual, Vital Mitochondria.

We present super-resolution microscopy of isolated functional mitochondria, enabling real-time studies of structure and function (voltages) in response to pharmacological manipulation. Changes in mitochondrial membrane potential as a function of time and position can be imaged in different metabolic states (not possible in whole cells), created by the addition of substrates and inhibitors of the electron transport chain, enabled by the isolation of vital mitochondria. By careful analysis of structure dyes and voltage dyes (lipophilic cations), we demonstrate that most of the fluorescent signal seen from voltage dyes is due to membrane bound dyes, and develop a model for the membrane potential dependence of the fluorescence contrast for the case of super-resolution imaging, and how it relates to membrane potential. This permits direct analysis of mitochondrial structure and function (voltage) of isolated, individual mitochondria as well as submitochondrial structures in the functional, intact state, a major advance in super-resolution studies of living organelles.

Analysis of seed quality indicators based on neural network

The paper presents a neural network study of the data of wheat seed quality. It is established that the analysis of bioelectrical signals of wheat seeds based on a neural network can be used in practice for the solution of two problems - diagnostics of seed material quality and the evaluation of cleaning line quality (separation into fractions). The paper presents the results of initial data preparation, formation of a neural network, analysis of training data for two practical problems of classification. It was established using a neural network that there is a nonlinear dependence of the membrane potential maximum value and the signal rise time on the seed yield. The model makes it possible to predict yield in terms of the seed material quality. A nonlinear dependence of the maximum membrane potential, the signal rise time of wheat seeds and the seeds variety to one or another faction (speed of separation into the fractions in this example) was also established in this paper. Studies have shown that the seeds variety is an important informative feature for solving the problem of classifying seeds by fractions. Therefore, it is necessary to conduct additional studies with other wheat seeds varieties to apply this method in practice.

Modulation of TRPC store‐operated channels by Orai and STIM proteins

Store‐operated calcium entry is significant pathway of calcium concentration rise in cytoplasm. The main players in this process are Orai store‐operated channels, which are activated directly by STIM calcium sensors. Data on participation of TRPC channels in store‐operated calcium entry is controversial.Study was focused on interaction between STIM and Orai proteins with endogenous TRPC and its role in pathology. We investigated activity of TRPC channels in a model object — HEK293 cells and in the podocytes of the rat model of diabetic nephropathy, using single channel recording patch camp technique.To eliminate Orai channels activity in HEK293 cells we used several experimental approaches: overexpression of dominant‐negative Orai mutant, Orai genes knockout and knockdown via CRISPR‐Cas 9 system and shRNA. Endogenous TRPC1 channels remain active in cells without functional Orai proteins and become insensitive to store depletion.In experiments with different extracellular calcium concentration we confirmed that calcium entry is needed for TRPC1 activation by store depletion.In experiments with calcium, barium or sodium as a charge carrier we observed similarities in dependence of open channel probability versus membrane potential between TRPC1 and Orai channels.The role of STIM calcium sensors in TRPC1 channels activation was investigated in cells with different expression level of STIM1 and STIM2 proteins.The findings allow us to propose that STIM proteins don’t activate the endogenous TRPC channels directly. TRPC channels are activated downstream to calcium entry through the Orai channels.Support or Funding InformationThe study was supported by grant of Russian science foundation № 19‐14‐00114 (Glushankova L., Skopin A., Kaznacheyeva E.), and by grant of Russian foundation for basic research № 19‐315‐90065 (Shalygin A., Kolesnikov D.).

Method of Determining Seed Germination by Using Membrane Potential of Wheat Seeds

Introduction. The germination of wheat seeds is an important indicator of their quality, used to calculate and adjust the seeding rate. It is necessary to take into account germination changes at the storage stage. The solution of this problem will be development of a method that will allow to determinate germination at any technological stage (at the stage of harvesting, storage, seeding).The aim of the article is to study the dependence of membrane potential on grain quality, to develop a method for determining the germination of wheat seeds based on their membrane potentials. Materials and Methods. The authors' review of research papers about methods of assessing the wheat seeds quality indicates the need for the development of highly sensitive methods of the germination test, which allow one to ensure the speed of measurement and obtain more accurate results for further use. An approach was developed on the basis of the review, which allows for solving the problem using the method based on the study of membrane potentials of wheat seeds. Results. In this article, the study of the dependence of wheat seeds membrane potential from their germination was conducted. The results of experiments confirmed that the value of the potential could be used as quality assessment parameter. The requirements and optimal conditions for conducting the experiment were determined. Discussion and Conclusion. The dependence of the wheat seeds membrane potential on their germination was established and the method for determining wheat seeds germination was developed. The implementation of this method will allow agricultural enterprises and farms to carry out the rapid assessment of wheat seeds germination at any technological stage (at the stage of harvesting, storage, seeding).

Modelling of Electrochemically Switchable Ion Transport in Nanoporous Membranes with Conductive Surface

The impact of potential applied to the conductive surface of nanoporous membrane on the membrane potential at zero current is investigated theoretically on the basis of two–dimensional Space–charge model. The membrane separates two reservoirs with different salt concentrations. It is shown that the variation of applied potential from negative to positive values results in the continuous change of membrane selectivity from cation to anion. For equal ion diffusion coefficients, the dependence of membrane potential on the applied potential is an odd function, while for different ion diffusion coefficients it is shifted along the applied potential axis due to contribution of diffusion potential enhanced by the induced charge effect. The decrease of pore radius results in the increase of ionic selectivity and steep transition between cation– selective and anion–selective states when the applied potential is changing

A Computer Simulation of an Intracellular Mechanism for the Generation and Suppression of Cardiac Arrhythmias

Abstract—This paper reports an analysis of a stochastic model of ion dynamics in the cardiac pacemaker cell within the framework of the generalized two-oscillator Maltsev–Lakatta model, including the electron-conformational model of ryanodine receptors. It has been demonstrated that generation of an action potential depends significantly on the nature of the interaction between the external membrane and the internal (Ca2+ clock) oscillators. Constructive interaction between oscillators leads to the formation of a stable action potential, while destructive interaction leads to parasitic effects, in particular, to arrhythmias. The effects of the model parameters that are characteristic of the rabbit sinoatrial heart node on the shape of the time dependence of the cell membrane potential has been investigated. The conditions under which spontaneous transition to the abnormally fast oscillatory mode takes place have been determined and the mechanism of this transition has been described; the pacemaker cell behavior in tachycardia has actually been simulated. It has been demonstrated that suppression of the rapid potassium current leads to the recovery of the normal oscillation mode of ion dynamics in a pacemaker cell, which corresponds to the mode of action of class III antiarrhythmic agents.

Membrane potential and delta pH dependency of reverse electron transport-associated hydrogen peroxide production in brain and heart mitochondria

Succinate-driven reverse electron transport (RET) is one of the main sources of mitochondrial reactive oxygen species (mtROS) in ischemia-reperfusion injury. RET is dependent on mitochondrial membrane potential (Δψm) and transmembrane pH difference (ΔpH), components of the proton motive force (pmf); a decrease in Δψm and/or ΔpH inhibits RET. In this study we aimed to determine which component of the pmf displays the more dominant effect on RET-provoked ROS generation in isolated guinea pig brain and heart mitochondria respiring on succinate or α-glycerophosphate (α-GP). Δψm was detected via safranin fluorescence and a TPP+ electrode, the rate of H2O2 formation was measured by Amplex UltraRed, the intramitochondrial pH (pHin) was assessed via BCECF fluorescence. Ionophores were used to dissect the effects of the two components of pmf. The K+/H+ exchanger, nigericin lowered pHin and ΔpH, followed by a compensatory increase in Δψm that led to an augmented H2O2 production. Valinomycin, a K+ ionophore, at low [K+] increased ΔpH and pHin, decreased Δψm, which resulted in a decline in H2O2 formation. It was concluded that Δψm is dominant over ∆pH in modulating the succinate- and α-GP-evoked RET. The elevation of extramitochondrial pH was accompanied by an enhanced H2O2 release and a decreased ∆pH. This phenomenon reveals that from the pH component not ∆pH, but rather absolute value of pH has higher impact on the rate of mtROS formation. Minor decrease of Δψm might be applied as a therapeutic strategy to attenuate RET-driven ROS generation in ischemia-reperfusion injury.

Persistent Sodium Current Mediates the Steep Voltage Dependence of Spatial Coding in Hippocampal Pyramidal Neurons

The mammalian hippocampus forms a cognitive map using neurons that fire according to an animal's position ("place cells") and many other behavioral and cognitive variables. The responses of these neurons are shaped by their presynaptic inputs and the nature of their postsynaptic integration. In CA1 pyramidal neurons, spatial responses invivo exhibit a strikingly supralinear dependence on baseline membrane potential. The biophysical mechanisms underlying this nonlinear cellular computation are unknown. Here, through a combination of invitro, invivo, and in silico approaches, we show that persistent sodium current mediates the strong membrane potential dependence of place cell activity. This current operates at membrane potentials below the action potential threshold and over seconds-long timescales, mediating a powerful and rapidly reversible amplification of synaptic responses, which drives place cell firing. Thus, we identify a biophysical mechanism that shapes the coding properties of neurons composing the hippocampal cognitive map.

Relocation of active site carboxylates in major facilitator superfamily multidrug transporter LmrP reveals plasticity in proton interactions.

The expression of polyspecific membrane transporters is one important mechanism by which cells can obtain resistance to structurally different antibiotics and cytotoxic agents. These transporters reduce intracellular drug concentrations to subtoxic levels by mediating drug efflux across the cell envelope. The major facilitator superfamily multidrug transporter LmrP from Lactococcus lactis catalyses drug efflux in a membrane potential and chemical proton gradient-dependent fashion. To enable the interaction with protons and cationic substrates, LmrP contains catalytic carboxyl residues on the surface of a large interior chamber that is formed by transmembrane helices. These residues co-localise together with polar and aromatic residues, and are predicted to be present in two clusters. To investigate the functional role of the catalytic carboxylates, we generated mutant proteins catalysing membrane potential-independent dye efflux by removing one of the carboxyl residues in Cluster 1. We then relocated this carboxyl residue to six positions on the surface of the interior chamber, and tested for restoration of wildtype energetics. The reinsertion at positions towards Cluster 2 reinstated the membrane potential dependence of dye efflux. Our data uncover a remarkable plasticity in proton interactions in LmrP, which is a consequence of the flexibility in the location of key residues that are responsible for proton/multidrug antiport.

Theoretical study of electrolyte transport in nanofiltration membranes with constant surface potential/charge density

The pressure–driven electrolyte transport through nanofiltration membrane pores with constant surface potential or charge density is investigated theoretically. Two approaches are employed in the study. The first one is based on one–dimensional Nernst–Planck equation coupled with electroneutrality, zero current, and Donnan equilibrium conditions. This model is extended to account for interfacial effects by using a smooth approximation of step function for the volume charge density. The second approach is based on two–dimensional Nernst–Planck, Poisson, and Navier–Stokes equations, which are solved in a high aspect ratio nanopore connecting two reservoirs with much larger diameter. The modification of equations on the basis of Slotboom transformation is employed to speed up the convergence rate. The distributions of potential, pressure, ion concentrations and fluxes due to convection, diffusion, and migration in the nanopore and reservoirs are discussed and analyzed. It is found that for constant surface charge density, the convective flux of counter–ions in the nanopore is almost completely balanced by the opposite migration flux, while for constant surface potential, the convective flux is balanced by the opposite diffusion and migration fluxes. The co–ions in the nanopore are mainly transported by diffusion. A particular attention is focused on describing the interfacial effects at the nanopore entrance/exit. Detailed comparison between one– and two–dimensional models is performed in terms of rejection, pressure drop, and membrane potential dependence on the surface potential/charge density, volume flux, ion concentration, and pore radius. A good agreement between these models is found when the Debye length is smaller than the pore radius and the surface potential or charge density are sufficiently low.

A mutation in the low voltage-gated calcium channel CACNA1G alters the physiological properties of the channel, causing spinocerebellar ataxia.

BackgroundSpinocerebellar ataxia (SCA) is a genetically heterogeneous disease. To date, 36 dominantly inherited loci have been reported, and 31 causative genes have been identified.ResultsIn this study, we analyzed a Japanese family with autosomal dominant SCA using linkage analysis and exome sequencing, and identified CACNA1G, which encodes the calcium channel CaV3.1, as a new causative gene. The same mutation was also found in another family with SCA. Although most patients exhibited the pure form of cerebellar ataxia, two patients showed prominent resting tremor in addition to ataxia. CaV3.1 is classified as a low-threshold voltage-dependent calcium channel (T-type) and is expressed abundantly in the central nervous system, including the cerebellum. The mutation p.Arg1715His, identified in this study, was found to be located at S4 of repeat IV, the voltage sensor of the CaV3.1. Electrophysiological analyses revealed that the membrane potential dependency of the mutant CaV3.1 transfected into HEK293T cells shifted toward a positive potential. We established induced pluripotent stem cells (iPSCs) from fibroblasts of the patient, and to our knowledge, this is the first report of successful differentiation from the patient-derived iPSCs into Purkinje cells. There was no significant difference in the differentiation status between control- and patient-derived iPSCs.ConclusionsTo date, several channel genes have been reported as causative genes for SCA. Our findings provide important insights into the pathogenesis of SCA as a channelopathy.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-015-0180-4) contains supplementary material, which is available to authorized users.

Preparation, characterization and study of nanofiltration composite membrane: Electrochemical and optical properties

The polystyrene based molybdate composite membranes were prepared by the sol–gel method by applying different pressures. XRD data shows that formation of nanocomposite and exhibit no other impurity phase. The membrane potential is found to be effected by both pressure and ion concentration. The effective charge density of these membranes was determined by TMS method and reveal dependence of membrane potential on physicochemical properties. The change in membrane capacitance and resistance values with the change in electrolyte concentration and applied frequency had been interpreted in terms of the charges produced in the electrical double layer at the membrane solution interface.

Calcium permeable AMPA receptor-dependent long lasting plasticity of intrinsic excitability in fast spiking interneurons of the dentate gyrus decreases inhibition in the granule cell layer.

The local fast-spiking interneurons (FSINs) are considered to be crucial for the generation, maintenance, and modulation of neuronal network oscillations especially in the gamma frequency band. Gamma frequency oscillations have been associated with different aspects of behavior. But the prolonged effects of gamma frequency synaptic activity on the FSINs remain elusive. Using whole cell current clamp patch recordings, we observed a sustained decrease of intrinsic excitability in the FSINs of the dentate gyrus (DG) following repetitive stimulations of the mossy fibers at 30 Hz (gamma bursts). Surprisingly, the granule cells (GCs) did not express intrinsic plastic changes upon similar synaptic excitation of their apical dendritic inputs. Interestingly, pairing the gamma bursts with membrane hyperpolarization accentuated the plasticity in FSINs following the induction protocol, while the plasticity attenuated following gamma bursts paired with membrane depolarization. Paired pulse ratio measurement of the synaptic responses did not show significant changes during the experiments. However, the induction protocols were accompanied with postsynaptic calcium rise in FSINs. Interestingly, the maximum and the minimum increase occurred during gamma bursts with membrane hyperpolarization and depolarization respectively. Including a selective blocker of calcium-permeable AMPA receptors (CP-AMPARs) in the bath; significantly attenuated the calcium rise and blocked the membrane potential dependence of the calcium rise in the FSINs, suggesting their involvement in the observed phenomenon. Chelation of intracellular calcium, blocking HCN channel conductance or blocking CP-AMPARs during the experiment forbade the long lasting expression of the plasticity. Simultaneous dual patch recordings from FSINs and synaptically connected putative GCs confirmed the decreased inhibition in the GCs accompanying the decreased intrinsic excitability in the FSINs. Experimentally constrained network simulations using NEURON predicted increased spiking in the GC owing to decreased input resistance in the FSIN. We hypothesize that the selective plasticity in the FSINs induced by local network activity may serve to increase information throughput into the downstream hippocampal subfields besides providing neuroprotection to the FSINs.

Synthesis, characterization and electrochemical properties of cation selective ion exchange composite membranes

In this work polystyrene based strontium phosphate membranes (SPMs) were prepared by applying different pressures. The membrane potential is measured with uni-univalent electrolytes (KCl, NaCl, and LiCl) solutions using saturated calomel electrodes (SCEs). The effective fixed charge density of these membranes is determined by the Torell, Meyer and Sievers method and it showed the dependence of membrane potential on the porosity, the charge on the membrane matrix, charge and size of permeating ions. The membranes are characterized by X-ray diffraction, scanning electron microscopy and IR spectroscopy. The order of surface charge density for electrolytes is KCl>NaCl>LiCl. Other parameters such as transport number, distribution coefficient, charge effectiveness and related parameters are calculated. The membrane was found to be mechanically stable, and can be operated over a wide pH range.

Joint analysis of flow cytometry data and fluorescence spectra as a non-negative array factorization problem

The paper presents a novel approach to the processing of flow cytometry data sequences. It consists in decomposing a sequence of multidimensional probability density functions by using the multilinear block tensor decomposition approach [1,2]. Also a formal link between flow cytometry data and fluorescence spectra is provided allowing the joint processing of both data. To illustrate the effectiveness of the approach, a study of the T47D cell line mitochondrial membrane potential as a function of the CCCP decoupling agent concentration is performed. The main advantages of the method are: (i) the flow cytometry data compensation is no longer necessary, and (ii) the cell sorting capacity of the method is significantly improved as compared to classical clustering methods. As a byproduct, it was possible to observe directly on the result of the processing, the dependence of the cell mitochondrial membrane potential with respect to the cell cycle phase. The proposed method is quite general provided that it is possible to design an experiment allowing the observation of the response of cell populations to an environmental/chemical/biological parameter.

PREPARATION, CHARACTERIZATION AND ELECTROCHEMICAL PROPERTIES OF CATION SELECTIVE MEMBRANES

Polystyrene based strontium phosphate membranes (SPM) prepared by applying different pressures. The membrane potential was measured with uni-univalent electrolytes (KCl, NaCl, and LiCl) solutions using saturated calomel electrode (SCEs). The effective fixed charge density of these membranes was determined by TMS method and it showed dependence of membrane potential on the porosity, charge on the membrane matrix, charge and size of permeating ions. The membranes were characterized by X-ray diffraction, scanning electron microscopy, and IR spectroscopy. The order of surface charge density for electrolytes is found to be KCl > NaCl > LiCl. Other important parameters such as transport number, distribution coefficient, charge effectiveness and related parameters were calculated. The membrane was found to be mechanically stable, and can be operated over a wide pH range. Moreover, the experimental results were found to be quite satisfactorily with theoretical values.

Synthesis, characterization and influence of electrolyte solutions on electrical properties of organic–inorganic composite membrane

In this work various electrical properties of titanium molybdate composite membrane had been discussed. The membrane was characterized by X-ray diffraction, scanning electron microscopy, particle size analysis and Infra-red spectroscopy. The effective fixed charge density of the membrane was determined by TMS method and it showed the dependence of membrane potential on, the charge on the membrane matrix, porosity and size of permeating ions. The change in membrane capacitance and resistance values with the change in electrolyte concentration and applied frequency had been interpreted in terms of the charges produced in the electrical double layer at the membrane solution interface. The magnitude of membrane capacitance had been found to be dependent on the capacitance of the double layer. In higher frequency range the impedance data evaluated on the basis of simple equivalent electrical circuit model and had been found to follow theoretical prediction. Other parameters such as transport number, distribution coefficient and charge effectiveness were also calculated.

Calpain Inhibition Reduces Amplitude and Accelerates Decay of the Late Sodium Current in Ventricular Myocytes from Dogs with Chronic Heart Failure

Calpain is an intracellular Ca2+ -activated protease that is involved in numerous Ca2+ dependent regulation of protein function in many cell types. This paper tests a hypothesis that calpains are involved in Ca2+ -dependent increase of the late sodium current (INaL) in failing heart. Chronic heart failure (HF) was induced in 2 dogs by multiple coronary artery embolization. Using a conventional patch-clamp technique, the whole-cell INaL was recorded in enzymatically isolated ventricular cardiomyocytes (VCMs) in which INaL was activated by the presence of a higher (1μM) intracellular [Ca2+] in the patch pipette. Cell suspensions were exposed to a cell- permeant calpain inhibitor MDL-28170 for 1–2 h before INaL recordings. The numerical excitation-contraction coupling (ECC) model was used to evaluate electrophysiological effects of calpain inhibition in silico. MDL caused acceleration of INaL decay evaluated by the two-exponential fit (τ1 = 42±3.0 ms τ2 = 435±27 ms, n = 6, in MDL vs. τ1 = 52±2.1 ms τ2 = 605±26 control no vehicle, n = 11, and vs. τ1 = 52±2.8 ms τ2 = 583±37 ms n = 7, control with vehicle, P<0.05 ANOVA). MDL significantly reduced INaL density recorded at –30 mV (0.488±0.03, n = 12, in control no vehicle, 0.4502±0.0210, n = 9 in vehicle vs. 0.166±0.05pA/pF, n = 5, in MDL). Our measurements of current-voltage relationships demonstrated that the INaL density was decreased by MDL in a wide range of potentials, including that for the action potential plateau. At the same time the membrane potential dependency of the steady-state activation and inactivation remained unchanged in the MDL-treated VCMs. Our ECC model predicted that calpain inhibition greatly improves myocyte function by reducing the action potential duration and intracellular diastolic Ca2+ accumulation in the pulse train.ConclusionsCalpain inhibition reverses INaL changes in failing dog ventricular cardiomyocytes in the presence of high intracellular Ca2+. Specifically it decreases INaL density and accelerates INaL kinetics resulting in improvement of myocyte electrical response and Ca2+ handling as predicted by our in silico simulations.

Preparation and characterization of polystyrene based Nickel molybdate composite membrane electrical–electrochemical properties

The functional properties of the polystyrene based Nickel Molybdate composite membrane prepared by applying 70MPa pressure are described. The fabricated membrane was characterized by using Fourier Transform Infrared, X-ray diffraction, particle size analyzer and Scanning electron microscopy technique and has been investigated for its functional, diffusive, electrochemical and electrical properties. The impedance data of membrane having capacitive and resistive components are plotted, which show the sequence of semicircles representing an electrical phenomenon due to grain material, grain boundary and interfacial phenomenon. The diffusion of electrolytes was determined by the TMS method revealing dependence of membrane potential on the charge on the membrane matrix, charge and size of permeating ions. The membrane determined the activity of cations with good accuracy in the higher concentration range and shows a great selectivity for K+. Other electrochemical properties like transport number have been discussed its selectivity.