Changes In Electrical Potential Research Articles

The V499G/Y501H Mutation Impairs Fast Motor Kinetics of Prestin and Has Significance for Defining Functional Independence of Individual Prestin Subunits

Outer hair cells (OHCs) are a mammalian innovation for mechanically amplifying sound energy to overcome the viscous damping of the cochlear partition. Although the voltage-dependent OHC membrane motor, prestin, has been demonstrated to be essential for mammalian cochlear amplification, the molecular mechanism by which prestin converts electrical energy into mechanical displacement/force remains elusive. Identifying mutations that alter the motor function of prestin provides vital information for unraveling the energy transduction mechanism of prestin. We show that the V499G/Y501H mutation does not deprive prestin of its voltage-induced motor activity, but it does significantly impair the fast motor kinetics and voltage operating range. Furthermore, mutagenesis studies suggest that Val-499 is the primary site responsible for these changes. We also show that V499G/Y501H prestin forms heteromers with wild-type prestin and that the fast motor kinetics of wild-type prestin is not affected by heteromer formation with V499G/Y501H prestin. These results suggest that prestin subunits are individually functional within a given multimer.

On the theory of action potential propagation in plant cells

The distribution of an electric field in plant cells and zooblasts has been investigated at propagation of the action potential. The behavior of ions in the cytoplasm and in the extracellular fluid has been described with the equations of electric charge motion in the electrolytes. It has been shown that the action potential causes an electric potential change not only in the depth of the cytoplasm but also in the extracellular area far from the lipidic bilayer. The biomembrane resistance has been expressed by physical parameters of a cell, such as ionic diffusion coefficient in fluid, Debye-Huckel radius, dielectric conductivity etc. The presence of breakings in the action potential diagrams has been explained as a result of insufficient resolving power of the measuring devices at the instant the sodium ionic canals of the bilayer opens.

Microscopic Origin of Gating Current Fluctuations in a Potassium Channel Voltage Sensor

Voltage-dependent ion channels open and close in response to changes in membrane electrical potential due to the motion of their voltage-sensing domains (VSDs). VSD charge displacements within the membrane electric field are observed in electrophysiology experiments as gating currents preceding ionic conduction. The elementary charge motions that give rise to the gating current cannot be observed directly, but appear as discrete current pulses that generate fluctuations in gating current measurements. Here we report direct observation of gating-charge displacements in an atomistic molecular dynamics simulation of the isolated VSD from the KvAP channel in a hydrated lipid bilayer on the timescale (10-μs) expected for elementary gating charge transitions. The results reveal that gating-charge displacements are associated with the water-catalyzed rearrangement of salt bridges between the S4 arginines and a set of conserved acidic side chains on the S1–S3 transmembrane segments in the hydrated interior of the VSD.

Voltage-sensor cycle fully described

Ion channels provide the most rapid way of communication between the cell interior and the external environment by exploiting the differences in electrolyte composition between the internal and external cellular milieu to transmit electrical and chemical signals (1). Voltage-gated ion channels in particular open and close in response to changes in the membrane electrical potential. Voltage-gated K+ and Na+ channels induce nerve impulses whereas voltage-gated Ca2+ channels initiate muscle contraction and other cellular processes (1). High-resolution X-ray crystallographic structures of some of these proteins have already been determined, showing that they are composed of four subunits, each consisting of six transmembrane segments (S1–S6) and forming two functionally linked, although structurally independent, domains (2⇓–4). The ion conduction pore responsible for selectivity is formed by helices S5 and S6. This pore domain is surrounded by the loosely adherent segments, S1 to S4, which form the voltage sensor. S3 is actually composed of two helices referred as S3a and S3b. S3b forms with S4 a helix–turn–helix called the voltage-sensor paddle (3). The fourth transmembrane helix, S4, is the primary voltage-sensing unit. Four to seven positively charged amino acid spaced at intervals of three in the S4 helix and known as gating charges, and some negatively charged residues distributed in S1, S2, and S3, …

Observing a model ion channel gating action in model cell membranes in real time in situ: membrane potential change induced alamethicin orientation change.

Ion channels play crucial roles in transport and regulatory functions of living cells. Understanding the gating mechanisms of these channels is important to understanding and treating diseases that have been linked to ion channels. One potential model peptide for studying the mechanism of ion channel gating is alamethicin, which adopts a split α/3(10)-helix structure and responds to changes in electric potential. In this study, sum frequency generation vibrational spectroscopy (SFG-VS), supplemented by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), has been applied to characterize interactions between alamethicin (a model for larger channel proteins) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayers in the presence of an electric potential across the membrane. The membrane potential difference was controlled by changing the pH of the solution in contact with the bilayer and was measured using fluorescence spectroscopy. The orientation angle of alamethicin in POPC lipid bilayers was then determined at different pH values using polarized SFG amide I spectra. Assuming that all molecules adopt the same orientation (a δ distribution), at pH = 6.7 the α-helix at the N-terminus and the 3(10)-helix at the C-terminus tilt at about 72° (θ(1)) and 50° (θ(2)) versus the surface normal, respectively. When pH increases to 11.9, θ(1) and θ(2) decrease to 56.5° and 45°, respectively. The δ distribution assumption was verified using a combination of SFG and ATR-FTIR measurements, which showed a quite narrow distribution in the angle of θ(1) for both pH conditions. This indicates that all alamethicin molecules at the surface adopt a nearly identical orientation in POPC lipid bilayers. The localized pH change in proximity to the bilayer modulates the membrane potential and thus induces a decrease in both the tilt and the bend angles of the two helices in alamethicin. This is the first reported application of SFG to the study of model ion channel gating mechanisms in model cell membranes.

Nonlinear vibration of embedded SWBNNTs based on nonlocal Timoshenko beam theory using DQ method

In the present work, effect of von Kàrmàn geometric nonlinearity on the vibration behavior of a single-walled boron nitride nanotube (SWBNNT) is investigated based on nonlocal piezoelasticity theory. The SWBNNT is considered as a nanobeam within the framework of Timoshenko beam (TB). Loading is composed of a temperature change and an imposed axially electric potential throughout the SWBNNT. The interactions between the SWBNNT and its surrounding elastic medium are simulated by Winkler and Pasternak foundation models. The higher order governing equations of motion are derived using Hamilton's principle and the numerical solution of equations is obtained using Differential Quadrature (DQ) method. The effects of geometric nonlinearity, elastic foundation modulus, electric potential field, temperature change and nonlocal parameter on the frequency of the SWBNNT are studied in detail.

Evolution of the Voltage Sensor Domain of the Voltage-Sensitive Phosphoinositide Phosphatase VSP/TPTE Suggests a Role as a Proton Channel in Eutherian Mammals

The voltage-sensitive phosphoinositide phosphatases provide a mechanism to couple changes in the transmembrane electrical potential to intracellular signal transduction pathways. These proteins share a domain architecture that is conserved in deuterostomes. However, gene duplication events in primates, including humans, give rise to the paralogs TPTE and TPTE2 that retain protein domain organization but, in the case of TPTE, have lost catalytic activity. Here, we present evidence that these human proteins contain a functional voltage sensor, similar to that in nonmammalian orthologs. However, domains of these human proteins can also generate a noninactivating outward current that is not observed in zebra fish or tunicate orthologs. This outward current has the anticipated characteristics of a voltage-sensitive proton current and is due to the appearance of a single histidine residue in the S4 transmembrane segment of the voltage sensor. Histidine is observed at this position only during the eutherian radiation. Domains from both human paralogs generate proton currents. This apparent gain of proton channel function during the evolution of the TPTE protein family may account for the conservation of voltage sensor domains despite the loss of phosphatase activity in some human paralogs.

Jasmonic acid accumulation and systemic photosynthetic and electrical changes in locally burned wild type tomato, ABA-deficient sitiens mutants and sitiens pre-treated by ABA

Burning the terminal leaflet of younger tomato (Lycopersicon esculentum Mill.) leaf caused local and systemic changes in the surface electrical potential (SEP) and gas exchange (GE) parameters. The local and systemic accumulation of endogenous abscisic acid (ABA) and jasmonic acid (JA) was measured 85min after burning. The experiments were conducted with wild type (WT) plants, ABA-deficient mutant sitiens (SIT) and ABA pre-treated SIT plants (SITA). First changes in SEP were detected within 1.5min after burning and were followed by a decrease in GE parameters within 3-6min in WT, SIT and SITA plants. GE and SEP time courses of SIT were different and wave amplitudes of SEP of SIT were lower compared to WT and SITA. ABA content in WT and SITA control plants was similar and substantially higher compared to SIT, JA content was similar among WT, SIT and SITA. While changes in the ABA content in systemic leaves have not been recorded after burning, the systemic JA content was substantially increased in WT and more in SIT and SITA. The results suggest that ABA content governs the systemic reaction of GE and the SEP shape upon local burning. ABA, JA and SEP participate in triggering the GE reaction. The ABA shortage in the SIT in the reaction to burning is partly compensated by an enhanced JA accumulation. This JA compensation is maintained even in SIT endogenously supplied with ABA. A correlation between the systemic JA content and changes in GE parameters or SEP was not found.

Microscopic Origin of Gating Current Fluctuations in a Potassium Channel Voltage Sensor

Voltage-sensing domains (VSDs) regulate the opening of voltage-dependent ion channels in response to changes in membrane electrical potential. They are comprised of four transmembrane segments (S1 through S4) and their overall architecture is conserved from Archaea to mammals. VSD charge displacements within the membrane electric field after a sudden change in membrane potential are measured in electrophysiology experiments as capacitive currents, termed gating currents, which precede ion conduction. The elementary charge motions that give rise to the gating current appear as shot-like events in high-bandwidth recordings of gating current fluctuations, but cannot be observed directly due to limitations of present recording technology. To characterize the conformational dynamics of the VSD under an applied membrane potential, we performed all-atom MD simulations of the isolated Kv VSD from Aeropyrum pernix (KvAP) in a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer in excess water under a constant electric field on the timescale (10-μs) expected for elementary gating charge transitions. The results suggest that shot-like events of gating current are associated with the water-catalyzed rearrangement of salt bridges between the S4 arginines and a set of conserved acidic side chains on the S1-S3 transmembrane segments in the hydrated interior of the VSD. Research supported by NIH grants GM74637 and GM86685 and NSF grant CHE-0750175. The computations were carried out on the Anton computer at the National Resource for Biomedical Supercomputing at the Pittsburgh Supercomputing Center, which is funded by NIH grant RC2GM093307.

Spreading Depolarization, A Pathophysiological Mechanism of Stroke and Migraine Aura

Spreading depolarization is a mechanism of abrupt, massive ion translocation between intraneuronal and extracellular space that entails cytotoxic edema in the brain’s gray matter. It is observed in patients as a large change of the slow electrical potential. Dependent on the energy status of the tissue, spreading depolarization is either preceded by nonspreading silencing due to neuronal hyperpolarization or accompanied by spreading silencing of electrical brain activity due to a depolarization block. Nonspreading silencing seems to translate into the initial clinical symptoms of ischemic stroke and spreading silencing translates into migraine aura. Direct electrophysiological evidence exists that spreading depolarization occurs in abundance in aneurysmal subarachnoid hemorrhage, delayed ischemic stroke after subarachnoid hemorrhage, malignant hemispheric stroke, spontaneous intracerebral hemorrhage and traumatic brain injury. Indirect evidence suggests its occurrence during migraine aura. In animals, spreading depolarizations facilitate neuronal death when they invade metabolically compromised tissue, whereas they are relatively innocuous in healthy tissue. Therapies targeting spreading depolarization may potentially treat these neurological conditions.

The role of Ca2+, H+, and Cl− ions in generation of variation potential in pumpkin plants

The contributions of Ca2+, H+, and Cl− in generation of variation potentials (VP) in 3- to 4-week-old pumpkin (Cucurbita pepo L., cv. Mozoleevskaya) plants were assessed. During VP generation, transient alkalinization of the medium around the stem was recorded with a potentiometric method. The pH changes were kinetically similar to the electric potential changes and were apparently due to temporal suppression of the plasma-membrane electrogenic H+ pump. These data and the observed inhibition of VP in the stem zone treated locally with a metabolic inhibitor (NaN3) indicate that the VP generation is related to the reversible suppression of the H+-pump. The anion channel blocker (ethacrynic acid) decelerated significantly the front slope of VP and reduced the VP amplitude. A short-term increase in external Cl− concentration around the stem was observed during potential transients representing the VP front slope and the pulses integrated into VP. The removal of Ca2+ from extracellular medium inhibited the VP generation. It is proposed that Ca2+ plays a role in activation of anion channels and in the H+-pump inactivation. The VP generation is probably determined by a complex mechanism, with contributions from passive ion fluxes (Ca2+, Cl−) moving along the electrochemical gradients and from changes in the electrogenic pump activity.

Modeling of Temperature-Sensitive Polyelectrolyte Gels by the Use of the Coupled Chemo-Electro-Mechanical Formulation

Polyelectrolyte gels show adaptive viscoelastic characteristics. In water-based solutions they have enormous swelling capabilities under the influence of different possible stimulation types, such as chemical, electrical, or thermal stimulation. Possible applications for these intelligent materials can be either actuators, e.g., when used as artificial muscles or chemo-electric energy converters, or sensors, e.g., for measuring ion concentrations or pH-values of the solutions. In order to represent this active behavior, a coupled multi-field model is applied. The chemo-electro-mechanical multi-field formulation considers changes of concentrations, electric potential, or strains due to varying (initial) conditions. In the present work, a fully coupled 3-field formulation for polyelectrolyte gels using the Finite Element Method is applied. This formulation consists of a chemical, electrical, and mechanical field equation. The chemical field is described by a partial differential equation (PDE) first order in time and second order in space and includes diffusional, migrational, and convectional effects. The electrical field is represented by the Poisson equation, an elliptical PDE of second order in space. Finally, the mechanical field is described by a PDE of first order derived from the conservation of momentum. Due to the slow processes in time, inertia terms are neglected. The mechanical field is coupled to the chemo-electrical field by a prescribed strain stemming from an osmotic pressure term. A large dependency between the applied temperature and the actual swelling degree of the gel has been proven in experiments. In the present research, the thermal stimulation is investigated using two alternative approaches: The first is a straight forward modeling by modifying the actual temperature in the osmotic pressure term. As this approach does not lead to promising results, as a second alternative temperature-dependent material parameters obtained from experimental measurements are applied. The calibration of the derived simulation results is performed with experimental results from the literature. The Finite Elements introduced for the coupled multi-field formulation contain degrees of freedom for concentrations, electric potential, and mechanical displacements. They are adopted and applied in the commercial software package ABAQUS as a user defined element. For the numerical solution, the Newton-Raphson method in conjunction with the implicit backward Euler time integration scheme is applied.

Resolution Limits of Secondary Electron Dopant Contrast in Helium Ion and Scanning Electron Microscopy

As the miniaturization of semiconductor devices continues, characterization of dopant distribution within the structures becomes increasingly challenging. One potential solution is the use of the secondary electron signal produced in scanning electron (SEMs) or helium ion microscopes (HeIMs) to image the changes in electrical potential caused by the dopant atoms. In this article, the contrast mechanisms and resolution limits of secondary electron dopant contrast are explored. It is shown that the resolution of the technique is dependent on the extent of electrical potential present at a junction and that the resolution of dopant contrast can be improved in the HeIM after an in-situ plasma cleaning routine, which causes an oxide to form on the surface altering the contrast mechanism from electrical potential to material contrast.

Development of a portable, high throughput biosensor system for rapid plant virus detection

Biosensors based on living cells are characterized by high sensitivity, selectivity and rapid response times. A novel portable cell biosensor system for the detection of plant viruses, based on immobilized ‘Vero’ cells carrying on their membrane virus specific antibodies was developed and was designated as High Throughput Bioelectric Recognition Assay (BERA-HTP). BERA-HTP was tested for the detection of purified Potato virus Y (PVY), Cucumber mosaic virus (CMV) and Tobacco rattle virus (TRV) and of CMV and TRV in single, as well as in mixed infections in two different plant host species. The sensor was based on live, mammalian cells, the membrane of which has been artificially saturated with antibodies specific to different plant viruses. The attachment of PVY, CMV or TRV viral particles to the homologous electroinserted antibodies caused a virus-specific change of the cell membrane electric potential that was not observed with virus-free samples or with heterologous viruses. Fluorescence microscopy observations showed that attachment of virus particles to the cell membrane bearing the homologous antibody, was associated with a decrease of [Ca2+]cyt. The perspective for the development of BERA-HTP as a portable, reliable and rapid (duration of assay for 96 samples: ∼70min) detection method of plant viruses in the field is discussed.

Four‐chamber cochlea box model: Establishing acoustic comfort, illustrating injury and toward therapy.

The unrolled cochlea is modeled using the finite‐element software ANSYS with four inner chambers representing the Scala Vestibuli contiguous with the Scala Tympani thru a rounded helicotrema, the Scala Media, the inner and the outer hair cells. The tectorial membrane is represented as a plate in contact with the hair cells. An improvement from previously presented results is the inclusion of a tapered helicotrema. Various geometries are compared, i.e. with straight sides and with tapered sides, and differences in the frequency response of the models are seen. Applying real values for material properties and the human hearing range and using characteristic frequency at certain nodes inside the Scala Media, the tapered model is calibrated to establish the reference comfort sound level. Hearing injury is regarded by subjecting nodes to increased sound pressure levels until the frequency response disappears. This is done at the same time monitoring the change in electrical potential in the inner and outer hair cell regions. The potential change between the normal and the injured conditions is inputted to the Gibbs energy equation for the ATP‐ADPase glycolysis to identify a possible route to remedy.

The role of spreading depression, spreading depolarization and spreading ischemia in neurological disease

The term spreading depolarization describes a wave in the gray matter of the central nervous system characterized by swelling of neurons, distortion of dendritic spines, a large change of the slow electrical potential and silencing of brain electrical activity (spreading depression). In the clinic, unequivocal electrophysiological evidence now exists that spreading depolarizations occur abundantly in individuals with aneurismal subarachnoid hemorrhage, delayed ischemic stroke after subarachnoid hemorrhage, malignant hemispheric stroke, spontaneous intracerebral hemorrhage or traumatic brain injury. Spreading depolarization is induced experimentally by various noxious conditions including chemicals such as potassium, glutamate, inhibitors of the sodium pump, status epilepticus, hypoxia, hypoglycemia and ischemia, but it can can also invade healthy, naive tissue. Resistance vessels respond to it with tone alterations, causing either transient hyperperfusion (physiological hemodynamic response) in healthy tissue or severe hypoperfusion (inverse hemodynamic response, or spreading ischemia) in tissue at risk for progressive damage, which contributes to lesion progression. Therapies that target spreading depolarization or the inverse hemodynamic response may potentially treat these neurological conditions.

Application of fluorescent techniques to evaluate the survival of probiotic lactobacilli to bile acid

To apply a fluorescent dye as an alternative technique to evaluate the survival of potentially probiotic lactobacilli to bile acids (BA) as first step in the design of probiotic functional foods. The use of lactic acid bacteria (LAB) in the functional food design depends on their ability to survive in the gastrointestinal tract where bile is an important natural barrier. Bile is mainly constituted by conjugated BA, which can be hydrolyzed to free BA and taurine or glycine. Changes in the transmembrane electrical potential (ΔΨ) of probiotic LAB strains due to the effect of conjugated and free BA were measured and showed that the majority of the tested LAB strains had greater sensibility to free BA than to their respective conjugated acids. Variations in the ΔΨ of the microorganism correlated well with bacterial viability determined by standard plate count method. We therefore propose the DiSC(3)-based fluorescent technique as a rapid and effective method to evaluate the resistance of probiotic lactobacilli to bile as first step for strain selection to be included in functional foods.

Electric potential changes associated with nucleation of stick-slip of simulated gouges

Our friction experiments using simulated gouges detected premonitory changes in electric potential before stick-slip events. These precursor electric signals have been detected both in piezoelectric quartz and non-piezoelectric gabbroic gouges. The changes in the potential were locally detected by electrodes set very close to the fault surface associated with slow slip prior to stick-slip events. The magnitude of electrification is proportional to fault slip associated with gradual stress releases, indicating that the electrification is slip-dependent process. From the detailed microstructural analyses on a representative sample, Riedel (R 1) shears known to be formed during stable sliding were the most densely developed around the electrode pair which detected the precursory voltage changes. This indicates that local increases in the voltages were likely caused by frictional electrification due to slow slip on R 1 shears in nucleation phases of stick-slip events. Our experimental results imply that natural faults with thicker gouge zones would require greater precursory slips, resulting in larger electric signals in the nucleation phase of earthquakes.

Lunar surface electric potential changes associated with traversals through the Earth's foreshock

We report an analysis of one year of Suprathermal Ion Detector Experiment (SIDE) Total Ion Detector (TID) “resonance” events observed between January 1972 and January 1973. The study includes only those events during which upstream solar wind conditions were readily available. The analysis shows that these events are associated with lunar traversals through the dawn flank of the terrestrial magnetospheric bow shock. We propose that the events result from an increase in lunar surface electric potential effected by secondary electron emission due to primary electrons in the Earth's foreshock region (although primary ions may play a role as well). This work establishes (1) the lunar surface potential changes as the Moon moves through the terrestrial bow shock, (2) the lunar surface achieves potentials in the upstream foreshock region that differ from those in the downstream magnetosheath region, (3) these differences can be explained by the presence of energetic electron beams in the upstream foreshock region and (4) if this explanation is correct, the location of the Moon with respect to the terrestrial bow shock influences lunar surface potential.

Optical Detection of Charged Biomolecules: Towards Novel Drug Delivery Systems

This paper presents work done on developing optically-traceable intracellular nanodiamond sensors, where the photoluminescence can be changed by a biomolecular attachment/delivery event. Their high biocompatibility, small size and stable luminescence from their color centers make nanodiamond (ND) particles an attractive alternative to molecular dyes for drug-delivery and cell-imaging applications. In our work, we study how surface modification of ND can change the color of ND luminescence (PL). This method can be used as a novel detection tool for remote monitoring of chemical processes in biological systems. Recently, we showed that PL can be driven by atomic functionalization, leading to a change in the color of ND luminescence from red (oxidized ND) to orange (hydrogenated ND). In this work, we show how PL of ND changes similarly when interacting with positively and negatively charged molecules. The effect is demonstrated on fluorinated ND, where the high dipole moment of the C-F bond is favorable for the formation of non-covalent bonds with charged molecules. We model this effect using electrical potential changes at the diamond surface. The final aim of the work is to develop a “smart” optically traceable drug carrier, where the delivery event is optically detectable.