Propagation Of Electrical Signals Research Articles

Ion permeability of artificial membranes evaluated by diffusion potential and electrical resistance measurements

In the present article, a novel model of artificial membranes that provides efficient assistance in teaching the origins of diffusion potentials is proposed. These membranes are made of polycarbonate filters fixed to 12-mm plastic rings and then saturated with a mixture of creosol and n-decane. The electrical resistance and potential difference across these membranes can be easily measured using a low-cost volt-ohm meter and home-made Ag/AgCl electrodes. The advantage of the model is the lack of ionic selectivity of the membrane, which can be modified by the introduction of different ionophores to the organic liquid mixture. A membrane treated with the mixture containing valinomycin generates voltages from -53 to -25 mV in the presence of a 10-fold KCl gradient (in to out) and from -79 to -53 mV in the presence of a bi-ionic KCl/NaCl gradient (in to out). This latter bi-ionic gradient potential reverses to a value from +9 to +20 mV when monensin is present in the organic liquid mixture. Thus, the model can be build stepwise, i.e., all factors leading to the development of diffusion potentials can be introduced sequentially, helping students to understand the quantitative relationships of ionic gradients and differential membrane permeability in the generation of cell electrical signals.

Radio-frequency electromagnetic radiation alters the electric potential of Myriophyllum aquaticum

Electric signaling pathways are important for rapid and long-distance communication within a plant. Changes in the electric potential (EP) inside plants have been observed during the propagation of electric signals. Increasing radiofrequency electromagnetic radiation (EMR) in the environment raise the question about possible effects of EMR on the EP of plants. In the present experiment, we investigated the effect of 2, 2.5, 3.5, and 5.5 GHz EMR with a maximum field intensity of 23–25 V m−1 on the EP in emergent Myriophyllum aquaticum plants. The 2 and 5.5 GHz exposures caused significant (16 and 13 %) decreases in the standard deviation of rapid fluctuations observed in the EP. The greatest change was caused by 2.5 GHz EMR (23 % increment), although it was not statistically significant. A recovery of the EP was only after 2.5 GHz EMR exposure. The temperature of the plants was not changed by the EMR exposure. These findings confirm the frequency-dependent non-thermal effects of EMR on the EP of plants.

Advances in biomedical applications of time reversal acoustic focusing of ultrasound

Time reversal acoustics (TRA) is one of the most efficient methods of ultrasound focusing in heterogeneous composite biological media, especially inside reverberating cavities, such as the skull. In this talk, we will overview several recently developed therapeutic applications of TRA focusing of ultrasound including enhanced drug delivery to brain tumors, generation of focal regions of complex shape tailored to the geometry of the target lesion and TRA dynamic focusing, that allows to maintain the constant acoustic intensity in the focus regardless the variation of acoustical parameters of the media. We are currently developing several new medical applications of TRA, such as remote charging of batteries in internal implants and leadless energizing deep brain stimulators, which are based on the possibility to remotely generate an electrical signal in tissue using TRA principles. These applications employ a TRA focusing system with wireless electromagnetic feedback from the tiny implanted piezotransducer acting as a beacon. The acoustic energy is accurately focused at the piezotransducer generating required electrical signal while providing minimum exposure of surrounding tissues to ultrasound energy. Possibility of remote generation of electrical signals in tissue with amplitudes reaching tens of volts was demonstrated. [Work supported by NIH R21 CA164935-01.]

Stress‐Sensor Device Based on Flexoelectric Liquid Crystalline Membranes

Membrane flexoelectricity is an electromechanical coupling process that describes membrane bending and membrane electrical polarization caused by bending under electric fields. In this paper we propose, formulate, and characterize a stress-sensor device for mechanically loaded solids, consisting of a soft flexoelectric thin membrane attached to the loaded deformed solid. Because the curvature of the deformed solid is transferred to the attached flexoelectric membrane, the electromechanical transduction of the latter produces a charge that is proportional to the stress of the solid. The model of the stress-sensor device is based on the integration of the thermodynamics of polarizable membranes with isotropic solid elasticity, leading to a transfer function that identifies the elastic, electromechanical, and geometrical parameters involved in electrical-signal generation. The model is applied to representative normal bending and then to more complex off-axis bending of elastic bars. In all cases, a common transfer function shows the generic material and its geometric contributions. The sensor sensitivity increases linearly with flexoelectricity and the membrane-solid interface, and the sensitivity decreases with increasing membrane thickness and Young's modulus of the solid. The theoretical results contribute to ongoing experimental efforts towards the development of anisotropic soft-matter-based stress-sensor devices through solid-membrane interactions and electromechanical transduction.

Optical microwave generation using modified sideband injection synchronization with wide line-width lasers for broadband communications

In future generation space based phased arrays and in pico-cellular broadband mobile communication systems operating at microwave frequencies optical techniques for transport and generation of electrical signals are widely used. In general, there are two main classes of optical transmitting and generating microwave frequencies: (1) methods using direct or external intensity modulation of lasers and (2) heterodyning method using two coherent optical waves. The present paper dwells on the second method. The present paper overcomes the major practical limitations of optical sideband injection locking. Simulation results have been given in support of the analytical result.

Temporal-Spatial Interaction between Reactive Oxygen Species and Abscisic Acid Regulates Rapid Systemic Acclimation in Plants

Being sessile organisms, plants evolved sophisticated acclimation mechanisms to cope with abiotic challenges in their environment. These are activated at the initial site of exposure to stress, as well as in systemic tissues that have not been subjected to stress (termed systemic acquired acclimation [SAA]). Although SAA is thought to play a key role in plant survival during stress, little is known about the signaling mechanisms underlying it. Here, we report that SAA in plants requires at least two different signals: an autopropagating wave of reactive oxygen species (ROS) that rapidly spreads from the initial site of exposure to the entire plant and a stress-specific signal that conveys abiotic stress specificity. We further demonstrate that SAA is stress specific and that a temporal-spatial interaction between ROS and abscisic acid regulates rapid SAA to heat stress in plants. In addition, we demonstrate that the rapid ROS signal is associated with the propagation of electric signals in Arabidopsis thaliana. Our findings unravel some of the basic signaling mechanisms underlying SAA in plants and reveal that signaling events and transcriptome and metabolome reprogramming of systemic tissues in response to abiotic stress occur at a much faster rate than previously envisioned.

Domain IV voltage-sensor movement is both sufficient and rate limiting for fast inactivation in sodium channels

Voltage-gated sodium channels are critical for the generation and propagation of electrical signals in most excitable cells. Activation of Na+ channels initiates an action potential, and fast inactivation facilitates repolarization of the membrane by the outward K+ current. Fast inactivation is also the main determinant of the refractory period between successive electrical impulses. Although the voltage sensor of domain IV (DIV) has been implicated in fast inactivation, it remains unclear whether the activation of DIV alone is sufficient for fast inactivation to occur. Here, we functionally neutralize each specific voltage sensor by mutating several critical arginines in the S4 segment to glutamines. We assess the individual role of each voltage-sensing domain in the voltage dependence and kinetics of fast inactivation upon its specific inhibition. We show that movement of the DIV voltage sensor is the rate-limiting step for both development and recovery from fast inactivation. Our data suggest that activation of the DIV voltage sensor alone is sufficient for fast inactivation to occur, and that activation of DIV before channel opening is the molecular mechanism for closed-state inactivation. We propose a kinetic model of sodium channel gating that can account for our major findings over a wide voltage range by postulating that DIV movement is both necessary and sufficient for fast inactivation.

FitzHugh-Nagumo to model a large number of diffusive coupled neurons

The aim of our work is to investigate the dynamics of a neural network, in which neurons, individually described by the FitzHugh-Nagumo model [1], are coupled by a generalized diffusive term. The formulation we exploit is based on the general framework of graph theory, where neurons are represented by vertices and links by edges. With the aim of defining the connection structure among the excitable elements, the discrete Laplacian matrix plays a fundamental role. Indeed, it allows us to model the instantaneous propagation of (electric) signals between neurons, which need not be physically close to each other. This approach enables us to address three fundamental issues. Firstly, each neuron is described using the well-known FitzHugh-Nagumo model which might allow to differentiate their individual behavior. Furthermore, exploiting the Laplacian matrix, a well defined connection structure is formalized. A thoroughly explained mathematical structure allows us to formally describe several fundamental features of interactions in neural populations. Indeed, the description of not only nearest neighbor interactions and the presence of inhibitory synapses has been achieved. Several simulations are performed to graphically present how the action potential within a network evolves. In general, placing the neuron in line and stimulating one of them, two waves which carry out the connection rule arise. While the number of neurons N increases in a bounded domain, without any changes in the model, the effect is that the two arisen waves travel slower along the whole set of neurons. Neglecting in a first approximation the time delays due to the chemical synapses, we formalize two approaches which allow us to reproduce the qualitative behavior of the action potential as N increases, i.e., waves assume the same shape and spend the same time to travel along the same length interval. Concisely, Approach I consists of rescaling the diffusion coefficient while Approach II consists of increasing, in accordance with a specific law, the number of connections per neuron. In order to make clear the graphical comprehension of the dynamics, only nearest neighbor interactions are allowed in Approach I. Furthermore, a comparison between them has been performed. An example of dynamics obtained by exploiting both approaches in one-dimension is shown (see Figure ​Figure11). Figure 1 Comparison of dynamics obtained by considering 1024 neurons. The stimulus consists in imposing a non-null initial action potential on the central node of the set. At the end of the integration all neurons return to the quiescent state due to the physiological ... A continuum of neurons is the results of the limit process of letting N to infinity and a system of convection/reaction/diffusion partial differential equations describes the action potential and the recovery variable in the whole set of neurons. Finally, our two approaches immediately extend to higher dimensions.

The energetics of electric organ discharge generation in gymnotiform weakly electric fish

Gymnotiform weakly electric fish produce an electric signal to sense their environment and communicate with conspecifics. Although the generation of such relatively large electric signals over an entire lifetime is expected to be energetically costly, supporting evidence to date is equivocal. In this article, we first provide a theoretical analysis of the energy budget underlying signal production. Our analysis suggests that wave-type and pulse-type species invest a similar fraction of metabolic resources into electric signal generation, supporting previous evidence of a trade-off between signal amplitude and frequency. We then consider a comparative and evolutionary framework in which to interpret and guide future studies. We suggest that species differences in signal generation and plasticity, when considered in an energetics context, will not only help to evaluate the role of energetic constraints in the evolution of signal diversity but also lead to important general insights into the energetics of bioelectric signal generation.

Morphing structures and signal transduction in Mimosa pudica L. induced by localized thermal stress

Leaf movements in Mimosa pudica, are in response to thermal stress, touch, and light or darkness, appear to be regulated by electrical, hydrodynamical, and chemical signal transduction. The pulvinus of the M. pudica shows elastic properties. We have found that the movements of the petiole, or pinnules, are accompanied by a change of the pulvinus morphing structures. After brief flaming of a pinna, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of electrolytes between these parts of the pulvinus; as a result of these changes the petiole falls. During the relaxation of the petiole, the process goes in the opposite direction. Ion and water channel blockers, uncouplers as well as anesthetic agents diethyl ether or chloroform decrease the speed of alert wave propagation along the plant. Brief flaming of a pinna induces bidirectional propagation of electrical signal in pulvini. Transduction of electrical signals along a pulvinus induces generation of an action potential in perpendicular direction between extensor and flexor sides of a pulvinus. Inhibition of signal transduction and mechanical responses in M. pudica by volatile anesthetic agents chloroform or by blockers of voltage gated ion channels shows that the generation and propagation of electrical signals is a primary effect responsible for turgor change and propagation of an excitation. There is an electrical coupling in a pulvinus similar to the electrical synapse in the animal nerves.

Super high sensitive low‐dimensional IR‐detector

AbstractThe original design of the infrared detector providing ultrahigh parameters of responsivity is proposed. The idea lies in separation of the areas between charge carrier optical generation and formation of electrical signal. The calculations performed for CdxHg1–xTe photodetectors with x ∼ 0.21 and x ∼ 0.28 at electric bias 200 mV yield values such as Su = 108–1010 V/W for voltage response. That is several orders of magnitude more than experimentally reached values for CdxHg1–xTe‐based IR‐detectors (Su =106V/W for λ c = 11 µm, T = 77 K [Singh and Mittal, Def. Sci. J. 53(31), 281 (2003)]). Offered detector is different with very large resistance and small power consumption and dimensions of active area. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Challenges of ITER diagnostic electrical services

Diagnostic electrical services provide the electrical infrastructure to serve diagnostic components installed on the ITER tokamak. This infrastructure is composed of cables, connectors, cable tails, looms, conduits and feedthroughs. The diagnostic services offer as well a shelter for various instrumentations – vacuum vessel (VV), blanket and divertor. The diagnostic sensors are located on the inner and outer VV wall, on blanket shield modules, divertor cassettes and in port plugs. They require electrical cabling to extract the measurement and, in some cases, to supply electrical power to the sensors. These cables run from the sensors to feedthroughs on the VV and the port interspace or cryostat.The design and integration of all components that are part of diagnostic electrical services is an important engineering activity that is being challenged by the multiple requirements and constraints which have to be satisfied while at the same time delivering the required diagnostic performance. The positioning of the components must correlate not only with their functional specifications but also with the design of the major ITER components. This is a particular challenge because not all systems have reached the same level of design maturity.This paper outlines the engineering challenges of ITER diagnostics electrical services. The environmental conditions inside the VV will have an important impact. Leading risks to these components include poor electrical contact at connectors, the effects of exposure to nuclear irradiation, such as material transmutation, heating, and generation of spurious electrical signals etc., failure due to electromagnetic forces and electrical interference due to the noisy environment. Last but not least are the challenges for confinement and vacuum requirements set up on electrical feedthroughs. It will focus as well on the design and structural assessment of all components, and their requirements. Besides the integration limitations, the loads are the main design driver.

Numerical Solution of Telegraph Equation by Using LT Inversion Technique

In this paper, the numerical solution of one-dimensional linear hyperbolic telegraph equation, which describe wave propagation of electric signals in a cable transmission line, is proposed employing the well known homotopy perturbation method(HPM) and laplace transform(LT). Using Laplace transform scheme, the problem is converted into a partial difierential equation without any difierentiation respect to time. Homotopy perturbation method is applied in the Laplace transform domain. We use Stehfest’s numerical inversion algorithm of Laplace transform to retrieve the time domain solution. The performance was found to be very good. The approximate solutions are in excellent agreement with those by the Chebyshev spectral collocation method (CSCM) and the method uses interpolating scaling functions. To illustrate the method some examples are provided. The results show the simplicity and the e‐ciency of the method.

Microscale Inhomogeneity of Brain Tissue Distorts Electrical Signal Propagation

Interpretations of local field potentials (LFPs) are typically shaped on an assumption that the brain is a homogenous conductive milieu. However, microscale inhomogeneities including cell bodies, dendritic structures, axonal fiber bundles and blood vessels are unequivocally present and have different conductivities and permittivities than brain extracellular fluid. To determine the extent to which these obstructions affect electrical signal propagation on a microscale, we delivered electrical stimuli intracellularly to individual cells while simultaneously recording the extracellular potentials at different locations in a rat brain slice. As compared with relatively unobstructed paths, signals were attenuated across frequencies when fiber bundles were in between the stimulated cell and the extracellular electrode. Across group of cell bodies, signals were attenuated at low frequencies, but facilitated at high frequencies. These results show that LFPs do not reflect a democratic representation of neuronal contributions, as certain neurons may contribute to the LFP more than others based on the local extracellular environment surrounding them.

Dissecting Single-Molecule Signal Transduction in Carbon Nanotube Circuits with Protein Engineering

Single-molecule experimental methods have provided new insights into biomolecular function, dynamic disorder, and transient states that are all invisible to conventional measurements. A novel, nonfluorescent single-molecule technique involves attaching single molecules to single-walled carbon nanotube field-effective transistors (SWNT FETs). These ultrasensitive electronic devices provide long-duration, label-free monitoring of biomolecules and their dynamic motions. However, generalization of the SWNT FET technique first requires design rules that can predict the success and applicability of these devices. Here, we report on the transduction mechanism linking enzymatic processivity to electrical signal generation by a SWNT FET. The interaction between SWNT FETs and the enzyme lysozyme was systematically dissected using eight different lysozyme variants synthesized by protein engineering. The data prove that effective signal generation can be accomplished using a single charged amino acid, when appropriately located, providing a foundation to widely apply SWNT FET sensitivity to other biomolecular systems.

Defining the Interactive Surfaces of Tarantula Toxins for Voltage Sensors in Kv Channels

Voltage-gated ion channels play crucial roles in the generation and propagation of electrical signals within the nervous system. Peptide toxins from tarantula venom interact with voltage-sensing domains in Kv channels and have provided useful tools for exploring their structures and gating mechanisms. However, relatively little is known about the specific molecular interactions between these toxins and voltage sensors. In the present study we set out to define the surface of GxTx-1E that interacts with the voltage sensors in the Kv2.1 channel. GxTx-1E is a particularly attractive candidate for further study because the structure of this amphipathic toxin has been solved, and it binds with high affinity to the voltage-sensor paddle motif in the Kv2.1 channel to inhibit opening, providing the opportunity to undertake mutant cycle analysis between toxin and channel. Towards this goal we mutated 28 of the 36 non-Cys residues in GxTx-1E to Ala using solid-phase chemical synthesis, folded the mutants in vitro and studied their interactions with the Kv2.1 channel using voltage-clamp electrophysiological recording techniques. Of all the mutations studied thus far, none of the polar residue mutants produced changes in toxin affinity greater than 5-fold, whereas five hydrophobic residue mutants produced > 10-fold changes in toxin affinity. In the structure of the toxin, all of these hydrophobic residues are positioned to form a contiguous surface. We are currently undertaking mutant cycle analysis between these mutants and those within the paddle motif to define the protein-protein interface between toxin and channel.

Access to the Pore of a Voltage-Dependent Na+ Channel is Controlled by an Intracellular Gate

Voltage-gated sodium channels (VGSCs) are transmembrane proteins responsible for the initiation and propagation of electrical signals within excitable cells. Upon activation, VGSCs undergo a series of conformational rearrangements transiently opening a Na+ selective pore. Exactly how Na+ access the pore remains unclear. It is known that intracellular application of quaternary derivatives of lidocaine, as well as the cytoplasmic tail of the beta-4 subunit produces open channel blockade. Also, mutated residues in the pore-lining S6 helices alter channel gating and disrupt local anesthetic binding.

Biocompatibility evaluation of electrically conductive nanofibrous scaffolds for cardiac tissue engineering.

Myocardial tissue engineering offers a novel technology to improve or regenerate cardiac functions using a combination of cells, biomaterials and engineering strategies. Inspired by low-resistance pathways for electrical signal propagation in the native heart tissue, electrically conductive nanofibrous scaffolds composed of melanin, poly(l-lactide-co-ε-caprolactone) and gelatin were fabricated to provide electrophysiological cues to cardiac myocytes and mimic the native myocardial environment. Our results show that by increasing the concentration of melanin to 40% within the composite, the fiber diameters reduced to 153 ± 30 nm, modulus decreased to 7.1 ± 0.6 MPa, and conductance increased to 259.51 ± 187.60 μS cm-1. Results of cell proliferation and immunostaining analysis of human cardiac myocytes demonstrated that the conductive nanofibers containing 10% melanin promote cell interaction with expression of cardiac-specific proteins compared to other scaffolds. Electrical stimulation through the scaffolds showed enhanced cell proliferation and the expression of connexin-43, signifying the potential of using melanin containing nanofibers as a suitable cardiac patch for the regeneration of infarct myocardium.

Single Molecule Dynamic Transduction by Carbon Nanotube Circuits

Nanoscale electronic devices like field-effect transistors (FETs) have long promised to provide sensitive, label-free detection of biomolecules. In particular, single-walled carbon nanotubes (SWNTs) have the requisite sensitivity to detect single molecule events, and have sufficient bandwidth to directly monitor single molecule dynamics in real time. Recent measurements have demonstrated this premise by monitoring the dynamic, single-molecule processivity of three different enzymes: lysozyme, protein kinase A, and the Klenow Fragment of polymerase I. Initial successes in each case indicated the generality and attractiveness of SWNT FETs as a new tool to complement other single molecule techniques. However, further generalization of the SWNT FET technique demands reliable design rules that can predict the success and applicability of these devices. Here, we address this need by focusing on the transduction mechanisms that link enzyme processivity to electrical signal generation in a SWNT FET. Using ten different lysozyme variants synthesized by mutagenesis, we systematically dissect the enzyme-SWNT interaction in order to understand this transduction. The data prove that mechanical displacements of charged functionalities near the SWNT attachment site are the primary sources of transduction, and that the resulting devices are sensitive enough to track the motions of just one charged amino acid. The purposeful incorporation of a charged group at a particular location allows the device to be designed to have sensitivity to particular chemical activities or allosterically-driven mechanical motions. The findings provide rules for the creation of similarly effective nanocircuits using a wide range of enzymes or proteins.

Protecting White Matter From Stroke Injury

White matter (WM) exclusively contains axons and their glial cell partners including astrocytes, oligodendrocytes (myelinating and nonmyelinating), and microglia. WM comprises about half of the forebrain volume of humans, a 3- to 4-fold increase over rodents, the animals most used for neuroscience research.1,2 The low relative volume of WM in rodents led to neglect of this specialized brain area in studies of stroke pathophysiology and under-appreciation of the clinical importance of WM that has slowed progress to effective therapy.3 WM axons interconnect distant regions of the central nervous system and are metabolically independent of their cell bodies with regard to energy metabolism. Hence, proper propagation of electrical signals through WM axons demands a continuous supply of energy along their entire length and focal disruption of blood supply may compromise the viability of the whole axon. Yet, WM receives disproportionally less circulation than gray matter (GM) and is highly vulnerable to reduced blood supply exemplified by the frequency of pure WM strokes called lacunes or lacunar infarcts,4 which can accumulate, sometimes silently, and produce vascular dementia.5 Damage of WM is a major cause of functional disability in cerebrovascular disease and the majority of ischemic strokes involve both WM and GM.2,6 Early animal studies indicate that WM can be damaged by even brief focal ischemia.7 Thus, after 30 minutes of arterial occlusion massive swelling of oligodendrocytes and astrocytes occurs, and about 3 hours later most oligodendrocytes die. These changes precede by several hours the appearance of necrotic neurons in ischemic regions.7 Other pathological changes in ischemic WM include segmental swelling of myelinated axons and the formation of spaces or vacuoles between the myelin sheath and axolemma (Figure 1).7,8 These observations confirm that WM is vulnerable to ischemia …