scholarly journals Electrodiffusion model of synaptic potentials in dendritic spines

2018 ◽  
Author(s):  
Thibault Lagache ◽  
Krishna Jayant ◽  
Rafael Yuste
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Dendritic Spines ◽  
Ionic Currents ◽  
Ion Concentration ◽  
Excitable Cells ◽  
Main Site ◽  
Synaptic Potentials ◽  
Concentration Changes ◽  
Kinetics Of

ABSTRACTWhen modeling electric current flow in neurons and excitable cells, traditional cable theory ignores electrodiffusion (i.e. the interaction between electric fields and ionic diffusion) as it assumes that concentration changes associated with ionic currents are negligible. This assumption, while true for large neuronal compartments, fails when applied to femto-liter size compartments such as dendritic spines - small protrusions that form the main site of synaptic inputs in the brain. Here, we use the Poisson (P) and Nernst-Planck (NP) equations, which relate electric field to charge and couple Fick’s law of diffusion to the electric field, to model ion concentration dynamics in dendritic spines. We use experimentally measured voltage transients from spines with nanoelectrodes to explore these dynamics with realistic parameters. We find that (i) passive diffusion and electrodiffusion jointly affect the kinetics of spine excitatory post-synaptic potentials (EPSPs); (ii) spine geometry plays a key role in shaping EPSPs; and, (iii) the spine-neck resistance dynamically decreases during EPSPs, leading to short-term synaptic facilitation. Our formulation can be easily adopted to model ionic biophysics in a variety of nanoscale bio-compartments.

scholarly journals Heterogeneous Intramolecular Electric Field as a Descriptor of Diels-Alder Reactivity

2020 ◽  
Author(s):  
Matthew Hennefarth ◽  
Anastassia N. Alexandrova
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Electric Fields ◽  
Alder Reaction ◽  
Diels Alder ◽  
Charge Movement ◽  
External Electric Fields ◽  
Topological Features ◽  
Diels Alder Reaction ◽  
Kinetics Of

<div> <div> <div> <p>External electric fields have proven to be an effective tool in catalysis, on par with pressure and temperature, affecting the thermodynamics and kinetics of a reaction. However, fields in molecules are complicated heterogeneous vector objects, and there is no universal recipe for grasping the exact features of these fields that implicate reactivity. Herein, we demonstrate that topological features of the heterogeneous electric field within the reactant state, as well as of the quantum mechanical electron density – a scalar reporter on the field experienced by the system – can be identified as rigorous descriptors of the reactivity to follow. We scrutinize specifically the Diels-Alder reaction. Its 3-D nature and the lack of a singular directionality of charge movement upon barrier crossing makes the effect of the electric field not obvious. We show that the electric field topology around the dienophile double bond, and the associated changes in the topology of the electron density in this bond are predictors of the reaction barrier. They are also the metrics by which to rationalize and predict how the external field would inhibit or enhance the reaction. The findings pave the way toward designing external fields for catalysis, as well as reading the reactivity without an explicit mechanistic interrogation, for a variety of reactions. </p> </div> </div> </div>

Cardiac Ionic Currents and Acute Ischemia: From Channels to Arrhythmias

1999 ◽  
Vol 79 (3) ◽  
pp. 917-1017 ◽  
Author(s):  
Edward Carmeliet
Keyword(s):  
Ion Channels ◽  
Ionic Currents ◽  
Ion Concentration ◽  
Acute Ischemia ◽  
Ischemia And Reperfusion ◽  
General Description ◽  
Basic Information ◽  
Intracellular Organelles ◽  
Concentration Changes ◽  
Short Section

The aim of this review is to provide basic information on the electrophysiological changes during acute ischemia and reperfusion from the level of ion channels up to the level of multicellular preparations. After an introduction, section ii provides a general description of the ion channels and electrogenic transporters present in the heart, more specifically in the plasma membrane, in intracellular organelles of the sarcoplasmic reticulum and mitochondria, and in the gap junctions. The description is restricted to activation and permeation characterisitics, while modulation is incorporated in section iii. This section (ischemic syndromes) describes the biochemical (lipids, radicals, hormones, neurotransmitters, metabolites) and ion concentration changes, the mechanisms involved, and the effect on channels and cells. Sectioniv (electrical changes and arrhythmias) is subdivided in two parts, with first a description of the electrical changes at the cellular and multicellular level, followed by an analysis of arrhythmias during ischemia and reperfusion. The last short section suggests possible developments in the study of ischemia-related phenomena.

scholarly journals Compact Electro-Permeabilization System for Controlled Treatment of Biological Cells and Cell Medium Conductivity Change Measurement

2014 ◽  
Vol 14 (5) ◽  
pp. 279-284 ◽  
Author(s):  
Vitalij Novickij ◽  
Audrius Grainys ◽  
Jurij Novickij ◽  
Sonata Tolvaisiene ◽  
Svetlana Markovskaja
Keyword(s):  
Experimental Data ◽  
Cell Membrane ◽  
Electric Field ◽  
Ion Concentration ◽  
Biological Cells ◽  
Conductivity Change ◽  
Controlled Treatment ◽  
Concentration Changes ◽  
Cell Medium ◽  
Medium Conductivity

Abstract Subjection of biological cells to high intensity pulsed electric field results in the permeabilization of the cell membrane. Measurement of the electrical conductivity change allows an analysis of the dynamics of the process, determination of the permeabilization thresholds, and ion efflux influence. In this work a compact electro-permeabilization system for controlled treatment of biological cells is presented. The system is capable of delivering 5 μs - 5 ms repetitive square wave electric field pulses with amplitude up to 1 kV. Evaluation of the cell medium conductivity change is implemented in the setup, allowing indirect measurement of the ion concentration changes occurring due to the cell membrane permeabilization. The simulation model using SPICE and the experimental data of the proposed system are presented in this work. Experimental data with biological cells is also overviewed

scholarly journals The effect of successful low-dose immunotherapy ascertained by provocation neutralization on lymphocytic calcium ion influx following electric field exposure

2019 ◽  
Vol 17 (1) ◽  
Author(s):  
Basant K. Puri ◽  
Daniel R. Segal ◽  
Jean A. Monro
Keyword(s):  
Electric Field ◽  
Intracellular Calcium ◽  
Electric Fields ◽  
Calcium Ion ◽  
Low Dose ◽  
Ion Concentration ◽  
Field Exposure ◽  
Intracellular Calcium Ion ◽  
Ion Influx ◽  
Calcium Ion Concentration

AbstractBackgroundLow-dose immunotherapy affects baseline levels of intracellular calcium. However, the effect of background electric fields is yet to be ascertained. The aim of this study was to test the following hypotheses: desensitization by low-dose immunotherapy is associated with reduced calcium ion influx during electric field exposure; the effect of low-dose immunotherapy on intracellular calcium ion concentration does not depend on electric field exposure; and the intracellular calcium ion concentration is amplified by electric field exposure.MethodsThe experimental design was balanced and orthogonal. Intracellular lymphocytic calcium ion concentrations were assayed in 47 patients, following incubation with picogram amounts of 12 test allergens, using a cell-permeable calcium-sensing ratiometric fluorescent dye and fluorescence spectroscopy, both at baseline and following successful provocation neutralization treatment with low-dose immunotherapy. Duplicates were also exposed to an electric field which replicated the frequency spectrum measured in a non-Faraday shielded room.ResultsA significant or trend-level main effect was found for low-dose immunotherapy for: benzoate; formaldehyde; metabisulfite; natural gas; nitrosamines; organophosphates; salicylate; azo-dyes and precursors; nickel; and petrol (gasoline) exhaust. Significant or trend-level main effects for electric field exposure were observed for: formaldehyde; mercury (inorganic); natural gas; nickel; nitrosamines; petrol exhaust; salicylate; benzoate; and metabisulfite. There was no evidence of a statistical interaction between these two factors. Electric field exposure was associated with a higher intracellular calcium ion concentration.ConclusionThere was support for all three hypotheses. The results suggest that patients may experience increased sensitivity to allergens as a result of exposure to everyday electric fields.

scholarly journals Reaction-free concentration gradient generation in spatially non-uniform AC electric fields

2022 ◽  
Author(s):  
Ran An ◽  
Adrienne Minerick
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Concentration Gradient ◽  
Electrochemical Techniques ◽  
Hafnium Dioxide ◽  
Ion Concentration ◽  
Concentration Gradients ◽  
Free Concentration ◽  
Bulk Fluid ◽  
Ac Electric Fields

The ability to generate stable, spatiotemporally controllable concentration gradients is critical for both electrokinetic and biological applications such as directional wetting and chemotaxis. Electrochemical techniques for generating solution and surface gradients display benefits such as simplicity, controllability, and compatibility with automation. Here, we present an exploratory study for generating micro-scale spatiotemporally controllable gradients using a reaction-free electrokinetic technique in a microfluidic environment. Methanol solutions with ionic Fluorescein isothiocyanate (FITC) molecules were used as an illustrative electrolyte. Spatially non-uniform alternating current (AC) electric fields were applied using hafnium dioxide (HfO2) coated Ti/Au electrode pairs. Results from spatial and temporal analysis, along with control experiments suggest that the FITC ion concentration gradient in bulk fluid (over 50 µm from the electrode) was established due to spatial variation of electric field density, and was independent of electrochemical reactions at the electrode surface. The established ion concentration gradients depended on both amplitudes and the frequencies of the oscillating AC electric field. Overall, this work reports a novel approach for generating stable and spatiotemporally tunable gradients in a microfluidic chamber using a reaction-free electrochemical methodology.

scholarly journals Reaction-free concentration gradient generation in spatially non-uniform AC electric fields

2022 ◽  
Author(s):  
Ran An ◽  
Adrienne Minerick
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Concentration Gradient ◽  
Electrochemical Techniques ◽  
Hafnium Dioxide ◽  
Ion Concentration ◽  
Concentration Gradients ◽  
Free Concentration ◽  
Bulk Fluid ◽  
Ac Electric Fields

The ability to generate stable, spatiotemporally controllable concentration gradients is critical for both electrokinetic and biological applications such as directional wetting and chemotaxis. Electrochemical techniques for generating solution and surface gradients display benefits such as simplicity, controllability, and compatibility with automation. Here, we present an exploratory study for generating micro-scale spatiotemporally controllable gradients using a reaction-free electrokinetic technique in a microfluidic environment. Methanol solutions with ionic Fluorescein isothiocyanate (FITC) molecules were used as an illustrative electrolyte. Spatially non-uniform alternating current (AC) electric fields were applied using hafnium dioxide (HfO2) coated Ti/Au electrode pairs. Results from spatial and temporal analysis, along with control experiments suggest that the FITC ion concentration gradient in bulk fluid (over 50 µm from the electrode) was established due to spatial variation of electric field density, and was independent of electrochemical reactions at the electrode surface. The established ion concentration gradients depended on both amplitudes and the frequencies of the oscillating AC electric field. Overall, this work reports a novel approach for generating stable and spatiotemporally tunable gradients in a microfluidic chamber using a reaction-free electrochemical methodology.

scholarly journals Effects of Sesamin, the Major Furofuran Lignan of Sesame Oil, on the Amplitude and Gating of Voltage-Gated Na+ and K+ Currents

Molecules ◽  
2020 ◽  
Vol 25 (13) ◽  
pp. 3062 ◽  
Author(s):  
Ping-Chung Kuo ◽  
Zi-Han Kao ◽  
Shih-Wei Lee ◽  
Sheng-Nan Wu
Keyword(s):  
Ionic Currents ◽  
Sesame Oil ◽  
Delayed Rectifier ◽  
Excitable Cells ◽  
Voltage Gated ◽  
Ic50 Value ◽  
Different Types ◽  
Nav Channels ◽  
Kinetics Of ◽  
K Currents

Sesamin (SSM) and sesamolin (SesA) are the two major furofuran lignans of sesame oil and they have been previously noticed to exert various biological actions. However, their modulatory actions on different types of ionic currents in electrically excitable cells remain largely unresolved. The present experiments were undertaken to explore the possible perturbations of SSM and SesA on different types of ionic currents, e.g., voltage-gated Na+ currents (INa), erg-mediated K+ currents (IK(erg)), M-type K+ currents (IK(M)), delayed-rectifier K+ currents (IK(DR)) and hyperpolarization-activated cation currents (Ih) identified from pituitary tumor (GH3) cells. The exposure to SSM or SesA depressed the transient and late components of INa with different potencies. The IC50 value of SSM needed to lessen the peak or sustained INa was calculated to be 7.2 or 0.6 μM, while that of SesA was 9.8 or 2.5 μM, respectively. The dissociation constant of SSM-perturbed inhibition on INa, based on the first-order reaction scheme, was measured to be 0.93 μM, a value very similar to the IC50 for its depressant action on sustained INa. The addition of SSM was also effective at suppressing the amplitude of resurgent INa. The addition of SSM could concentration-dependently inhibit the IK(M) amplitude with an IC50 value of 4.8 μM. SSM at a concentration of 30 μM could suppress the amplitude of IK(erg), while at 10 μM, it mildly decreased the IK(DR) amplitude. However, the addition of neither SSM (10 μM) nor SesA (10 μM) altered the amplitude or kinetics of Ih in response to long-lasting hyperpolarization. Additionally, in this study, a modified Markovian model designed for SCN8A-encoded (or NaV1.6) channels was implemented to evaluate the plausible modifications of SSM on the gating kinetics of NaV channels. The model demonstrated herein was well suited to predict that the SSM-mediated decrease in peak INa, followed by increased current inactivation, which could largely account for its favorable decrease in the probability of the open-blocked over open state of NaV channels. Collectively, our study provides evidence that highlights the notion that SSM or SesA could block multiple ion currents, such as INa and IK(M), and suggests that these actions are potentially important and may participate in the functional activities of various electrically excitable cells in vivo.

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