268 research outputs found
Mathematical Model Investigating the Effects of Neurostimulation Therapies on Neural Functioning: Comparing the Effects of Neuromodulation Techniques on Ion Channel Gating and Ionic Flux Using Finite Element Analysis
Neurostimulation therapies demonstrate success as a medical intervention for individuals with neurodegenerative diseases, such as Parkinson’s and Alzheimer’s disease. Despite promising results from these treatments, the influence of an electric current on ion concentrations and subsequent transmembrane voltage is unclear. This project focuses on developing a unique cellular-level mathematical model of neurostimulation to better understand its e↵ects on neuronal electrodynamics. The mathematical model presented here integrates the Poisson-Nernst-Planck system of PDEs and Hodgkin-Huxley based ODEs to model the e↵ects of this neurotherapy on transmembrane voltage, ion channel gating, and ionic mobility. This system is decoupled using the Gauss-Seidel method and then the equations are solved using the finite element method on a biologically-inspired discretized domain. Results demonstrate the influence of transcranial electrical stimulation on membrane voltage, ion channel gating, and transmembrane flux. Simulations also compare the e↵ects of two di↵erent types of neurostimulation (transcranial electrical stimulation and deep brain stimulation) showcasing cellular-level di↵erences resulting from these distinct forms of electrical therapy. Hopefully this work will ultimately help elucidate the principles by which neurostimulation alleviates disease symptoms
Electrokinetic Lattice Boltzmann solver coupled to Molecular Dynamics: application to polymer translocation
We develop a theoretical and computational approach to deal with systems that
involve a disparate range of spatio-temporal scales, such as those comprised of
colloidal particles or polymers moving in a fluidic molecular environment. Our
approach is based on a multiscale modeling that combines the slow dynamics of
the large particles with the fast dynamics of the solvent into a unique
framework. The former is numerically solved via Molecular Dynamics and the
latter via a multi-component Lattice Boltzmann. The two techniques are coupled
together to allow for a seamless exchange of information between the
descriptions. Being based on a kinetic multi-component description of the fluid
species, the scheme is flexible in modeling charge flow within complex
geometries and ranging from large to vanishing salt concentration. The details
of the scheme are presented and the method is applied to the problem of
translocation of a charged polymer through a nanopores. In the end, we discuss
the advantages and complexities of the approach
Testing the Applicability of Nernst-Planck Theory in Ion Channels: Comparisons with Brownian Dynamics Simulations
The macroscopic Nernst-Planck (NP) theory has often been used for predicting ion channel currents in recent years, but the validity of this theory at the microscopic scale has not been tested. In this study we systematically tested the ability of the NP theory to accurately predict channel currents by combining and comparing the results with those of Brownian dynamics (BD) simulations. To thoroughly test the theory in a range of situations, calculations were made in a series of simplified cylindrical channels with radii ranging from 3 to 15 Å, in a more complex ‘catenary’ channel, and in a realistic model of the mechanosensitive channel MscS. The extensive tests indicate that the NP equation is applicable in narrow ion channels provided that accurate concentrations and potentials can be input as the currents obtained from the combination of BD and NP match well with those obtained directly from BD simulations, although some discrepancies are seen when the ion concentrations are not radially uniform. This finding opens a door to utilising the results of microscopic simulations in continuum theory, something that is likely to be useful in the investigation of a range of biophysical and nano-scale applications and should stimulate further studies in this direction
Interacting Ions in Biophysics: Real is not Ideal
Ions in water are important in biology, from molecules to organs.
Classically, ions in water are treated as ideal noninteracting particles in a
perfect gas. Excess free energy of ion was zero. Mathematics was not available
to deal consistently with flows, or interactions with ions or boundaries.
Non-classical approaches are needed because ions in biological conditions flow
and interact. The concentration gradient of one ion can drive the flow of
another, even in a bulk solution. A variational multiscale approach is needed
to deal with interactions and flow. The recently developed energetic
variational approach to dissipative systems allows mathematically consistent
treatment of bio-ions Na, K, Ca and Cl as they interact and flow. Interactions
produce large excess free energy that dominate the properties of the high
concentration of ions in and near protein active sites, channels, and nucleic
acids: the number density of ions is often more than 10 M. Ions in such crowded
quarters interact strongly with each other as well as with the surrounding
protein. Non-ideal behavior has classically been ascribed to allosteric
interactions mediated by protein conformation changes. Ion-ion interactions
present in crowded solutions--independent of conformation changes of
proteins--are likely to change interpretations of allosteric phenomena.
Computation of all atoms is a popular alternative to the multiscale approach.
Such computations involve formidable challenges. Biological systems exist on
very different scales from atomic motion. Biological systems exist in ionic
mixtures (extracellular/intracellular solutions), and usually involve flow and
trace concentrations of messenger ions (e.g., 10-7 M Ca2+). Energetic
variational methods can deal with these characteristic properties of biological
systems while we await the maturation and calibration of all atom simulations
of ionic mixtures and divalents
Rectification properties of conically shaped nanopores: consequences of miniaturization
Nanopores attracted a great deal of scientific interest as templates for
biological sensors as well as model systems to understand transport phenomena
at the nanoscale. The experimental and theoretical analysis of nanopores has
been so far focused on understanding the effect of the pore opening diameter on
ionic transport. In this article we present systematic studies on the
dependence of ion transport properties on the pore length. Particular attention
was given to the effect of ion current rectification exhibited for conically
shaped nanopores with homogeneous surface charges. We found that reducing the
length of conically shaped nanopores significantly lowered their ability to
rectify ion current. However, rectification properties of short pores can be
enhanced by tailoring the surface charge and the shape of the narrow opening.
Furthermore we analyze the relationship of the rectification behavior and ion
selectivity for different pore lengths. All simulations were performed using
MsSimPore, a software package for solving the Poisson-Nernst-Planck (PNP)
equations. It is based on a novel finite element solver and allows for
simulations up to surface charge densities of -2 e/nm^2. MsSimPore is based on
1D reduction of the PNP model, but allows for a direct treatment of the pore
with bulk electrolyte reservoirs, a feature which was previously used in higher
dimensional models only. MsSimPore includes these reservoirs in the
calculations; a property especially important for short pores, where the ionic
concentrations and the electric potential vary strongly inside the pore as well
as in the regions next to pore entrance
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