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Related Concept Videos

Ion Channels01:19

Ion Channels

The movement of ions like sodium, potassium, and calcium into and out of the cell is essential to maintain the electrochemical gradient in living cells. The ion channels—a class of membrane transport proteins—help maintain this ionic gradient for the smooth functioning of physiological activities such as maintaining cell size and volume, conducting nerve impulses, and gas and nutrient exchange.
Ion channels are specialized integral membrane proteins on the plasma membrane that allow specific...
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Ionic Crystal Structures

Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
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Electrochemical Gradient and Channel Proteins: An Overview

An electrochemical gradient is a fundamental concept in biology and chemistry. It regulates the movement of ions across cell membranes. This movement is influenced by two factors:
The electrical gradient: The electrical gradient across cell membranes refers to the difference in electric charge between the inside and outside of a cell.  This difference drives the movement of ions towards or away from the cells. For instance, if the inside of the cell is more negatively charged relative to the...
Voltage-gated Ion Channels01:26

Voltage-gated Ion Channels

Voltage-gated ion channels are transmembrane proteins that open and close in response to changes in the membrane potential. They are present on the membranes of all electrically excitable cells such as neurons, heart, and muscle cells.
Generally, all voltage-gated ion channels have a 'voltage-sensing domain' that spans the lipid bilayer. The charged residues in the sensor move in response to the membrane potential changes that open the channel allowing ions movement. There are several types of...
Voltage-gated Ion Channels01:26

Voltage-gated Ion Channels

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The Role of Ion Channels in Neuronal Computation01:19

The Role of Ion Channels in Neuronal Computation

A postsynaptic neuron usually receives numerous impulses from several other presynaptic neurons. The axon hillock of the postsynaptic neuron integrates all these signals and determines the likelihood of firing an action potential.
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Protein structure and ionic selectivity in calcium channels: selectivity filter size, not shape, matters.

Attila Malasics1, Dirk Gillespie, Wolfgang Nonner

  • 1Department of Physical Chemistry, University of Pannonia, Veszprém, Hungary.

Biochimica Et Biophysica Acta
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PubMed
Summary

Calcium channels use charge/space competition to select ions. Ion selectivity depends on filter volume and shape, not protein side chain confinement, influencing channel conductance.

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Area of Science:

  • Biophysics
  • Computational Biology
  • Ion Channel Physiology

Background:

  • Calcium channels possess charged selectivity filters crucial for ion transport.
  • Ion selectivity mechanisms, particularly for sodium (Na+) and calcium (Ca2+) ions, are complex.
  • The charge/space competition (CSC) model offers a framework for understanding ion selectivity.

Purpose of the Study:

  • To investigate the role of filter geometry (volume and shape) in calcium channel ion selectivity.
  • To test the hypothesis that ion density within the filter is the primary determinant of Ca2+ vs. Na+ selectivity.
  • To evaluate the influence of protein side chain confinement on ion selectivity.

Main Methods:

  • Development of a reduced computational model for calcium channels.
  • Simulation of ion permeation through selectivity filters with varied dimensions (length and radius).
  • Application of the integrated Nernst-Planck equation to calculate channel conductance.

Main Results:

  • Varying filter volume and shape together significantly impacts ion selectivity.
  • Filter volume and shape are more critical than shape alone for selectivity.
  • Depletion zones of ions play a vital role in determining channel conductance.
  • Confinement of protein side chains does not affect ion selectivity.

Conclusions:

  • The charge/space competition mechanism is supported by the geometric dependence of ion selectivity.
  • Filter volume and shape are key determinants of Ca2+ vs. Na+ selectivity in calcium channels.
  • Computational models are valuable for elucidating the biophysical principles of ion channel function.