Modeling of the Physical Mechanism of Activation (Opening) of Ion Channels in Nerve Impulse Transmission

2015 ◽  
pp. 313-324
Keyword(s):  
Ion Channels ◽  
Physical Mechanism ◽  
Nerve Impulse

A physical mechanism for large-ion selectivity of ion channels

2002 ◽  
Vol 4 (19) ◽  
pp. 4763-4769 ◽  
Author(s):  
Dirk Gillespie ◽  
Wolfgang Nonner ◽  
Douglas Henderson ◽  
Robert S. Eisenberg
Keyword(s):  
Ion Channels ◽  
Physical Mechanism ◽  
Ion Selectivity

scholarly journals Ion channel depolarization increases repulsions between positive S4 charges to drive activation

2019 ◽  
Author(s):  
H. R. Leuchtag
Keyword(s):  
Amino Acids ◽  
Ion Channels ◽  
Ion Channel ◽  
Nerve Impulse ◽  
Electrostatic Repulsion ◽  
Channel Activation ◽  
Voltage Sensors ◽  
Repulsion Energy ◽  
Repulsive Forces ◽  
The Way

AbstractThe positively charged residues, arginine and lysine, of the S4 segments of voltage-sensitive ion channels repel each other with Coulomb forces inversely proportional to the mean channel dielectric permittivity ε. Dipole moments induced at rest potential in the branched sidechains of leucine, isoleucine and valine lend high values of ε to the channel. High ε keeps electrostatic forces small at rest, leaving the channel in a compact conformation closed to ion conduction. On membrane depolarization beyond threshold, the repulsive forces between positive S4 charges increase greatly on a sharp decrease in ε due to the collapse of induced dipoles, causing an expansion of the S4 segments, which drives the channel into activation. Model calculations based on α helical S4 geometry, neglecting the small number of negative charges, provide estimates of electrostatic energy for different values of open-channel ε and numbers of positive S4 charges. When theShakerK+channel is depolarized, the repulsion energy in each S4 segment increases from about 0.2 kcal/mol to about 120 kJ/mol (30 kcal/mol). The S4 expansions lengthen and widen the pore domain, expanding the hydrogen bonds of its α helices, thus providing sites for permeant ions. Ion percolation via these sites produces the stochastic ion currents observed in activated channels. The model proposed, Channel Activation by Electrostatic Repulsion (CAbER), explains observed features of voltage-sensitive channel behavior and offers predictions that can be tested by experiment.SIGNIFICANCE STATEMENTScience walks on two legs, experiment and theory. Experiment provides the facts that theory seeks to explain; the predictions of a theoretical model are then tested in the laboratory.Rigid adherence to an inadequate model can lead to stagnation of a field.The way in which a protein molecule straddling a lipid membrane in a nerve or muscle fiber responds to a voltage change by allowing certain ions to cross it is currently modeled by simple devices such as gated pores, screws and paddles. Since molecules and everyday objects are worlds apart, these devices don’t provide productive models of the way a voltage-sensitive ion channel is activated when the voltage across the resting membrane is eliminated in a nerve impulse. A change of paradigm is needed.Like all matter, ion channels obey the laws of physics. One such law says that positive charges repel other positive charges. Since each of these ion channels has four “voltage sensors” studded with positive charges, they store repulsion energy in a membrane poised to conduct an impulse. To see how that stored energy is released in activation, we must turn to condensed-state physics. Recent advances in materials called ferroelectric liquid crystals, with structures resembling those of voltage-sensitive ion channels, provide a bridge between physics and biology. This bridge leads to a new model, Channel Activation by Electrostatic Repulsion,Three amino acids scattered throughout the molecules have side chains split at their ends, which makes them highly sensitive to changing electric fields. The calculations that form the core of this report examine the effect of these branched-chain amino acids on the repulsions between the positive charges in the voltage sensors. The numbers tell us that the voltage sensors expand on activation, popping the ion channel into a porous structure through which specific ions are able to cross the membrane and so carry the nerve impulse along.This model may someday enable us to learn more about diseases caused by mutations in voltage-sensitive ion channels. But for now, the ball is in the court of the experimentalists to test whether the predictions of this model are confirmed in the laboratory.

scholarly journals The versatile synapse

1984 ◽  
Vol 112 (1) ◽  
pp. 199-224
Author(s):  
R. M. Pitman
Keyword(s):  
Ion Channels ◽  
Nerve Impulse ◽  
Synaptic Cleft ◽  
Ionic Species ◽  
Postsynaptic Membrane ◽  
Voltage Dependent ◽  
Biochemical Systems ◽  
Characteristics Analysis ◽  
Neurotransmitter Substances ◽  
Neurotransmitter Substance

‘Typically’ chemical synaptic transmission takes place when an influx of calcium ions during a presynaptic nerve impulse triggers exocytosis of neurotransmitter substance from synaptic vesicles. The neurotransmitter diffuses across the synaptic cleft and occupies receptors embedded in the subsynaptic membrane. This interaction (directly or via a second messenger) operates characteristic ion channels and produces an increase in the postsynaptic membrane permeability to particular ions. Depending on the ionic species to which the postsynaptic membrane becomes more permeable, the physiological response will be an excitatory or an inhibitory postsynaptic potential. The action of neurotransmitters may be terminated either by enzymic inactivation or by cellular uptake mechanisms. Over the last decade it has become clear that a neurotransmitter substance may exert a number of different actions on a single postsynaptic neurone. These may involve opening or closure of either voltage-independent or voltage-dependent ion channels. It is also possible that in some instances transmitters may act on neuronal biochemical systems to modify the physiology of postsynaptic cells without directly altering their electrical characteristics. Analysis of the postsynaptic actions of neurotransmitter substances has become further complicated by the increasing body of evidence which indicates that more than one transmitter substance (one of which may be a peptide) can be released from a single presynaptic neurone. The significance of such dual transmitter systems has yet to be fully elucidated. The efficacy of transmission across many synapses may be modified by either presynaptic or postsynaptic mechanisms; both transmitter release and postsynaptic responsiveness may depend on the recent history of a single synapse, on synaptic inputs from other neurones or on circulating neuroactive substances.

scholarly journals Unraveling the mechanism of selective ion transport in hydrophobic subnanometer channels

2015 ◽  
Vol 112 (35) ◽  
pp. 10851-10856 ◽  
Author(s):  
Hui Li ◽  
Joseph S. Francisco ◽  
Xiao Cheng Zeng
Keyword(s):  
Ion Channels ◽  
Ion Transport ◽  
Formation Energy ◽  
Physical Mechanism ◽  
Hydration Shell ◽  
Single Walled Carbon Nanotubes ◽  
Ab Initio Molecular Dynamics ◽  
Water Molecules ◽  
Dynamics Simulations ◽  
Walled Carbon Nanotubes

Recently reported synthetic organic nanopore (SONP) can mimic a key feature of natural ion channels, i.e., selective ion transport. However, the physical mechanism underlying the K+/Na+ selectivity for the SONPs is dramatically different from that of natural ion channels. To achieve a better understanding of the selective ion transport in hydrophobic subnanometer channels in general and SONPs in particular, we perform a series of ab initio molecular dynamics simulations to investigate the diffusivity of aqua Na+ and K+ ions in two prototype hydrophobic nanochannels: (i) an SONP with radius of 3.2 Å, and (ii) single-walled carbon nanotubes (CNTs) with radii of 3–5 Å (these radii are comparable to those of the biological potassium K+ channels). We find that the hydration shell of aqua Na+ ion is smaller than that of aqua K+ ion but notably more structured and less yielding. The aqua ions do not lower the diffusivity of water molecules in CNTs, but in SONP the diffusivity of aqua ions (Na+ in particular) is strongly suppressed due to the rugged inner surface. Moreover, the aqua Na+ ion requires higher formation energy than aqua K+ ion in the hydrophobic nanochannels. As such, we find that the ion (K+ vs. Na+) selectivity of the (8, 8) CNT is ∼20× higher than that of SONP. Hence, the (8, 8) CNT is likely the most efficient artificial K+ channel due in part to its special interior environment in which Na+ can be fully solvated, whereas K+ cannot. This work provides deeper insights into the physical chemistry behind selective ion transport in nanochannels.

XRF and PIXE Analysis of light and Dark Adapted Ocular Tissue

1982 ◽  
Vol 40 ◽  
pp. 190-191
Author(s):  
B. J. Panessa ◽  
H. W. Kraner ◽  
J. B. Warren ◽  
K. W. Jones
Keyword(s):  
Trace Metals ◽  
Pigment Epithelium ◽  
Nerve Impulse ◽  
Light Response ◽  
Ocular Tissue ◽  
Emission Spectrometry ◽  
Retinol Dehydrogenase ◽  
Pixe Analysis ◽  
X Ray ◽  
Optimal Function

During photoexcitation the retina requires specific electrolytes and trace metals for optimal function (Na, Mg, Cl, K, Ca, S, P, Cu and Zn). According to Hagins (1981), photoexcitation and generation of a nerve impulse involves the movement of Ca from the rhodopsin-ladened membranes of the rod outer segment (ROS) to the plasmalemma, which in turn decreases the in-flow of Na into the photoreceptor, resulting in hyperpolarization. In toad isolated retinas, the presence of Ba has been found to increase the amplitude and prolong the delay of the light response (Brown and Flaming, 1978). Trace metals such as Cu, Zn and Se are essential for the activity of the metalloenzymes of the retina and retina pigment epithelium (RPE) (i.e. carbonic anhydrase, retinol dehydrogenase, tyrosinase, glutathione peroxidase, superoxide dismutase...). Therefore the content and fluctuations of these elements in the retina and choroid are of fundamental importance for the maintenance of vision. This paper presents elemental data from light and dark adapted frog ocular tissues examined by electron beam induced x-ray microanalysis, x-ray fluorescence spectrometry (XRF) and proton induced x-ray emission spectrometry (PIXE).

Signalling gates in abscisic acid-mediated control of guard cell ion channels

1997 ◽  
Vol 100 (3) ◽  
pp. 481-490 ◽  
Author(s):  
Michael R. Blatt ◽  
Alexander Grabov
Keyword(s):  
Abscisic Acid ◽  
Ion Channels ◽  
Guard Cell
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