The early phase of sodium channel gating current in the squid giant axon. Characteristics of a fast component of displacement charge movement

A fast component of displacement current which accompanies the sodium channel gating current has been recorded from the membrane of the giant axon of the squid Loligo forbesii. This component is characterized by relaxation time constants typically shorter than 25 microseconds. The charge displaced a...

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Veröffentlicht in:European biophysics journal 1992-05, Vol.21 (2), p.99-116
Hauptverfasser: FORSTER, I. C, GREEFF, N. G
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description A fast component of displacement current which accompanies the sodium channel gating current has been recorded from the membrane of the giant axon of the squid Loligo forbesii. This component is characterized by relaxation time constants typically shorter than 25 microseconds. The charge displaced accounts for about 10% (or 2 nC/cm2) of the total displacement charge attributed to voltage-dependent sodium channels. Using a low noise, wide-band voltage clamp system and specially designed voltage step protocols we could demonstrate that this component: (i) is not a recording artifact; (ii) is kinetically independent from the sodium channel activation and inactivation processes; (iii) can account for a significant fraction of the initial amplitude of recorded displacement current and (iv) has a steady state charge transfer which saturates for membrane potentials above +20 mV and below -100 mV. This component can be modelled as a single step transition using the Eyring-Boltzmann formalism with a quantal charge of 1 e- and an asymmetrical energy barrier. Furthermore, if it were associated with the squid sodium channel, our data would suggest one fast transition per channel. A possible role as a sodium channel activation trigger, which would still be consistent with kinetic independence, is discussed. Despite uncertainties about its origin, the property of kinetic independence allows subtraction of this component from the total displacement current to reveal a rising phase in the early time course of the remaining current. This will have to be taken into account when modelling the voltage-dependent sodium channel.
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Using a low noise, wide-band voltage clamp system and specially designed voltage step protocols we could demonstrate that this component: (i) is not a recording artifact; (ii) is kinetically independent from the sodium channel activation and inactivation processes; (iii) can account for a significant fraction of the initial amplitude of recorded displacement current and (iv) has a steady state charge transfer which saturates for membrane potentials above +20 mV and below -100 mV. This component can be modelled as a single step transition using the Eyring-Boltzmann formalism with a quantal charge of 1 e- and an asymmetrical energy barrier. Furthermore, if it were associated with the squid sodium channel, our data would suggest one fast transition per channel. A possible role as a sodium channel activation trigger, which would still be consistent with kinetic independence, is discussed. 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Psychology</topic><topic>In Vitro Techniques</topic><topic>Ion Channel Gating - physiology</topic><topic>Kinetics</topic><topic>Membrane and intracellular transports</topic><topic>Membrane Potentials</topic><topic>Models, Biological</topic><topic>Molecular and cellular biology</topic><topic>Sodium Channels - metabolism</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>FORSTER, I. C</creatorcontrib><creatorcontrib>GREEFF, N. G</creatorcontrib><collection>Pascal-Francis</collection><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>MEDLINE - Academic</collection><jtitle>European biophysics journal</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>FORSTER, I. C</au><au>GREEFF, N. 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Using a low noise, wide-band voltage clamp system and specially designed voltage step protocols we could demonstrate that this component: (i) is not a recording artifact; (ii) is kinetically independent from the sodium channel activation and inactivation processes; (iii) can account for a significant fraction of the initial amplitude of recorded displacement current and (iv) has a steady state charge transfer which saturates for membrane potentials above +20 mV and below -100 mV. This component can be modelled as a single step transition using the Eyring-Boltzmann formalism with a quantal charge of 1 e- and an asymmetrical energy barrier. Furthermore, if it were associated with the squid sodium channel, our data would suggest one fast transition per channel. A possible role as a sodium channel activation trigger, which would still be consistent with kinetic independence, is discussed. 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source MEDLINE; SpringerNature Journals
subjects Animals
Axons - metabolism
Biological and medical sciences
Biophysical Phenomena
Biophysics
Cell physiology
Decapodiformes
Electrochemistry
Fundamental and applied biological sciences. Psychology
In Vitro Techniques
Ion Channel Gating - physiology
Kinetics
Membrane and intracellular transports
Membrane Potentials
Models, Biological
Molecular and cellular biology
Sodium Channels - metabolism
title The early phase of sodium channel gating current in the squid giant axon. Characteristics of a fast component of displacement charge movement
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