scholarly journals α-Scorpion Toxin Impairs a Conformational Change that Leads to Fast Inactivation of Muscle Sodium Channels

2008 ◽  
Vol 132 (2) ◽  
pp. 251-263 ◽  
Author(s):  
Fabiana V. Campos ◽  
Baron Chanda ◽  
Paulo S.L. Beirão ◽  
Francisco Bezanilla
Keyword(s):  
Sodium Channels ◽  
Slow Component ◽  
Scorpion Toxin ◽  
Fast Inactivation ◽  
Gating Current ◽  
Voltage Sensors ◽  
Current Decay ◽  
Fluorescence Measurements ◽  
Gating Charge ◽  
Domain Iii

α-Scorpion toxins bind in a voltage-dependent way to site 3 of the sodium channels, which is partially formed by the loop connecting S3 and S4 segments of domain IV, slowing down fast inactivation. We have used Ts3, an α-scorpion toxin from the Brazilian scorpion Tityus serrulatus, to analyze the effects of this family of toxins on the muscle sodium channels expressed in Xenopus oocytes. In the presence of Ts3 the total gating charge was reduced by 30% compared with control conditions. Ts3 accelerated the gating current kinetics, decreasing the contribution of the slow component to the ON gating current decay, indicating that S4-DIV was specifically inhibited by the toxin. In addition, Ts3 accelerated and decreased the fraction of charge in the slow component of the OFF gating current decay, which reflects an acceleration in the recovery from the fast inactivation. Site-specific fluorescence measurements indicate that Ts3 binding to the voltage-gated sodium channel eliminates one of the components of the fluorescent signal from S4-DIV. We also measured the fluorescent signals produced by the movement of the first three voltage sensors to test whether the bound Ts3 affects the movement of the other voltage sensors. While the fluorescence–voltage (F-V) relationship of domain II was only slightly affected and the F-V of domain III remained unaffected in the presence of Ts3, the toxin significantly shifted the F-V of domain I to more positive potentials, which agrees with previous studies showing a strong coupling between domains I and IV. These results are consistent with the proposed model, in which Ts3 specifically impairs the fraction of the movement of the S4-DIV that allows fast inactivation to occur at normal rates.

scholarly journals Fast Inactivation in Shaker K+ Channels

1998 ◽  
Vol 111 (5) ◽  
pp. 625-638 ◽  
Author(s):  
Michel J. Roux ◽  
Riccardo Olcese ◽  
Ligia Toro ◽  
Francisco Bezanilla ◽  
Enrico Stefani
Keyword(s):  
Time Course ◽  
Ionic Current ◽  
Fast Inactivation ◽  
Gating Current ◽  
Gating Currents ◽  
Current Decay ◽  
Gating Charge ◽  
External Potassium ◽  
Kinetics Of ◽  
Full Charge

Fast inactivating Shaker H4 potassium channels and nonconducting pore mutant Shaker H4 W434F channels have been used to correlate the installation and recovery of the fast inactivation of ionic current with changes in the kinetics of gating current known as “charge immobilization” (Armstrong, C.M., and F. Bezanilla. 1977. J. Gen. Physiol. 70:567–590.). Shaker H4 W434F gating currents are very similar to those of the conducting clone recorded in potassium-free solutions. This mutant channel allows the recording of the total gating charge return, even when returning from potentials that would largely inactivate conducting channels. As the depolarizing potential increased, the OFF gating currents decay phase at −90 mV return potential changed from a single fast component to at least two components, the slower requiring ∼200 ms for a full charge return. The charge immobilization onset and the ionic current decay have an identical time course. The recoveries of gating current (Shaker H4 W434F) and ionic current (Shaker H4) in 2 mM external potassium have at least two components. Both recoveries are similar at −120 and −90 mV. In contrast, at higher potentials (−70 and −50 mV), the gating charge recovers significantly more slowly than the ionic current. A model with a single inactivated state cannot account for all our data, which strongly support the existence of “parallel” inactivated states. In this model, a fraction of the charge can be recovered upon repolarization while the channel pore is occupied by the NH2-terminus region.

scholarly journals β-Scorpion Toxin Modifies Gating Transitions in All Four Voltage Sensors of the Sodium Channel

2007 ◽  
Vol 130 (3) ◽  
pp. 257-268 ◽  
Author(s):  
Fabiana V. Campos ◽  
Baron Chanda ◽  
Paulo S.L. Beirão ◽  
Francisco Bezanilla
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Integrated Approach ◽  
Voltage Sensor ◽  
Scorpion Toxin ◽  
Charge Voltage ◽  
Voltage Sensors ◽  
Fluorescence Measurements ◽  
Voltage Gated Sodium Channels ◽  
Activated State

Several naturally occurring polypeptide neurotoxins target specific sites on the voltage-gated sodium channels. Of these, the gating modifier toxins alter the behavior of the sodium channels by stabilizing transient intermediate states in the channel gating pathway. Here we have used an integrated approach that combines electrophysiological and spectroscopic measurements to determine the structural rearrangements modified by the β-scorpion toxin Ts1. Our data indicate that toxin binding to the channel is restricted to a single binding site on domain II voltage sensor. Analysis of Cole-Moore shifts suggests that the number of closed states in the activation sequence prior to channel opening is reduced in the presence of toxin. Measurements of charge–voltage relationships show that a fraction of the gating charge is immobilized in Ts1-modified channels. Interestingly, the charge–voltage relationship also shows an additional component at hyperpolarized potentials. Site-specific fluorescence measurements indicate that in presence of the toxin the voltage sensor of domain II remains trapped in the activated state. Furthermore, the binding of the toxin potentiates the activation of the other three voltage sensors of the sodium channel to more hyperpolarized potentials. These findings reveal how the binding of β-scorpion toxin modifies channel function and provides insight into early gating transitions of sodium channels.

scholarly journals Inactivation of the sodium channel. II. Gating current experiments.

1977 ◽  
Vol 70 (5) ◽  
pp. 567-590 ◽  
Author(s):  
C M Armstrong ◽  
F Bezanilla
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Slow Component ◽  
Base Line ◽  
Charge Movement ◽  
Gating Current ◽  
Small Current ◽  
Gating Charge ◽  
Recovery From Inactivation ◽  
Activation Gate

Gating current (Ig) has been studied in relation to inactivation of Na channels. No component of Ig has the time course of inactivation; apparently little or no charge movement is associated with this step. Inactivation nonetheless affects Ig by immobilizing about two-thirds of gating charge. Immobilization can be followed by measuring ON charge movement during a pulse and comparing it to OFF charge after the pulse. The OFF:ON ratio is near 1 for a pulse so short that no inactivation occurs, and the ratio drops to about one-third with a time course that parallels inactivation. Other correlations between inactivation and immobilization are that: (a) they have the same voltage dependence; (b) charge movement recovers with the time coures of recovery from inactivation. We interpret this to mean that the immobilized charge returns slowly to "off" position with the time course of recovery from inactivation, and that the small current generated is lost in base-line noise. At -150 mV recover is very rapid, and the immobilized charge forms a distinct slow component of current as it returns to off position. After destruction of inactivation by pronase, there is no immobilization of charge. A model is presented in which inactivation gains its voltage dependence by coupling to the activation gate.

scholarly journals The AMIGO1 adhesion protein modulates movement of Kv2.1 voltage sensors

2021 ◽  
Author(s):  
Rebecka J Sepela ◽  
Robert G Stewart ◽  
Luis Valencia ◽  
Parashar Thapa ◽  
Zeming Wang ◽  
...  
Keyword(s):  
Neuronal Excitability ◽  
Voltage Sensor ◽  
Charge Voltage ◽  
Adhesion Protein ◽  
Voltage Sensors ◽  
Kv Channels ◽  
Mammalian Cell Lines ◽  
Fluorescence Measurements ◽  
Gating Charge ◽  
And Shifts

Voltage-gated potassium (Kv) channels sense voltage and facilitate transmembrane flow of K+ to control the electrical excitability of cells. The Kv2.1 channel subtype is abundant in most brain neurons and its conductance is critical for homeostatic regulation of neuronal excitability. Many forms of regulation modulate Kv2.1 conductance, yet the biophysical mechanisms through which the conductance is modulated are unknown. Here, we investigate the mechanism by which the neuronal adhesion protein AMIGO1 modulates Kv2.1 channels. With voltage clamp recordings and spectroscopy of heterologously expressed Kv2.1 and AMIGO1 in mammalian cell lines, we show that AMIGO1 modulates Kv2.1 voltage sensor movement to change Kv2.1 conductance. AMIGO1 speeds early voltage sensor movements and shifts the gating charge-voltage relationship to more negative voltages. Fluorescence measurements from voltage sensor toxins bound to Kv2.1 indicate that the voltage sensors enter their earliest resting conformation, yet this conformation is less stable upon voltage stimulation. We conclude that AMIGO1 modulates the Kv2.1 conductance activation pathway by destabilizing the earliest resting state of the voltage sensors.

scholarly journals Molecular Action of Lidocaine on the Voltage Sensors of Sodium Channels

2003 ◽  
Vol 121 (2) ◽  
pp. 163-175 ◽  
Author(s):  
Michael F. Sheets ◽  
Dorothy A. Hanck
Keyword(s):  
Channel Gating ◽  
Ionic Current ◽  
Na Channel ◽  
Relative Reduction ◽  
Charge Movement ◽  
Charge Voltage ◽  
Voltage Sensors ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Domain Iii

Block of sodium ionic current by lidocaine is associated with alteration of the gating charge-voltage (Q-V) relationship characterized by a 38% reduction in maximal gating charge (Qmax) and by the appearance of additional gating charge at negative test potentials. We investigated the molecular basis of the lidocaine-induced reduction in cardiac Na channel–gating charge by sequentially neutralizing basic residues in each of the voltage sensors (S4 segments) in the four domains of the human heart Na channel (hH1a). By determining the relative reduction in the Qmax of each mutant channel modified by lidocaine we identified those S4 segments that contributed to a reduction in gating charge. No interaction of lidocaine was found with the voltage sensors in domains I or II. The largest inhibition of charge movement was found for the S4 of domain III consistent with lidocaine completely inhibiting its movement. Protection experiments with intracellular MTSET (a charged sulfhydryl reagent) in a Na channel with the fourth outermost arginine in the S4 of domain III mutated to a cysteine demonstrated that lidocaine stabilized the S4 in domain III in a depolarized configuration. Lidocaine also partially inhibited movement of the S4 in domain IV, but lidocaine's most dramatic effect was to alter the voltage-dependent charge movement of the S4 in domain IV such that it accounted for the appearance of additional gating charge at potentials near −100 mV. These findings suggest that lidocaine's actions on Na channel gating charge result from allosteric coupling of the binding site(s) of lidocaine to the voltage sensors formed by the S4 segments in domains III and IV.

Kinetic properties and inactivation of the gating currents of sodium channels in squid axon

1975 ◽  
Vol 270 (908) ◽  
pp. 449-458 ◽  
Keyword(s):  
Sodium Channels ◽  
Sodium Current ◽  
Kinetic Properties ◽  
Gating Current ◽  
Gating Currents ◽  
Similar Time ◽  
Sodium Permeability ◽  
Small Component ◽  
Current Decay ◽  
Time Courses

Associated with the opening and closing of the sodium channels of nerve membrane is a small component of capacitative current, the gating current. After termination of a depolarizing step the gating current and sodium current decay with similar time courses. Both currents decay more rapidly at relatively negative membrane voltages than at positive ones. The gating current that flows during a depolarizing step is diminished by a pre-pulse that inactivates the sodium permeability. A pre-pulse has no effect after inactivation has been destroyed by internal perfusion with the proteolytic enzyme pronase. Gating charge (considered as positive charge) moves outward during a positive voltage step, with voltage dependent kinetics. The time constant of the outward gating current is a maximum at about —10 mV, and has a smaller value at voltages either more positive or negative than this value.

scholarly journals The Role of the Putative Inactivation Lid in Sodium Channel Gating Current Immobilization

2000 ◽  
Vol 115 (5) ◽  
pp. 609-620 ◽  
Author(s):  
Michael F. Sheets ◽  
John W. Kyle ◽  
Dorothy A. Hanck
Keyword(s):  
Sodium Channel ◽  
Time Constant ◽  
Time Course ◽  
Gating Current ◽  
Similar Time ◽  
Charge Voltage ◽  
Voltage Gated Sodium Channels ◽  
Gating Charge ◽  
Domain Iii ◽  
A Site

We investigated the contribution of the putative inactivation lid in voltage-gated sodium channels to gating charge immobilization (i.e., the slow return of gating charge during repolarization) by studying a lid-modified mutant of the human heart sodium channel (hH1a) that had the phenylalanine at position 1485 in the isoleucine, phenylalanine, and methionine (IFM) region of the domain III–IV linker mutated to a cysteine (ICM-hH1a). Residual fast inactivation of ICM-hH1a in fused tsA201 cells was abolished by intracellular perfusion with 2.5 mM 2-(trimethylammonium)ethyl methanethiosulfonate (MTSET). The time constants of gating current relaxations in response to step depolarizations and gating charge–voltage relationships were not different between wild-type hH1a and ICM-hH1aMTSET. The time constant of the development of charge immobilization assayed at −180 mV after depolarization to 0 mV was similar to the time constant of inactivation of INa at 0 mV for hH1a. By 44 ms, 53% of the gating charge during repolarization returned slowly; i.e., became immobilized. In ICM-hH1aMTSET, immobilization occurred with a similar time course, although only 31% of gating charge upon repolarization (OFF charge) immobilized. After modification of hH1a and ICM-hH1aMTSET with Anthopleurin-A toxin, a site-3 peptide toxin that inhibits movement of the domain IV-S4, charge immobilization did not occur for conditioning durations up to 44 ms. OFF charge for both hH1a and ICM-hH1aMTSET modified with Anthopleurin-A toxin were similar in time course and in magnitude to the fast component of OFF charge in ICM-hH1aMTSET in control. We conclude that movement of domain IV-S4 is the rate-limiting step during repolarization, and it contributes to charge immobilization regardless of whether the inactivation lid is bound. Taken together with previous reports, these data also suggest that S4 in domain III contributes to charge immobilization only after binding of the inactivation lid.

Structural basis of α-scorpion toxin action on Nav channels

Science ◽  
2019 ◽  
Vol 363 (6433) ◽  
pp. eaav8573 ◽  
Author(s):  
Thomas Clairfeuille ◽  
Alexander Cloake ◽  
Daniel T. Infield ◽  
José P. Llongueras ◽  
Christopher P. Arthur ◽  
...  
Keyword(s):  
Electromechanical Coupling ◽  
Receptor Site ◽  
Scorpion Toxin ◽  
Structural Basis ◽  
Fast Inactivation ◽  
Gating Charge ◽  
Nav Channels ◽  
Fast Activation ◽  
Electrical Signaling ◽  
Voltage Sensing Domain

Fast inactivation of voltage-gated sodium (Nav) channels is essential for electrical signaling, but its mechanism remains poorly understood. Here we determined the structures of a eukaryotic Nav channel alone and in complex with a lethal α-scorpion toxin, AaH2, by electron microscopy, both at 3.5-angstrom resolution. AaH2 wedges into voltage-sensing domain IV (VSD4) to impede fast activation by trapping a deactivated state in which gating charge interactions bridge to the acidic intracellular carboxyl-terminal domain. In the absence of AaH2, the S4 helix of VSD4 undergoes a ~13-angstrom translation to unlatch the intracellular fast-inactivation gating machinery. Highlighting the polypharmacology of α-scorpion toxins, AaH2 also targets an unanticipated receptor site on VSD1 and a pore glycan adjacent to VSD4. Overall, this work provides key insights into fast inactivation, electromechanical coupling, and pathogenic mutations in Nav channels.

scholarly journals Mapping the Receptor Sites for a β-Scorpion Toxin on the Pore Module in Domain III of Voltage-Gated Sodium Channels

2012 ◽  
Vol 102 (3) ◽  
pp. 325a
Author(s):  
Joel Z. Zhang ◽  
Vladimir Yarov-Yarovoy ◽  
Todd Scheuer ◽  
Izhar Karbat ◽  
Lior Cohen ◽  
...  
Keyword(s):  
Sodium Channels ◽  
Scorpion Toxin ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Receptor Sites ◽  
Domain Iii
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