scholarly journals Sodium channel activation in the squid giant axon. Steady state properties.

1985 ◽  
Vol 85 (1) ◽  
pp. 65-82 ◽  
Author(s):  
J R Stimers ◽  
F Bezanilla ◽  
R E Taylor
Keyword(s):  
Giant Axon ◽  
Open Channels ◽  
Na Channel ◽  
Channel Activation ◽  
Voltage Range ◽  
Linear Sequence ◽  
Center Point ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Loligo Pealei

Treatment of giant axons from the squid, Loligo pealei, with pronase removes Na channel inactivation. It was found that the peak Na current is increased, but the activation kinetics are not significantly altered, by pronase. Measurements of the fraction of open channels as a function of voltage (F-V) showed an e-folding at 7 mV and a center point near -15 mV. The rate of e-folding implies that a minimum of 4 e-/channel must cross the membrane field to open the channel. The charge vs. voltage (Q-V) curve measured in a pronase-treated axon is not significantly different from that measured when inactivation is intact: approximately 1,850 e-/micron2 were measured over the voltage range -150 to 50 mV, and the center point was near -30 mV. Normalizing these two curves (F-V and Q-V) and plotting them together reveals that they cross when inactivation is intact but saturate together when inactivation is removed. This illustrates the error one makes when measuring peak conductance with intact inactivation and interpreting that to be the fraction of open channels. A model is described that was used to interpret these results. In the model, we propose that inactivation must be slightly voltage dependent and that an interaction occurs between the inactivating particle and the gating charge. A linear sequence of seven states (a single open state with six closed states) is sufficient to describe the data presented here for Na channel activation in pronase-treated axons.

scholarly journals Rapid voltage-dependent dissociation of scorpion alpha-toxins coupled to Na channel inactivation in amphibian myelinated nerves.

1986 ◽  
Vol 88 (3) ◽  
pp. 413-435 ◽  
Author(s):  
G R Strichartz ◽  
G K Wang
Keyword(s):  
Cumulative Effect ◽  
Single Pulse ◽  
Dissociation Rate ◽  
Na Channel ◽  
Myelinated Nerve ◽  
Voltage Range ◽  
Channel Inactivation ◽  
Voltage Dependent ◽  
Centruroides Sculpturatus ◽  
Myelinated Nerves

The voltage-dependent action of several scorpion alpha-toxins on Na channels was studied in toad myelinated nerve under voltage clamp. These toxins slow the declining phase of macroscopic Na current, apparently by inhibiting an irreversible channel inactivation step and thus permitting channels to reopen from a closed state in depolarized membranes. In this article, we describe the rapid reversal of alpha-toxin action by membrane depolarizations more positive than +20 mV, an effect not achieved by extensive washing. Depolarizations that were increasingly positive and of longer duration caused the toxin to dissociate faster and more completely, but only up to a limiting extent. Repetitive pulses had a cumulative effect equal to that of a single pulse lasting as long as their combined duration. When the membrane of a nonperfused fiber was repolarized, the effects of the toxin returned completely, but if the fiber was perfused during the conditioning procedure, recovery was incomplete and occurred more slowly, as it did at lower applied toxin concentrations. Other alpha-type toxins, from the scorpion Centruroides sculpturatus (IVa) and the sea anemone Anemonia sulcata (ATXII), exhibited similar voltage-dependent binding, though each had its own voltage range and dissociation rate. We suggest that the dissociation of the toxin molecule from the Na channel is coupled to the inactivation process. An equivalent valence for inactivation gating, of less than 1 e per channel, is calculated from the voltage-dependent change in toxin affinity.

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.

Outward stabilization of the voltage sensor in domain II but not domain I speeds inactivation of voltage-gated sodium channels

2013 ◽  
Vol 305 (8) ◽  
pp. H1213-H1221 ◽  
Author(s):  
Michael F. Sheets ◽  
Tiehua Chen ◽  
Dorothy A. Hanck
Keyword(s):  
Sodium Current ◽  
Voltage Sensor ◽  
Inactivation Kinetics ◽  
Na Channel ◽  
Time To Peak ◽  
Voltage Gated Sodium Channels ◽  
Gating Charge ◽  
Voltage Dependent ◽  
The Individual ◽  
A Site

To determine the roles of the individual S4 segments in domains I and II to activation and inactivation kinetics of sodium current ( INa) in NaV1.5, we used a tethered biotin and avidin approach after a site-directed cysteine substitution was made in the second outermost Arg in each S4 (DI-R2C and DII-R2C). We first determined the fraction of gating charge contributed by the individual S4's to maximal gating current (Qmax), and found that the outermost Arg residue in each S4 contributed ∼19% to Qmax with minimal contributions by other arginines. Stabilization of the S4's in DI-R2C and DII-R2C was confirmed by measuring the expected reduction in Qmax. In DI-R2C, stabilization resulted in a decrease in peak INa of ∼45%, while its peak current-voltage ( I-V) and voltage-dependent Na channel availability (SSI) curves were nearly unchanged from wild type (WT). In contrast, stabilization of the DII-R2C enhanced activation with a negative shift in the peak I-V relationship by −7 mV and a larger −17 mV shift in the voltage-dependent SSI curve. Furthermore, its INa decay time constants and time-to-peak INa became more rapid than WT. An explanation for these results is that the depolarized conformation of DII-S4, but not DI-S4, affects the receptor for the inactivation particle formed by the interdomain linker between DIII and IV. In addition, the leftward shifts of both activation and inactivation and the decrease in Gmax after stabilization of the DII-S4 support previous studies that showed β-scorpion toxins trap the voltage sensor of DII in an activated conformation.

Time-dependent changes in kinetics of Na+ current in single canine cardiac Purkinje cells

1992 ◽  
Vol 262 (4) ◽  
pp. H1197-H1207 ◽  
Author(s):  
D. A. Hanck ◽  
M. F. Sheets
Keyword(s):  
Purkinje Cells ◽  
Time Constant ◽  
Decay Time ◽  
Voltage Dependence ◽  
Na Channel ◽  
Time Constants ◽  
Voltage Range ◽  
Time To Peak ◽  
Cardiac Purkinje Cells ◽  
Voltage Dependent

The spontaneous hyperpolarizing shift in Na+ channel kinetics that occurs during a series of voltage-clamp recordings was characterized in single canine cardiac Purkinje cells at 10-13.5 degrees C. The change in the half-point of voltage-dependent availability, in the half-point of peak conductance, in the voltage dependence of deactivation and time to peak Na+ channel current (INa), and in the time constants of INa decay in response to step depolarizations were examined. The half points of availability and conductance shifted similarly, -0.41 +/- 0.13 and -0.47 +/- 0.19 mV/min, respectively (n = 14). These were directly correlated (slope 1.14 +/- 0.06, R2 = 0.81) with conductance shifting on average only -0.05 mV/min faster than availability. The deactivation time constant-voltage relationship shifted similarly to availability and conductance. Tail current decay time constants predicted the voltage dependence of the open to closed transition to be 0.9e-. Time to peak INa in response to step depolarizations changed e-fold for 25 mV but plateaued at positive potentials (531 microseconds, n = 22). INa decay was multiexponential between -40 and 80 mV. Decay time constants changed little as a function of voltage at positive potentials. The contribution of the second time constant to decay amplitude was 15-20% over the entire voltage range. Time to peak INa shifted in a curvilinear fashion, changing less late in an experiment. We conclude that the channel-voltage sensor responds to a changing fraction of the applied voltage during an experiment, producing similar rates of shift of voltage-dependent availability, conductance, and deactivation time constants.

scholarly journals Voltage-dependent open-state inactivation of cardiac sodium channels: gating current studies with Anthopleurin-A toxin.

1995 ◽  
Vol 106 (4) ◽  
pp. 617-640 ◽  
Author(s):  
M F Sheets ◽  
D A Hanck
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Na Channel ◽  
Total Charge ◽  
Na Channels ◽  
Gating Currents ◽  
Gating Charge ◽  
Cardiac Purkinje Cells ◽  
Voltage Dependent ◽  
Cardiac Sodium Channels

The gating charge and voltage dependence of the open state to the inactivated state (O-->I) transition was measured for the voltage-dependent mammalian cardiac Na channel. Using the site 3 toxin, Anthopleurin-A (Ap-A), which selectively modifies the O-->I transition (see Hanck, D. A., and M. F. Sheets. 1995. Journal of General Physiology. 106:601-616), we studied Na channel gating currents (Ig) in voltage-clamped single canine cardiac Purkinje cells at approximately 12 degrees C. Comparison of Ig recorded in response to step depolarizations before and after modification by Ap-A toxin showed that toxin-modified gating currents decayed faster and had decreased initial amplitudes. The predominate change in the charge-voltage (Q-V) relationship was a reduction in gating charge at positive potentials such that Qmax was reduced by 33%, and the difference between charge measured in Ap-A toxin and in control represented the gating charge associated with Na channels undergoing inactivation by O-->I. By comparing the time course of channel activation (represented by the gating charge measured in Ap-A toxin) and gating charge associated with the O-->I transition (difference between control and Ap-A charge), the influence of activation on the time course of inactivation could be accounted for and the inherent voltage dependence of the O-->I transition determined. The O-->I transition for cardiac Na channels had a valence of 0.75 e-. The total charge of the cardiac voltage-gated Na channel was estimated to be 5 e-. Because charge is concentrated near the opening transition for this isoform of the channel, the time constant of the O-->I transition at 0 mV could also be estimated (0.53 ms, approximately 12 degrees C). Prediction of the mean channel open time-voltage relationship based upon the magnitude and valence of the O-->C and O-->I rate constants from INa and Ig data matched data previously reported from single Na channel studies in heart at the same temperature.

Developmental Changes in Two Voltage-Dependent Sodium Currents in Utricular Hair Cells

2007 ◽  
Vol 97 (2) ◽  
pp. 1684-1704 ◽  
Author(s):  
Julian R. A. Wooltorton ◽  
Sophie Gaboyard ◽  
Karen M. Hurley ◽  
Steven D. Price ◽  
Jasmine L. Garcia ◽  
...  
Keyword(s):  
Hair Cells ◽  
Sodium Current ◽  
Na Channel ◽  
Type I ◽  
Voltage Range ◽  
Negative Voltage ◽  
Vestibular Hair Cells ◽  
Voltage Dependent ◽  
Channel Expression ◽  
I Cells

Two kinds of sodium current ( INa) have been separately reported in hair cells of the immature rodent utricle, a vestibular organ. We show that rat utricular hair cells express one or the other current depending on age (between postnatal days 0 and 22, P0—P22), hair cell type (I, II, or immature), and epithelial zone (striola vs. extrastriola). The properties of these two currents, or a mix, can account for descriptions of INa in hair cells from other reports. The patterns of Na channel expression during development suggest a role in establishing the distinct synapses of vestibular hair cells of different type and epithelial zone. All type I hair cells expressed INa,1, a TTX-insensitive current with a very negative voltage range of inactivation (midpoint: −94 mV). INa,2 was TTX sensitive and had less negative voltage ranges of activation and inactivation (inactivation midpoint: −72 mV). INa,1 dominated in the striola at all ages, but current density fell by two-thirds after the first postnatal week. INa,2 was expressed by 60% of hair cells in the extrastriola in the first week, then disappeared. In the third week, all type I cells and about half of type II cells had INa,1; the remaining cells lacked sodium current. INa,1 is probably carried by NaV1.5 subunits based on biophysical and pharmacological properties, mRNA expression, and immunoreactivity. NaV1.5 was also localized to calyx endings on type I hair cells. Several TTX-sensitive subunits are candidates for INa,2.

scholarly journals Sodium ions as blocking agents and charge carriers in the potassium channel of the squid giant axon.

1977 ◽  
Vol 70 (6) ◽  
pp. 707-724 ◽  
Author(s):  
R J French ◽  
J B Wells
Keyword(s):  
Giant Axon ◽  
Negative Slope ◽  
K Channel ◽  
Voltage Range ◽  
Channel Current ◽  
Outward Currents ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Series Of Experiments ◽  
Pass Through

Instantaneous K channel current-voltage (I-V) relations were determined by using internally perfused squid axons. When K was the only internal cation, the I-V relation was linear for outward currents at membrane potentials up to +240 mV inside. With 25-200 mM Na plus 300 mM K in the internal solution, an N-shaped I-V curve was seen. Voltage-dependent blocking of the K channels by Na produces a region of negative slope in the I-V plot (F. Bezanilla and C. M. Armstrong. 1972. J. Gen Physiol, 60: 588). At higher voltages (greater than or equal to 160 mV) we observed a second region of increasing current and a decrease in the fraction of the K conductance blocked by Na. Internal tetraethylammonium (TEA) ions blocked currents over the whole voltage range. In a second series of experiments with K-free, Na-containing internal solutions, the I-V curve turned sharply upward about +160 mV. The current at high voltages increased with increasing internal Na concentration was largely blocked by internal TEA. These data suggest that the K channel becomes substantially more permeable to Na at high voltages. This change is apparently responsible for the relief, at high transmembrane voltages, of the blocking effect seen in axons perfused with Na plus K mixtures. Each time a Na ion passed through, vacating the blocking site, the channel would transiently allow K ions to pass through freely.

scholarly journals Patch recordings from the electrocytes of electrophorus. Na channel gating currents.

1991 ◽  
Vol 98 (3) ◽  
pp. 465-478 ◽  
Author(s):  
S Shenkel ◽  
F Bezanilla
Keyword(s):  
Giant Axon ◽  
Na Channel ◽  
Na Current ◽  
Gating Currents ◽  
Open Probability ◽  
Probability Curve ◽  
Gating Charge ◽  
Pipette Tip ◽  
Effective Valence ◽  
Time Courses

Gating currents were recorded at 11 degrees C in cell-attached and inside-out patches from the innervated membrane of Electrophorus main organ electrocytes. With pipette tip diameters of 3-8 microns, maximal charge measured in patches ranged from 0.74 to 7.19 fC. The general features of the gating currents are similar to those from the squid giant axon. The steady-state voltage dependence of the ON gating charge was characterized by an effective valence of 1.3 +/- 0.4 and a midpoint voltage of -56 +/- 7 mV. The charge vs. voltage relation lies approximately 30 mV negative to the channel open probability curve. The ratio of the time constants of the OFF gating current and the Na current was 2.3 at -120 mV and equal at -80 mV. Charge immobilization and Na current inactivation develop with comparable time courses and have very similar voltage dependences. Between 60 and 80% of the charge is temporarily immobilized by inactivation.

scholarly journals Molecular and biophysical basis of glutamate and trace metal modulation of voltage-gated Cav2.3 calcium channels

2012 ◽  
Vol 139 (3) ◽  
pp. 219-234 ◽  
Author(s):  
Aleksandr Shcheglovitov ◽  
Iuliia Vitko ◽  
Roman M. Lazarenko ◽  
Peihan Orestes ◽  
Slobodan M. Todorovic ◽  
...  
Keyword(s):  
Trace Metals ◽  
Voltage Dependence ◽  
Voltage Sensitivity ◽  
Amino Acid Residues ◽  
Voltage Range ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Charge Movements ◽  
The Brain ◽  
Gating Charges

Here, we describe a new mechanism by which glutamate (Glu) and trace metals reciprocally modulate activity of the Cav2.3 channel by profoundly shifting its voltage-dependent gating. We show that zinc and copper, at physiologically relevant concentrations, occupy an extracellular binding site on the surface of Cav2.3 and hold the threshold for activation of these channels in a depolarized voltage range. Abolishing this binding by chelation or the substitution of key amino acid residues in IS1–IS2 (H111) and IS2–IS3 (H179 and H183) loops potentiates Cav2.3 by shifting the voltage dependence of activation toward more negative membrane potentials. We demonstrate that copper regulates the voltage dependence of Cav2.3 by affecting gating charge movements. Thus, in the presence of copper, gating charges transition into the “ON” position slower, delaying activation and reducing the voltage sensitivity of the channel. Overall, our results suggest a new mechanism by which Glu and trace metals transiently modulate voltage-dependent gating of Cav2.3, potentially affecting synaptic transmission and plasticity in the brain.

scholarly journals MAPbI3 Microrods-Based Photo Resistor Switches: Fabrication and Electrical Characterization

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4385
Author(s):  
Ehsan Raza ◽  
Fakhra Aziz ◽  
Arti Mishra ◽  
Noora Jabor Al-Thani ◽  
Zubair Ahmad
Keyword(s):  
Carrier Transport ◽  
Solution Process ◽  
Electrical Characterization ◽  
Lead Iodide ◽  
Voltage Range ◽  
Conduction Mechanisms ◽  
Voltage Dependent ◽  
Conduction Behavior ◽  
Temperature Solution ◽  
Methylammonium Lead Iodide

The current work proposed the application of methylammonium lead iodide (MAPbI3) perovskite microrods toward photo resistor switches. A metal-semiconductor-metal (MSM) configuration with a structure of silver-MAPbI3(rods)-silver (Ag/MAPbI3/Ag) based photo-resistor was fabricated. The MAPbI3 microrods were prepared by adopting a facile low-temperature solution process, and then an independent MAPbI3 microrod was employed to the two-terminal device. The morphological and elemental compositional studies of the fabricated MAPbI3 microrods were performed using FESEM and EDS, respectively. The voltage-dependent electrical behavior and electronic conduction mechanisms of the fabricated photo-resistors were studied using current–voltage (I–V) characteristics. Different conduction mechanisms were observed at different voltage ranges in dark and under illumination. In dark conditions, the conduction behavior was dominated by typical trap-controlled charge transport mechanisms within the investigated voltage range. However, under illumination, the carrier transport is dominated by the current photogenerated mechanism. This study could extend the promising application of perovskite microrods in photo-induced resistor switches and beyond.

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