scholarly journals Inhibition of sodium currents by local anesthetics in chloramine-T-treated squid axons. The role of channel activation.

1987 ◽  
Vol 89 (4) ◽  
pp. 645-667 ◽  
Author(s):  
G K Wang ◽  
M S Brodwick ◽  
D C Eaton ◽  
G R Strichartz
Keyword(s):  
Local Anesthetics ◽  
Voltage Dependence ◽  
Time Dependent ◽  
Na Channel ◽  
Dependent Manner ◽  
Channel Activation ◽  
Channel Inactivation ◽  
Phasic Block ◽  
Na Currents ◽  
Chloramine T

In order to test the requirement of Na channel inactivation for the action of local anesthetics, we investigated the inhibitory effects of quaternary and tertiary amine anesthetics on normally inactivating and noninactivating Na currents in squid axons under voltage clamp. Either the enzymatic mixture pronase, or chloramine-T (CT), a noncleaving, oxidizing reagent, was used to abolish Na channel inactivation. We found that both the local anesthetics QX-314 and etidocaine, when perfused internally at 1 mM, elicited a "tonic" (resting) block of Na currents, a "time-dependent" block that increased during single depolarizations, and a "use-dependent" (phasic) block that accumulated as a result of repetitive depolarizations. All three effects occurred in both control and CT-treated axons. As in previous reports, little time-dependent or phasic block by QX-314 appeared in pronase-treated axons, although tonic block remained. Time-dependent block was greatest and fastest at large depolarizations (Em greater than +60 mV) for both the control and CT-treated axons. The recovery kinetics from phasic block were the same in control and CT-modified axons. The voltage dependence of the steady state phasic block in CT-treated axons differed from that in the controls; an 8-10% reduction of the maximum phasic block and a steepening and shift of the voltage dependence in the hyperpolarizing direction resulted from CT treatment. The results show that these anesthetics can bind rapidly to open Na channels in a voltage-dependent manner, with no requirement for fast inactivation. We propose that the rapid phasic blocking reactions in nerve are consequences primarily of channel activation, mediated by binding of anesthetics to open channels, and that the voltage dependence of phasic block arises directly from that of channel activation.

scholarly journals Kinetic analysis of the action of Leiurus scorpion alpha-toxin on ionic currents in myelinated nerve.

1985 ◽  
Vol 86 (5) ◽  
pp. 739-762 ◽  
Author(s):  
G K Wang ◽  
G Strichartz
Keyword(s):  
Steady State ◽  
Ionic Currents ◽  
Na Channel ◽  
Dependent Manner ◽  
Na Current ◽  
Toxin Concentration ◽  
Toxin Molecule ◽  
Channel Inactivation ◽  
Na Currents ◽  
Voltage Dependent

The effects of a neurotoxin, purified from the venom of the scorpion Leiurus quinquestriatus, on the ionic currents of toad single myelinated fibers were studied under voltage-clamp conditions. Unlike previous investigations using crude scorpion venom, purified Leiurus toxin II alpha at high concentrations (200-400 nM) did not affect the K currents, nor did it reduce the peak Na current in the early stages of treatment. The activation of the Na channel was unaffected by the toxin, the activation time course remained unchanged, and the peak Na current vs. voltage relationship was not altered. In contrast, Na channel inactivation was considerably slowed and became incomplete. As a result, a steady state Na current was maintained during prolonged depolarizations of several seconds. These steady state Na currents had a different voltage dependence from peak Na currents and appeared to result from the opening of previously inactivated Na channels. The opening kinetics of the steady state current were exponential and had rates approximately 100-fold slower than the normal activation processes described for transitions from the resting state to the open state. In addition, the dependence of the peak Na current on the potential of preceding conditioning pulses was also dramatically altered by toxin treatment; this parameter reached a minimal value near a membrane potential of -50 mV and then increased continuously to a "plateau" value at potentials greater than +50 mV. The amplitude of this plateau was dependent on toxin concentration, reaching a maximum value equal to approximately 50% of the peak current; voltage-dependent reversal of the toxin's action limits the amplitude of the plateauing effect. The measured plateau effect was half-maximum at a toxin concentration of 12 nM, a value quite similar to the concentration producing half of the maximum slowing of Na channel inactivation. The results of Hill plots for these actions suggest that one toxin molecule binds to one Na channel. Thus, the binding of a single toxin molecule probably both produces the steady state currents and slows the Na channel inactivation. We propose that Leiurus toxin inhibits the conversion of the open state to inactivated states in a voltage-dependent manner, and thereby permits a fraction of the total Na permeability to remain at membrane potentials where inactivation is normally complete.

Different voltage dependence of transient and persistent Na+ currents is compatible with modal-gating hypothesis for sodium channels

1994 ◽  
Vol 71 (6) ◽  
pp. 2562-2565 ◽  
Author(s):  
A. M. Brown ◽  
P. C. Schwindt ◽  
W. E. Crill
Keyword(s):  
Pyramidal Neurons ◽  
Voltage Dependence ◽  
Sufficient Evidence ◽  
Na Channel ◽  
Na Channels ◽  
Activation Curve ◽  
Neocortical Neurons ◽  
Na Currents ◽  
Flow Through ◽  
The Difference

1. These experiments tested the hypothesis that the differing voltage dependence of the transient (INa) and persistent (INaP) Na+ currents in neocortical neurons results from the state of inactivation of one type of Na+ channel rather than from the existence of different types of Na+ channels. This question was examined in acutely isolated pyramidal neurons from the sensorimotor cortex of rats by using papain to remove inactivation from INa and comparing the resulting activation curve with that of INaP. 2. In control cells, INaP activated at more negative potentials than INa. Inclusion of papain in the recording pipette removed inactivation from INa and caused the INa activation curve to be shifted leftward to the position of the curve for INaP measured in control cells. Papain greatly increased both INa amplitude and the time to reach peak INa during smaller depolarizations, whereas the difference between control and test currents was reduced during large depolarizations. 3. We conclude that differences in the voltage dependence of INa and INaP activation does not provide sufficient evidence that these currents flow through separate sets of Na+ channels. Instead, our results are consistent with the idea that INaP largely arises from a fraction of the transient Na+ channels that intermittently lose their inactivation.

scholarly journals BTX modification of Na channels in squid axons. I. State dependence of BTX action.

1991 ◽  
Vol 97 (3) ◽  
pp. 499-519 ◽  
Author(s):  
J Tanguy ◽  
J Z Yeh
Keyword(s):  
Time Constant ◽  
Slow Rate ◽  
Open Channel ◽  
Voltage Dependence ◽  
State Dependence ◽  
Na Channel ◽  
Na Channels ◽  
Fast Inactivation ◽  
Similar Time ◽  
Chloramine T

The state dependence of Na channel modification by batrachotoxin (BTX) was investigated in voltage-clamped and internally perfused squid giant axons before (control axons) and after the pharmacological removal of the fast inactivation by pronase, chloramine-T, or NBA (pretreated axons). In control axons, in the presence of 2-5 microM BTX, a repetitive depolarization to open the channels was required to achieve a complete BTX modification, characterized by the suppression of the fast inactivation and a simultaneous 50-mV shift of the activation voltage dependence in the hyperpolarizing direction, whereas a single long-lasting (10 min) depolarization to +50 mV could promote the modification of only a small fraction of the channels, the noninactivating ones. In pretreated axons, such a single sustained depolarization as well as the repetitive depolarization could induce a complete modification, as evidenced by a similar shift of the activation voltage dependence. Therefore, the fast inactivated channels were not modified by BTX. We compared the rate of BTX modification of the open and slow inactivated channels in control and pretreated axons using different protocols: (a) During a repetitive depolarization with either 4- or 100-ms conditioning pulses to +80 mV, all the channels were modified in the open state in control axons as well as in pretreated axons, with a similar time constant of approximately 1.2 s. (b) In pronase-treated axons, when all the channels were in the slow inactivated state before BTX application, BTX could modify all the channels, but at a very slow rate, with a time constant of approximately 9.5 min. We conclude that at the macroscopic level BTX modification can occur through two different pathways: (a) via the open state, and (b) via the slow inactivated state of the channels that lack the fast inactivation, spontaneously or pharmacologically, but at a rate approximately 500-fold slower than through the main open channel pathway.

scholarly journals Block of Neuronal Na+Channels by Antidepressant Duloxetine in a State-dependent Manner

2010 ◽  
Vol 113 (3) ◽  
pp. 655-665 ◽  
Author(s):  
Sho-Ya Wang ◽  
Joanna Calderon ◽  
Ging Kuo Wang
Keyword(s):  
Open Channel ◽  
Site Directed Mutagenesis ◽  
Na Channel ◽  
Dependent Manner ◽  
Channel Block ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Open Channel Block ◽  
Human Embryonic Kidney Cells ◽  
Na Currents

Background Duloxetine is a mixed serotonin-norepinephrine reuptake inhibitor used for major depressive disorder. Duloxetine is also beneficial for patients with diabetic peripheral neuropathy and with fibromyalgia, but how it works remains unclear. Methods We used the whole cell, patch clamp technique to test whether duloxetine interacts with the neuronal Nav1.7 Na+ channel as a potential target. Resting and inactivated Nav1.7 Na+ channel block by duloxetine were measured by conventional pulse protocols in transfected human embryonic kidney cells. The open-channel block was determined directly using inactivation-deficient mutant Nav1.7 Na+ channels. Results The 50% inhibitory concentration (IC50) of duloxetine for the resting and inactivated wild-type hNav1.7 Na+ channel were 22.1+/-0.4 and 1.79+/-0.10 microM, respectively (mean+/-SE, n=5). The IC50 for the open Na+ channel was 0.25+/-0.02 microM (n=5), as determined by the block of persistent late Nav1.7 Na+ currents. Similar open-channel block by duloxetine was found in the muscle Nav1.4 isoform (IC50=0.51+/-0.05 microM; n=5). Block by duloxetine appeared via the conserved local anesthetic receptor as determined by site-directed mutagenesis. Finally, duloxetine elicited strong use-dependent block of neuronal transient Nav1.7 Na+ currents during repetitive stimulations. Conclusions Duloxetine blocks persistent late Nav1.7 Na+ currents preferentially, which may in part account for its analgesic action.

scholarly journals Interactions between Local Anesthetics and Na+ Channel Inactivation Gate Peptides in Phosphatidylserine Suspensions as Studied by 1H-NMR Spectroscopy.

2000 ◽  
Vol 48 (9) ◽  
pp. 1293-1298 ◽  
Author(s):  
Yoshihiro KURODA ◽  
Kazuhide MIYAMOTO ◽  
Kazufumi TANAKA ◽  
Yoshitaka MAEDA ◽  
Junya ISHIKAWA ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
Local Anesthetics ◽  
1H Nmr Spectroscopy ◽  
Na Channel ◽  
Channel Inactivation

Operantly conditioned motoneuron plasticity: possible role of sodium channels

1995 ◽  
Vol 73 (2) ◽  
pp. 867-871 ◽  
Author(s):  
J. A. Halter ◽  
J. S. Carp ◽  
J. R. Wolpaw
Keyword(s):  
Voltage Dependence ◽  
Myelinated Axon ◽  
H Reflex ◽  
Na Channel ◽  
Channel Activation ◽  
Positive Shift ◽  
Fiber Properties ◽  
Kinase C ◽  
Experimental Findings

1. Learning is traditionally thought to depend on synaptic plasticity. However, recent work shows that operantly conditioned decrease in the primate H reflex is associated with an increase in the depolarization needed to fire the spinal motoneuron (VDEP) and a decrease in its conduction velocity (CV). Furthermore, the increase in VDEP appears to be largely responsible for the H-reflex decrease. The conjunction of these changes in VDEP and CV suggests that an alteration in Na+ channel properties throughout the soma and axon could be responsible. 2. A mathematical model of the mammalian myelinated axon was used to test whether a positive shift in the voltage dependence of Na+ channel activation, a decrease in Na+ channel peak permeability, or changes in other fiber properties could have accounted for the experimental findings. 3. A positive shift of 2.2 mV in Na+ channel activation reproduced the experimentally observed changes in VDEP and CV, whereas a reduction in Na+ channel permeability or changes in other fiber properties did not. 4. These results are consistent with the hypothesis that operantly conditioned decrease in the primate H reflex is largely due to a positive shift in the voltage dependence of Na+ channel activation. Recent studies suggest that change in activation of protein kinase C may mediate this effect.

Pharmacological properties of voltage-gated Na+ currents in motor neurones from a hydrozoan jellyfish Polyorchis penicillatus

1996 ◽  
Vol 199 (4) ◽  
pp. 941-948 ◽  
Author(s):  
J Spafford ◽  
N Grigoriev ◽  
A Spencer
Keyword(s):  
Local Anaesthetics ◽  
Bay K 8644 ◽  
Na Channel ◽  
Pharmacological Properties ◽  
Dependent Manner ◽  
Na Current ◽  
Polyorchis Penicillatus ◽  
Na Currents ◽  
Motor Neurones ◽  
High Concentrations

The Na+ current of 'swimming motor neurones' in the hydromedusan Polyorchis penicillatus was tetrodotoxin-insensitive. The local anaesthetics lidocaine and procainamide caused partial, non use-dependent blockade of the Na+ channel. Veratridine produced partial blockade of the Na+ channel without affecting inactivation. An order of blocking potency of di- and trivalent cations was established as: La3+ = Zn2+ = Cd2+ > Ni2+ > Mn2+ = Co2+ > Ca2+ > Ba2+ > Mg2+. All these cations, except Ba2+, produced depolarizing shifts in the conductance-voltage curves. Even at relatively high concentrations, the dihydropyridines nicardipine, nitrendipine and (+)Bay K 8644 produced only weak blockade of the Na+ current; while nimodipine, nifedipine and (-)Bay K 8644 were ineffective. Diltiazem and verapamil weakly blocked the Na+ current in a dose-dependent manner with no evidence of use-dependence. The calmodulin inhibitors W7 and calmidazolium were ineffective blockers of Na+ currents. Crude Conus venoms and the Conus peptides, µ-conotoxin GIIA, µO-conotoxin MrVIA, omega-conotoxin GVIA and omega-conotoxin MVIIC, were without effect. Capsaicin produced rapid, reversable blockade of Na+ current. It has been suggested that 'primitive' Na+ channels could be expected to have pharmacological properties that are intermediate between those of Na+ and Ca2+ channels. If such channels exist, the Na+ channel described here is clearly not one of them.

Differential Effects of Anesthetic and Nonanesthetic Cyclobutanes on Neuronal Voltage-gated Sodium Channels

2000 ◽  
Vol 92 (2) ◽  
pp. 529-529 ◽  
Author(s):  
Lingamaneni Ratnakumari ◽  
Tatyana N. Vysotskaya ◽  
Daniel S. Duch ◽  
Hugh C. Hemmings
Keyword(s):  
Dorsal Root Ganglion ◽  
Dorsal Root ◽  
Voltage Dependence ◽  
Glutamate Release ◽  
Dorsal Root Ganglion Neurons ◽  
Na Channel ◽  
Na Channels ◽  
Na Currents ◽  
Steady State Inactivation ◽  
Ganglion Neurons

Background Despite their key role in the generation and propagation of action potentials in excitable cells, voltage-gated sodium (Na+) channels have been considered to be insensitive to general anesthetics. The authors tested the sensitivity of neuronal Na+ channels to structurally similar anesthetic (1-chloro-1,2,2-trifluorocyclobutane; F3) and nonanesthetic (1,2-dichlorohexafluorocyclobutane; F6) polyhalogenated cyclobutanes by neurochemical and electrophysiologic methods. Methods Synaptosomes (pinched-off nerve terminals) from adult rat cerebral cortex were used to determine the effects of F3 and F6 on 4-aminopyridine- or veratridine-evoked (Na+ channel-dependent) glutamate release (using an enzyme-coupled spectrofluorimetric assay) and increases in intracellular Ca2+ ([Ca2+]i) (using ion-specific spectrofluorimetry). Effects of F3 and F6 on Na+ currents were evaluated directly in rat lumbar dorsal root ganglion neurons by whole-cell patch-clamp recording. Results F3 inhibited glutamate release evoked by 4-aminopyridine (inhibitory concentration of 50% [IC50] = 0.77 mM [approximately 0.8 minimum alveolar concentration (MAC)] or veratridine (IC50 = 0.42 mM [approximately 0.4 MAC]), and veratridine-evoked increases in [Ca2+]i (IC50 = 0.5 mM [approximately 0.5 MAC]) in synaptosomes; F6 had no significant effects up to 0.05 mM (approximately twice the predicted MAC). F3 caused reversible membrane potential-independent inhibition of peak Na+ currents (70+/-9% block at 0.6 mM [approximately 0.6 MAC]), and a hyperpolarizing shift in the voltage-dependence of steady state inactivation in dorsal root ganglion neurons (-21+/-9.3 mV at 0.6 mM). F6 inhibited peak Na+ currents to a lesser extent (16+/-2% block at 0.018 mM [predicted MAC]) and had minimal effects on steady state inactivation. Conclusions The anesthetic cyclobutane F3 significantly inhibited Na+ channel-mediated glutamate release and increases in [Ca2+]i. In contrast, the nonanesthetic cyclobutane F6 had no significant effects at predicted anesthetic concentrations. F3 inhibited dorsal root ganglion neuron Na+ channels with a potency and by mechanisms similar to those of conventional volatile anesthetics; F6 was less effective and did not produce voltage-dependent block. This concordance between anesthetic activity and Na+ channel inhibition supports a role for presynaptic Na+ channels as targets for general anesthetic effects and suggests that shifting the voltage-dependence of Na+ channel inactivation is an important property of volatile anesthetic compounds.

scholarly journals Mechanisms of Two Modulatory Actions of the Channel-binding Protein Slob on the Drosophila Slowpoke Calcium-dependent Potassium Channel

2006 ◽  
Vol 128 (5) ◽  
pp. 583-591 ◽  
Author(s):  
Haoyu Zeng ◽  
Thomas M. Weiger ◽  
Hong Fei ◽  
Irwin B. Levitan
Keyword(s):  
Potassium Channel ◽  
Voltage Dependence ◽  
Calcium Sensitivity ◽  
Dependent Manner ◽  
Voltage Shift ◽  
Calcium Dependent ◽  
Channel Inactivation ◽  
And Shifts ◽  
Dose Dependent ◽  
Independent Mutation

Slob57 is an ion channel auxiliary protein that binds to and modulates the Drosophila Slowpoke calcium-dependent potassium channel (dSlo). We reported recently that residues 1–39 of Slob57 comprise the key domain that both causes dSlo inactivation and shifts its voltage dependence of activation to more depolarized voltages. In the present study we show that removal of residues 2–6 from Slob57 abolishes the inactivation, but the ability of Slob57 to rightward shift the voltage dependence of activation of dSlo remains. A synthetic peptide corresponding in sequence to residues 1–6 of Slob57 blocks dSlo in a voltage- and dose-dependent manner. Two Phe residues and at least one Lys residue in this peptide are required for the blocking action. These data indicate that the amino terminus of Slob57 directly blocks dSlo, thereby leading to channel inactivation. Further truncation to residue Arg16 eliminates the modulation of voltage dependence of activation. Thus these two modulatory actions of Slob57 are independent. Mutation within the calcium bowl of dSlo greatly reduces its calcium sensitivity (Bian, S., I. Favre, and E. Moczydlowski. 2001. Proc. Natl. Acad. Sci. USA. 98:4776–4781). We found that Slob57 still causes inactivation of this mutant channel, but does not shift its voltage dependence of activation. This result confirms further the independence of the inactivation and the voltage shift produced by Slob57. It also suggests that the voltage shift requires high affinity Ca2+ binding to an intact calcium bowl. Furthermore, Slob57 inhibits the shift in the voltage dependence of activation of dSlo evoked by Ca2+, and this inhibition by Slob57 is greater at higher free Ca2+ concentrations. These results implicate distinct calcium-dependent and -independent mechanisms in the modulation of dSlo by Slob.

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