Upregulation of a Silent Sodium Channel After Peripheral, but not Central, Nerve Injury in DRG Neurons

1999 ◽  
Vol 82 (5) ◽  
pp. 2776-2785 ◽  
Author(s):  
J. A. Black ◽  
T. R. Cummins ◽  
C. Plumpton ◽  
Y. H. Chen ◽  
W. Hormuzdiar ◽  
...  
Keyword(s):  
Sciatic Nerve ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Sodium Current ◽  
Sodium Currents ◽  
Drg Neurons ◽  
Adult Rats ◽  
Voltage Range ◽  
Type Iii ◽  
Axonal Projections

After transection of their axons within the sciatic nerve, DRG neurons become hyperexcitable. Recent studies have demonstrated the emergence of a rapidly repriming tetrodotoxin (TTX)-sensitive sodium current that may account for this hyperexcitability in axotomized small (<27 μm diam) DRG neurons, but its molecular basis has remained unexplained. It has been shown previously that sciatic nerve transection leads to an upregulation of sodium channel III transcripts, which normally are present at very low levels in DRG neurons, in adult rats. We show here that TTX-sensitive currents in small DRG neurons, after transection of their peripheral axonal projections, reprime more rapidly than those in control neurons throughout a voltage range of −140 to −60 mV, a finding that suggests that these currents are produced by a different sodium channel. After transection of the central axonal projections (dorsal rhizotomy) of these small DRG neurons, in contrast, the repriming kinetics of TTX-sensitive sodium currents remain similar to those of control (uninjured) neurons. We also demonstrate, with two distinct antibodies directed against different regions of the type III sodium channel, that small DRG neurons display increased brain type III immunostaining when studied 7–12 days after transection of their peripheral, but not central, projections. Type III sodium channel immunoreactivity is present within somata and neurites of peripherally axotomized, but not centrally axotomized, neurons studied after <24 h in vitro. Peripherally axotomized DRG neurons in situ also exhibit enhanced type III staining compared with control neurons, including an accumulation of type III sodium channels in the distal portion of the ligated and transected sciatic nerve, but these changes are not seen in centrally axotomized neurons. These observations are consistent with a contribution of type III sodium channels to the rapidly repriming sodium currents observed in peripherally axotomized DRG neurons and suggest that type III channels may at least partially account for the hyperexcitibility of these neurons after injury.

In Vivo NGF Deprivation Reduces SNS Expression and TTX-R Sodium Currents in IB4-Negative DRG Neurons

1999 ◽  
Vol 81 (2) ◽  
pp. 803-810 ◽  
Author(s):  
Jenny Fjell ◽  
Theodore R. Cummins ◽  
Kaj Fried ◽  
Joel A. Black ◽  
Stephen G. Waxman
Keyword(s):  
Sodium Channel ◽  
Current Density ◽  
Sodium Current ◽  
High Antibody ◽  
Sodium Currents ◽  
Drg Neurons ◽  
Adult Rats ◽  
Antibody Titers

In vivo NGF deprivation reduces SNS expression and TTX-R sodium currents in IB4-negative DRG neurons. Recent evidence suggests that changes in sodium channel expression and localization may be involved in some pathological pain syndromes. SNS, a tetrodotoxin-resistant (TTX-R) sodium channel, is preferentially expressed in small dorsal root ganglion (DRG) neurons, many of which are nociceptive. TTX-R sodium currents and SNS mRNA expression have been shown to be modulated by nerve growth factor (NGF) in vitro and in vivo. To determine whether SNS expression and TTX-R currents in DRG neurons are affected by reduced levels of systemic NGF, we immunized adult rats with NGF, which causes thermal hypoalgesia in rats with high antibody titers to NGF. DRG neurons cultured from rats with high antibody titers to NGF, which do not bind the isolectin IB4 (IB4−) but do express TrkA, were studied with whole cell patch-clamp and in situ hybridization. Mean TTX-R sodium current density was decreased from 504 ± 77 pA/pF to 307 ± 61 pA/pF in control versus NGF-deprived neurons, respectively. In comparison, the mean TTX-sensitive sodium current density was not significantly different between control and NGF-deprived neurons. Quantification of SNS mRNA hybridization signal showed a significant decrease in the signal in NGF-deprived neurons compared with the control neurons. The data suggest that NGF has a major role in the maintenance of steady-state levels of TTX-R sodium currents and SNS mRNA in IB4− DRG neurons in adult rats in vivo.

scholarly journals GPER mediated  estrogenic amelioration of sodium channel dysfunction in stressed human induced  pluripotent stem cell-derived cardiomyocytes            

2021 ◽  
Author(s):  
Xide Hu ◽  
Lu Fu ◽  
Mingming Zhao ◽  
Hongyuan Zhang ◽  
Zheng Gong ◽  
...  
Keyword(s):  
Stem Cell ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Small Interfering Rna ◽  
Pluripotent Stem Cell ◽  
Sodium Current ◽  
Induced Pluripotent Stem Cell ◽  
Sodium Currents ◽  
Induced Pluripotent ◽  
Interfering Rna

Stress-induced excessive activation of the adrenergic system or changes in estrogen levels promote the occurrence of arrhythmias. Sodium channel, a responder to β-adrenergic stimulation, is involved in stress-induced cardiac electrophysiological abnormalities. However, it has not been established whether estrogen regulates sodium channels during acute stress. Our study aimed to explore whether voltage-gated sodium channels play roles in the rapid regulation of various concentrations of estrogen in stressed human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), and reveal the possible mechanism of estrogen signaling pathway modulating stress. An isoproterenol-induced stress model of hiPSC-CMs was pre-incubated with β-Estradiol at different concentrations (0.01 nmol/L, 1 nmol/L, and 100 nmol/L). Action potential (AP) and sodium currents were detected by patch clamp. The G protein-coupled estrogen receptor (GPER)-specific effect was determined with agonists G1, antagonists G15 and small interfering RNA. β-Estradiol at concentrations of 0.01 nmol/L, 1 nmol/L, and 100 nmol/L increased the peak sodium current and prolonged AP duration (APD) at 1 nmol/L. Stress increased peak sodium current, late sodium current, and shortened APD. The effects of stress on sodium currents and APD were eliminated by β-Estradiol. Activation of GPER by G1 exhibited similar effects as β-Estradiol, while inhibition of GPER with G15 and small interfering RNA ameliorated estrogenic actions. Estrogen, antagonized the stress-related abnormal electrical activity, and through GPER alleviated sodium channel dysfunctions in stress state in hiPSC-CMs. These results provide a novel mechanism through which estrogenic rapid signaling against stress by regulating ion channels.

scholarly journals Type III sodium channel mRNA is expressed in embryonic but not adult spinal sensory neurons, and is reexpressed following axotomy

1994 ◽  
Vol 72 (1) ◽  
pp. 466-470 ◽  
Author(s):  
S. G. Waxman ◽  
J. D. Kocsis ◽  
J. A. Black
Keyword(s):  
In Situ Hybridization ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Developmental Stages ◽  
Type I ◽  
Drg Neurons ◽  
Altered Expression ◽  
Type Iii ◽  
Adult Rat

1. In situ hybridization with subtype-specific probes was used to ask whether there is a change in the types of sodium channels that are expressed in dorsal root ganglion (DRG) neurons after axotomy. 2. Types I and II sodium channel mRNA are expressed at moderate-to-high levels in control DRG neurons of adult rat, but type III sodium channel mRNA is not detectable. 3. When adult rat DRG neurons are examined by in situ hybridization 7–9 days following axotomy, type III sodium channel mRNA is expressed at moderate-to-high levels, in addition to types I and II mRNA that are present at relatively high levels. 4. To determine whether the expression of type III sodium channel mRNA following axotomy represents up-regulation of a gene that had been expressed at earlier developmental stages, we also studied DRG neurons from embryonic (E17) rats. In these embryonic DRG neurons, type I sodium channel mRNA is expressed at low levels, type II mRNA at high levels, and type III at high levels. 5. These results demonstrate altered expression of sodium channel mRNA in DRG neurons following axotomy, and suggest that in at least some DRG neurons, there is a de-differentiation after axotomy that includes a reversion to an embryonic mode of sodium channel expression. Different channel characteristics, as well as an altered spatial distribution of sodium channels, may contribute to the electrophysiological changes that are observed in axotomized neurons.

Effects of New World scorpion toxins on single-channel and whole cell cardiac sodium currents

1988 ◽  
Vol 254 (3) ◽  
pp. H443-H451 ◽  
Author(s):  
A. Yatani ◽  
G. E. Kirsch ◽  
L. D. Possani ◽  
A. M. Brown
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
New World ◽  
Single Channel ◽  
Sodium Current ◽  
Sodium Currents ◽  
Scorpion Toxins ◽  
Whole Cell ◽  
Cardiac Sodium Channels ◽  
Single Channel Currents

Purified toxins from a North American scorpion, Centruroides noxius (Cn II-10), and a South American scorpion, Tityus serrulatus (Ts-gamma), were tested on cardiac sodium channels using patch-clamp methods to record whole cell and single-channel currents. The two toxins produced similar effects on sodium currents; potassium and calcium currents were not affected. Macroscopic sodium current amplitudes, measured at test potentials greater than -20 mV where the opening probability was high, decreased in a concentration-dependent manner with a half maximum inhibitory concentration of 6 X 10(-8) M. Block was unchanged by repetitive depolarizing pulses. In the presence of scorpion toxin, the currents were rapidly blocked by tetrodotoxin (3 X 10(-5) M). Both toxins shifted the voltage dependence of sodium channel inactivation to more negative potentials. At test potentials between -50 and -70 mV, where the sodium channel opening probability is normally low, both toxins produced an increase in sodium current and slowed the rates of activation and inactivation. At intermediate potentials between -50 and -20 mV the currents in the presence of toxins crossed over the control currents. At a test potential of -20 mV, the toxins decreased single-channel activity and increased the latency to first opening. At a test potential of -60 mV, the toxins significantly prolonged channel open time. The unitary current amplitudes were unchanged at either potential. We conclude that New World scorpion toxins produce apparently complex effects on whole cell currents primarily by retarding activation gating of cardiac sodium channels.

Sodium Currents in Neurons From the Rostroventrolateral Medulla of the Rat

2003 ◽  
Vol 90 (3) ◽  
pp. 1635-1642 ◽  
Author(s):  
Ilya A. Rybak ◽  
Krzysztof Ptak ◽  
Natalia A. Shevtsova ◽  
Donald R. McCrimmon
Keyword(s):  
Sodium Channels ◽  
Sodium Current ◽  
Cell Voltage ◽  
Kinetic Properties ◽  
Persistent Sodium Current ◽  
Sodium Currents ◽  
Bötzinger Complex ◽  
Window Current ◽  
Bursting Activity

Rapidly inactivating and persistent sodium currents have been characterized in acutely dissociated neurons from the area of rostroventrolateral medulla that included the pre-Bötzinger Complex. As demonstrated in many studies in vitro, this area can generate endogenous rhythmic bursting activity. Experiments were performed on neonate and young rats (P1-15). Neurons were investigated using the whole cell voltage-clamp technique. Standard activation and inactivation protocols were used to characterize the steady-state and kinetic properties of the rapidly inactivating sodium current. Slow depolarizing ramp protocols were used to characterize the noninactivating sodium current. The “window” component of the rapidly inactivating sodium current was calculated using mathematical modeling. The persistent sodium current was revealed by subtraction of the window current from the total noninactivating sodium current. Our results provide evidence of the presence of persistent sodium currents in neurons of the rat rostroventrolateral medulla and determine voltage-gated characteristics of activation and inactivation of rapidly inactivating and persistent sodium channels in these neurons.

Rescue of α-SNS Sodium Channel Expression in Small Dorsal Root Ganglion Neurons After Axotomy by Nerve Growth Factor In Vivo

1998 ◽  
Vol 79 (5) ◽  
pp. 2668-2676 ◽  
Author(s):  
S. D. Dib-Hajj ◽  
J. A. Black ◽  
T. R. Cummins ◽  
A. M. Kenney ◽  
J. D. Kocsis ◽  
...  
Keyword(s):  
Nerve Growth Factor ◽  
Growth Factor ◽  
Dorsal Root Ganglion ◽  
Sodium Channel ◽  
Dorsal Root ◽  
Sodium Current ◽  
Mrna Levels ◽  
Drg Neurons ◽  
Nerve Growth

Dib-Hajj, S. D., J. A. Black, T. R. Cummins, A. M. Kenney, J. D. Kocsis, and S. G. Waxman. Rescue of α-SNS sodium channel expression in small dorsal root ganglion neurons after axotomy by nerve growth factor in vivo. J. Neurophysiol. 79: 2668–2676, 1998. Small (18–25 μm diam) dorsal root ganglion (DRG) neurons are known to express high levels of tetrodotoxin-resistant (TTX-R) sodium current and the mRNA for the α-SNS sodium channel, which encodes a TTX-R channel when expressed in oocytes. These neurons also preferentially express the high affinity receptor for nerve growth factor (NGF), TrkA. Levels of TTX-R sodium current and of α-SNS mRNA are reduced in these cells after axotomy. To determine whether NGF participates in the regulation of TTX-R current and α-SNS mRNA in small DRG neurons in vivo, we axotomized small lumbar DRG neurons by sciatic nerve transection and administered NGF or Ringer solution to the proximal nerve stump using osmotic pumps. Ten to 12 days after pump implant, whole cell patch-clamp recording demonstrated that TTX-R current density was decreased in Ringer-treated axotomized neurons (154 ± 45 pA/pF; mean ± SE) compared with nonaxotomized control neurons (865 ± 123 pA/pF) and was restored partially toward control levels in NGF-treated axotomized neurons (465 ± 78 pA/pF). The V 1/2 for steady-state activation and inactivation of TTX-R currents were similar in control, Ringer- and NGF-treated axotomized neurons. Reverse transcription polymerase chain reaction revealed an upregulation of α-SNS mRNA levels in NGF-treated compared with Ringer-treated axotomized DRG. In situ hybridization showed that α-SNS mRNA levels were decreased significantly in small Ringer-treated axotomized DRG neurons in vivo and also in small DRG neurons that were dissociated and maintained in vitro, so as to correspond to the patch-clamp conditions. NGF-treated axotomized neurons had a significant increase in α-SNS mRNA expression, compared with Ringer-treated axotomized cells. These results show that the administration of exogenous NGF in vivo, to the proximal nerve stump of the transected sciatic nerve, results in an upregulation of TTX-R sodium current and of α-SNS mRNA levels in small DRG neurons. Retrogradely transported NGF thus appears to participate in the control of excitability in these cells via actions that include the regulation of sodium channel gene expression in vivo.

Suppression of Central Nervous System Sodium Channels by Propofol 

1999 ◽  
Vol 91 (2) ◽  
pp. 512-520 ◽  
Author(s):  
Benno Rehberg ◽  
Daniel S. Duch
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Chinese Hamster ◽  
Inhibitory Effect ◽  
Ovary Cell ◽  
Sodium Currents ◽  
Action Potential Firing ◽  
Steady State Inactivation ◽  
Potential Firing ◽  
Ovary Cell Line

Background Previous studies have provided evidence that clinical levels of propofol alter the functions of voltage-dependent sodium channels, thereby inhibiting synaptic release of glutamate. However, most of these experiments were conducted in the presence of sodium-channel activators, which alter channel inactivation. This study electrophysiologically characterized the interactions of propofol with unmodified sodium channels. Methods Sodium currents were measured using whole-cell patch-clamp recordings of rat brain IIa sodium channels expressed in a stably transfected Chinese hamster ovary cell line. Standard electrophysiologic protocols were used to record sodium currents in the presence or absence of externally applied propofol. Results Propofol, at concentrations achieved clinically in the brain, significantly altered sodium channel currents by two mechanisms: a voltage-independent block of peak currents and a concentration-dependent shift in steady-state inactivation to hyperpolarized potentials, leading to a voltage dependence of current suppression. The two effects combined to give an apparent concentration yielding a half-maximal inhibitory effect of 10 microM near the threshold potential of action potential firing (about -60 mV). Propofol inhibition was also use-dependent, causing a further block of sodium currents at these anesthetic concentrations. Conclusions In these experiments with pharmacologically unaltered sodium channels, propofol inhibition of currents occurred at concentrations about eight-fold above clinical plasma levels and thus at brain concentrations reached during clinical anesthesia. Therefore, the results indicate a possible role for sodium-channel suppression in propofol anesthesia.

scholarly journals Analysis of sodium current fluctuations in the cut-open squid giant axon.

1984 ◽  
Vol 83 (2) ◽  
pp. 133-142 ◽  
Author(s):  
I Llano ◽  
F Bezanilla
Keyword(s):  
Sodium Channel ◽  
Sodium Channels ◽  
Sodium Current ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Statistical Techniques ◽  
Current Fluctuations ◽  
Small Populations ◽  
Squid Axon ◽  
Single Sodium Channel

Patch pipettes were used to record the current arising from small populations of sodium channels in voltage-clamped cut-open squid axons. The current fluctuations associated with the time-variant sodium conductance were analyzed with nonstationary statistical techniques in order to obtain an estimate for the conductance of a single sodium channel. The results presented support the notion that the open sodium channel in the squid axon has only one value of conductance, 3.5 pS.

scholarly journals Knock-in model of Dravet syndrome reveals a constitutive and conditional reduction in sodium current

2014 ◽  
Vol 112 (4) ◽  
pp. 903-912 ◽  
Author(s):  
Ryan J. Schutte ◽  
Soleil S. Schutte ◽  
Jacqueline Algara ◽  
Eden V. Barragan ◽  
Jeff Gilligan ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Sodium Current ◽  
Dravet Syndrome ◽  
Repetitive Firing ◽  
Gabaergic Interneurons ◽  
Sodium Currents ◽  
Channel Gene ◽  
Sodium Channel Gene ◽  
Current Activity ◽  
Scn1a Mutation

Hundreds of mutations in the SCN1A sodium channel gene confer a wide spectrum of epileptic disorders, requiring efficient model systems to study cellular mechanisms and identify potential therapeutic targets. We recently demonstrated that Drosophila knock-in flies carrying the K1270T SCN1A mutation known to cause a form of genetic epilepsy with febrile seizures plus (GEFS+) exhibit a heat-induced increase in sodium current activity and seizure phenotype. To determine whether different SCN1A mutations cause distinct phenotypes in Drosophila as they do in humans, this study focuses on a knock-in line carrying a mutation that causes a more severe seizure disorder termed Dravet syndrome (DS). Introduction of the DS SCN1A mutation (S1231R) into the Drosophila sodium channel gene para results in flies that exhibit spontaneous and heat-induced seizures with distinct characteristics and lower onset temperature than the GEFS+ flies. Electrophysiological studies of GABAergic interneurons in the brains of adult DS flies reveal, for the first time in an in vivo model system, that a missense DS mutation causes a constitutive and conditional reduction in sodium current activity and repetitive firing. In addition, feeding with the serotonin precursor 5-HTP suppresses heat-induced seizures in DS but not GEFS+ flies. The distinct alterations of sodium currents in DS and GEFS+ GABAergic interneurons demonstrate that both loss- and gain-of-function alterations in sodium currents are capable of causing reduced repetitive firing and seizure phenotypes. The mutation-specific effects of 5-HTP on heat-induced seizures suggest the serotonin pathway as a potential therapeutic target for DS.

scholarly journals GS-967 and Eleclazine Block Sodium Channels in Human Induced Pluripotent Stem Cell-derived Cardiomyocytes

2020 ◽  
Author(s):  
Franck Potet ◽  
Defne E. Egecioglu ◽  
Paul W. Burridge ◽  
Alfred L. George
Keyword(s):  
Stem Cell ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Pluripotent Stem Cell ◽  
Sodium Current ◽  
Induced Pluripotent Stem Cell ◽  
Slow Inactivation ◽  
Molecular Pharmacology ◽  
Recovery From Inactivation ◽  
Induced Pluripotent

ABSTRACTGS-967 and eleclazine (GS-6615) are novel sodium channel inhibitors exhibiting antiarrhythmic effects in various in vitro and in vivo models. The antiarrhythmic mechanism has been attributed to preferential suppression of late sodium current (INaL). Here, we took advantage of a throughput automated electrophysiology platform (SyncroPatch 768PE) to investigate the molecular pharmacology of GS-967 and eleclazine on peak sodium current (INaP) recorded from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. We compared GS-967 and eleclazine to the antiarrhythmic drug lidocaine, the prototype INaL inhibitor ranolazine, and the slow inactivation enhancing drug lacosamide. In human induced pluripotent stem cell-derived cardiomyocytes, GS-967 and eleclazine caused a reduction of INaP in a frequency-dependent manner consistent with use-dependent block (UDB). GS-967 and eleclazine had similar efficacy but evoked more potent UDB of INaP (IC50=0.07 and 0.6 μM, respectively) than ranolazine (7.8 μM), lidocaine (133.5 μM) and lacosamide (158.5 μM). In addition, GS-967 and eleclazine exerted more potent effects on slow inactivation and recovery from inactivation compared to the other sodium channel blocking drugs we tested. The greater UDB potency of GS-967 and eleclazine was attributed to the significantly higher association rates (KON) and moderate unbinding rate (KOFF) of these two compounds with sodium channels. We propose that substantial UDB contributes to the observed antiarrhythmic efficacy of GS-967 and eleclazine.SIGNIFICANCE STATEMENTWe investigated the molecular pharmacology of GS-967 and eleclazine on sodium channels in human induced pluripotent stem cell derived cardiomyocytes using a high throughput automated electrophysiology platform. Sodium channel inhibition by GS-967 and eleclazine has unique features including accelerating the onset of slow inactivation and impairing recovery from inactivation. These effects combined with rapid binding and moderate unbinding kinetics explain potent use-dependent block, which we propose contributes to their observed antiarrhythmic efficacy.

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