Potentiation of rat brain sodium channel currents by PKA inXenopus oocytes involves the I-II linker

2000 ◽  
Vol 278 (4) ◽  
pp. C638-C645 ◽  
Author(s):  
Raymond D. Smith ◽  
Alan L. Goldin
Keyword(s):  
Sodium Channel ◽  
Xenopus Oocytes ◽  
Sodium Current ◽  
Sodium Currents ◽  
Voltage Gated Sodium Channels ◽  
Single Region ◽  
Functional Modulation ◽  
Excitability Of Neurons ◽  
Channel Currents ◽  
The Brain

Functional modulation of voltage-gated sodium channels affects the electrical excitability of neurons. Protein kinase A (PKA) can decrease sodium currents by phosphorylation at consensus sites in the cytoplasmic I-II linker. Once the sites are phosphorylated, however, additional PKA activity can increase sodium currents by an unknown mechanism. When the PKA sites were eliminated by substitutions of alanine for serine, peak sodium current amplitudes were increased by 20–80% when PKA was activated in Xenopus oocytes either by stimulation of a coexpressed β2-adrenergic receptor or by perfusion with reagents that increase cAMP. Potentiation required the I-II linker of the brain channel, in that a chimeric channel in which the brain linker was replaced with the comparable linker from the skeletal muscle channel did not demonstrate potentiation. Using a series of chimeric and deleted channels, we demonstrate that potentiation is not dependent on any single region of the linker and that the extent of potentiation varies depending on the total length and the residues throughout the linker. These data are consistent with the hypothesis that potentiation by PKA is an indirect process involving phosphorylation of an accessory protein that interacts with the I-II linker of the sodium channel.

Protein kinase A phosphorylation enhances sodium channel currents in Xenopus oocytes

1992 ◽  
Vol 263 (3) ◽  
pp. C660-C666 ◽  
Author(s):  
R. D. Smith ◽  
A. L. Goldin
Keyword(s):  
Protein Kinase ◽  
Sodium Channel ◽  
Protein Kinase A ◽  
Rat Brain ◽  
Xenopus Oocytes ◽  
Kinase Inhibitor ◽  
Sodium Current ◽  
Specific Inhibitor ◽  
Channel Currents ◽  
Kinase A

The voltage-sensitive rat brain sodium channel is known to be phosphorylated by adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA), but the functional significance of that phosphorylation is unknown. We have shown that rat brain sodium channel currents expressed in Xenopus oocytes were enhanced by induction of PKA activity. Stimulation of the beta 2-adrenergic receptor or treatment with dibutyryl cAMP resulted in increased sodium current amplitudes without affecting the voltage dependence of channel activation or inactivation. These increases were completely blocked by preinjection of protein kinase inhibitor, a specific inhibitor of PKA. Injection of phosphatase into the oocytes resulted in a significant decrease in sodium current amplitude, indicating that phosphorylation is important for basal levels of sodium channel activity in oocytes. The enhancement was specific for the rat brain IIA sodium channel, because currents expressed from the rat muscle microI sodium channel were not enhanced by the same procedures. These data demonstrate a modulatory role of PKA phosphorylation on brain sodium channel function and suggest a means by which the electrical excitability of cells may be regulated.

scholarly journals Neurosteroids Allopregnanolone Sulfate and Pregnanolone Sulfate Have Diverse Effect on the α Subunit of the Neuronal Voltage-gated Sodium Channels Nav1.2, Nav1.6, Nav1.7, and Nav1.8 Expressed in Xenopus Oocytes

2014 ◽  
Vol 121 (3) ◽  
pp. 620-631 ◽  
Author(s):  
Takafumi Horishita ◽  
Nobuyuki Yanagihara ◽  
Susumu Ueno ◽  
Yuka Sudo ◽  
Yasuhito Uezono ◽  
...  
Keyword(s):  
Sodium Channels ◽  
Xenopus Oocytes ◽  
Sodium Current ◽  
Dependent Manner ◽  
Sodium Currents ◽  
Concentration Dependent Manner ◽  
Α Subunit ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Α Subunits

Abstract Background: The neurosteroids allopregnanolone and pregnanolone are potent positive modulators of γ-aminobutyric acid type A receptors. Antinociceptive effects of allopregnanolone have attracted much attention because recent reports have indicated the potential of allopregnanolone as a therapeutic agent for refractory pain. However, the analgesic mechanisms of allopregnanolone are still unclear. Voltage-gated sodium channels (Nav) are thought to play important roles in inflammatory and neuropathic pain, but there have been few investigations on the effects of allopregnanolone on sodium channels. Methods: Using voltage-clamp techniques, the effects of allopregnanolone sulfate (APAS) and pregnanolone sulfate (PAS) on sodium current were examined in Xenopus oocytes expressing Nav1.2, Nav1.6, Nav1.7, and Nav1.8 α subunits. Results: APAS suppressed sodium currents of Nav1.2, Nav1.6, and Nav1.7 at a holding potential causing half-maximal current in a concentration-dependent manner, whereas it markedly enhanced sodium current of Nav1.8 at a holding potential causing maximal current. Half-maximal inhibitory concentration values for Nav1.2, Nav1.6, and Nav1.7 were 12 ± 4 (n = 6), 41 ± 2 (n = 7), and 131 ± 15 (n = 5) μmol/l (mean ± SEM), respectively. The effects of PAS were lower than those of APAS. From gating analysis, two compounds increased inactivation of all α subunits, while they showed different actions on activation of each α subunit. Moreover, two compounds showed a use-dependent block on Nav1.2, Nav1.6, and Nav1.7. Conclusion: APAS and PAS have diverse effects on sodium currents in oocytes expressing four α subunits. APAS inhibited the sodium currents of Nav1.2 most strongly.

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.

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 Chemometric Models of Differential Amino Acids at the Navα and Navβ Interface of Mammalian Sodium Channel Isoforms

Molecules ◽  
2020 ◽  
Vol 25 (15) ◽  
pp. 3551
Author(s):  
Fernando Villa-Diaz ◽  
Susana Lopez-Nunez ◽  
Jordan E. Ruiz-Castelan ◽  
Eduardo Marcos Salinas-Stefanon ◽  
Thomas Scior
Keyword(s):  
Sodium Channel ◽  
Sodium Current ◽  
Schematic Model ◽  
Excitable Cells ◽  
Protein Protein Interaction ◽  
Voltage Gated Sodium Channels ◽  
Gating Mechanism ◽  
In Silico Modeling ◽  
Variable Extent ◽  
Domain I

(1) Background: voltage-gated sodium channels (Navs) are integral membrane proteins that allow the sodium ion flux into the excitable cells and initiate the action potential. They comprise an α (Navα) subunit that forms the channel pore and are coupled to one or more auxiliary β (Navβ) subunits that modulate the gating to a variable extent. (2) Methods: after performing homology in silico modeling for all nine isoforms (Nav1.1α to Nav1.9α), the Navα and Navβ protein-protein interaction (PPI) was analyzed chemometrically based on the primary and secondary structures as well as topological or spatial mapping. (3) Results: our findings reveal a unique isoform-specific correspondence between certain segments of the extracellular loops of the Navα subunits. Precisely, loop S5 in domain I forms part of the PPI and assists Navβ1 or Navβ3 on all nine mammalian isoforms. The implied molecular movements resemble macroscopic springs, all of which explains published voltage sensor effects on sodium channel fast inactivation in gating. (4) Conclusions: currently, the specific functions exerted by the Navβ1 or Navβ3 subunits on the modulation of Navα gating remain unknown. Our work determined functional interaction in the extracellular domains on theoretical grounds and we propose a schematic model of the gating mechanism of fast channel sodium current inactivation by educated guessing.

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.

scholarly journals Voltage Gated Sodium Channel Genes in Epilepsy: Mutations, Functional Studies, and Treatment Dimensions

2021 ◽  
Vol 12 ◽  
Author(s):  
Ibitayo Abigail Ademuwagun ◽  
Solomon Oladapo Rotimi ◽  
Steffen Syrbe ◽  
Yvonne Ukamaka Ajamma ◽  
Ezekiel Adebiyi
Keyword(s):  
Ion Channel ◽  
Sodium Channel ◽  
Sodium Channels ◽  
De Novo ◽  
Single Gene ◽  
Voltage Gated ◽  
Functional Studies ◽  
Voltage Gated Sodium Channels ◽  
Genomic Studies ◽  
The Brain

Genetic epilepsy occurs as a result of mutations in either a single gene or an interplay of different genes. These mutations have been detected in ion channel and non-ion channel genes. A noteworthy class of ion channel genes are the voltage gated sodium channels (VGSCs) that play key roles in the depolarization phase of action potentials in neurons. Of huge significance are SCN1A, SCN1B, SCN2A, SCN3A, and SCN8A genes that are highly expressed in the brain. Genomic studies have revealed inherited and de novo mutations in sodium channels that are linked to different forms of epilepsies. Due to the high frequency of sodium channel mutations in epilepsy, this review discusses the pathogenic mutations in the sodium channel genes that lead to epilepsy. In addition, it explores the functional studies on some known mutations and the clinical significance of VGSC mutations in the medical management of epilepsy. The understanding of these channel mutations may serve as a strong guide in making effective treatment decisions in patient management.

scholarly journals A Heart Failure-Associated SCN5A Splice Variant Leads to a Reduction in Sodium Current Through Coupled-Gating With the Wild-Type Channel

2021 ◽  
Vol 12 ◽  
Author(s):  
Yang Zheng ◽  
Xiaoping Wan ◽  
Dandan Yang ◽  
Angelina Ramirez-Navarro ◽  
Haiyan Liu ◽  
...  
Keyword(s):  
Heart Failure ◽  
Sodium Channel ◽  
Splice Variant ◽  
Sodium Current ◽  
Heart Rhythm ◽  
Dominant Negative ◽  
Sodium Currents ◽  
Coupled Gating ◽  
And Function ◽  
Type 3

Nav1.5, encoded by the gene SCN5A, is the predominant voltage-gated sodium channel expressed in the heart. It initiates the cardiac action potential and thus is crucial for normal heart rhythm and function. Dysfunctions in Nav1.5 have been involved in multiple congenital or acquired cardiac pathological conditions such as Brugada syndrome (BrS), Long QT Syndrome Type 3, and heart failure (HF), all of which can lead to sudden cardiac death (SCD) – one of the leading causes of death worldwide. Our lab has previously reported that Nav1.5 forms dimer channels with coupled gating. We also found that Nav1.5 BrS mutants can exert a dominant-negative (DN) effect and impair the function of wildtype (WT) channels through coupled-gating with the WT. It was previously reported that reduction in cardiac sodium currents (INa), observed in HF, could be due to the increased expression of an SCN5A splice variant – E28D, which results in a truncated sodium channel (Nav1.5-G1642X). In this study, we hypothesized that this SCN5A splice variant leads to INa reduction in HF through biophysical coupling with the WT. We showed that Nav1.5-G1642X is a non-functional channel but can interact with the WT, resulting in a DN effect on the WT channel. We found that both WT and the truncated channel Nav1.5-G1642X traffic at the cell surface, suggesting biophysical coupling. Indeed, we found that the DN effect can be abolished by difopein, an inhibitor of the biophysical coupling. Interestingly, the sodium channel polymorphism H558R, which has beneficial effect in HF patients, could also block the DN effect. In summary, the HF-associated splice variant Nav1.5-G1642X suppresses sodium currents in heart failure patients through a mechanism involving coupled-gating with the wildtype sodium channel.

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.

C2C12 skeletal muscle cells adopt cardiac-like sodium current properties in a cardiac cell environment

2007 ◽  
Vol 292 (1) ◽  
pp. H439-H450 ◽  
Author(s):  
Eva Zebedin ◽  
Markus Mille ◽  
Maria Speiser ◽  
Touran Zarrabi ◽  
Walter Sandtner ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Sodium Channel ◽  
Sodium Current ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Cardiac Cell ◽  
Sodium Currents ◽  
Current Function ◽  
Electrophysiological Properties ◽  
Cardiac Sodium Channel

Intracardiac transplantation of undifferentiated skeletal muscle cells (myoblasts) has emerged as a promising therapy for myocardial infarct repair and is already undergoing clinical trials. The fact that cells originating from skeletal muscle have different electrophysiological properties than cardiomyocytes, however, may considerably limit the success of this therapy and, in addition, cause side effects. Indeed, a major problem observed after myoblast transplantation is the occurrence of ventricular arrhythmias. The most often transient nature of these arrhythmias may suggest that, once transplanted into cardiac tissue, skeletal muscle cells adopt more cardiac-like electrophysiological properties. To test whether a cardiac cell environment can indeed modify electrophysiological parameters of skeletal muscle cells, we treated mouse C2C12 myocytes with medium preconditioned by primary cardiocytes and compared their functional sodium current properties with those of control cells. We found this treatment to significantly alter the activation and inactivation properties of sodium currents from “skeletal muscle” to more “cardiac”-like ones. Sodium currents of cardiac-conditioned cells showed a reduced sensitivity to block by tetrodotoxin. These findings and reverse transcription PCR experiments suggest that an upregulation of the expression of the cardiac sodium channel isoform Nav1.5 versus the skeletal muscle isoform Nav1.4 is responsible for the observed changes in sodium current function. We conclude that cardiomyocytes alter sodium channel isoform expression of skeletal muscle cells via a paracrine mechanism. Thereby, skeletal muscle cells with more cardiac-like sodium current properties are generated.

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