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Baeza-Loya S, Eatock RA. Effects of transient, persistent, and resurgent sodium currents on excitability and spike regularity in vestibular ganglion neurons. bioRxiv 2023:2023.11.28.569044. [PMID: 38076890 PMCID: PMC10705474 DOI: 10.1101/2023.11.28.569044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/20/2023]
Abstract
Vestibular afferent neurons occur as two populations, regular and irregular, that provide distinct information about head motions. Differences in spike timing regularity are correlated with the different sensory responses important for vestibular processing. Relative to irregular afferents, regular afferents have more sustained firing patterns in response to depolarizing current steps, are more excitable, and have different complements of ion channels. Models of vestibular regularity and excitability emphasize the influence of increased expression of low-voltage-activated potassium currents in irregular neurons. We investigated the potential impact of different modes of voltage-gated sodium (NaV) current (transient, persistent, and resurgent) in cell bodies from vestibular ganglion neurons (VGNs), dissociated and cultured overnight. We hypothesized that regular VGNs would show the greatest impact of persistent (non-inactivating) NaV currents and of resurgent NaV currents, which flow when NaV channels are blocked and then unblocked. Whole-cell patch clamp experiments showed that much of the NaV current modes is carried by NaV1.6 channels. With simulations, we detected little substantial effect in any model VGN of persistent or resurgent modes on regularity of spike timing driven by postsynaptic current trains. For simulated irregular neurons, we also saw little effect on spike rate or firing pattern. For simulated regular VGNs, adding resurgent current changed the detailed timing of spikes during a current step, while the small persistent conductance (less than10% of transient NaV conductance density) strongly depolarized resting potential, altered spike waveform, and increased spike rate. These results suggest that persistent and resurgent NaV current can have a greater effect on the regular VGNs than on irregular VGNs, where low-voltage-activated K conductances dominate.
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Affiliation(s)
- Selina Baeza-Loya
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology-HNS, University of Washington, Seattle, WA, United States
| | - Ruth Anne Eatock
- Department of Neurobiology, University of Chicago, Chicago, IL, United States
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2
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Araújo FRV, da Costa DR, Chaves AJC, de Sousa FEB, Pereira JM. Modulation of persistent current in graphene quantum rings. J Phys Condens Matter 2022; 34:125503. [PMID: 34933297 DOI: 10.1088/1361-648x/ac452e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 12/21/2021] [Indexed: 06/14/2023]
Abstract
We investigate the effect of long-range impurity potentials on the persistent current of graphene quantum rings in the presence of an uniform perpendicular magnetic field. The impurity potentials are modeled as finite regions of the ring with a definite length. We show that, due to the relativistic and massless character of the charge carriers in graphene, the effect of such non-uniform potentials on the energy spectrum and on the persistent current of the rings can be reliably modeled by assuming a non-perturbed ring and including an additional phase due to the interaction of the charge carriers with the potential. In addition, the results show the presence of localized states in the impurity regions. Moreover, we show that for the case of a potential created by a p-n-p junction, the persistent current can be modulated by controlling the voltage at the junction.
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Affiliation(s)
- F R V Araújo
- Instituto Federal do Piauí-Campus São Raimundo Nonato, 64670-000, São Raimundo Nonato, PI, Brazil
- Departamento de Física, Universidade Federal do Ceará, 60455-900, Fortaleza, CE, Brazil
| | - D R da Costa
- Departamento de Física, Universidade Federal do Ceará, 60455-900, Fortaleza, CE, Brazil
| | - A J C Chaves
- Departamento de Física, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil
| | - F E B de Sousa
- Departamento de Física, Universidade Federal do Ceará, 60455-900, Fortaleza, CE, Brazil
| | - J M Pereira
- Departamento de Física, Universidade Federal do Ceará, 60455-900, Fortaleza, CE, Brazil
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3
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Nikulov A. The Law of Entropy Increase and the Meissner Effect. Entropy (Basel) 2022; 24:83. [PMID: 35052109 DOI: 10.3390/e24010083] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 11/27/2021] [Revised: 12/28/2021] [Accepted: 12/30/2021] [Indexed: 11/17/2022]
Abstract
The law of entropy increase postulates the existence of irreversible processes in physics: the total entropy of an isolated system can increase, but cannot decrease. The annihilation of an electric current in normal metal with the generation of Joule heat because of a non-zero resistance is a well-known example of an irreversible process. The persistent current, an undamped electric current observed in a superconductor, annihilates after the transition into the normal state. Therefore, this transition was considered as an irreversible thermodynamic process before 1933. However, if this transition is irreversible, then the Meissner effect discovered in 1933 is experimental evidence of a process reverse to the irreversible process. Belief in the law of entropy increase forced physicists to change their understanding of the superconducting transition, which is considered a phase transition after 1933. This change has resulted to the internal inconsistency of the conventional theory of superconductivity, which is created within the framework of reversible thermodynamics, but predicts Joule heating. The persistent current annihilates after the transition into the normal state with the generation of Joule heat and reappears during the return to the superconducting state according to this theory and contrary to the law of entropy increase. The success of the conventional theory of superconductivity forces us to consider the validity of belief in the law of entropy increase.
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Dajka J. Currents in a Quantum Nanoring Controlled by Non-Classical Electromagnetic Field. Entropy (Basel) 2021; 23:e23060652. [PMID: 34070969 PMCID: PMC8224575 DOI: 10.3390/e23060652] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 05/18/2021] [Accepted: 05/19/2021] [Indexed: 11/23/2022]
Abstract
Quantum ring accommodating interacting spin-less fermions threaded by magnetic flux with a non-classical component added to a static, inducing persistent current, is considered. It is investigated how current flowing in the ring becomes affected by a state of non-classical flux and how Coulomb interaction between fermions influences entanglement of quantum ring and the driving field. In particular it is shown that in an absence of decoherence and under certain conditions fermion–fermion interaction is necessary for a ring–field entanglement to occur.
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Affiliation(s)
- Jerzy Dajka
- Institute of Physics, University of Silesia in Katowice, 40-007 Katowice, Poland;
- Silesian Center for Education and Interdisciplinary Research, University of Silesia in Katowice, 41-500 Chorzów, Poland
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Mason ER, Cummins TR. Differential Inhibition of Human Nav1.2 Resurgent and Persistent Sodium Currents by Cannabidiol and GS967. Int J Mol Sci 2020; 21:ijms21072454. [PMID: 32244818 PMCID: PMC7177867 DOI: 10.3390/ijms21072454] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Revised: 03/27/2020] [Accepted: 03/28/2020] [Indexed: 12/24/2022] Open
Abstract
Many epilepsy patients are refractory to conventional antiepileptic drugs. Resurgent and persistent currents can be enhanced by epilepsy mutations in the Nav1.2 channel, but conventional antiepileptic drugs inhibit normal transient currents through these channels, along with aberrant resurgent and persistent currents that are enhanced by Nav1.2 epilepsy mutations. Pharmacotherapies that specifically target aberrant resurgent and/or persistent currents would likely have fewer unwanted side effects and be effective in many patients with refractory epilepsy. This study investigated the effects of cannbidiol (CBD) and GS967 (each at 1 μM) on transient, resurgent, and persistent currents in human embryonic kidney (HEK) cells stably expressing wild-type hNav1.2 channels. We found that CBD preferentially inhibits resurgent currents over transient currents in this paradigm; and that GS967 preferentially inhibits persistent currents over transient currents. Therefore, CBD and GS967 may represent a new class of more targeted and effective antiepileptic drugs.
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Affiliation(s)
- Emily R. Mason
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, IUPUI campus, Indianapolis, IN 46202, USA
- Correspondence:
| | - Theodore R. Cummins
- Department of Biology, Purdue School of Science, IUPUI campus, Indianapolis, IN 46202, USA;
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Bułka BR, Łuczak J. Current Correlations in a Quantum Dot Ring: A Role of Quantum Interference. Entropy (Basel) 2019; 21:E527. [PMID: 33267241 DOI: 10.3390/e21050527] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 05/17/2019] [Accepted: 05/22/2019] [Indexed: 12/19/2022]
Abstract
We present studies of the electron transport and circular currents induced by the bias voltage and the magnetic flux threading a ring of three quantum dots coupled with two electrodes. Quantum interference of electron waves passing through the states with opposite chirality plays a relevant role in transport, where one can observe Fano resonance with destructive interference. The quantum interference effect is quantitatively described by local bond currents and their correlation functions. Fluctuations of the transport current are characterized by the Lesovik formula for the shot noise, which is a composition of the bond current correlation functions. In the presence of circular currents, the cross-correlation of the bond currents can be very large, but it is negative and compensates for the large positive auto-correlation functions.
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Bertelli S, Barbieri R, Pusch M, Gavazzo P. Gain of function of sporadic/familial hemiplegic migraine-causing SCN1A mutations: Use of an optimized cDNA. Cephalalgia 2018; 39:477-488. [PMID: 29986598 DOI: 10.1177/0333102418788336] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
INTRODUCTION Familial hemiplegic migraine 3 is an autosomal dominant headache disorder associated with aura and transient hemiparesis, caused by mutations of the neuronal voltage-gated sodium channel Nav1.1. While a gain-of function phenotype is generally assumed to underlie familial hemiplegic migraine, this has not been fully explored. Indeed, a major obstacle in studying in vitro neuronal sodium channels is the difficulty in propagating and mutagenizing expression plasmids containing their cDNAs. The aim of this work was to study the functional effect of two previously uncharacterized hemiplegic migraine causing mutations, Leu1670Trp (L1670W) and Phe1774Ser (F1774S). METHODS A novel SCN1A containing-plasmid was designed in silico and synthesized, and migraine mutations were inserted in this background. Whole-cell patch clamp was performed to investigate the functional properties of mutant Nav1.1 transiently expressed in Human Embryonic Kidney 293 cells. RESULTS AND CONCLUSIONS We generated an optimized Nav1.1 expression plasmid that was extremely simple to handle and used the novel plasmid to study the functional effects of two migraine mutations. We observed that L1670W, but not F1774S, reduced current density and that both mutations led to a dramatic increase in persistent sodium currents, a depolarizing shift of the steady state-inactivation voltage-dependence, and a faster recovery from inactivation. The results are consistent with a major gain-of function effect underlying familial hemiplegic migraine 3. Our optimization strategy will help to characterize in an efficient manner the effect in vitro of mutations of neuronal voltage-gated sodium channels.
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Affiliation(s)
- Sara Bertelli
- 1 Istituto di Biofisica (Biophysics Institute, National Research Council), Genova, Italy.,2 Scuola Internazionale Superiore di Studi Avanzati (SISSA) (International School for Advanced Studies), Trieste, Italy
| | - Raffaella Barbieri
- 1 Istituto di Biofisica (Biophysics Institute, National Research Council), Genova, Italy
| | - Michael Pusch
- 1 Istituto di Biofisica (Biophysics Institute, National Research Council), Genova, Italy
| | - Paola Gavazzo
- 1 Istituto di Biofisica (Biophysics Institute, National Research Council), Genova, Italy
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Browne L, Smith KE, Jagger DJ. Identification of Persistent and Resurgent Sodium Currents in Spiral Ganglion Neurons Cultured from the Mouse Cochlea. eNeuro 2017; 4:ENEURO. [PMID: 29138759 DOI: 10.1523/ENEURO.0303-17.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 10/13/2017] [Accepted: 10/17/2017] [Indexed: 01/11/2023] Open
Abstract
In spiral ganglion neurons (SGNs), the afferent single units of the auditory nerve, high spontaneous and evoked firing rates ensure preservation of the temporal code describing the key features of incoming sound. During postnatal development, the spatiotemporal distribution of ion channel subtypes contributes to the maturation of action potential generation in SGNs, and to their ability to generate spike patterns that follow rapidly changing inputs. Here we describe tetrodotoxin (TTX)-sensitive Na+ currents in SGNs cultured from mice, whose properties may support this fast spiking behavior. A subthreshold persistent Na+ current (INaP) and a resurgent Na+ current (INaR) both emerged prior to the onset of hearing and became more prevalent as hearing matured. Navβ4 subunits, which are proposed to play a key role in mediating INaR elsewhere in the nervous system, were immunolocalized to the first heminode where spikes are generated in the auditory nerve, and to perisomatic nodes of Ranvier. ATX-II, a sea anemone toxin that slows classical Na+ channel inactivation selectively, enhanced INaP five-fold and INaR three-fold in voltage clamp recordings. In rapidly-adapting SGNs under current clamp, ATX-II increased the likelihood of firing additional action potentials. The data identify INaP and INaR as novel regulators of excitability in SGNs, and consistent with their roles in other neuronal types, we suggest that these nonclassical Na+ currents may contribute to the control of refractoriness in the auditory nerve.
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Estacion M, Waxman SG. Nonlinear effects of hyperpolarizing shifts in activation of mutant Na v1.7 channels on resting membrane potential. J Neurophysiol 2017; 117:1702-1712. [PMID: 28148645 DOI: 10.1152/jn.00898.2016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Revised: 01/11/2017] [Accepted: 01/26/2017] [Indexed: 01/16/2023] Open
Abstract
The Nav1.7 sodium channel is preferentially expressed within dorsal root ganglion (DRG) and sympathetic ganglion neurons. Gain-of-function mutations that cause the painful disorder inherited erythromelalgia (IEM) shift channel activation in a hyperpolarizing direction. When expressed within DRG neurons, these mutations produce a depolarization of resting membrane potential (RMP). The biophysical basis for the depolarized RMP has to date not been established. To explore the effect on RMP of the shift in activation associated with a prototypical IEM mutation (L858H), we used dynamic-clamp models that represent graded shifts that fractionate the effect of the mutation on activation voltage dependence. Dynamic-clamp recording from DRG neurons using a before-and-after protocol for each cell made it possible, even in the presence of cell-to-cell variation in starting RMP, to assess the effects of these graded mutant models. Our results demonstrate a nonlinear, progressively larger effect on RMP as the shift in activation voltage dependence becomes more hyperpolarized. The observed differences in RMP were predicted by the "late" current of each mutant model. Since the depolarization of RMP imposed by IEM mutant channels is known, in itself, to produce hyperexcitability of DRG neurons, the development of pharmacological agents that normalize or partially normalize activation voltage dependence of IEM mutant channels merits further study.NEW & NOTEWORTHY Inherited erythromelalgia (IEM), the first human pain disorder linked to a sodium channel, is widely regarded as a genetic model of neuropathic pain. IEM is produced by Nav1.7 mutations that hyperpolarize activation. These mutations produce a depolarization of resting membrane potential (RMP) in dorsal root ganglion neurons. Using dynamic clamp to explore the effect on RMP of the shift in activation, we demonstrate a nonlinear effect on RMP as the shift in activation voltage dependence becomes more hyperpolarized.
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Affiliation(s)
- Mark Estacion
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut; and.,Rehabilitation Research Center, Department of Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut
| | - Stephen G Waxman
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut; and .,Rehabilitation Research Center, Department of Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut
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10
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Han C, Estacion M, Huang J, Vasylyev D, Zhao P, Dib-Hajj SD, Waxman SG. Human Na(v)1.8: enhanced persistent and ramp currents contribute to distinct firing properties of human DRG neurons. J Neurophysiol 2015; 113:3172-85. [PMID: 25787950 DOI: 10.1152/jn.00113.2015] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Accepted: 03/13/2015] [Indexed: 12/19/2022] Open
Abstract
Although species-specific differences in ion channel properties are well-documented, little has been known about the properties of the human Nav1.8 channel, an important contributor to pain signaling. Here we show, using techniques that include voltage clamp, current clamp, and dynamic clamp in dorsal root ganglion (DRG) neurons, that human Na(v)1.8 channels display slower inactivation kinetics and produce larger persistent current and ramp current than previously reported in other species. DRG neurons expressing human Na(v)1.8 channels unexpectedly produce significantly longer-lasting action potentials, including action potentials with half-widths in some cells >10 ms, and increased firing frequency compared with the narrower and usually single action potentials generated by DRG neurons expressing rat Na(v)1.8 channels. We also show that native human DRG neurons recapitulate these properties of Na(v)1.8 current and the long-lasting action potentials. Together, our results demonstrate strikingly distinct properties of human Na(v)1.8, which contribute to the firing properties of human DRG neurons.
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Affiliation(s)
- Chongyang Han
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Mark Estacion
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Jianying Huang
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Dymtro Vasylyev
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Peng Zhao
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Sulayman D Dib-Hajj
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Stephen G Waxman
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
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Ling J, Voccio J, Hahn S, Kim Y, Song J, Bascuñán J, Iwasa Y. Development of a 0.5-T/240-mm MgB 2 MRI Magnet: Assembly Design and Module Coils. IEEE Trans Appl Supercond 2014; 24:4400805. [PMID: 34025088 PMCID: PMC8136753 DOI: 10.1109/tasc.2013.2283217] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
This paper presents the latest results from our continued development of a 0.5-T/240-mm MgB2 MRI magnet at the MIT Francis Bitter Magnet Laboratory. Because we have successfully developed our superconducting joint technique with a monofilament MgB2 wire, manufactured by Hyper Tech Research, Inc. (Columbus, OH), we have decided to use a monofilament wire to wind our MgB2 MRI magnet. The magnet, comprising eight module coils, has a winding inner diameter of 276 mm, an outer diameter of 290 mm, and a total height of 460 mm. Each coil has its own persistent-current switch (PCS) and a superconducting joint. In order to guard against a few bad coils forcing the entire magnet to be inoperative, each coil will be heat-treated and tested individually. After eight coils are successfully operated, they will be assembled into an MRI magnet and series-connected with soldering joints between adjacent coils. The PCS in each coil is designed in such way that it will also serve as a detect-and-heat protection absorber when the magnet quenches over a small "localized" region: The conductor volume in the eight switches is designed to absorb the entire magnet energy while still remaining below 200 K. This paper reports 1) the design of the whole magnet and 2) the fabrication and test results of the two real-size test coils, with their PCSs and superconducting joints. The tests were conducted in gas helium in the temperature range of 10-15 K and in the self-field of the coils.
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Affiliation(s)
- Jiayin Ling
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - John Voccio
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Seungyong Hahn
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Youngjae Kim
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Jungbin Song
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Juan Bascuñán
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Yukikazu Iwasa
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
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Gao R, Du Y, Wang L, Nomura Y, Satar G, Gordon D, Gurevitz M, Goldin AL, Dong K. Sequence variations at I260 and A1731 contribute to persistent currents in Drosophila sodium channels. Neuroscience 2014; 268:297-308. [PMID: 24662849 DOI: 10.1016/j.neuroscience.2014.03.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 02/02/2014] [Accepted: 03/09/2014] [Indexed: 12/19/2022]
Abstract
Tetrodotoxin-sensitive persistent sodium currents, INaP, that activate at subthreshold voltages, have been detected in numerous vertebrate and invertebrate neurons. These currents are believed to be critical for regulating neuronal excitability. However, the molecular mechanism underlying INaP is controversial. In this study, we identified an INaP with a broad range of voltage dependence, from -60mV to 20mV, in a Drosophila sodium channel variant expressed in Xenopus oocytes. Mutational analysis revealed that two variant-specific amino acid changes, I260T in the S4-S5 linker of domain I (ILS4-S5) and A1731V in the voltage sensor S4 of domain IV (IVS4), contribute to the INaP. I260T is critical for the portion of INaP at hyperpolarized potentials. The T260-mediated INaP is likely the result of window currents flowing in the voltage range where the activation and inactivation curves overlap. A1731V is responsible for impaired inactivation and contributes to the portion of INaP at depolarized potentials. Furthermore, A1731V causes enhanced activity of two site-3 toxins which induce persistent currents by inhibiting the outward movement of IVS4, suggesting that A1731V inhibits the outward movement of IVS4. These results provided molecular evidence for the involvement of distinct mechanisms in the generation of INaP: T260 contributes to INaP via enhancement of the window current, whereas V1731 impairs fast inactivation probably by inhibiting the outward movement of IVS4.
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Affiliation(s)
- R Gao
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - Y Du
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - L Wang
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - Y Nomura
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - G Satar
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - D Gordon
- Department of Plant Molecular Biology & Ecology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Israel
| | - M Gurevitz
- Department of Plant Molecular Biology & Ecology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Israel
| | - A L Goldin
- Department of Microbiology and Molecular Genetics, University of California, Irvine, CA 92697, United States
| | - K Dong
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States.
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13
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Cummins TR, Black JA, Dib-Hajj SD, Waxman SG. Glial-derived neurotrophic factor upregulates expression of functional SNS and NaN sodium channels and their currents in axotomized dorsal root ganglion neurons. J Neurosci 2000; 20:8754-61. [PMID: 11102483 PMCID: PMC6773074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023] Open
Abstract
Dorsal root ganglion (DRG) neurons produce multiple sodium currents, including several different TTX-sensitive (TTX-S) currents and TTX-resistant (TTX-R) currents, which are produced by distinct sodium channels. We previously demonstrated that, after sciatic nerve transection, the levels of SNS and NaN sodium channel alpha-subunit transcripts and protein in small (18-30 micrometer diameter) DRG neurons are reduced, as are the amplitudes and densities of the slowly inactivating and persistent TTX-R currents produced by these two channels. In this study, we asked whether glial-derived neurotrophic factor (GDNF), which has been shown to prevent some axotomy-induced changes such as the loss of somatostatin expression in DRG neurons, can ameliorate the axotomy-induced downregulation of SNS and NaN TTX-R sodium channels. We show here that exposure to GDNF can significantly increase both slowly inactivating and persistent TTX-R sodium currents, which are paralleled by increases in SNS and NaN mRNA and protein levels, in axotomized DRG neurons in vitro. We also show that intrathecally administered GDNF increases the amplitudes of the slowly inactivating and persistent TTX-R currents, and SNS and NaN protein levels, in peripherally axotomized DRG neurons in vivo. Finally, we demonstrate that GDNF upregulates the persistent TTX-R current in SNS-null mice, thus demonstrating that the upregulated persistent sodium current is not produced by SNS. Because TTX-R sodium channels have been shown to be important in nociception, the effects of GDNF on axotomized DRG neurons may have important implications for the regulation of nociceptive signaling by these cells.
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Affiliation(s)
- T R Cummins
- Department of Neurology and Paralyzed Veterans of America and Eastern Paralyzed Veterans Association Neuroscience Research Center, Yale Medical School, New Haven, Connecticut 06510, USA
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Cummins TR, Howe JR, Waxman SG. Slow closed-state inactivation: a novel mechanism underlying ramp currents in cells expressing the hNE/PN1 sodium channel. J Neurosci 1998; 18:9607-19. [PMID: 9822722 PMCID: PMC6793269] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023] Open
Abstract
To better understand why sensory neurons express voltage-gated Na+ channel isoforms that are different from those expressed in other types of excitable cells, we compared the properties of the hNE sodium channel [a human homolog of PN1, which is selectively expressed in dorsal root ganglion (DRG) neurons] with that of the skeletal muscle Na+ channel (hSkM1) [both expressed in human embryonic kidney (HEK293) cells]. Although the voltage dependence of activation was similar, the inactivation properties were different. The V1/2 for steady-state inactivation was slightly more negative, and the rate of open-state inactivation was approximately 50% slower for hNE. However, the greatest difference was that closed-state inactivation and recovery from inactivation were up to fivefold slower for hNE than for hSkM1 channels. TTX-sensitive (TTX-S) currents in small DRG neurons also have slow closed-state inactivation, suggesting that hNE/PN1 contributes to this TTX-S current. Slow ramp depolarizations (0.25 mV/msec) elicited TTX-S persistent currents in cells expressing hNE channels, and in DRG neurons, but not in cells expressing hSkM1 channels. We propose that slow closed-state inactivation underlies these ramp currents. This conclusion is supported by data showing that divalent cations such as Cd2+ and Zn2+ (50-200 microM) slowed closed-state inactivation and also dramatically increased the ramp currents for DRG TTX-S currents and hNE channels but not for hSkM1 channels. The hNE and DRG TTX-S ramp currents activated near -65 mV and therefore could play an important role in boosting stimulus depolarizations in sensory neurons. These results suggest that differences in the kinetics of closed-state inactivation may confer distinct integrative properties on different Na+ channel isoforms.
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Affiliation(s)
- T R Cummins
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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Smith MR, Smith RD, Plummer NW, Meisler MH, Goldin AL. Functional analysis of the mouse Scn8a sodium channel. J Neurosci 1998; 18:6093-102. [PMID: 9698304 PMCID: PMC6793187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The mouse Scn8a sodium channel and its ortholog Na6 in the rat are abundantly expressed in the CNS. Mutations in mouse Scn8a result in neurological disorders, including paralysis, ataxia, and dystonia. In addition, Scn8a has been observed to mediate unique persistent and resurgent currents in cerebellar Purkinje cells (Raman et al., 1997). To examine the functional characteristics of this channel, we constructed a full-length cDNA clone encoding the mouse Scn8a sodium channel and expressed it in Xenopus oocytes. The electrophysiological properties of the Scn8a channels were compared with those of the Rat1 and Rat2 sodium channels. Scn8a channels were sensitive to tetrodotoxin at a level comparable to that of Rat1 or Rat2. Scn8a channels inactivated more rapidly and showed differences in their voltage-dependent properties compared with Rat1 and Rat2 when only the alpha subunits were expressed. Coexpression of the beta1 and beta2 subunits modulated the properties of Scn8a channels, but to a lesser extent than for the Rat1 or Rat2 channels. Therefore, all three channels showed similar voltage dependence and inactivation kinetics in the presence of the beta subunits. Scn8a channels coexpressed with the beta subunits exhibited a persistent current that became larger with increasing depolarization, which was not observed for either Rat1 or Rat2 channels. The unique persistent current observed for Scn8a channels is consistent with the hypothesis that this channel is responsible for distinct sodium conductances underlying repetitive firing of action potentials in Purkinje neurons.
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Affiliation(s)
- M R Smith
- Department of Microbiology and Molecular Genetics and Physiology and Biophysics, University of California, Irvine, California 92697-4025, USA
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