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Chin AC, Lau AY. Structural biology and thermodynamics of GluD receptors. Neuropharmacology 2021; 191:108542. [PMID: 33845075 DOI: 10.1016/j.neuropharm.2021.108542] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 03/25/2021] [Accepted: 03/26/2021] [Indexed: 10/21/2022]
Abstract
Glutamate delta (GluD) receptors are a functionally enigmatic subfamily of ionotropic glutamate receptors. Despite sharing similar sequences and structures with AMPA, NMDA, and kainate receptors, GluD receptors do not bind glutamate nor function as ligand-gated ion channels. Binding d-serine and engaging in transsynaptic protein-protein interactions, GluD receptors are thought to undergo complex conformational rearrangements for non-ionotropic signaling that regulates synaptic plasticity. Recent structural, biochemical, and computational studies have elucidated multiple conformational and thermodynamic factors governing the unique properties of GluD receptors. Here, we review advances in biophysical insights into GluD receptors and discuss the structural thermodynamic relationships that underpin their neurobiological functions.
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Affiliation(s)
- Alfred C Chin
- Weill Cornell/Rockefeller/Sloan Kettering Tri-Institutional MD-PhD Program, New York, NY, USA
| | - Albert Y Lau
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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2
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Beaurain M, Salabert AS, Ribeiro MJ, Arlicot N, Damier P, Le Jeune F, Demonet JF, Payoux P. Innovative Molecular Imaging for Clinical Research, Therapeutic Stratification, and Nosography in Neuroscience. Front Med (Lausanne) 2019; 6:268. [PMID: 31828073 PMCID: PMC6890558 DOI: 10.3389/fmed.2019.00268] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 11/01/2019] [Indexed: 01/06/2023] Open
Abstract
Over the past few decades, several radiotracers have been developed for neuroimaging applications, especially in PET. Because of their low steric hindrance, PET radionuclides can be used to label molecules that are small enough to cross the blood brain barrier, without modifying their biological properties. As the use of 11C is limited by its short physical half-life (20 min), there has been an increasing focus on developing tracers labeled with 18F for clinical use. The first such tracers allowed cerebral blood flow and glucose metabolism to be measured, and the development of molecular imaging has since enabled to focus more closely on specific targets such as receptors, neurotransmitter transporters, and other proteins. Hence, PET and SPECT biomarkers have become indispensable for innovative clinical research. Currently, the treatment options for a number of pathologies, notably neurodegenerative diseases, remain only supportive and symptomatic. Treatments that slow down or reverse disease progression are therefore the subject of numerous studies, in which molecular imaging is proving to be a powerful tool. PET and SPECT biomarkers already make it possible to diagnose several neurological diseases in vivo and at preclinical stages, yielding topographic, and quantitative data about the target. As a result, they can be used for assessing patients' eligibility for new treatments, or for treatment follow-up. The aim of the present review was to map major innovative radiotracers used in neuroscience, and explain their contribution to clinical research. We categorized them according to their target: dopaminergic, cholinergic or serotoninergic systems, β-amyloid plaques, tau protein, neuroinflammation, glutamate or GABA receptors, or α-synuclein. Most neurological disorders, and indeed mental disorders, involve the dysfunction of one or more of these targets. Combinations of molecular imaging biomarkers can afford us a better understanding of the mechanisms underlying disease development over time, and contribute to early detection/screening, diagnosis, therapy delivery/monitoring, and treatment follow-up in both research and clinical settings.
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Affiliation(s)
- Marie Beaurain
- CHU de Toulouse, Toulouse, France.,ToNIC, Toulouse NeuroImaging Center, Inserm U1214, Toulouse, France
| | - Anne-Sophie Salabert
- CHU de Toulouse, Toulouse, France.,ToNIC, Toulouse NeuroImaging Center, Inserm U1214, Toulouse, France
| | - Maria Joao Ribeiro
- UMR 1253, iBrain, Université de Tours, Inserm, Tours, France.,Inserm CIC 1415, University Hospital, Tours, France.,CHRU Tours, Tours, France
| | - Nicolas Arlicot
- UMR 1253, iBrain, Université de Tours, Inserm, Tours, France.,Inserm CIC 1415, University Hospital, Tours, France.,CHRU Tours, Tours, France
| | - Philippe Damier
- Inserm U913, Neurology Department, University Hospital, Nantes, France
| | | | - Jean-François Demonet
- Leenards Memory Centre, Department of Clinical Neuroscience, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland
| | - Pierre Payoux
- CHU de Toulouse, Toulouse, France.,ToNIC, Toulouse NeuroImaging Center, Inserm U1214, Toulouse, France
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Abstract
Wollmuth highlights recent work identifying two cysteine substitutions in kainate receptors that result in direct activation by cadmium.
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Affiliation(s)
- Lonnie P Wollmuth
- Departments of Neurobiology & Behavior and Biochemistry & Cell Biology, Center for Nervous System Disorders, Stony Brook University, Stony Brook, NY
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4
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Fernández-Montoya J, Avendaño C, Negredo P. The Glutamatergic System in Primary Somatosensory Neurons and Its Involvement in Sensory Input-Dependent Plasticity. Int J Mol Sci 2017; 19:ijms19010069. [PMID: 29280965 PMCID: PMC5796019 DOI: 10.3390/ijms19010069] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 12/19/2017] [Accepted: 12/21/2017] [Indexed: 01/25/2023] Open
Abstract
Glutamate is the most common neurotransmitter in both the central and the peripheral nervous system. Glutamate is present in all types of neurons in sensory ganglia, and is released not only from their peripheral and central axon terminals but also from their cell bodies. Consistently, these neurons express ionotropic and metabotropic receptors, as well as other molecules involved in the synthesis, transport and release of the neurotransmitter. Primary sensory neurons are the first neurons in the sensory channels, which receive information from the periphery, and are thus key players in the sensory transduction and in the transmission of this information to higher centers in the pathway. These neurons are tightly enclosed by satellite glial cells, which also express several ionotropic and metabotropic glutamate receptors, and display increases in intracellular calcium accompanying the release of glutamate. One of the main interests in our group has been the study of the implication of the peripheral nervous system in sensory-dependent plasticity. Recently, we have provided novel evidence in favor of morphological changes in first- and second-order neurons of the trigeminal system after sustained alterations of the sensory input. Moreover, these anatomical changes are paralleled by several molecular changes, among which those related to glutamatergic neurotransmission are particularly relevant. In this review, we will describe the state of the art of the glutamatergic system in sensory ganglia and its involvement in input-dependent plasticity, a fundamental ground for advancing our knowledge of the neural mechanisms of learning and adaptation, reaction to injury, and chronic pain.
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Affiliation(s)
- Julia Fernández-Montoya
- Department of Anatomy, Histology and Neuroscience, Medical School, Autonoma University of Madrid, 28029 Madrid, Spain.
| | - Carlos Avendaño
- Department of Anatomy, Histology and Neuroscience, Medical School, Autonoma University of Madrid, 28029 Madrid, Spain.
| | - Pilar Negredo
- Department of Anatomy, Histology and Neuroscience, Medical School, Autonoma University of Madrid, 28029 Madrid, Spain.
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Chimeric Glutamate Receptor Subunits Reveal the Transmembrane Domain Is Sufficient for NMDA Receptor Pore Properties but Some Positive Allosteric Modulators Require Additional Domains. J Neurosci 2017; 36:8815-25. [PMID: 27559165 DOI: 10.1523/jneurosci.0345-16.2016] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Accepted: 06/15/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED NMDA receptors are ligand-gated ion channels that underlie transmission at excitatory synapses and play an important role in regulating synaptic strength and stability. Functional NMDA receptors require two copies of the GluN1 subunit coassembled with GluN2 (and/or GluN3) subunits into a heteromeric tetramer. A diverse array of allosteric modulators can upregulate or downregulate NMDA receptor activity. These modulators include both synthetic compounds and endogenous modulators, such as cis-unsaturated fatty acids, 24(S)-hydroxycholesterol, and various neurosteroids. To evaluate the structural requirements for the formation and allosteric modulation of NMDA receptor pores, we have replaced portions of the rat GluN1, GluN2A, and GluN2B subunits with homologous segments from the rat GluK2 kainate receptor subunit. Our results with these chimeric constructs show that the NMDA receptor transmembrane domain is sufficient to account for most pore properties, but that regulation by some allosteric modulators requires additional cytoplasmic or extracellular domains. SIGNIFICANCE STATEMENT Glutamate receptors mediate excitatory synaptic transmission by forming cation channels through the membrane that open upon glutamate binding. Although many compounds have been identified that regulate glutamate receptor activity, in most cases the detailed mechanisms that underlie modulation are poorly understood. To identify what parts of the receptor are essential for pore formation and sensitivity to allosteric modulators, we generated chimeric subunits that combined segments from NMDA and kainate receptors, subtypes with distinct pharmacological profiles. Surprisingly, our results identify separate domain requirements for allosteric potentiation of NMDA receptor pores by pregnenolone sulfate, 24(S)-hydroxycholesterol, and docosahexaenoic acid, three endogenous modulators derived from membrane constituents. Understanding where and how these compounds act on NMDA receptors should aid in designing better therapeutic agents.
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The low binding affinity of D-serine at the ionotropic glutamate receptor GluD2 can be attributed to the hinge region. Sci Rep 2017; 7:46145. [PMID: 28387240 PMCID: PMC5384001 DOI: 10.1038/srep46145] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Accepted: 03/13/2017] [Indexed: 01/24/2023] Open
Abstract
Ionotropic glutamate receptors (iGluRs) are responsible for most of the fast excitatory communication between neurons in our brain. The GluD2 receptor is a puzzling member of the iGluR family: It is involved in synaptic plasticity, plays a role in human diseases, e.g. ataxia, binds glycine and D-serine with low affinity, yet no ligand has been discovered so far that can activate its ion channel. In this study, we show that the hinge region connecting the two subdomains of the GluD2 ligand-binding domain is responsible for the low affinity of D-serine, by analysing GluD2 mutants with electrophysiology, isothermal titration calorimetry and molecular dynamics calculations. The hinge region is highly variable among iGluRs and fine-tunes gating activity, suggesting that in GluD2 this region has evolved to only respond to micromolar concentrations of D-serine.
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Hepp Y, Salles A, Carbo-Tano M, Pedreira ME, Freudenthal R. Surface expression of NMDA receptor changes during memory consolidation in the crab Neohelice granulata. ACTA ACUST UNITED AC 2016; 23:427-34. [PMID: 27421895 PMCID: PMC4947233 DOI: 10.1101/lm.041707.116] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 05/25/2016] [Indexed: 11/25/2022]
Abstract
The aim of the present study was to analyze the surface expression of the NMDA-like receptors during the consolidation of contextual learning in the crab Neohelice granulata Memory storage is based on alterations in the strength of synaptic connections between neurons. The glutamatergic synapses undergo various forms of N-methyl-D aspartate receptor (NMDAR)-dependent changes in strength, a process that affects the abundance of other receptors at the synapse and underlies some forms of learning and memory. Here we propose a direct regulation of the NMDAR. Changes in NMDAR's functionality might be induced by the modification of the subunit's expression or cellular trafficking. This trafficking does not only include NMDAR's movement between synaptic and extra-synaptic localizations but also the cycling between intracellular compartments and the plasma membrane, a process called surface expression. Consolidation of contextual learning affects the surface expression of the receptor without affecting its general expression. The surface expression of the GluN1 subunit of the NMDAR is down-regulated immediately after training, up-regulated 3 h after training and returns to naïve and control levels 24 h after training. The changes in NMDAR surface expression observed in the central brain are not seen in the thoracic ganglion. A similar increment in surface expression of GluN1 in the central brain is observed 3 h after administration of the competitive GABAA receptor antagonist, bicuculline. These consolidation changes are part of a plasticity event that first, during the down-regulation, stabilizes the trace and later, at 3-h post-training, changes the threshold for synapse activation.
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Affiliation(s)
- Yanil Hepp
- Laboratorio de Neurobiología de la Memoria, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Universidad de Buenos Aires, IFIBYNE, CONICET. Pab. II, 2° piso, Int. Güiraldes 2160, CP 1428, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Angeles Salles
- Laboratorio de Neurobiología de la Memoria, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Universidad de Buenos Aires, IFIBYNE, CONICET. Pab. II, 2° piso, Int. Güiraldes 2160, CP 1428, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Martin Carbo-Tano
- Laboratorio de Neurobiología de la Memoria, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Universidad de Buenos Aires, IFIBYNE, CONICET. Pab. II, 2° piso, Int. Güiraldes 2160, CP 1428, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Maria Eugenia Pedreira
- Laboratorio de Neurobiología de la Memoria, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Universidad de Buenos Aires, IFIBYNE, CONICET. Pab. II, 2° piso, Int. Güiraldes 2160, CP 1428, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Ramiro Freudenthal
- Laboratorio de Neurobiología de la Memoria, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Universidad de Buenos Aires, IFIBYNE, CONICET. Pab. II, 2° piso, Int. Güiraldes 2160, CP 1428, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
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Jarius S, Wildemann B. 'Medusa head ataxia': the expanding spectrum of Purkinje cell antibodies in autoimmune cerebellar ataxia. Part 2: Anti-PKC-gamma, anti-GluR-delta2, anti-Ca/ARHGAP26 and anti-VGCC. J Neuroinflammation 2015; 12:167. [PMID: 26377184 PMCID: PMC4574118 DOI: 10.1186/s12974-015-0357-x] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 07/02/2015] [Indexed: 01/18/2023] Open
Abstract
Serological testing for anti-neural autoantibodies is important in patients presenting with idiopathic cerebellar ataxia, since these autoantibodies may indicate cancer, determine treatment and predict prognosis. While some of them target nuclear antigens present in all or most CNS neurons (e.g. anti-Hu, anti-Ri), others more specifically target antigens present in the cytoplasm or plasma membrane of Purkinje cells (PC). In this series of articles, we provide a detailed review of the clinical and paraclinical features, oncological, therapeutic and prognostic implications, pathogenetic relevance, and differential laboratory diagnosis of the 12 most common PC autoantibodies (often referred to as 'Medusa head antibodies' due their characteristic somatodendritic binding pattern when tested by immunohistochemistry). To assist immunologists and neurologists in diagnosing these disorders, typical high-resolution immunohistochemical images of all 12 reactivities are presented, diagnostic pitfalls discussed and all currently available assays reviewed. Of note, most of these antibodies target antigens involved in the mGluR1/calcium pathway essential for PC function and survival. Many of the antigens also play a role in spinocerebellar ataxia. Part 1 focuses on anti-metabotropic glutamate receptor 1-, anti-Homer protein homolog 3-, anti-Sj/inositol 1,4,5-trisphosphate receptor- and anti-carbonic anhydrase-related protein VIII-associated autoimmune cerebellar ataxia (ACA); part 2 covers anti-protein kinase C gamma-, anti-glutamate receptor delta-2-, anti-Ca/RhoGTPase-activating protein 26- and anti-voltage-gated calcium channel-associated ACA; and part 3 reviews the current knowledge on anti-Tr/delta notch-like epidermal growth factor-related receptor-, anti-Nb/AP3B2-, anti-Yo/cerebellar degeneration-related protein 2- and Purkinje cell antibody 2-associated ACA, discusses differential diagnostic aspects, and provides a summary and outlook.
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Affiliation(s)
- S Jarius
- Molecular Neuroimmunology Group, Department of Neurology, University of Heidelberg, Otto Meyerhof Center, Im Neuenheimer Feld 350, D-69120, Heidelberg, Germany.
| | - B Wildemann
- Molecular Neuroimmunology Group, Department of Neurology, University of Heidelberg, Otto Meyerhof Center, Im Neuenheimer Feld 350, D-69120, Heidelberg, Germany.
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9
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Salabert AS, Fonta C, Fontan C, Adel D, Alonso M, Pestourie C, Belhadj-Tahar H, Tafani M, Payoux P. Radiolabeling of [18F]-fluoroethylnormemantine and initial in vivo evaluation of this innovative PET tracer for imaging the PCP sites of NMDA receptors. Nucl Med Biol 2015; 42:643-53. [PMID: 25963911 DOI: 10.1016/j.nucmedbio.2015.04.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Revised: 03/19/2015] [Accepted: 04/01/2015] [Indexed: 01/01/2023]
Abstract
INTRODUCTION The N-methyl-D-aspartate receptor (NMDAr) is an ionotropic receptor that mediates excitatory transmission. NMDAr overexcitation is thought to be involved in neurological and neuropsychiatric disorders such as Alzheimer disease and schizophrenia. We synthesized [(18)F]-fluoroethylnormemantine ([(18)F]-FNM), a memantine derivative that binds to phencyclidine (PCP) sites within the NMDA channel pore. These sites are primarily accessible when the channel is in the active and open state. METHODS Radiosynthesis was carried out using the Raytest® SynChrom R&D fluorination module. Affinity of this new compound was determined by competition assay. We ran a kinetic study in rats and computed a time-activity curve based on a volume-of-interest analysis, using CARIMAS® software. We performed an ex vivo autoradiography, exposing frozen rat brain sections to a phosphorscreen. Adjacent sections were used to detect NMDAr by immunohistochemistry with an anti-NR1 antibody. As a control of the specificity of our compound for NMDAr, we used a rat anesthetized with ketamine. Correlation analysis was performed with ImageJ software between signal of autoradiography and immunostaining. RESULTS Fluorination yield was 10.5% (end of synthesis), with a mean activity of 3145 MBq and a specific activity above 355 GBq/μmol. Affinity assessment allowed us to determine [(19)F]-FNM IC50 at 6.1 10(-6)M. [(18)F]-FMN concentration gradually increased in the brain, stabilizing at 40 minutes post injection. The brain-to-blood ratio was 6, and 0.4% of the injected dose was found in the brain. Combined ex vivo autoradiography and immunohistochemical staining demonstrated colocalization of NMDAr and [(18)F]-FNM (r=0.622, p<0.0001). The highest intensity was found in the cortex and cerebellum, and the lowest in white matter. A low and homogeneous signal corresponding to unspecific binding was observed when PCP sites were blocked with ketamine. CONCLUSIONS [(18)F]-FNM appears to be a promising tracer for imaging NMDAr activity for undertaking preclinical studies in perspective of clinical detection of neurological or neuropsychological disorders.
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Affiliation(s)
- Anne-Sophie Salabert
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Radiopharmacy Department, University Hospital, Toulouse, France.
| | - Caroline Fonta
- Research Center for Brain and Cognition, University of Toulouse UPS, Toulouse, France; CerCo, CNRS, Toulouse, France
| | - Charlotte Fontan
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Radiopharmacy Department, University Hospital, Toulouse, France
| | - Djilali Adel
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France
| | - Mathieu Alonso
- Radiopharmacy Department, University Hospital, Toulouse, France
| | | | - Hafid Belhadj-Tahar
- Research and Expertise Group, French Association for the Promotion of Medical Research (AFPREMED), Toulouse, France
| | - Mathieu Tafani
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Radiopharmacy Department, University Hospital, Toulouse, France
| | - Pierre Payoux
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Nuclear Medicine Department, University Hospital, Toulouse, France
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10
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Lörinczi É, Gómez-Posada JC, de la Peña P, Tomczak AP, Fernández-Trillo J, Leipscher U, Stühmer W, Barros F, Pardo LA. Voltage-dependent gating of KCNH potassium channels lacking a covalent link between voltage-sensing and pore domains. Nat Commun 2015; 6:6672. [PMID: 25818916 PMCID: PMC4389246 DOI: 10.1038/ncomms7672] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Accepted: 02/18/2015] [Indexed: 12/25/2022] Open
Abstract
Voltage-gated channels open paths for ion permeation upon changes in membrane potential, but how voltage changes are coupled to gating is not entirely understood. Two modules can be recognized in voltage-gated potassium channels, one responsible for voltage sensing (transmembrane segments S1 to S4), the other for permeation (S5 and S6). It is generally assumed that the conversion of a conformational change in the voltage sensor into channel gating occurs through the intracellular S4–S5 linker that provides physical continuity between the two regions. Using the pathophysiologically relevant KCNH family, we show that truncated proteins interrupted at, or lacking the S4–S5 linker produce voltage-gated channels in a heterologous model that recapitulate both the voltage-sensing and permeation properties of the complete protein. These observations indicate that voltage sensing by the S4 segment is transduced to the channel gate in the absence of physical continuity between the modules. The pore of voltage-gated ion channels opens in response to membrane depolarization sensed by a separate voltage-sensing domain. Here, Lörinczi et al. show that, contrary to assumptions, no physical linker is required to transmit changes from the voltage-sensing to the permeation domain of KCNH channels.
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Affiliation(s)
- Éva Lörinczi
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Juan Camilo Gómez-Posada
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Pilar de la Peña
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Campus de El Cristo, 33006 Oviedo, Spain
| | - Adam P Tomczak
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Jorge Fernández-Trillo
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Ulrike Leipscher
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Walter Stühmer
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany.,Cluster of Excellence Nanoscale Microscopy and Molecular Physiology of the Brain, 37073 Göttingen, Germany
| | - Francisco Barros
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Campus de El Cristo, 33006 Oviedo, Spain
| | - Luis A Pardo
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
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Orth A, Tapken D, Hollmann M. The delta subfamily of glutamate receptors: characterization of receptor chimeras and mutants. Eur J Neurosci 2013; 37:1620-30. [DOI: 10.1111/ejn.12193] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Revised: 02/08/2013] [Accepted: 02/20/2013] [Indexed: 12/14/2022]
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12
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Terhag J, Gottschling K, Hollmann M. The Transmembrane Domain C of AMPA Receptors is Critically Involved in Receptor Function and Modulation. Front Mol Neurosci 2010; 3:117. [PMID: 21206529 PMCID: PMC3009476 DOI: 10.3389/fnmol.2010.00117] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Accepted: 11/30/2010] [Indexed: 11/13/2022] Open
Abstract
Ionotropic glutamate receptors are major players in synaptic transmission and are critically involved in many cognitive events. Although receptors of different subfamilies serve different functions, they all show a conserved domain topology. For most of these domains, structure–function relationships have been established and are well understood. However, up to date the role of the transmembrane domain C in receptor function has been investigated only poorly. We have constructed a series of receptor chimeras and point mutants designed to shed light on the structural and/or functional importance of this domain. We here present evidence that the role of transmembrane domain C exceeds that of a mere scaffolding domain and that several amino acid residues located within the domain are crucial for receptor gating and desensitization. Furthermore, our data suggest that the domain may be involved in receptor interaction with transmembrane AMPA receptor regulatory proteins.
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Affiliation(s)
- Jan Terhag
- Department of Biochemistry I - Receptor Biochemistry, Ruhr University Bochum Bochum, Germany
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Cavara NA, Orth A, Hicking G, Seebohm G, Hollmann M. Residues at the tip of the pore loop of NR3B-containing NMDA receptors determine Ca2+ permeability and Mg2+ block. BMC Neurosci 2010; 11:133. [PMID: 20958962 PMCID: PMC2974739 DOI: 10.1186/1471-2202-11-133] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Accepted: 10/19/2010] [Indexed: 11/26/2022] Open
Abstract
Background Members of the complex N-methyl-D-aspartate receptor (NMDAR) subfamily of ionotropic glutamate receptors (iGluRs) conventionally assemble from NR1 and NR2 subunits, the composition of which determines receptor properties. Hallmark features of conventional NMDARs include the requirement for a coagonist, voltage-dependent block by Mg2+, and high permeability for Ca2+. Both Mg2+ sensitivity and Ca2+ permeability are critically dependent on the amino acids at the N and N+1 positions of NR1 and NR2. The recently discovered NR3 subunits feature an unprecedented glycine-arginine combination at those critical sites within the pore. Diheteromers assembled from NR1 and NR3 are not blocked by Mg2+ and are not permeable for Ca2+. Results Employing site-directed mutagenesis of receptor subunits, electrophysiological characterization of mutants in a heterologous expression system, and molecular modeling of the NMDAR pore region, we have investigated the contribution of the unusual NR3 N and N+1 site residues to the unique functional characteristics of receptors containing these subunits. Contrary to previous studies, we provide evidence that both the NR3 N and N+1 site amino acids are critically involved in mediating the unique pore properties. Ca2+ permeability could be rescued by mutating the NR3 N site glycine to the NR1-like asparagine. Voltage-dependent Mg2+ block could be established by providing an Mg2+ coordination site at either the NR3 N or N+1 positions. Conversely, "conventional" receptors assembled from NR1 and NR2 could be made Mg2+ insensitive and Ca2+ impermeable by equipping either subunit with the NR3-like glycine at their N positions, with a stronger contribution of the NR1 subunit. Conclusions This study sheds light on the structure-function relationship of the least characterized member of the NMDAR subfamily. Contrary to previous reports, we provide evidence for a critical functional involvement of the NR3 N and N+1 site amino acids, and propose them to be the essential determinants for the unique pore properties mediated by this subunit.
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Affiliation(s)
- Nora A Cavara
- Department of Biochemistry I - Receptor Biochemistry, Ruhr University Bochum, Universitaetsstrasse 150, D-44780 Bochum, Germany
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A light-gated, potassium-selective glutamate receptor for the optical inhibition of neuronal firing. Nat Neurosci 2010; 13:1027-32. [PMID: 20581843 PMCID: PMC2915903 DOI: 10.1038/nn.2589] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Accepted: 05/26/2010] [Indexed: 12/12/2022]
Abstract
Genetically targeted light-activated ion channels and pumps make it possible to determine the role of specific neurons in neuronal circuits, information processing and behavior. Here, we describe the development of a K+-selective ionotropic glutamate receptor that reversibly inhibits neuronal activity in response to light in dissociated neurons and brain slice and reversibly suppresses behavior in zebrafish. The receptor is a chimera of the pore region of a K+-selective bacterial glutamate receptor and the ligand binding domain of the light-gated mammalian kainate receptor (iGluR6/GluK2). This hyperpolarizing light-gated channel, HyLighter, is turned on by a brief light pulse at one wavelength and turned off by a pulse at a second wavelength. The control is obtained at moderate intensity. After optical activation, the photo-current and optical silencing of activity persist in the dark for extended periods. The low light requirement and bi-stability of HyLighter represent advantages for the dissection of neural circuitry.
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15
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Sager C, Terhag J, Kott S, Hollmann M. C-terminal domains of transmembrane alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor regulatory proteins not only facilitate trafficking but are major modulators of AMPA receptor function. J Biol Chem 2009; 284:32413-24. [PMID: 19773551 DOI: 10.1074/jbc.m109.039891] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate receptors are essential players in fast synaptic transmission in the vertebrate central nervous system. Their synaptic delivery and localization as well as their electrophysiological properties are regulated by transmembrane AMPA receptor regulatory proteins (TARPs). However, the exact mechanisms of how the four originally designated TARPs (gamma2, gamma3, gamma4, and gamma8) modulate AMPA receptor function remain largely unknown. Previous studies suggested the C-terminal domain (CTD) of gamma2 to mediate increased trafficking and reduced desensitization of AMPA receptors. As it remained unclear whether these findings extend to other TARPs, we set out to investigate and compare the role of the CTDs of the four original TARPs in AMPA receptor modulation. To address this issue, we replaced the TARP CTDs with the CTD of the homologous subunit gamma1, a voltage-dependent calcium channel subunit expressed in skeletal muscle that lacks TARP properties. We analyzed the impact of the resulting chimeras on GluR1 functional properties in Xenopus oocytes and HEK293 cells. Interestingly, the CTDs of all TARPs not only modulate the extent and kinetics of desensitization but also modulate agonist potencies of AMPA receptors. Furthermore, the CTDs are required for TARP-induced modulation of AMPA receptor gating, including conversion of antagonists to partial agonists and constitutive channel openings. Strikingly, we found a special role of the cytoplasmic tail of gamma4, suggesting that the underlying mechanisms of modulation of AMPA receptor function are different among the TARPs. We propose that the intracellularly located CTD is the origin of TARP-specific functional modulation and not merely a facilitator of trafficking.
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Affiliation(s)
- Charlotte Sager
- Department of Biochemistry I-Receptor Biochemistry, Ruhr University Bochum, Germany
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16
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Schmidt C, Klein C, Hollmann M. Xenopus laevis Oocytes Endogenously Express All Subunits of the Ionotropic Glutamate Receptor Family. J Mol Biol 2009; 390:182-95. [DOI: 10.1016/j.jmb.2009.05.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Revised: 05/07/2009] [Accepted: 05/07/2009] [Indexed: 01/27/2023]
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17
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Schmid SM, Kott S, Sager C, Huelsken T, Hollmann M. The glutamate receptor subunit delta2 is capable of gating its intrinsic ion channel as revealed by ligand binding domain transplantation. Proc Natl Acad Sci U S A 2009; 106:10320-5. [PMID: 19506248 PMCID: PMC2700928 DOI: 10.1073/pnas.0900329106] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Indexed: 11/18/2022] Open
Abstract
The family of ionotropic glutamate receptors includes 2 subunits, delta1 and delta2, the physiological relevance of which remains poorly understood. Both are nonfunctional in heterologous expression systems, although the isolated, crystallized ligand binding domain (LBD) of delta2 is capable of binding D-serine. To investigate these seemingly contradictory observations we tested whether delta receptors can be ligand gated at all. We used a strategy that replaced the native LBD of delta2 by a proven glutamate-binding LBD. Test transplantations between alpha-amino-3-hydroxy-5-methylisoxazole propionate (AMPA) and kainate receptors (GluR1 and GluR6, respectively) showed that this approach can produce functional chimeras even if only one part of the bipartite LBD is swapped. Upon outfitting delta2 with the LBD of GluR6, the chimera formed glutamate-gated ion channels with low Ca(2+) permeability and unique rectification properties. Ligand-induced conformational changes can thus gate delta2, suggesting that the LBD of this receptor works fundamentally differently from that of other ionotropic glutamate receptors.
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Affiliation(s)
- Sabine M. Schmid
- Department of Biochemistry I–Receptor Biochemistry
- International Graduate School of Neuroscience
| | - Sabine Kott
- Department of Biochemistry I–Receptor Biochemistry
| | - Charlotte Sager
- Department of Biochemistry I–Receptor Biochemistry
- Ruhr University Research School, Ruhr University Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany
| | | | - Michael Hollmann
- Department of Biochemistry I–Receptor Biochemistry
- International Graduate School of Neuroscience
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18
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Cavara NA, Orth A, Hollmann M. Effects of NR1 splicing on NR1/NR3B-type excitatory glycine receptors. BMC Neurosci 2009; 10:32. [PMID: 19348678 PMCID: PMC2669480 DOI: 10.1186/1471-2202-10-32] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2008] [Accepted: 04/06/2009] [Indexed: 11/23/2022] Open
Abstract
Background N-methyl-D-aspartate receptors (NMDARs) are the most complex of ionotropic glutamate receptors (iGluRs). Subunits of this subfamily assemble into heteromers, which – depending on the subunit combination – may display very different pharmacological and electrophysiological properties. The least studied members of the NMDAR family, the NR3 subunits, have been reported to assemble with NR1 to form excitatory glycine receptors in heterologous expression systems. The heterogeneity of NMDARs in vivo is in part conferred to the receptors by splicing of the NR1 subunit, especially with regard to proton sensitivity. Results Here, we have investigated whether the NR3B subunit is capable of assembly with each of the eight functional NR1 splice variants, and whether the resulting receptors share the unique functional properties described for NR1-1a/NR3. We provide evidence that functional excitatory glycine receptors formed regardless of the NR1 isoform, and their pharmacological profile matched the one reported for NR1-1a/NR3: glycine alone fully activated the receptors, which were insensitive to glutamate and block by Mg2+. Surprisingly, amplitudes of agonist-induced currents showed little dependency on the C-terminally spliced NR1 variants in NR1/NR3B diheteromers. Even more strikingly, NR3B conferred proton sensitivity also to receptors containing NR1b variants – possibly via disturbing the "proton shield" of NR1b splice variants. Conclusion While functional assembly could be demonstrated for all combinations, not all of the specific interactions seen for NR1 isoforms with coexpressed NR2 subunits could be corroborated for NR1 assembly with NR3. Rather, NR3 abates trafficking effects mediated by the NR1 C terminus as well as the N-terminally mediated proton insensitivity. Thus, this study establishes that NR3B overrides important NR1 splice variant-specific receptor properties in NR1/NR3B excitatory glycine receptors.
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Affiliation(s)
- Nora A Cavara
- Department of Biochemistry I - Receptor Biochemistry, Ruhr University Bochum, Universitätsstr, 150, D-44780 Bochum, Germany.
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19
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Comparative analysis of the pharmacology of GluR1 in complex with transmembrane AMPA receptor regulatory proteins γ2, γ3, γ4, and γ8. Neuroscience 2009; 158:78-88. [DOI: 10.1016/j.neuroscience.2007.12.047] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2007] [Revised: 12/21/2007] [Accepted: 12/26/2007] [Indexed: 11/23/2022]
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20
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Tapken D, Hollmann M. Arabidopsis thaliana glutamate receptor ion channel function demonstrated by ion pore transplantation. J Mol Biol 2008; 383:36-48. [PMID: 18625242 DOI: 10.1016/j.jmb.2008.06.076] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Revised: 06/18/2008] [Accepted: 06/25/2008] [Indexed: 11/24/2022]
Abstract
Ionotropic glutamate receptors (iGluRs) are ligand-gated cation channels that mediate fast excitatory neurotransmission in the mammalian central nervous system. In the model plant Arabidopsis thaliana, a large family of 20 genes encoding proteins that share similarities with animal iGluRs in sequence and predicted secondary structure has been discovered. Members of this family, termed AtGLRs (A. thaliana glutamate receptors), have been implicated in root development, ion transport, and several metabolic and signalling pathways. However, there is still no direct proof of ligand-gated ion channel function of any AtGLR subunit. We used a domain transplantation technique to directly test whether the putative ion pore domains of AtGLRs can conduct ions. To this end, we transplanted the ion pore domains of 17 AtGLR subunits into rat alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (GluR1) and kainate (GluR6) receptor subunits and tested the resulting chimaeras for ion channel function in the Xenopus oocyte expression system. We show that AtGLR1.1 and AtGLR1.4 have functional Na(+)-, K(+)-, and Ca(2+)-permeable ion pore domains. The properties of currents through the AtGLR1.1 ion pore match those of glutamate-activated currents, depolarisations, and glutamate-triggered Ca(2+) influxes observed in plant cells. We conclude that some AtGLRs have functional non-selective cation pores.
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MESH Headings
- Amino Acid Sequence
- Animals
- Arabidopsis/genetics
- Arabidopsis/metabolism
- Arabidopsis Proteins/chemistry
- Arabidopsis Proteins/genetics
- Arabidopsis Proteins/metabolism
- Calcium Channels/chemistry
- Calcium Channels/genetics
- Calcium Channels/metabolism
- Electrophysiology
- Female
- In Vitro Techniques
- Ion Channels/chemistry
- Ion Channels/genetics
- Ion Channels/metabolism
- Models, Molecular
- Molecular Sequence Data
- Oocytes/metabolism
- Protein Structure, Tertiary
- Protein Subunits
- Rats
- Receptors, AMPA/chemistry
- Receptors, AMPA/genetics
- Receptors, AMPA/metabolism
- Receptors, Glutamate/chemistry
- Receptors, Glutamate/genetics
- Receptors, Glutamate/metabolism
- Receptors, Kainic Acid/chemistry
- Receptors, Kainic Acid/genetics
- Receptors, Kainic Acid/metabolism
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Sequence Homology, Amino Acid
- Xenopus laevis
- GluK2 Kainate Receptor
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Affiliation(s)
- Daniel Tapken
- Department of Biochemistry I-Receptor Biochemistry, NC6/170, Ruhr University Bochum, Bochum, Germany
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21
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Villmann C, Hoffmann J, Werner M, Kott S, Strutz-Seebohm N, Nilsson T, Hollmann M. Different structural requirements for functional ion pore transplantation suggest different gating mechanisms of NMDA and kainate receptors. J Neurochem 2008; 107:453-65. [DOI: 10.1111/j.1471-4159.2008.05623.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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22
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Shuffling the Deck Anew: How NR3 Tweaks NMDA Receptor Function. Mol Neurobiol 2008; 38:16-26. [DOI: 10.1007/s12035-008-8029-9] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Accepted: 05/16/2008] [Indexed: 10/21/2022]
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23
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To gate or not to gate: are the delta subunits in the glutamate receptor family functional ion channels? Mol Neurobiol 2008; 37:126-41. [PMID: 18521762 DOI: 10.1007/s12035-008-8025-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Accepted: 05/09/2008] [Indexed: 01/01/2023]
Abstract
The two delta receptor subunits remain the most puzzling enigma within the ionotropic glutamate receptor family. Despite the recent elucidation of the ligand-binding domain structure of delta2, many fundamental questions with regard to the subunits' mechanism of function still remain unanswered. Of necessity, the majority of studies on delta receptors focused on the metabotropic function of delta2, since electrophysiological approaches to date are limited to the characterization of spontaneous currents through the delta2-lurcher mutant. Indeed, accumulated evidence primarily from delta2-deficient transgenic mice suggest that major physiological roles of delta2 are mediated via metabotropic signaling by the subunit's C terminus. Why then would the subunits retain a conserved ion channel domain if they do not form functional ion channels? Any progress with regard to ionotropic function of the two delta subunits has been hampered by their largely unknown pharmacology. Even now that a pharmacological profile for delta2 is being established on the basis of the ligand-binding domain structure, wild-type delta2 channels in heterologous expression systems stay closed in the presence of molecules that have been demonstrated to bind to the receptor's ligand-binding domain. In this paper, we review the current knowledge of delta subunits focusing on the disputed ionotropic function.
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Tong G, Takahashi H, Tu S, Shin Y, Talantova M, Zago W, Xia P, Nie Z, Goetz T, Zhang D, Lipton SA, Nakanishi N. Modulation of NMDA receptor properties and synaptic transmission by the NR3A subunit in mouse hippocampal and cerebrocortical neurons. J Neurophysiol 2008; 99:122-32. [PMID: 18003876 PMCID: PMC4586267 DOI: 10.1152/jn.01044.2006] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Expression of the NR3A subunit with NR1/NR2 in Xenopus oocytes or mammalian cell lines leads to a reduction in N-methyl-d-aspartate (NMDA)-induced currents and decreased Mg(2+) sensitivity and Ca(2+) permeability compared with NR1/NR2 receptors. Consistent with these findings, neurons from NR3A knockout (KO) mice exhibit enhanced NMDA-induced currents. Recombinant NR3A can also form excitatory glycine receptors with NR1 in the absence of NR2. However, the effects of NR3A on channel properties in neurons and synaptic transmission have not been fully elucidated. To study physiological roles of NR3A subunits, we generated NR3A transgenic (Tg) mice. Cultured NR3A Tg neurons exhibited two populations of NMDA receptor (NMDAR) channels, reduced Mg(2+) sensitivity, and decreased Ca(2+) permeability in response to NMDA/glycine, but glycine alone did not elicit excitatory currents. In addition, NMDAR-mediated excitatory postsynaptic currents (EPSCs) in NR3A Tg hippocampal slices showed reduced Mg(2+) sensitivity, consistent with the notion that NR3A subunits incorporated into synaptic NMDARs. To study the function of endogenous NR3A subunits, we compared NMDAR-mediated EPSCs in NR3A KO and WT control mice. In NR3A KO mice, the ratio of the amplitudes of the NMDAR-mediated component to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated component of the EPSC was significantly larger than that seen in WT littermates. This result suggests that NR3A subunits contributed to the NMDAR-mediated component of the EPSC in WT mice. Taken together, these results show that NR3A subunits contribute to NMDAR responses from both synaptic and extrasynaptic receptors, likely composed of NR1, NR2, and NR3 subunits.
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Affiliation(s)
- Gary Tong
- Center for Neuroscience, Aging, and Stem Cell Research, Burnham Institute for Medical Research, La Jolla, California 92037, USA.
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25
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A domain linking the AMPA receptor agonist binding site to the ion pore controls gating and causes lurcher properties when mutated. J Neurosci 2007; 27:12230-41. [PMID: 17989289 DOI: 10.1523/jneurosci.3175-07.2007] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Ionotropic, AMPA-type glutamate receptors (GluRs) critically shape excitatory synaptic signals in the CNS. Ligand binding induces conformational changes in the glutamate-binding domain of the receptors that are converted into opening of the channel pore via three short linker sequences, a process referred to as gating. Although crystallization of the glutamate-binding domain and structural models of the ion pore advanced our understanding of ligand-binding dynamics and pore movements, the allosteric coupling of both events by the short linkers has not been described in detail. To study the role of the linkers in gating GluR1, we transplanted them between different GluRs and examined the electrophysiological properties of the resulting chimeric receptors in Xenopus laevis oocytes and HEK293 cells. We found that all three linkers decisively affect receptor functionality, agonist potency, and desensitization. One linker chimera was nondesensitizing and exhibited strongly increased agonist potencies, while fluxing ions even in the absence of agonist, similar to properties reported for the GluR1 lurcher mutation. Combining this new lurcher-like linker chimera with the original lurcher mutation allowed us to reassess the effect of lurcher on GluR1 gating properties. The observed differential but interdependent influence of linker and lurcher mutations on receptor properties suggests that the linkers are part of a fine-tuned structural element that normally stabilizes the closed ion pore. We propose that lurcher-like mutations act by disrupting this element such that ligand-induced conformational changes are not necessarily required to gate the channel.
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26
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Villmann C, Becker CM. On the hypes and falls in neuroprotection: targeting the NMDA receptor. Neuroscientist 2007; 13:594-615. [PMID: 17911221 DOI: 10.1177/1073858406296259] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Activation of the NMDA (N-methyl-D-aspartate) responsive subclass of glutamate receptors is an important mechanism of excitatory synaptic transmission. Moreover, NMDA receptors are widely involved in many forms of synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD), which are thought to underlie complex tasks, including learning and memory. Dysfunction of these ligand-gated cation channels has been identified as an underlying molecular mechanism in neurological disorders ranging from acute stroke to chronic neurodegeneration in amyotrophic lateral sclerosis. Excessive glutamate levels have been detected following brain trauma and cerebral ischemia, resulting in an unregulated stimulation of NMDA receptors. These conditions are thought to elicit a cascade of excitation-mediated neuronal damage where massive increases in intracellular calcium concentrations finally trigger neuronal damage and apoptosis. Consistent with the hypothesis of NMDA receptors as essential mediators of excitotoxicity, the different functional domains of these ion channels have been identified as potential targets for neuroprotective agents. Following an initial hype on potential NMDA receptor therapeutics, the authors currently see a period of skepticism that, in reverse, appears to neglect the therapeutic potential of this receptor class. This review attempts a reappraisal of this important class of neurotransmitter receptors, with a focus on NMDA receptor heterogeneity, ligand binding domains, and candidate diseases for a potential neuroprotective therapy.
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Affiliation(s)
- Carmen Villmann
- Institut für Biochemie, Emil-Fischer-Zentrum Universität Erlangen-Nürnberg, Germany
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27
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Körber C, Werner M, Hoffmann J, Sager C, Tietze M, Schmid SM, Kott S, Hollmann M. Stargazin Interaction with α-Amino-3-hydroxy-5-methyl-4-isoxazole Propionate (AMPA) Receptors Is Critically Dependent on the Amino Acid at the Narrow Constriction of the Ion Channel. J Biol Chem 2007; 282:18758-66. [PMID: 17483093 DOI: 10.1074/jbc.m611182200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The subunit GluR2 of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subfamily of ionotropic glutamate receptors (GluRs) features a single amino acid at the narrow constriction of the pore loop that is altered from glutamine to arginine by RNA editing. This so-called Q/R site has been shown to play an important role in the determination of the electrophysiological properties of AMPA receptor complexes as well as of trafficking to the plasma membrane. The protein stargazin has also been shown to modulate electrophysiological properties and trafficking to the plasma membrane of AMPA receptors. In this study we examined via a series of mutants of the Q/R site of the AMPA receptor GluR1 whether the amino acid at this position has any influence on the modulatory effects mediated by stargazin. To this end, we analyzed current responses of Q/R site mutants upon application of glutamate and kainate and determined the amount of mutant receptor protein in the plasma membrane in Xenopus oocytes. Desensitization kinetics of several mutants were analyzed in HEK293 cells. We found that the stargazin-mediated decrease in receptor desensitization, the slowing of desensitization kinetics, and the kainate efficacy were all dependent on the amino acid at the Q/R site, whereas the stargazin-mediated increase in trafficking toward the plasma membrane remained independent of this amino acid. We propose that the Q/R site modulates the interaction of stargazin with the transmembrane domains of AMPA receptors via an allosteric mechanism and that this modulation leads to the observed differences in the electrophysiological properties of the receptor.
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Affiliation(s)
- Christoph Körber
- Department of Biochemistry I-Receptor Biochemistry, Ruhr University Bochum, D-44780 Bochum, Germany
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28
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Kott S, Werner M, Körber C, Hollmann M. Electrophysiological properties of AMPA receptors are differentially modulated depending on the associated member of the TARP family. J Neurosci 2007; 27:3780-9. [PMID: 17409242 PMCID: PMC6672393 DOI: 10.1523/jneurosci.4185-06.2007] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The family of AMPA receptors is encoded by four genes that are differentially spliced to result in the flip or flop versions of the four subunits GluR1 to GluR4. GluR2 is further modified at the so-called Q/R site by posttranscriptional RNA editing. Delivery of AMPA receptors to the plasma membrane and synaptic trafficking are controlled by transmembrane AMPA receptor regulatory proteins (TARPs). Additionally, TARPs influence essential electrophysiological properties of AMPA receptor channels such as desensitization and agonist efficacies. Here, we compare the influence of all known TARPs (gamma2, gamma3, gamma4, and gamma8) on agonist-induced currents of the four AMPA receptor subunits, including flip and flop splice variants and editing variants. We show that, although agonist-induced currents of all homomeric AMPA receptor subunits as well as all heteromeric combinations tested are significantly potentiated when coexpressed with members of the TARP family in Xenopus laevis oocytes, the extent of TARP-mediated increase in agonist-induced responses is highly dependent on both the AMPA receptor subunit and the coexpressed TARP. Moreover, we demonstrate that the splice variant of the AMPA receptor plays a key role in determining the modulation of electrophysiological properties by associated TARPs. We furthermore present evidence that individual TARP-AMPA receptor interactions control the degree of desensitization of AMPA receptors. Consequently, because of their subunit-specific impact on the electrophysiological properties, TARPs play a major role as modulatory subunits of AMPA receptors and thus contribute to the functional diversity of AMPA receptors encountered in the CNS.
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Affiliation(s)
- Sabine Kott
- Department of Biochemistry I, Receptor Biochemistry, Ruhr University Bochum, D-44780 Bochum, Germany
| | - Markus Werner
- Department of Biochemistry I, Receptor Biochemistry, Ruhr University Bochum, D-44780 Bochum, Germany
| | - Christoph Körber
- Department of Biochemistry I, Receptor Biochemistry, Ruhr University Bochum, D-44780 Bochum, Germany
| | - Michael Hollmann
- Department of Biochemistry I, Receptor Biochemistry, Ruhr University Bochum, D-44780 Bochum, Germany
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Wada A, Takahashi H, Lipton SA, Chen HSV. NR3A modulates the outer vestibule of the "NMDA" receptor channel. J Neurosci 2007; 26:13156-66. [PMID: 17182766 PMCID: PMC6675006 DOI: 10.1523/jneurosci.2552-06.2006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Classical NMDA receptors (NMDARs), activated by glycine and glutamate, are heteromultimers comprised of NR1 and NR2 subunits. Coexpression of the novel NR3 family of NMDAR subunits decreases the magnitude of NR1/NR2 receptor-mediated currents or forms glycine-activated channels with the NR1 subunit alone. The second (M2) and third (M3) membrane segments of NR1 and NR2 subunits of classical NMDARs form the core of the channel permeation pathway. Structural information regarding NR1/NR3 channels remains unknown. Using the Xenopus oocyte expression system and the SCAM (substituted cysteine accessibility method), we found that M3 segments of both NR1 and NR3A form a narrow constriction in the outer vestibule of the channel, which prevents passage of externally applied sulfhydryl-specific agents. The most internal reactive residue in each M3 segment is the threonine in the conserved SYTANLAAF motif. These threonines appear to be symmetrically aligned. Several NR3A M3 mutations change the behavior of NR1/NR3A channels. Unlike NR1, however, the M3 segment of NR3A does not undergo extensive molecular rearrangement during channel gating by added glycine. Additionally, in the M2 segment, our data suggest that the amino acid at the asparagine (N) site of NR1, but not NR3A, contributes to the selectivity filter of NR1/3A channels. We therefore conclude that NR3A modulates the NR1/NR3A permeation pathway via a novel mechanism of forming a narrow constriction at the outer channel vestibule. This modified channel vestibule may also explain the dominant-negative effect of the NR3 subunit on channel behavior when coexpressed with NR1 and NR2 subunits.
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Affiliation(s)
- Akira Wada
- Center for Neuroscience and Aging, Burnham Institute for Medical Research, and
| | - Hiroto Takahashi
- Center for Neuroscience and Aging, Burnham Institute for Medical Research, and
| | - Stuart A. Lipton
- Center for Neuroscience and Aging, Burnham Institute for Medical Research, and
- Departments of Neurosciences and
| | - H.-S. Vincent Chen
- Center for Neuroscience and Aging, Burnham Institute for Medical Research, and
- Cardiology, University of California, San Diego, La Jolla, California 92037
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30
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Hoffmann J, Gorodetskaia A, Hollmann M. Ion pore properties of ionotropic glutamate receptors are modulated by a transplanted potassium channel selectivity filter. Mol Cell Neurosci 2006; 33:335-43. [PMID: 17010644 DOI: 10.1016/j.mcn.2006.08.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Revised: 08/02/2006] [Accepted: 08/17/2006] [Indexed: 11/30/2022] Open
Abstract
The canonical potassium channel selectivity filter motif TVGYG was transplanted into ionotropic glutamate receptors (iGluRs) of the AMPA and NMDA subtype to test whether it renders the iGluRs K(+) selective. The TVGYG motif modulated several ion pore properties of AMPA receptor as well as NMDA receptor mutants, e.g., the intra- and extracellular polyamine block, current/voltage relationships, open channel block by MK801 and Mg(2+), and permeability for divalent cations. However, introduction of the selectivity filter failed to increase the K(+) selectivity of homomeric AMPA and heteromeric NMDA receptor complexes, which may be due to absence of selectivity filter-stabilizing interaction sites in the iGluR pore domain. Our findings indicate that even if glutamate receptors appear to have the intrinsic capacity for K(+) permeability, as is demonstrated by the prokaryotic, glutamate-gated, K(+) selective GluR0, the isolated selectivity filter is not able to confer K(+) permeability to the relatively unselective iGluR cation pore.
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Affiliation(s)
- Jutta Hoffmann
- Dept. of Biochemistry I-Receptor Biochemistry, Ruhr University Bochum, Building NC, Level 6, Rm. 170, D-44787 Bochum, Germany
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31
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Jeong GB, Werner M, Gazula VR, Itoh T, Roberts M, David S, Pfister B, Cohen A, Neve RL, Hollmann M, Kalb R. Bi-directional control of motor neuron dendrite remodeling by the calcium permeability of AMPA receptors. Mol Cell Neurosci 2006; 32:299-314. [PMID: 16790357 DOI: 10.1016/j.mcn.2006.04.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Revised: 03/20/2006] [Accepted: 04/14/2006] [Indexed: 11/30/2022] Open
Abstract
Motor neurons express particularly high levels of the AMPA receptor subunit GluR1(Q)flip (GluR1(Q)i) during the period in early postnatal life when their dendritic tree grows and becomes more branched. To investigate how GluR1-containing AMPA receptors contribute to dendrite morphogenesis, we characterized a mutant form of GluR1 (containing a histidine in the Q/R editing site) with unique electrophysiological properties. Most notably, AMPA receptors assembled from GluR1(H)i display less calcium permeability than AMPA receptors assembled from GluR1(Q)i. Expression of GluR1(Q)i in vivo or in vitro led to an increase in dendrite branching with no net change in the overall tree size while GluR1(H)i led to a loss of branches and a net reduction in overall tree size. GluR1(H)i-dependent dendrite atrophy is mediated by protein phosphatase 2B. The results suggest that the electrophysiological properties of cell surface AMPA receptors, specifically their permeability to calcium, can be a central determinant of whether the dendrites undergo activity-dependent branching or atrophy.
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Affiliation(s)
- Goo-Bo Jeong
- Department of Anatomy, College of Medicine, Chungbuk National University, Cheong-ju 361-763, Republic of Korea
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32
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Yao Y, Mayer ML. Characterization of a soluble ligand binding domain of the NMDA receptor regulatory subunit NR3A. J Neurosci 2006; 26:4559-66. [PMID: 16641235 PMCID: PMC6674067 DOI: 10.1523/jneurosci.0560-06.2006] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
NR3A is expressed widely in the developing CNS of mammals. Coassembly of NR3A with NR1 and NR2 modifies NMDA receptor-mediated responses, reducing calcium permeability and single-channel conductance. The ligand binding properties of NR3A are unknown but shape the role NR3A plays when incorporated into NMDA receptors. Here, a soluble NR3A ligand binding domain (NR3A S1S2) was constructed based on amino acid sequence alignments with other glutamate receptor ion channels and is expressed in Escherichia coli. After purification by affinity, gel filtration, and ion exchange chromatography, NR3A S1S2 behaves as a monomer even at a concentration of 20 mg/ml, as determined by size-exclusion chromatography and dynamic light scattering. NR3A S1S2 has very high affinity for glycine with an apparent dissociation constant (Kd) of 40 nm, 650-fold less than the Kd for NR1. Glutamate, which binds to NR2 subunits, also binds to NR3A, but with very low affinity (Kd = 9.6 mm); in contrast, binding of glutamate to NR1 was not detectable even at a 300 mm concentration. The antagonist binding profiles of NR3A and NR1 also show striking differences. 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline (CNQX), and its analog CGP78608, bind to NR3A S1S2 with low micromolar affinity, whereas for NR1, the affinity of CGP78608 increases 1000-fold compared with CNQX. Other high-affinity NR1 antagonists also show very weak binding to NR3A. Proteolysis protection experiments reveal that CNQX and CGP78608 bind to and stabilize domain 1 of NR3A S1S2 but increase proteolysis of domain 2, indicating that they produce conformational changes distinct from those induced by glycine and D-serine.
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33
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Hu X, Ma M, Dahl G. Conductance of connexin hemichannels segregates with the first transmembrane segment. Biophys J 2006; 90:140-50. [PMID: 16214855 PMCID: PMC1367013 DOI: 10.1529/biophysj.105.066373] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Accepted: 09/13/2005] [Indexed: 11/18/2022] Open
Abstract
Gap junction channels are intercellular channels that mediate the gated transfer of molecules between adjacent cells. To identify the domain determining channel conductance, the first transmembrane segment (M1) was reciprocally exchanged between Cx46 and Cx32E(1)43. The resulting chimeras exhibited conductances similar to that of the respective M1 donor. Furthermore, a chimera with the carboxy-terminal half of M1 in Cx46 replaced by that of Cx32 exhibited a conductance similar to that of Cx32E(1)43, whereas the chimera with only the amino-terminal half of M1 replaced retained the unitary conductance of wild-type Cx46. Extending the M1 domain swapping to other connexins by replacing the carboxy-terminal half of M1 in Cx46 with that of Cx37 yielded a chimera channel with increased unitary conductance close to that of Cx37. Furthermore, a point mutant of Cx46, with leucine substituted by glycine in position 35, displayed a conductance much larger than that of the wild type. Thus, the M1 segment, especially the second half, contains important determinants of conductance of the connexin channel.
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Affiliation(s)
- Xinge Hu
- Department of Physiology and Biophysics, University of Miami, School of Medicine, Miami, Florida 33101, USA
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34
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Baltaev R, Strutz-Seebohm N, Korniychuk G, Myssina S, Lang F, Seebohm G. Regulation of cardiac shal-related potassium channel Kv 4.3 by serum- and glucocorticoid-inducible kinase isoforms in Xenopus oocytes. Pflugers Arch 2004; 450:26-33. [PMID: 15578212 DOI: 10.1007/s00424-004-1369-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2004] [Accepted: 10/27/2004] [Indexed: 12/28/2022]
Abstract
The human cardiac transient outward potassium current I(to) is formed by co-assembly of voltage-dependent K(+) channel (Kv 4.3) pore-forming alpha-subunits with differently spliced K channel interacting protein (KChIP) accessory proteins. I(to) is of considerable importance for the normal course of the cardiac ventricular action potential. The present study was performed to determine whether isoforms of the serum- and glucocorticoid-inducible kinase (SGK) family influence Kv 4.3/KChIP2b channel activity in the Xenopus laevis heterologous expression system. Co-expression of SGK1, but not of SGK2 or SGK3, increased Kv 4.3/KChIP2b channel currents. The up-regulation of the current was not due to changes in the activation curve or changes of channel inactivation. The currents in oocytes expressing Kv 4.3 alone were smaller than those in Kv 4.3/KChIP2b expressing oocytes, but were still stimulated by SGK1. The effect of wild-type SGK1 was mimicked by constitutively active SGK1 (SGK1 S422D) but not by an inactive mutant (SGK1 K127N). The current amplitude increase mediated by SGK1 was not dependent on NEDD4.2 or RAB5, nor did it reflect increased cell surface expression. In conclusion, SGK1 stimulates Kv 4.3 potassium channels expressed in Xenopus oocytes by a novel mechanism distinct from the known NEDD4.2-dependent pathway.
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Affiliation(s)
- Ravshan Baltaev
- Department of Physiology I, University of Tübingen, Tübingen, Germany
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35
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Waterhouse RN, Slifstein M, Dumont F, Zhao J, Chang RC, Sudo Y, Sultana A, Balter A, Laruelle M. In vivo evaluation of [11C]N-(2-chloro-5-thiomethylphenyl)-N′- (3-methoxy-phenyl)-N′-methylguanidine ([11C]GMOM) as a potential PET radiotracer for the PCP/NMDA receptor. Nucl Med Biol 2004; 31:939-48. [PMID: 15464396 DOI: 10.1016/j.nucmedbio.2004.03.012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2003] [Revised: 01/12/2004] [Accepted: 03/14/2004] [Indexed: 10/26/2022]
Abstract
The development of imaging methods to measure changes in NMDA ion channel activation would provide a powerful means to probe the mechanisms of drugs and device based treatments (e.g., ECT) thought to alter glutamate neurotransmission. To provide a potential NMDA/PCP receptor PET tracer, we synthesized the radioligand [11C]GMOM (ki = 5.2 +/-0.3 nM; log P = 2.34) and evaluated this ligand in vivo in awake male rats and isoflurane anesthetized baboons. In rats, the regional brain uptake of [11C]GMOM ranged from 0.75+/-0.13% ID/g in the medulla and pons to 1.15+/-0.17% ID/g in the occipital cortex. MK801 (1 mg/kg i.v.) significantly reduced (24-28%) [11C]GMOM uptake in all regions. D-serine (10 mg/kg i.v.) increased [11C]GMOM %ID/g values in all regions (10-24%) reaching significance in the frontal cortex and cerebellum only. The NR2B ligand RO 25-6981 (10 mg/kg i.v.) reduced [11C]GMOM uptake significantly (24-38%) in all regions except for the cerebellum and striatum. Blood activity was 0.11+/-0.03 %ID/g in the controls group and did not vary significantly across groups. PET imaging in isoflurane-anesthetized baboons with high specific activity [11C]GMOM provided fairly uniform regional brain distribution volume (VT) values (12.8-17.1 ml g(-1)). MK801 (0.5 mg/kg, i.v., n = 1, and 1.0 mg/kg, i.v., n = 1) did not significantly alter regional VT values, indicating a lack of saturable binding. However, the potential confounding effects associated with ketamine induction of anesthesia along with isoflurane maintenance must be considered because both agents are known to reduce NMDA ion channel activation. Future and carefully designed studies, presumably utilizing an optimized NMDA/PCP site tracer, will be carried out to further explore these hypotheses. We conclude that, even though [11C]GMOM is not an optimized PCP site radiotracer, its binding is altered in vivo in awake rats as expected by modulation of NMDA ion channel activity by MK801, D-serine or RO 25-6981. The development of higher affinity NMDA/PCP site radioligands is in progress.
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Affiliation(s)
- Rikki N Waterhouse
- Department of Psychiatry, Columbia University College of Physicians and Surgeons and the New York State Psychiatric Institute, New York, NY 10032, USA
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36
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Milovanović DR, Janković SM. [Pharmacology of receptors and cellular glutamate transporters]. VOJNOSANIT PREGL 2004; 61:181-6. [PMID: 15296124 DOI: 10.2298/vsp0402181m] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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37
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Strutz-Seebohm N, Werner M, Madsen DM, Seebohm G, Zheng Y, Walker CS, Maricq AV, Hollmann M. Functional analysis of Caenorhabditis elegans glutamate receptor subunits by domain transplantation. J Biol Chem 2003; 278:44691-701. [PMID: 12930835 DOI: 10.1074/jbc.m305497200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glutamate receptors are not only abundant and important mediators of fast excitatory synaptic transmission in vertebrates, but they also serve a similar function in invertebrates such as Drosophila and the nematode Caenorhabditis elegans. In C. elegans, an animal with only 302 neurons, 10 different glutamate receptor subunits have been identified and cloned. To study the ion channel properties of these receptor subunits, we recorded glutamate-gated currents from Xenopus oocytes that expressed either C. elegans glutamate receptor subunits or chimeric rat/C. elegans glutamate receptor subunits. The chimeras were constructed between the C. elegans glutamate receptor pore domains and either the rat kainate receptor subunit GluR6, the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunit GluR1, or the N-methyl-d-aspartate (NMDA) receptor subunit NMDAR1-1a. Although native subunits were nonfunctional, 9 of 10 ion pores were found to conduct current upon transplantation into rat receptor subunits. A provisional classification of the C. elegans glutamate receptor subunits was attempted based on functionality of the chimeras. C. elegans glutamate receptor ion pores, at a position homologous to a highly conserved site critical for ion permeation properties in vertebrate glutamate receptor pores, contain amino acids not found in vertebrate glutamate receptors. We show that the pore-constricting Q/R site, which in vertebrate receptors determines calcium permeability and rectification properties of the ion channel, in C. elegans can be occupied by other amino acids, including, surprisingly, lysine and proline, without loss of these properties.
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MESH Headings
- Amino Acid Sequence
- Animals
- Caenorhabditis elegans/chemistry
- Caenorhabditis elegans Proteins/chemistry
- Caenorhabditis elegans Proteins/genetics
- Caenorhabditis elegans Proteins/physiology
- Cell Line
- Chemical Phenomena
- Chemistry, Physical
- Egtazic Acid/pharmacology
- Electric Conductivity
- Embryo, Mammalian
- Embryo, Nonmammalian
- Female
- Gene Expression
- Glutamic Acid/pharmacology
- Humans
- Hydrogen Bonding
- Ion Channels/physiology
- Kainic Acid/pharmacology
- Kidney
- Membrane Potentials
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Oocytes/physiology
- Oocytes/ultrastructure
- Protein Subunits/chemistry
- Protein Subunits/genetics
- Protein Subunits/physiology
- Rats
- Receptors, AMPA/genetics
- Receptors, Glutamate/chemistry
- Receptors, Glutamate/genetics
- Receptors, Glutamate/physiology
- Receptors, Kainic Acid/genetics
- Recombinant Fusion Proteins/genetics
- Recombinant Proteins
- Structure-Activity Relationship
- Transfection
- Xenopus laevis
- alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/pharmacology
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Affiliation(s)
- Nathalie Strutz-Seebohm
- Department of Biochemistry I, Receptor Biochemistry, Ruhr University Bochum, Bochum D-44780, Germany
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38
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Abstract
The N-methyl-D-aspartate (NMDA) ion channel plays a role in neuroprotection, neurodegeneration, long-term potentiation, memory, and cognition. It is implicated in the pathophysiology of several neurological and neuropsychiatric disorders including Parkinson's Disease, Huntington's Chorea, schizophrenia, alcoholism and stroke. The development of effective radiotracers for the study of NMDA receptors is critical for our understanding of their function, and their modulation by endogenous substances or therapeutic drugs. Since the NMDA/PCP receptor lies within the channel, it is a unique target and is theoretically accessible only when the channel is in the active and "open" state, but not when it is in the inactive or "closed" state. The physical location of the NMDA/PCP receptor not only makes it an important imaging target but also complicates the development of suitable PET and SPECT radiotracers for this site. An intimate understanding of the biochemical, pharmacological, physiological and behavioral processes associated with the NMDA ion channel is essential to develop improved imaging agents. This review outlines progress made towards the development of radiolabeled agents for PCP sites of the NMDA ion channel. In addition, the animal and pharmacological models used for in vitro and in vivo assessment of NMDA receptor targeted agents are discussed.
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Affiliation(s)
- Rikki N Waterhouse
- Department of Psychiatry, Columbia University College of Physicians and Surgeons and New York State Psychiatric Institute, New York, NY 10032, USA.
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39
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Abstract
The orphan glutamate receptor delta2 (GluRdelta2) is predominantly expressed in Purkinje cells and plays a crucial role in cerebellar functions: mice that lack the GluRdelta2 gene display ataxia and impaired synaptic plasticity. However, when expressed alone or with other glutamate receptors, GluRdelta2 does not form functional glutamate-gated ion channels nor does it bind to glutamate analogs. Therefore, the mechanisms by which GluRdelta2 participates in cerebellar functions have been elusive. Studies of mutant mice such as lurcher, hotfoot, and GluRdelta2 knockout mice have provided clues to the structure and function of GluRdelta2. GluRdelta2 has a channel pore similar to that of other glutamate receptors; the channel is functional at least when the lurcher mutation is present. GluRdelta2 must be transported to the Purkinje cell surface to function; the absence of surface GluRdelta2 causes the ataxic phenotype of hotfoot mice. In GluRdelta2-null mice, the presence of naked spines not innervated by parallel fibers may influence the sustained innervation of mutant Purkinje cells by multiple climbing fibers. From these results, several hypotheses about mechanisms by which GluRdelta2 functions are proposed in this article. Further characterization of GluRdelta2's functions will provide key insights into normal and abnormal cerebellar functions.
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Affiliation(s)
- Michisuke Yuzaki
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, 332 N. Lauderdale Street, Memphis, TN 38105-2794, USA.
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40
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Strutz N, Villmann C, Breitinger HG, Werner M, Wenthold RJ, Kizelsztein P, Teichberg VI, Hollmann M. Kainate-binding proteins are rendered functional ion channels upon transplantation of two short pore-flanking domains from a kainate receptor. J Biol Chem 2002; 277:48035-42. [PMID: 12370171 DOI: 10.1074/jbc.m209647200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kainate-binding proteins belong to an elusive class of putative ionotropic glutamate receptors that to date have not been shown to form functional ion channels in heterologous expression systems, despite binding glutamatergic agonists with high affinity. To test the hypothesis that inefficient or interrupted signal transduction from the ligand-binding site via linker domains to the ion pore (gating) might be responsible for this apparent lack of function, we transplanted the short homologous linker sequences from the fully functional rat kainate receptor GluR6 into frog kainate-binding protein. We were able to generate chimeric receptors that are functional in the Xenopus oocyte expression system and in human embryonic kidney 293 cells. The linker domains A and B in particular appear to be crucial for gating, because a functional kainate-binding protein was observed when at least parts of both linkers were derived from GluR6. We speculate that to enable signal transduction from the ligand-binding site to the ion pore of the frog kainate-binding protein, the linker structure of the protein has to undergo an essential conformational alteration, possibly mediated by an as yet unknown subunit or modulatory protein.
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Affiliation(s)
- Nathalie Strutz
- Department of Biochemistry I: Receptor Biochemistry, Ruhr University Bochum, Germany.
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41
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Carvalho AL, Correia S, Faro CJ, Duarte CB, Carvalho AP, Pires EMV. Phosphorylation of GluR4 AMPA-type glutamate receptor subunit by protein kinase C in cultured retina amacrine neurons. Eur J Neurosci 2002; 15:465-74. [PMID: 11876774 DOI: 10.1046/j.0953-816x.2001.01881.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have previously reported that the activity of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors is potentiated by protein kinase C (PKC) in cultured chick retina amacrine neurons, and that constitutive PKC activity is necessary for basal AMPA receptor activity (Carvalho et al., 1998). In this study, we evaluated the phosphorylation of the GluR4 subunit, which is very abundant in cultured amacrine neurons, to correlate it with the effects of PKC on AMPA receptor activity in these cells. 32P-labelling of GluR4 increased upon AMPA receptor stimulation or cell treatment with phorbol 12-myristate 13-acetate (PMA) before stimulating with kainate. By contrast, phosphorylation of GluR4 was not changed when PKC was inhibited by treating the cells with the selective PKC inhibitor GF 109203X before stimulation with kainate. We conclude that GluR4 is phosphorylated upon PKC activation and/or stimulation of AMPA receptors in cultured amacrine cells. Additionally, AMPA receptor activation with kainate in cultured chick amacrine cells leads to translocation of conventional and novel PKC isoforms to the cell membrane, suggesting that PKC could be activated upon AMPA receptor stimulation in these cells.
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Affiliation(s)
- Ana Luísa Carvalho
- Centre for Neuroscience and Cell Biology, University of Coimbra, Portugal.
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42
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Lalonde R, Strazielle C. Motor performance and regional brain metabolism of spontaneous murine mutations with cerebellar atrophy. Behav Brain Res 2001; 125:103-8. [PMID: 11682101 DOI: 10.1016/s0166-4328(01)00276-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Three spontaneous mutations with cerebellar atrophy were evaluated for motor coordination and regional brain metabolism, as assessed by cytochrome oxidase (CO) activity. Despite similar neuropathological characteristics, the behavioral phenotype of Lurcher is less severe than that of staggerer, possibly caused by the slower onset of their neuronal degeneration. Although fewer cerebellar cells degenerate in hot-foot than in Lurcher, their motor deficits are more severe, indicating the presence of dysfunctional cells. CO activity in the deep cerebellar nuclei was increased in Lurcher and staggerer but unchanged in hot-foot, probably due to the severe loss of GABAergic input from Purkinje cells in the first two mutants but not the third. Altered CO activity in cerebellar-related pathways was linearly correlated with motor performance, indicating that the activity of this enzyme is associated not only with neuronal activity but also with motor performance.
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Affiliation(s)
- R Lalonde
- Laboratoire de Neurobiologie de l'Apprentissage, Université de Rouen, Faculté des Sciences, UPRES PSY.CO-EA 1780, 76821 Mont-Saint-Aignan Cedex, France.
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43
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Abstract
The kainate receptors GluR6 and GluR7 differ considerably in their ion channel properties, despite sharing 86% amino acid sequence identity. When expressed in Xenopus oocytes GluR6 conducts large agonist-evoked currents, whereas GluR7 lacks measurable currents. In the present study, we localized the determinants that are responsible for the functional differences between GluR6 and GluR7 to the extracellular loop domain L3. In addition, we generated several GluR7 point mutants that are able to conduct currents that can be readily measured in Xenopus oocytes. In GluR6, glutamate- and kainate-evoked maximal currents are of the same magnitude when desensitization is inhibited with the lectin concanavalin A. By contrast, all functional GluR7 mutants were found to have glutamate current amplitudes significantly larger than those evoked by kainate. We localized the domain that determines the relative agonist efficacies to the C-terminal half of the L3 domain of GluR7. Our data show that EC(50) values for glutamate (but not for kainate) in GluR7 mutants or chimeras tend to be increased in comparison to the EC(50) values in GluR6. The high EC(50) for wild-type GluR7 reported in the literature appears to be linked to the S1 portion of the agonist-binding domain. Finally, we determined the C-terminal half of the L3 domain plus the far C-terminal domain of GluR7 to be responsible for the recently reported reduction of current amplitude seen when GluR7 is coexpressed with GluR6. We conclude that coexpression of GluR6 and GluR7 leads to nonstochastical assembly of heteromeric receptor complexes.
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44
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Strazielle C, Lalonde R, Reader TA. Autoradiography of glutamate receptor binding in adult Lurcher mutant mice. J Neuropathol Exp Neurol 2000; 59:707-22. [PMID: 10952061 DOI: 10.1093/jnen/59.8.707] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The mutation Lurcher, resulting from a gain of malfunction of the delta2 glutamate receptor expressed specifically by cerebellar Purkinje cells, causes a primary total loss of these neurons of the cerebellar cortex, as well as the secondary degeneration of cerebellar granule and inferior olive neurons. The distributions of glutamate receptors sensitive to amino-methylisoxazole-propionic acid (AMPA), to kainic acid (KA), and to N-methyl-D-aspartic acid (NMDA) as well as metabotropic sites (MET1 and MET2) were examined in wild type and Lurcher mice by quantitative autoradiography. This study was undertaken to determine the gene effect on the distribution of the various glutamate receptor subtypes, as well as how the cerebellar lesion affects the glutamatergic system in other brain regions. In cerebellum, there were postsynaptic AMPA and metabotropic receptors on Purkinje cells, postsynaptic NMDA receptors on granule cells, as well as KA receptors on granule cells or on parallel fibers. Taking into account surface areas, binding to all receptor subtypes was lower in the cerebellar cortex of Lurcher mutants than in wild type mice, while in the deep cerebellar nuclei only KA receptors were diminished. In other brain regions, the alterations followed always the same pattern characterized by a decrease of NMDA and KA receptors but with an increase of AMPA sites; these reciprocal changes were seen in thalamus. neostriatum, limbic regions, and motor cerebral cortical regions. Comparisons of glutamate receptor distribution in Lurcher mutants and in human autosomal cerebellar ataxia may permit further understanding of the role of glutamate-induced toxicity on neuronal death in these heredo-degenerative diseases.
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Affiliation(s)
- C Strazielle
- Centre de Recherche en Sciences Neurologiques, Faculté de Médecine, Université de Montréal, Qc, Canada
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Khan AM, Stanley BG, Bozzetti L, Chin C, Stivers C, Curr�s-Collazo MC. N-methyl-D-aspartate receptor subunit NR2B is widely expressed throughout the rat diencephalon: An immunohistochemical study. J Comp Neurol 2000. [DOI: 10.1002/1096-9861(20001218)428:3<428::aid-cne4>3.0.co;2-b] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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