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Grohs L, Cheng L, Cönen S, Haddad BG, Bülow A, Toklucu I, Ernst L, Körner J, Schmalzing G, Lampert A, Machtens JP, Hausmann R. Corrigendum: Diclofenac and other non-steroidal anti-inflammatory drugs (NSAIDs) are competitive antagonists of the human P2X3 receptor. Front Pharmacol 2023; 14:1225522. [PMID: 37332347 PMCID: PMC10274573 DOI: 10.3389/fphar.2023.1225522] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Accepted: 05/22/2023] [Indexed: 06/20/2023] Open
Abstract
[This corrects the article DOI: 10.3389/fphar.2023.1120360.].
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Affiliation(s)
- Laura Grohs
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
- Department of Neurology, University Hospital, RWTH Aachen University, Aachen, Germany
| | - Linhan Cheng
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
| | - Saskia Cönen
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
- Molecular and Cellular Physiology (IBI-1), Institute of Biological Information Processing (IBI), Jülich, Germany
| | - Bassam G. Haddad
- Molecular and Cellular Physiology (IBI-1), Institute of Biological Information Processing (IBI), Jülich, Germany
| | - Astrid Bülow
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
- Department of Plastic Surgery, Hand and Burn Surgery, University Hospital RWTH Aachen, Aachen, Germany
| | - Idil Toklucu
- Institute of Physiology (Neurophysiology), RWTH Aachen University, Aachen, Germany
| | - Lisa Ernst
- Institute for Laboratory Animal Science and Experimental Surgery, RWTH Aachen University, Aachen, Germany
| | - Jannis Körner
- Institute of Physiology (Neurophysiology), RWTH Aachen University, Aachen, Germany
- Department of Anesthesiology, University Hospital RWTH Aachen, Aachen, Germany
| | - Günther Schmalzing
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
| | - Angelika Lampert
- Institute of Physiology (Neurophysiology), RWTH Aachen University, Aachen, Germany
| | - Jan-Philipp Machtens
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
- Molecular and Cellular Physiology (IBI-1), Institute of Biological Information Processing (IBI), Jülich, Germany
| | - Ralf Hausmann
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany
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Gangwar SP, Yen LY, Yelshanskaya MV, Sobolevsky AI. Positive and negative allosteric modulation of GluK2 kainate receptors by BPAM344 and antiepileptic perampanel. Cell Rep 2023; 42:112124. [PMID: 36857176 PMCID: PMC10440371 DOI: 10.1016/j.celrep.2023.112124] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2022] [Revised: 01/23/2023] [Accepted: 01/31/2023] [Indexed: 02/24/2023] Open
Abstract
Kainate receptors (KARs) are a subtype of ionotropic glutamate receptors that control synaptic transmission in the central nervous system and are implicated in neurological, psychiatric, and neurodevelopmental disorders. Understanding the regulation of KAR function by small molecules is essential for exploring these receptors as drug targets. Here, we present cryoelectron microscopy (cryo-EM) structures of KAR GluK2 in complex with the positive allosteric modulator BPAM344, competitive antagonist DNQX, and negative allosteric modulator, antiepileptic drug perampanel. Our structures show that two BPAM344 molecules bind per ligand-binding domain dimer interface. In the absence of an agonist or in the presence of DNQX, BPAM344 stabilizes GluK2 in the closed state. The closed state is also stabilized by perampanel, which binds to the ion channel extracellular collar sites located in two out of four GluK2 subunits. The molecular mechanisms of positive and negative allosteric modulation of KAR provide a guide for developing new therapeutic strategies.
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Affiliation(s)
- Shanti Pal Gangwar
- Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168(th) Street, New York, NY 10032, USA
| | - Laura Y Yen
- Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168(th) Street, New York, NY 10032, USA; Cellular and Molecular Physiology and Biophysics Graduate Program, Columbia University Irving Medical Center, 630 West 168(th) Street, New York, NY 10032, USA
| | - Maria V Yelshanskaya
- Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168(th) Street, New York, NY 10032, USA
| | - Alexander I Sobolevsky
- Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168(th) Street, New York, NY 10032, USA.
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3
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Fujie Y, Liu G, Ozoe F, Ozoe Y. Structural insights into the interaction between gabazine (SR-95531) and Laodelphax striatellus GABA receptors. J Pestic Sci 2022; 47:78-85. [PMID: 35800394 PMCID: PMC9184248 DOI: 10.1584/jpestics.d22-007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 04/13/2022] [Indexed: 06/15/2023]
Abstract
γ-Aminobutyric acid receptors (GABARs) mediate fast inhibitory neurotransmission and are targets for insecticides. GABARs are composed of five subunits, the composition of which dictates the pharmacological characteristics of GABARs. Both competitive and noncompetitive GABAR antagonists can be used as insecticides. Gabazine is a potent competitive antagonist of mammalian α1β2γ2 GABARs; however, it is less potent against insect GABARs. To explore how gabazine interacts with GABARs, we examined whether the sensitivity of the small brown planthopper (Laodelphax striatellus) RDL GABAR (LsRDLR) to gabazine is increased when its amino acid residues are substituted with α1β2γ2 GABAR residues. In the results, two of the generated mutants showed enhanced gabazine sensitivity. Docking simulations of gabazine using LsRDLR homology models and an α1β2γ2 GABAR cryo-EM structure revealed that the accommodation of gabazine into the "aromatic box" in the orthosteric site lowered the binding energy. This information may help in designing GABAR-targeting insecticides with novel modes of action.
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Affiliation(s)
- Yuki Fujie
- Faculty of Life and Environmental Sciences, Shimane University, Matsue, Shimane 690–8504, Japan
| | - Genyan Liu
- Key Laboratory for Green Chemical Process of Ministry of Education, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan, Hubei 430205, People’s Republic of China
| | - Fumiyo Ozoe
- Interdisciplinary Institute for Science Research, Organization for Research and Academic Information, Shimane University, Matsue, Shimane 690–8504, Japan
| | - Yoshihisa Ozoe
- Faculty of Life and Environmental Sciences, Shimane University, Matsue, Shimane 690–8504, Japan
- Interdisciplinary Institute for Science Research, Organization for Research and Academic Information, Shimane University, Matsue, Shimane 690–8504, Japan
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4
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Manry D, Bolanos K, DiAndreth B, Mock JY, Kamb A. Robust In Vitro Pharmacology of Tmod, a Synthetic Dual-Signal Integrator for Cancer Cell Therapy. Front Immunol 2022; 13:826747. [PMID: 35359952 PMCID: PMC8960424 DOI: 10.3389/fimmu.2022.826747] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 02/18/2022] [Indexed: 01/09/2023] Open
Abstract
Progress toward improved solid-tumor treatment has long been hindered by the lack of truly tumor-specific targets. We have developed an approach to T cell therapy based on a dual-receptor system called Tmod™ that addresses this problem. The Tmod system exploits one of the few common genetic differences between tumor and normal cells: loss of heterozygosity (LOH). It utilizes the basic mechanistic logic that evolved in early vertebrates to mediate self vs. non-self discrimination, where an activation stimulus is blocked by self-ligands. Tmod constructs employ a chimeric antigen receptor (CAR) or T cell receptor (TCR) as activator component and a modified LIR-1 inhibitory receptor (blocker) to achieve high selectivity based on expression of the blocker antigen (Ag). Here we explore the in vitro pharmacology of a blocker directed at the HLA-A*02 Ag paired with either a mesothelin CAR or an HLA-A*11-restricted KRAS peptide TCR. While more sensitive to receptor expression changes on effector cells, we show that Tmod response is well-buffered against variations in Ag levels on target cells. In addition, the data reveal at least two distinguishable pharmacologic mechanisms of Tmod blocker function: (1) reducing activator sensitivity and (2) decreasing activation magnitude.
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Affiliation(s)
- Diane Manry
- A2 Biotherapeutics, Inc., Agoura Hills, CA, United States
| | | | | | - Jee-Young Mock
- A2 Biotherapeutics, Inc., Agoura Hills, CA, United States
| | - Alexander Kamb
- A2 Biotherapeutics, Inc., Agoura Hills, CA, United States
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5
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Krintel C, Dorosz J, Larsen AH, Thorsen TS, Venskutonytė R, Mirza O, Gajhede M, Boesen T, Kastrup JS. Binding of a negative allosteric modulator and competitive antagonist can occur simultaneously at the ionotropic glutamate receptor GluA2. FEBS J 2020; 288:995-1007. [PMID: 32543078 DOI: 10.1111/febs.15455] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Revised: 05/25/2020] [Accepted: 06/12/2020] [Indexed: 11/26/2022]
Abstract
Ionotropic glutamate receptors are ligand-gated ion channels governing neurotransmission in the central nervous system. Three major types of antagonists are known for the AMPA-type receptor GluA2: competitive, noncompetitive (i.e., negative allosteric modulators; NAMs) used for treatment of epilepsy, and uncompetitive antagonists. We here report a 4.65 Å resolution X-ray structure of GluA2, revealing that four molecules of the competitive antagonist ZK200775 and four molecules of the NAM GYKI53655 are capable of binding at the same time. Using negative stain electron microscopy, we show that GYKI53655 alone or ZK200775/GYKI53655 in combination predominantly results in compact receptor forms. The agonist AMPA provides a mixed population of compact and bulgy shapes of GluA2 not impacted by addition of GYKI53655. Taken together, this suggests that the two different mechanisms of antagonism that lead to channel closure are independent and that the distribution between bulgy and compact receptors primarily depends on the ligand bound in the glutamate binding site. DATABASE: The atomic coordinates and structure factors from the crystal structure determination have been deposited in the Protein Data Bank under accession code https://doi.org/10.2210/pdb6RUQ/pdb. The electron microscopy 3D reconstruction volumes have been deposited in EMDB (EMD-4875: Apo; EMD-4920: ZK200775/GYKI53655; EMD-4921: AMPA compact; EMD-4922: AMPA/GYKI53655 bulgy; EMD-4923: GYKI53655; EMD-4924: AMPA bulgy; EMD-4925: AMPA/GYKI53655 compact).
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Affiliation(s)
- Christian Krintel
- Research Cluster on Molecular Neuroprotection, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Jerzy Dorosz
- Research Cluster on Molecular Neuroprotection, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Andreas Haahr Larsen
- Structural Biophysics, X-ray and Neutron Science, The Niels Bohr Institute, University of Copenhagen, Denmark
| | - Thor Seneca Thorsen
- Research Cluster on Molecular Neuroprotection, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Raminta Venskutonytė
- Research Cluster on Molecular Neuroprotection, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.,Department of Experimental Medical Science, Lund University, Lund, 221 00, Sweden
| | - Osman Mirza
- Research Cluster on Molecular Neuroprotection, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Michael Gajhede
- Research Cluster on Molecular Neuroprotection, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Thomas Boesen
- Department of Molecular Biology and Genetics, Aarhus University, Denmark
| | - Jette Sandholm Kastrup
- Research Cluster on Molecular Neuroprotection, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
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Amaradhi R, Banik A, Mohammed S, Patro V, Rojas A, Wang W, Motati DR, Dingledine R, Ganesh T. Potent, Selective, Water Soluble, Brain-Permeable EP2 Receptor Antagonist for Use in Central Nervous System Disease Models. J Med Chem 2020; 63:1032-1050. [PMID: 31904232 PMCID: PMC7394479 DOI: 10.1021/acs.jmedchem.9b01218] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Activation of prostanoid EP2 receptor exacerbates neuroinflammatory and neurodegenerative pathology in central nervous system diseases such as epilepsy, Alzheimer's disease, and cerebral aneurysms. A selective and brain-permeable EP2 antagonist will be useful to attenuate the inflammatory consequences of EP2 activation and to reduce the severity of these chronic diseases. We recently developed a brain-permeable EP2 antagonist 1 (TG6-10-1), which displayed anti-inflammatory and neuroprotective actions in rodent models of status epilepticus. However, this compound exhibited moderate selectivity to EP2, a short plasma half-life in rodents (1.7 h) and low aqueous solubility (27 μM), limiting its use in animal models of chronic disease. With lead-optimization studies, we have developed several novel EP2 antagonists with improved water solubility, brain penetration, high EP2 potency, and selectivity. These novel inhibitors suppress inflammatory gene expression induced by EP2 receptor activation in a microglial cell line, reinforcing the use of EP2 antagonists as anti-inflammatory agents.
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Affiliation(s)
- Radhika Amaradhi
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Avijit Banik
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Shabber Mohammed
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Vidyavathi Patro
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Asheebo Rojas
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Wenyi Wang
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Damoder Reddy Motati
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Ray Dingledine
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
| | - Thota Ganesh
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, 1510 Clifton Rd; Atlanta, GA, 30322, United States of America
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Szymańska E, Chałupnik P, Johansen TN, Nielsen B, Cuñado Moral AM, Pickering DS, Więckowska A, Kieć-Kononowicz K. Aryl- and heteroaryl-substituted phenylalanines as AMPA receptor ligands. Chem Biol Drug Des 2017. [PMID: 28636281 DOI: 10.1111/cbdd.13048] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
A series of racemic unnatural amino acids was rationally designed on the basis of recently published X-ray structures of the GluA2 LBD with bound phenylalanine-based antagonists. Twelve new diaryl- or aryl/heteroaryl-substituted phenylalanine derivatives were synthesized and evaluated in vitro in radioligand binding assays at native rat ionotropic glutamate receptors. The most interesting compound in this series, (RS)-2-amino-3-(3'-hydroxy-5-(1H-pyrazol-4-yl)-[1,1'-biphenyl]-3-yl)propanoic acid 7e, showed the binding affinity of 4.6 μm for native AMPA receptors and over fourfold lower affinity for kainic acid receptors. Furthermore, 7e was evaluated at recombinant homomeric rat GluA2 and GluA3 receptors. Recently reported X-ray structures 5CBR and 5CBS, representing two distinct antagonist binding modes, were used as templates for molecular docking of the synthesized series. Binding data supported with molecular modeling confirmed that aryl/heteroaryl-substituted phenylalanine analogues effectively bind to AMPA receptors with low micromolar affinity and high selectivity over native NMDA and kainate receptors. These properties make 7e a promising lead for the further development of new AMPA receptor ligands.
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Affiliation(s)
- Ewa Szymańska
- Department of Technology and Biotechnology of Drugs, Jagiellonian University Medical College, Kraków, Poland
| | - Paulina Chałupnik
- Department of Technology and Biotechnology of Drugs, Jagiellonian University Medical College, Kraków, Poland
| | - Tommy N Johansen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Birgitte Nielsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Ana Maria Cuñado Moral
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Darryl S Pickering
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Anna Więckowska
- Department of Medicinal Chemistry, Jagiellonian University Medical College, Kraków, Poland
| | - Katarzyna Kieć-Kononowicz
- Department of Technology and Biotechnology of Drugs, Jagiellonian University Medical College, Kraków, Poland
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Neelands TR, Burgard EC, Uchic ME, McDonald HA, Niforatos W, Faltynek CR, Lynch KJ, Jarvis MF. 2', 3'-O-(2,4,6,trinitrophenyl)-ATP and A-317491 are competitive antagonists at a slowly desensitizing chimeric human P2X3 receptor. Br J Pharmacol 2003; 140:202-10. [PMID: 12967950 PMCID: PMC1574009 DOI: 10.1038/sj.bjp.0705411] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
(1) Rapid desensitization of ligand-gated ion channel receptors can alter the apparent activity of receptor modulators, as well as make detection of fast-channel activation difficult. Investigation of the antagonist pharmacology of ATP-sensitive homomeric P2X3 receptors is limited by agonist-evoked fast-desensitization kinetics. (2) In the present studies, chimeric receptors were created using the coding sequence for the N-terminus and the first transmembrane domain of either the nondesensitizing human P2X2a or fast-desensitizing P2X3 receptor joined to the sequence encoding the extracellular loop, second transmembrane domain, and C-terminus of the other receptor (designated P2X2-3 and P2X3-2, respectively). These clones were stably transfected into 1321N1 astrocytoma cells for biophysical and pharmacological experiments using both electrophysiological and calcium-imaging methods. (3) Chimeric P2X2-3 and P2X3-2 receptors were inwardly rectifying and agonist responses showed desensitization properties similar to the wild-type human P2X2a and P2X3 receptors, respectively. (4) The P2X2-3 chimera displayed an agonist pharmacological profile similar to the P2X3 wild-type receptor being activated by low concentrations of both ATP and alpha,beta-meATP. In contrast, the P2X3-2 chimera had markedly reduced sensitivity to both agonists. (5) The P2X3 receptor antagonists TNP-ATP and A-317491 were shown to be potent, competitive antagonists of the P2X2-3 chimera (Ki=2.2 and 52.1 nm, respectively), supporting the hypothesis that rapid receptor desensitization can mask the competitive antagonism of wild-type homomeric P2X3 receptors.
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Affiliation(s)
- Torben R Neelands
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
| | - Edward C Burgard
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
| | - Marie E Uchic
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
| | - Heath A McDonald
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
| | - Wende Niforatos
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
| | - Connie R Faltynek
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
| | - Kevin J Lynch
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
| | - Michael F Jarvis
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, U.S.A
- Author for correspondence:
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von Gersdorff H, Schneggenburger R, Weis S, Neher E. Presynaptic depression at a calyx synapse: the small contribution of metabotropic glutamate receptors. J Neurosci 1997; 17:8137-46. [PMID: 9334389 PMCID: PMC6573755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Synaptic depression of evoked EPSCs was quantified with stimulation frequencies ranging from 0.2 to 100 Hz at the single CNS synapse formed by the calyx of Held in the rat brainstem. Half-maximal depression occurred at approximately 1 Hz, with 10 and 100 Hz stimulation frequencies reducing EPSC amplitudes to approximately 30% and approximately 10% of their initial magnitude, respectively. The time constant of recovery from depression elicited by 10 Hz afferent fiber stimulation was 4.2 sec. AMPA and NMDA receptor-mediated EPSCs depressed in parallel at 1-5 Hz stimulation frequencies, suggesting that depression was induced by presynaptic mechanism(s) that reduced glutamate release. To determine the contribution of autoreceptors to depression, we studied the inhibitory effects of the metabotropic glutamate receptor (mGluR) agonists (1S, 3S)-ACPD and L-AP4 and found them to be reversed in a dose-dependent manner by (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG), a novel and potent competitive antagonist of mGluRs. At 300 microM, CPPG completely reversed the effects of L-AP4 and (1S, 3S)-ACPD, but reduced 5-10 Hz elicited depression by only approximately 6%. CPPG-sensitive mGluRs, presumably activated by glutamate spillover during physiological synaptic transmission, thus contribute on the order of only 10% to short-term synaptic depression. We therefore suggest that the main mechanism contributing to the robust depression elicited by 5-10 Hz afferent fiber stimulation of the calyx of Held synapse is synaptic vesicle pool depletion.
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Affiliation(s)
- H von Gersdorff
- Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
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10
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Kahn CR, Baird KL, Jarrett DB, Flier JS. Direct demonstration that receptor crosslinking or aggregation is important in insulin action. Proc Natl Acad Sci U S A 1978; 75:4209-13. [PMID: 279910 PMCID: PMC336081 DOI: 10.1073/pnas.75.9.4209] [Citation(s) in RCA: 274] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Exposure of adipocytes to antibodies to the insulin receptor results in a blockade of (125)I-labeled insulin binding, stimulation of glucose oxidation, and many more insulin-like effects. Allowing for differences in purity, antireceptor antibody is equipotent with insulin on a molar basis. Both the bivalent F(ab')(2) and monovalent Fab' fragments of the antireceptor antibody are fully active in inhibiting (125)I-labeled insulin binding. Bivalent F(ab')(2) also retains its insulin-like effects. In contrast, the monovalent Fab' loses almost all ability to stimulate glucose oxidation and acts as a competitive antagonist of insulin-stimulated glucose oxidation. Addition of anti-F(ab')(2) antisera, which crosslink the Fab'-receptor complexes, results in a restoration of the insulin-like activity of the antibody. Similarly, when cells are exposed to submaximal doses of insulin, addition of anti-insulin antibodies at low concentration enhances the biological activity of insulin. These data suggest that receptor occupancy by ligand is not sufficient for signal generation and that the insulin-like effects of antireceptor antibody (and perhaps insulin itself) require receptor aggregation or clustering. This aggregation, however, appears to be independent of microfilaments or microtubules because the insulin-like effects of antireceptor antibody, and in fact, of insulin itself, are unaffected by agents that are known to disrupt these structures.
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