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Ivica J, Lape R, Sivilotti LG. Acidic pH reduces agonist efficacy and responses to synaptic-like glycine applications in zebrafish α1 and rat α1β recombinant glycine receptors. J Physiol 2022; 600:333-347. [PMID: 34802146 PMCID: PMC8836455 DOI: 10.1113/jp282171] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 11/16/2021] [Indexed: 11/12/2022] Open
Abstract
Many pentameric ligand-gated ion channels are modulated by extracellular pH. Glycine receptors (GlyRs) share this property, but it is not well understood how they are affected by pH changes. Whole cell experiments on HEK293 cells expressing zebrafish homomeric α1 GlyR confirmed previous reports that acidic pH (6.4) reduces GlyR sensitivity to glycine, whereas alkaline pH (8.4) has small or negligible effects. In addition to that, at pH 6.4 we observed a reduction in the maximum responses to the partial agonists β-alanine and taurine relative to the full agonist glycine. In cell-attached single-channel recording, low pH reduced agonist efficacy, as the maximum open probability decreased from 0.97, 0.91 and 0.66 to 0.93, 0.57 and 0.34 for glycine, β-alanine and taurine, respectively, reflecting a threefold decrease in efficacy equilibrium constants for all three agonists. We also tested the effect of pH 6.4 in conditions that replicate those at the native synapse, recording outside-out currents elicited by fast application of millisecond pulses of agonists on α1 and α1β GlyR, at a range of intracellular chloride concentrations. Acidic pH reduced the area under the curve of the currents, by reducing peak amplitude, slowing activation and speeding deactivation. Our results show that acidification of the extracellular pH by one unit, as may occur in pathological conditions such as ischaemia, impairs GlyR gating and is likely to reduce the effectiveness of glycinergic synaptic inhibition. KEY POINTS: Extracellular pH in the central nervous system (CNS) is known to shift towards acidic values during pathophysiological conditions such as ischaemia and seizures. Acidic extracellular pH is known to affect GABAergic inhibitory synapses, but its effect on signals mediated by glycine receptors (GlyR) is not well characterised. Moderate acidic conditions (pH 6.4) reduce the maximum single channel open probability of recombinant homomeric GlyRs produced by the neurotransmitter glycine or other agonists, such as β-alanine and taurine. When glycine was applied with a piezoelectric stepper to outside out patches, to simulate its fast rise and short duration at the synapse, responses became shorter and smaller at pH 6.4. The effect was also observed with physiologically low intracellular chloride and in mammalian heteromeric GlyRs. This suggests that acidic pH is likely to reduce the strength of inhibitory signalling at glycinergic synapses.
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Affiliation(s)
- Josip Ivica
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Remigijus Lape
- Neurobiology Department, MRC Laboratory of Molecular Biology Cambridge Biomedical Campus Francis Crick Avenue, Cambridge, UK
| | - Lucia G Sivilotti
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
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2
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Rovšnik U, Zhuang Y, Forsberg BO, Carroni M, Yvonnesdotter L, Howard RJ, Lindahl E. Dynamic closed states of a ligand-gated ion channel captured by cryo-EM and simulations. Life Sci Alliance 2021; 4:e202101011. [PMID: 34210687 PMCID: PMC8326787 DOI: 10.26508/lsa.202101011] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 06/10/2021] [Accepted: 06/11/2021] [Indexed: 11/25/2022] Open
Abstract
Ligand-gated ion channels are critical mediators of electrochemical signal transduction across evolution. Biophysical and pharmacological characterization of these receptor proteins relies on high-quality structures in multiple, subtly distinct functional states. However, structural data in this family remain limited, particularly for resting and intermediate states on the activation pathway. Here, we report cryo-electron microscopy (cryo-EM) structures of the proton-activated Gloeobacter violaceus ligand-gated ion channel (GLIC) under three pH conditions. Decreased pH was associated with improved resolution and side chain rearrangements at the subunit/domain interface, particularly involving functionally important residues in the β1-β2 and M2-M3 loops. Molecular dynamics simulations substantiated flexibility in the closed-channel extracellular domains relative to the transmembrane ones and supported electrostatic remodeling around E35 and E243 in proton-induced gating. Exploration of secondary cryo-EM classes further indicated a low-pH population with an expanded pore. These results allow us to define distinct protonation and activation steps in pH-stimulated conformational cycling in GLIC, including interfacial rearrangements largely conserved in the pentameric channel family.
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Affiliation(s)
- Urška Rovšnik
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Yuxuan Zhuang
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Björn O Forsberg
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Marta Carroni
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Linnea Yvonnesdotter
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Rebecca J Howard
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Erik Lindahl
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
- Department of Applied Physics, Science for Life Laboratory, Kungliga Tekniska Högskolan Royal Institute of Technology, Solna, Sweden
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3
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Solntseva EI, Bukanova JV, Kondratenko RV, Skrebitsky VG. Copper Ions Reduce the Effect of Protons on Desensitization of Glycine Receptors. Bull Exp Biol Med 2020; 169:791-794. [PMID: 33098514 DOI: 10.1007/s10517-020-04980-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Indexed: 11/28/2022]
Abstract
Chloride current (IGly) evoked by the rapid (600 msec) application of glycine on isolated pyramidal neurons of the rat hippocampus was recorded using the patch clamp technique. We studied the effect of individual or combined application of copper ions (Cu2+) and protons (H+) on IGly. It was found that both Cu2+ (10 μM) and H+ (pH 7.0 and 6.0) applied separately caused a fast and reversible effect on IGly that included two components: a decrease in peak amplitude (Ipeak) and a decrease in the desensitization time constant (τdes). During combined application, the effects on Ipeak were additive, which indicates the independence of the mechanisms of these effects. At the same time, the effect of combined application of Cu2+ and H+ on τdes was not additive and sometimes a slowdown of the total desensitization was observed. The latter result suggests that H+ and Cu2+ can play the role of mutual antagonists when they affect the desensitization of GlyR.
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Abstract
The inhibitory glycine receptor is a member of the Cys-loop superfamily of ligand-gated ion channels. It is the principal mediator of rapid synaptic inhibition in the spinal cord and brainstem and plays an important role in the modulation of higher brain functions including vision, hearing, and pain signaling. Glycine receptor function is controlled by only a few agonists, while the number of antagonists and positive or biphasic modulators is steadily increasing. These modulators are important for the study of receptor activation and regulation and have found clinical interest as potential analgesics and anticonvulsants. High-resolution structures of the receptor have become available recently, adding to our understanding of structure-function relationships and revealing agonistic, inhibitory, and modulatory sites on the receptor protein. This Review presents an overview of compounds that activate, inhibit, or modulate glycine receptor function in vitro and in vivo.
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Affiliation(s)
- Ulrike Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo 11835, Egypt
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β-Amyloid Peptide Antagonizes the Effect of Protons on Taurine-Induced Chloride Current in Rat Hippocampal Pyramidal Neurons. Bull Exp Biol Med 2019; 167:237-241. [PMID: 31243680 DOI: 10.1007/s10517-019-04499-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Indexed: 10/26/2022]
Abstract
Taurine is an important endogenous agonist of glycine receptors (GlyR). Using the patchclamp technique, we measured chloride current induced by a short (600 msec) application of taurine (ITau) on isolated rat pyramidal neurons. pH of taurine solution in the applicator pipette was neutral (7.4) or acidic (7.0-5.0). Application of protons to a neuron causes a dosedependent decrease in the peak amplitude and acceleration of ITau desensitization. Addition of 100 nM β-amyloid peptide (Aβ) to the perfusate caused acceleration of ITau desensitization. The effects of Aβ and H+ on the rate of ITau desensitization were not additive. In addition, Aβ attenuated the effect of H+ on the peak amplitude of ITau. We also studied the effect of protons on the chloride current caused by activation of GABA receptors. In contrast to H+ effects on GlyR, Aβ did not modulate the effects of H+ on GABA receptors.
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Nemecz Á, Hu H, Fourati Z, Van Renterghem C, Delarue M, Corringer PJ. Full mutational mapping of titratable residues helps to identify proton-sensors involved in the control of channel gating in the Gloeobacter violaceus pentameric ligand-gated ion channel. PLoS Biol 2017; 15:e2004470. [PMID: 29281623 PMCID: PMC5760087 DOI: 10.1371/journal.pbio.2004470] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Revised: 01/09/2018] [Accepted: 12/04/2017] [Indexed: 11/19/2022] Open
Abstract
The Gloeobacter violaceus ligand-gated ion channel (GLIC) has been extensively studied by X-ray crystallography and other biophysical techniques. This provided key insights into the general gating mechanism of pentameric ligand-gated ion channel (pLGIC) signal transduction. However, the GLIC is activated by lowering the pH and the location of its putative proton activation site(s) still remain(s) unknown. To this end, every Asp, Glu, and His residue was mutated individually or in combination and investigated by electrophysiology. In addition to the mutational analysis, key mutations were structurally resolved to address whether particular residues contribute to proton sensing, or alternatively to GLIC-gating, independently of the side chain protonation. The data show that multiple residues located below the orthosteric site, notably E26, D32, E35, and D122 in the lower part of the extracellular domain (ECD), along with E222, H235, E243, and H277 in the transmembrane domain (TMD), alter GLIC activation. D122 and H235 were found to also alter GLIC expression. E35 is identified as a key proton-sensing residue, whereby neutralization of its side chain carboxylate stabilizes the active state. Thus, proton activation occurs allosterically to the orthosteric site, at the level of multiple loci with a key contribution of the coupling interface between the ECD and TMD. Pentameric ligand-gated ion channels are an important class of receptors that are involved in many neurological diseases. They have been extensively studied but a full understanding of their mechanism of action has yet to be achieved. In an effort to bypass obstacles in the research of human receptors, bacterial versions have been used to characterize the family’s structure-function relationship. One key bacterial receptor, known as GLIC, has lead the way in structural resolution of various mechanistic states along the gating pathway, yet its activation by protons is significantly less understood than its human counterparts. To define the site(s) involved in proton gating, we systematically mutated all titratable residues near the pH50 of activation: Asp, Glu, and His. We determined that a previously established His residue in the transmembrane domain is structurally important but likely plays little or no role in proton gating. We instead found that proton activation is a complex multiple loci mechanism, with the key contribution stemming from the coupling interface between the extracellular and transmembrane domain, with E35 acting as a key proton-sensing residue.
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Affiliation(s)
- Ákos Nemecz
- Unité Récepteurs-Canaux, Unité Mixte de Recherche 3571 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Haidai Hu
- Unité de Dynamique Structurale des Macromolécules, Unité Mixte de Recherche 3528 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Zaineb Fourati
- Unité de Dynamique Structurale des Macromolécules, Unité Mixte de Recherche 3528 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Catherine Van Renterghem
- Unité Récepteurs-Canaux, Unité Mixte de Recherche 3571 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Marc Delarue
- Unité de Dynamique Structurale des Macromolécules, Unité Mixte de Recherche 3528 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Pierre-Jean Corringer
- Unité Récepteurs-Canaux, Unité Mixte de Recherche 3571 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
- * E-mail:
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Bukanova JV, Solntseva EI, Kondratenko RV, Skrebitsky VG. The influence of acidic media on the effect of beta-amyloid peptide on the function of glycine receptor in hippocampal neurons. Neurochem Int 2017; 110:69-74. [PMID: 28919253 DOI: 10.1016/j.neuint.2017.09.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 09/05/2017] [Accepted: 09/13/2017] [Indexed: 11/25/2022]
Abstract
We have previously shown that application of beta-amyloid peptide 1-42 (Aβ) at picomolar/nanomolar concentrations caused a decrease in the peak amplitude and acceleration of desensitization of the glycine-activated chloride current (IGly) in hippocampal pyramidal neurons (Bukanova et al., 2016). The aim of this work was to study the effect of Aβ on IGly in an acidified medium. The relevance of this work is determined by the fact that the pathogenic effects of Aβ in Alzheimer's disease are usually accompanied by inflammatory processes and acidosis. The IGly was induced by 600 ms application of 100 μM (nearly EC50) or 500 μM (nearly saturating) glycine on isolated rat hippocampal neurons. The solution of glycine was neutral (pH 7.4) or acidic over a pH range of 5.0-7.0. It was found that 600 ms application of protons rapidly, reversibly and in dose-dependent manner decreased the peak amplitude and accelerated the desensitization of IGly. The effect of H+ on IGly desensitization did not depend on glycine concentration and may be considered noncompetitive, while the effect on IGly peak disappeared at saturating glycine concentration and can be regarded as a competitive. These characteristics of the proton effects on IGly coincide with the characteristics of the Aβ effects on IGly. Experiments with joint application of Aβ and H+ showed interdependence of their effects. Addition of Aβ to perfusing solution reduced H+ effects on IGly while long pretreatment of Aβ with acid solution prevented the effects of the peptide on IGly. Our results suggest the existence of common sites for Aβ and H+ on the GlyR and indicate a mutual weakening of the inhibitory action of these molecules on IGly.
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Raltschev C, Hetsch F, Winkelmann A, Meier JC, Semtner M. Electrophysiological Signature of Homomeric and Heteromeric Glycine Receptor Channels. J Biol Chem 2016; 291:18030-40. [PMID: 27382060 DOI: 10.1074/jbc.m116.735084] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Indexed: 11/06/2022] Open
Abstract
Glycine receptors are chloride-permeable, ligand-gated ion channels and contribute to the inhibition of neuronal firing in the central nervous system or to facilitation of neurotransmitter release if expressed at presynaptic sites. Recent structure-function studies have provided detailed insights into the mechanisms of channel gating, desensitization, and ion permeation. However, most of the work has focused only on comparing a few isoforms, and among studies, different cellular expression systems were used. Here, we performed a series of experiments using recombinantly expressed homomeric and heteromeric glycine receptor channels, including their splice variants, in the same cellular expression system to investigate and compare their electrophysiological properties. Our data show that the current-voltage relationships of homomeric channels formed by the α2 or α3 subunits change upon receptor desensitization from a linear to an inwardly rectifying shape, in contrast to their heteromeric counterparts. The results demonstrate that inward rectification depends on a single amino acid (Ala(254)) at the inner pore mouth of the channels and is closely linked to chloride permeation. We also show that the current-voltage relationships of glycine-evoked currents in primary hippocampal neurons are inwardly rectifying upon desensitization. Thus, the alanine residue Ala(254) determines voltage-dependent rectification upon receptor desensitization and reveals a physio-molecular signature of homomeric glycine receptor channels, which provides unprecedented opportunities for the identification of these channels at the single cell level.
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Affiliation(s)
- Constanze Raltschev
- From the Department of Biomedicine, Cellular Neurophysiology, University of Basel, Pestalozzistrasse 20, 4056 Basel, Switzerland
| | - Florian Hetsch
- the Division of Cell Physiology, Technische Universität Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany, and
| | - Aline Winkelmann
- the Division of Cell Physiology, Technische Universität Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany, and
| | - Jochen C Meier
- the Division of Cell Physiology, Technische Universität Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany, and
| | - Marcus Semtner
- Cellular Neurosciences, Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13092 Berlin, Germany
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9
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Lithium ions in nanomolar concentration modulate glycine-activated chloride current in rat hippocampal neurons. Neurochem Int 2016; 94:67-73. [DOI: 10.1016/j.neuint.2016.02.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 02/05/2016] [Accepted: 02/09/2016] [Indexed: 11/17/2022]
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10
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Fe2+ and Fe3+ in micromolar concentrations modulate glycine-induced Cl− current in rat hippocampal neurons. Brain Res Bull 2015; 115:9-16. [DOI: 10.1016/j.brainresbull.2015.04.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 04/06/2015] [Accepted: 04/07/2015] [Indexed: 11/22/2022]
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Chen ZL, Huang RQ. Extracellular pH modulates GABAergic neurotransmission in rat hypothalamus. Neuroscience 2014; 271:64-76. [PMID: 24780768 DOI: 10.1016/j.neuroscience.2014.04.028] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 04/14/2014] [Accepted: 04/17/2014] [Indexed: 11/16/2022]
Abstract
Changes in extracellular pH have a modulatory effect on GABAA receptor function. It has been reported that pH sensitivity of the GABA receptor is dependent on subunit composition and GABA concentration. Most of previous investigations focused on GABA-evoked currents, which only reflect the postsynaptic receptors. The physiological relevance of pH modulation of GABAergic neurotransmission is not fully elucidated. In the present studies, we examined the influence of extracellular pH on the GABAA receptor-mediated inhibitory neurotransmission in rat hypothalamic neurons. The inhibitory postsynaptic currents (IPSCs), tonic currents, and the GABA-evoked currents were recorded with whole-cell patch techniques on the hypothalamic slices from Sprague-Dawley rats at 15-26 postnatal days. The amplitude and frequency of spontaneous GABA IPSCs were significantly increased while the external pH was changed from 7.3 to 8.4. In the acidic pH (6.4), the spontaneous GABA IPSCs were reduced in amplitude and frequency. The pH induced changes in miniature GABA IPSCs (mIPSCs) similar to that in spontaneous IPSCs. The pH effect on the postsynaptic GABA receptors was assessed with exogenously applied varying concentrations of GABA. The tonic currents and the currents evoked by sub-saturating concentration of GABA ([GABA]) (10 μM) were inhibited by acidic pH and potentiated by alkaline pH. In contrast, the currents evoked by saturating [GABA] (1mM) were not affected by pH changes. We also investigated the influence of pH buffers and buffering capacity on pH sensitivity of GABAA receptors on human recombinant α1β2γ2 GABAA receptors stably expressed in HEK 293 cells. The pH influence on GABAA receptors was similar in HEPES- and MES-buffered media, and not dependent on protonated buffers, suggesting that the observed pH effect on GABA response is a specific consequence of changes in extracellular protons. Our data suggest that the hydrogen ions suppress the GABAergic neurotransmission, which is mediated by both presynaptic and postsynaptic mechanisms.
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Affiliation(s)
- Z L Chen
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center at Fort Worth, Fort Worth, TX 76107, United States
| | - R Q Huang
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center at Fort Worth, Fort Worth, TX 76107, United States.
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