1
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Jensen AA. Evolutionary conservation of Zinc-Activated Channel (ZAC) functionality in mammals: a range of mammalian ZACs assemble into cell surface-expressed functional receptors. Front Mol Biosci 2023; 10:1265429. [PMID: 37745686 PMCID: PMC10513076 DOI: 10.3389/fmolb.2023.1265429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2023] [Accepted: 08/21/2023] [Indexed: 09/26/2023] Open
Abstract
In contrast to the other pentameric ligand-gated ion channels in the Cys-loop receptor superfamily, the ZACN gene encoding for the Zinc-Activated Channel (ZAC) is exclusively found in the mammalian genome. Human ZAC assembles into homomeric cation-selective channels gated by Zn2+, Cu2+ and H+, but the function of the receptor in human physiology is presently poorly understood. In this study, the degree of evolutionary conservation of a functional ZAC in mammals was probed by investigating the abilities of a selection of ZACs from 10 other mammalian species than human to be expressed at the protein level and assemble into cell surface-expressed functional receptors in mammalian cells and in Xenopus oocytes. In an enzyme-linked immunosorbent assay, transient transfections of tsA201 cells with cDNAs of hemagglutinin (HA)-epitope-tagged versions of these 10 ZACs resulted in robust total expression and cell surface expression levels of all proteins. Moreover, injection of cRNAs for 6 of these ZACs in oocytes resulted in the formation of functional receptors in two-electrode voltage-clamp recordings. The ZACs exhibited robust current amplitudes in response to Zn2+ (10 mM) and H+ (pH 4.0), and the concentration-response relationships displayed by Zn2+ at these channels were largely comparable to that at human ZAC. In conclusion, the findings suggest that the functionality of ZAC at the molecular level may be conserved throughout mammalian species, and that the channel thus may govern physiological functions in mammals, including humans.
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Affiliation(s)
- Anders A. Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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2
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Gallagher CI, Ha DA, Harvey RJ, Vandenberg RJ. Positive Allosteric Modulators of Glycine Receptors and Their Potential Use in Pain Therapies. Pharmacol Rev 2022; 74:933-961. [PMID: 36779343 PMCID: PMC9553105 DOI: 10.1124/pharmrev.122.000583] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Revised: 04/26/2022] [Accepted: 05/13/2022] [Indexed: 11/22/2022] Open
Abstract
Glycine receptors are ligand-gated ion channels that mediate synaptic inhibition throughout the mammalian spinal cord, brainstem, and higher brain regions. They have recently emerged as promising targets for novel pain therapies due to their ability to produce antinociception by inhibiting nociceptive signals within the dorsal horn of the spinal cord. This has greatly enhanced the interest in developing positive allosteric modulators of glycine receptors. Several pharmaceutical companies and research facilities have attempted to identify new therapeutic leads by conducting large-scale screens of compound libraries, screening new derivatives from natural sources, or synthesizing novel compounds that mimic endogenous compounds with antinociceptive activity. Advances in structural techniques have also led to the publication of multiple high-resolution structures of the receptor, highlighting novel allosteric binding sites and providing additional information for previously identified binding sites. This has greatly enhanced our understanding of the functional properties of glycine receptors and expanded the structure activity relationships of novel pharmacophores. Despite this, glycine receptors are yet to be used as drug targets due to the difficulties in obtaining potent, selective modulators with favorable pharmacokinetic profiles that are devoid of side effects. This review presents a summary of the structural basis for how current compounds cause positive allosteric modulation of glycine receptors and discusses their therapeutic potential as analgesics. SIGNIFICANCE STATEMENT: Chronic pain is a major cause of disability, and in Western societies, this will only increase as the population ages. Despite the high level of prevalence and enormous socioeconomic burden incurred, treatment of chronic pain remains limited as it is often refractory to current analgesics, such as opioids. The National Institute for Drug Abuse has set finding effective, safe, nonaddictive strategies to manage chronic pain as their top priority. Positive allosteric modulators of glycine receptors may provide a therapeutic option.
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Affiliation(s)
- Casey I Gallagher
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
| | - Damien A Ha
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
| | - Robert J Harvey
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
| | - Robert J Vandenberg
- Molecular Biomedicine, School of Medical Sciences, University of Sydney, Sydney, Australia (C.I.G., D.A.H., R.J.V.) and Biomedical Science, School of Health and Behavioural Sciences and Sunshine Coast Health Institute, University of the Sunshine Coast, Maroochydore, Australia (R.J.H.)
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3
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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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4
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Madjroh N, Mellou E, Æbelø L, Davies PA, Söderhielm PC, Jensen AA. Probing the molecular basis for signal transduction through the Zinc-Activated Channel (ZAC). Biochem Pharmacol 2021; 193:114781. [PMID: 34560053 DOI: 10.1016/j.bcp.2021.114781] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 09/11/2021] [Accepted: 09/13/2021] [Indexed: 12/18/2022]
Abstract
The molecular basis for the signal transduction through the classical Cys-loop receptors (CLRs) has been delineated in great detail. The Zinc-Activated Channel (ZAC) constitutes a so far poorly elucidated fifth branch of the CLR superfamily, and in this study we explore the molecular mechanisms underlying ZAC signaling in Xenopus oocytes by two-electrode voltage clamp electrophysiology. In studies of chimeric receptors fusing either the extracellular domain (ECD) or the transmembrane/intracellular domain (TMD-ICD) of ZAC with the complementary domains of 5-HT3A serotonin or α1 glycine receptors, serotonin and Zn2+/H+ evoked robust concentration-dependent currents in 5-HT3A/ZAC- and ZAC/α1-Gly-expressing oocytes, respectively, suggesting that Zn2+ and protons activate ZAC predominantly through its ECD. The molecular basis for Zn2+-mediated ZAC signaling was probed further by introduction of mutations of His, Cys, Glu and Asp residues in this domain, but as none of the mutants tested displayed substantially impaired Zn2+ functionality compared to wild-type ZAC, the location of the putative Zn2+ binding site(s) in the ECD was not identified. Finally, the functional importance of Leu246 (Leu9') in the transmembrane M2 α-helix of ZAC was investigated by Ala, Val, Ile and Thr substitutions. In concordance with findings for this highly conserved residue in classical CLRs, the ZACL9'X mutants exhibited left-shifted agonist concentration-response relationships, markedly higher degrees of spontaneous activity and slower desensitization kinetics compared to wild-type ZAC. In conclusion, while ZAC is an atypical CLR in terms of its (identified) agonists and channel characteristics, its signal transduction seems to undergo similar conformational transitions as those in the classical CLR.
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Affiliation(s)
- Nawid Madjroh
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Eleni Mellou
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Laura Æbelø
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Paul A Davies
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States
| | - Pella C Söderhielm
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Anders A Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark.
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5
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Neumaier F, Alpdogan S, Hescheler J, Schneider T. Zn2+-induced changes in Cav2.3 channel function: An electrophysiological and modeling study. J Gen Physiol 2021; 152:151872. [PMID: 32559275 PMCID: PMC7478874 DOI: 10.1085/jgp.202012585] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 04/30/2020] [Accepted: 05/19/2020] [Indexed: 01/25/2023] Open
Abstract
Loosely bound Zn2+ ions are increasingly recognized as potential modulators of synaptic plasticity and neuronal excitability under normal and pathophysiological conditions. Cav2.3 voltage-gated Ca2+ channels are among the most sensitive targets of Zn2+ and are therefore likely to be involved in the neuromodulatory actions of endogenous Zn2+. Although histidine residues on the external side of domain I have been implicated in the effects on Cav2.3 channel gating, the exact mechanisms involved in channel modulation remain incompletely understood. Here, we use a combination of electrophysiological recordings, modification of histidine residues, and computational modeling to analyze Zn2+-induced changes in Cav2.3 channel function. Our most important findings are that multiple high- and low-affinity mechanisms contribute to the net Zn2+ action, that Zn2+ can either inhibit or stimulate Ca2+ influx through Cav2.3 channels depending on resting membrane potential, and that Zn2+ effects may persist for some time even after cessation of the Zn2+ signal. Computer simulations show that (1) most salient features of Cav2.3 channel gating in the absence of trace metals can be reproduced by an obligatory model in which activation of two voltage sensors is necessary to open the pore; and (2) most, but not all, of the effects of Zn2+ can be accounted for by assuming that Zn2+ binding to a first site is associated with an electrostatic modification and mechanical slowing of one of the voltage sensors, whereas Zn2+ binding to a second, lower-affinity site blocks the channel and modifies the opening and closing transitions. While still far from complete, our model provides a first quantitative framework for understanding Zn2+ effects on Cav2.3 channel function and a step toward the application of computational approaches for predicting the complex actions of Zn2+ on neuronal excitability.
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Affiliation(s)
- Felix Neumaier
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Neurophysiology, Cologne, Germany
| | - Serdar Alpdogan
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Neurophysiology, Cologne, Germany
| | - Jürgen Hescheler
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Neurophysiology, Cologne, Germany
| | - Toni Schneider
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Neurophysiology, Cologne, Germany
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6
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Breitinger U, Sticht H, Breitinger HG. Modulation of recombinant human alpha 1 glycine receptor by flavonoids and gingerols. Biol Chem 2021; 402:825-838. [PMID: 33752269 DOI: 10.1515/hsz-2020-0360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 03/09/2021] [Indexed: 11/15/2022]
Abstract
The inhibitory glycine receptor (GlyR) is a principal mediator of fast synaptic inhibition in mammalian spinal cord, brainstem, and higher brain centres. Flavonoids are secondary plant metabolites that exhibit many beneficial physiological effects, including modulatory action on neuronal receptors. Using whole-cell current recordings from recombinant human α1 GlyRs, expressed in HEK293 cells, we compared the flavonols kaempferol and quercetin, the flavanone naringenin, the flavones apigenin and nobiletin, the isoflavone genistein, and two gingerols, 6-gingerol and 8-gingerol for their modulation of receptor currents. All compounds were inhibitors of the GlyR with IC50 values ranging between 9.3 ± 2.6 µM (kaempferol) and 46.7 ± 6.5 µM (genistein), following a mixed mode of inhibition. Co-application of two inhibitors revealed distinct binding sites for flavonoids and gingerols. Pore-lining mutants T258A and T258S were strongly inhibited by quercetin and naringenin, but not by 6-gingerol, confirming the existence of distinct binding sites for flavonoids and gingerols. Apigenin, kaempferol, nobiletin, naringenin and 6-gingerol showed biphasic action, potentiating glycine-induced currents at low concentration of both, modulator and glycine, and inhibiting at higher concentrations. Identification of distinct modulatory sites for flavonoids and related compounds may present pharmacological target sites and aid the discovery of novel glycinergic drugs.
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Affiliation(s)
- Ulrike Breitinger
- Department of Biochemistry, The German University in Cairo, Main Entrance of Al Tagamoa Al Khames, New Cairo11835, Egypt
| | - Heinrich Sticht
- Bioinformatics, Institute of Biochemistry, Friedrich-Alexander-Universität Erlangen-Nümberg, Fahrstrasse 17, D-91054Erlangen, Germany
| | - Hans-Georg Breitinger
- Department of Biochemistry, The German University in Cairo, Main Entrance of Al Tagamoa Al Khames, New Cairo11835, Egypt
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7
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Krall RF, Tzounopoulos T, Aizenman E. The Function and Regulation of Zinc in the Brain. Neuroscience 2021; 457:235-258. [PMID: 33460731 DOI: 10.1016/j.neuroscience.2021.01.010] [Citation(s) in RCA: 53] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 01/05/2021] [Accepted: 01/08/2021] [Indexed: 12/31/2022]
Abstract
Nearly sixty years ago Fredrich Timm developed a histochemical technique that revealed a rich reserve of free zinc in distinct regions of the brain. Subsequent electron microscopy studies in Timm- stained brain tissue found that this "labile" pool of cellular zinc was highly concentrated at synaptic boutons, hinting a possible role for the metal in synaptic transmission. Although evidence for activity-dependent synaptic release of zinc would not be reported for another twenty years, these initial findings spurred decades of research into zinc's role in neuronal function and revealed a diverse array of signaling cascades triggered or regulated by the metal. Here, we delve into our current understanding of the many roles zinc plays in the brain, from influencing neurotransmission and sensory processing, to activating both pro-survival and pro-death neuronal signaling pathways. Moreover, we detail the many mechanisms that tightly regulate cellular zinc levels, including metal binding proteins and a large array of zinc transporters.
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Affiliation(s)
- Rebecca F Krall
- Department of Neurobiology, University of Pittsburgh School of Medicine, USA; Department of Otolaryngology, University of Pittsburgh School of Medicine, USA; Pittsburgh Hearing Research Center, University of Pittsburgh School of Medicine, USA; Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, USA
| | - Thanos Tzounopoulos
- Department of Otolaryngology, University of Pittsburgh School of Medicine, USA; Pittsburgh Hearing Research Center, University of Pittsburgh School of Medicine, USA.
| | - Elias Aizenman
- Department of Neurobiology, University of Pittsburgh School of Medicine, USA; Pittsburgh Hearing Research Center, University of Pittsburgh School of Medicine, USA; Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, USA.
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8
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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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9
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A loss-of-function mutation of an inhibitory zinc- and proton-binding site reduces channel blocker potency in the glycine receptor. Neuropharmacology 2019; 153:121-133. [PMID: 31063738 DOI: 10.1016/j.neuropharm.2019.05.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 04/16/2019] [Accepted: 05/02/2019] [Indexed: 02/05/2023]
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10
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Mohammad AB, Mohammad SHK, Mohammad MK, Khan AS, Al-Hajjaj MS. Quantification of Trace Elements in Different Dokha and Shisha Tobacco Products using EDXRF. J Anal Toxicol 2019; 43:e7-e22. [PMID: 30462216 DOI: 10.1093/jat/bky095] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 09/28/2018] [Accepted: 10/23/2018] [Indexed: 11/14/2022] Open
Abstract
The present study aims to quantify trace metals in different dokha (medwakh) and shisha tobacco products available in local markets. Recent research has shown that these products have higher amounts of nicotine and tar compared to various other tobacco products. No specific data are available on the concentration of trace elements in dokha (medwakh) and shisha tobacco products in the Middle East and North Africa (MENA) region. Harmful health effects due to the toxicity of these elements in tobacco and its smoke have not been adequately emphasized. Concentrations of trace elements were extensively studied using HORIBA XGT-7200 EDXRF fluorescence absorption spectroscopy. The mean concentrations of aluminum, calcium, chromium, copper, iron, magnesium, manganese, nickel, potassium, strontium and zinc in 13 dokha products in μg/g were 406.92 ± 41.72, 14703.27 ± 271.73, 11.73 ± 2.12, 25.58 ± 2.63, 753.85 ± 14.87, 5306.54 ± 134.94, 82.31 ± 4.55, 25.58 ± 2.50, 2212.12 ± 39.04, 816.92 ± 15.26 and 35.96 ± 2.63, respectively; and those in the three shisha products in μg/g were 244.83 ± 25.11, 8235.77 ± 144.51, 3.40 ± 0.38, 22.77 ± 4.50, 569.13 ± 10.22, 2096.20 ± 130.69, 72.13 ± 7.13, 27.67 ± 5.31, 4467.50 ± 168.06, 320.20 ± 6.03 and 36.40 ± 3.57, respectively. In our study, the quantified trace metal concentrations in dokha and shisha tobacco using the EDXRF method were ten times higher than the LODs. The percentage of RSD was <10%, validating the precision of the method. Tobacco smoking is a major source of consumption of toxic elements, not only in the smoker but also in non-smokers through passive smoking. In dokha (medwakh) and shisha tobacco products, compared with cigarettes, Ni levels were significantly higher, Cr, Cu and Zn levels were higher, and Fe levels were similar, while Al and Mn levels were lower. The dokha and shisha tobacco products have no filters; many toxic metals can quickly enter the lungs and cause different pulmonary diseases and oral infections. Tobacco smoking causes lung and oral cancers, chronic obstructive pulmonary disease and cardiovascular diseases.
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Affiliation(s)
| | | | | | - Abdus Sayeed Khan
- Department of Physics, University Laboratories, Khalifa University, Abu Dhabi, UAE
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11
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Blakemore LJ, Trombley PQ. Zinc as a Neuromodulator in the Central Nervous System with a Focus on the Olfactory Bulb. Front Cell Neurosci 2017; 11:297. [PMID: 29033788 PMCID: PMC5627021 DOI: 10.3389/fncel.2017.00297] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 09/06/2017] [Indexed: 12/19/2022] Open
Abstract
The olfactory bulb (OB) is central to the sense of smell, as it is the site of the first synaptic relay involved in the processing of odor information. Odor sensations are first transduced by olfactory sensory neurons (OSNs) before being transmitted, by way of the OB, to higher olfactory centers that mediate olfactory discrimination and perception. Zinc is a common trace element, and it is highly concentrated in the synaptic vesicles of subsets of glutamatergic neurons in some brain regions including the hippocampus and OB. In addition, zinc is contained in the synaptic vesicles of some glycinergic and GABAergic neurons. Thus, zinc released from synaptic vesicles is available to modulate synaptic transmission mediated by excitatory (e.g., N-methyl-D aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)) and inhibitory (e.g., gamma-aminobutyric acid (GABA), glycine) amino acid receptors. Furthermore, extracellular zinc can alter the excitability of neurons through effects on a variety of voltage-gated ion channels. Consistent with the notion that zinc acts as a regulator of neuronal activity, we and others have shown zinc modulation (inhibition and/or potentiation) of amino acid receptors and voltage-gated ion channels expressed by OB neurons. This review summarizes the locations and release of vesicular zinc in the central nervous system (CNS), including in the OB. It also summarizes the effects of zinc on various amino acid receptors and ion channels involved in regulating synaptic transmission and neuronal excitability, with a special emphasis on the actions of zinc as a neuromodulator in the OB. An understanding of how neuroactive substances such as zinc modulate receptors and ion channels expressed by OB neurons will increase our understanding of the roles that synaptic circuits in the OB play in odor information processing and transmission.
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Affiliation(s)
- Laura J Blakemore
- Program in Neuroscience, Florida State UniversityTallahassee, FL, United States.,Department of Biological Science, Florida State UniversityTallahassee, FL, United States
| | - Paul Q Trombley
- Program in Neuroscience, Florida State UniversityTallahassee, FL, United States.,Department of Biological Science, Florida State UniversityTallahassee, FL, United States
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12
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Cornelison GL, Daszkowski AW, Pflanz NC, Mihic SJ. Interactions between Zinc and Allosteric Modulators of the Glycine Receptor. J Pharmacol Exp Ther 2017; 361:1-8. [PMID: 28087784 DOI: 10.1124/jpet.116.239152] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 01/12/2017] [Indexed: 01/01/2023] Open
Abstract
The glycine receptor is a pentameric ligand-gated ion channel that is involved in fast inhibitory neurotransmission in the central nervous system. Zinc is an allosteric modulator of glycine receptor function, enhancing the effects of glycine at nanomolar to low-micromolar concentrations and inhibiting its effects at higher concentrations. Low-nanomolar concentrations of contaminating zinc in electrophysiological buffers are capable of synergistically enhancing receptor modulation by other compounds, such as ethanol. This suggests that, unless accounted for, previous studies of glycine receptor modulation were measuring the effects of modulator plus comodulation by zinc on receptor function. Since zinc is present in vivo at a variety of concentrations, it will influence glycine receptor modulation by other pharmacologic agents. We investigated the utility of previously described "zinc-enhancement-insensitive" α1 glycine receptor mutants D80A, D80G, and W170S to probe for interactions between zinc and other allosteric modulators at the glycine receptor. We found that only the W170S mutation conferred complete abolishment of zinc enhancement across a variety of agonist and zinc concentrations. Using α1 W170S receptors, we established that, in addition to ethanol, zinc interacts with inhalants, but not volatile anesthetics, to synergistically enhance channel function. Additionally, we determined that this interaction is abolished at higher zinc concentrations when receptor-enhancing binding sites are saturated, suggesting a mechanism by which modulators such as ethanol and inhalants are capable of increasing receptor affinity for zinc, in addition to enhancing channel function on their own.
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Affiliation(s)
- Garrett L Cornelison
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, Texas
| | - Anna W Daszkowski
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, Texas
| | - Natasha C Pflanz
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, Texas
| | - S John Mihic
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, Texas
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13
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Peralta FA, Huidobro-Toro JP. Zinc as Allosteric Ion Channel Modulator: Ionotropic Receptors as Metalloproteins. Int J Mol Sci 2016; 17:E1059. [PMID: 27384555 PMCID: PMC4964435 DOI: 10.3390/ijms17071059] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Revised: 06/20/2016] [Accepted: 06/22/2016] [Indexed: 12/20/2022] Open
Abstract
Zinc is an essential metal to life. This transition metal is a structural component of many proteins and is actively involved in the catalytic activity of cell enzymes. In either case, these zinc-containing proteins are metalloproteins. However, the amino acid residues that serve as ligands for metal coordination are not necessarily the same in structural proteins compared to enzymes. While crystals of structural proteins that bind zinc reveal a higher preference for cysteine sulfhydryls rather than histidine imidazole rings, catalytic enzymes reveal the opposite, i.e., a greater preference for the histidines over cysteines for catalysis, plus the influence of carboxylic acids. Based on this paradigm, we reviewed the putative ligands of zinc in ionotropic receptors, where zinc has been described as an allosteric modulator of channel receptors. Although these receptors do not strictly qualify as metalloproteins since they do not normally bind zinc in structural domains, they do transitorily bind zinc at allosteric sites, modifying transiently the receptor channel's ion permeability. The present contribution summarizes current information showing that zinc allosteric modulation of receptor channels occurs by the preferential metal coordination to imidazole rings as well as to the sulfhydryl groups of cysteine in addition to the carboxyl group of acid residues, as with enzymes and catalysis. It is remarkable that most channels, either voltage-sensitive or transmitter-gated receptor channels, are susceptible to zinc modulation either as positive or negative regulators.
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Affiliation(s)
- Francisco Andrés Peralta
- Laboratorio de Farmacología de Nucleótidos, Laboratorio de Farmacología, Departamento de Biología, Facultad de Química y Biología, y Centro para el Desarrollo de Nanociencias y Nanotecnología (CEDENNA), Universidad de Santiago de Chile, Alameda Libertador B. O'Higgins, 3363 Santiago, Chile.
| | - Juan Pablo Huidobro-Toro
- Laboratorio de Farmacología de Nucleótidos, Laboratorio de Farmacología, Departamento de Biología, Facultad de Química y Biología, y Centro para el Desarrollo de Nanociencias y Nanotecnología (CEDENNA), Universidad de Santiago de Chile, Alameda Libertador B. O'Higgins, 3363 Santiago, Chile.
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Kuenzel K, Friedrich O, Gilbert DF. A Recombinant Human Pluripotent Stem Cell Line Stably Expressing Halide-Sensitive YFP-I152L for GABAAR and GlyR-Targeted High-Throughput Drug Screening and Toxicity Testing. Front Mol Neurosci 2016; 9:51. [PMID: 27445687 PMCID: PMC4923258 DOI: 10.3389/fnmol.2016.00051] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 06/13/2016] [Indexed: 01/29/2023] Open
Abstract
GABAARs and GlyRs are considered attractive drug targets for therapeutic intervention and are also increasingly recognized in the context of in vitro neurotoxicity (NT) and developmental neurotoxicity (DNT) testing. However, systematic human-specific GABAAR and GlyR-targeted drug screening and toxicity testing is hampered due to lack of appropriate in vitro models that express native GABAARs and GlyRs. We have established a human pluripotent stem cell line (NT2) stably expressing YFP-I152L, a halide-sensitive variant of yellow fluorescent protein (YFP), allowing for fluorescence-based functional analysis of chloride channels. Upon stimulation with retinoic acid, NT2 cells undergo neuronal differentiation and allow pharmacological and toxicological evaluation of native GABAARs and GlyRs at different stages of brain maturation. We applied the cell line in concentration-response experiments with the neurotransmitters GABA and glycine as well as with the drugs strychnine, picrotoxin, fipronil, lindane, bicuculline, and zinc and demonstrate that the established in vitro model is applicable to GABAAR and GlyR-targeted pharmacological and toxicological profiling. We quantified the proportion of GABAAR and GlyR-sensitive cells, respectively, and identified percentages of approximately 20% each within the overall populations, rendering the cells a suitable model for systematic in vitro GABAAR and GlyR-targeted screening in the context of drug development and NT/DNT testing.
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Affiliation(s)
- Katharina Kuenzel
- Department of Chemical and Biological Engineering, Institute of Medical Biotechnology, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany; Erlangen Graduate School in Advanced Optical Technologies, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany
| | - Oliver Friedrich
- Department of Chemical and Biological Engineering, Institute of Medical Biotechnology, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany; Erlangen Graduate School in Advanced Optical Technologies, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany
| | - Daniel F Gilbert
- Department of Chemical and Biological Engineering, Institute of Medical Biotechnology, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany; Erlangen Graduate School in Advanced Optical Technologies, Friedrich-Alexander-Universität Erlangen-NürnbergErlangen, Germany
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15
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Wilkins ME, Caley A, Gielen MC, Harvey RJ, Smart TG. Murine startle mutant Nmf11 affects the structural stability of the glycine receptor and increases deactivation. J Physiol 2016; 594:3589-607. [PMID: 27028707 PMCID: PMC4929309 DOI: 10.1113/jp272122] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 03/21/2016] [Indexed: 11/10/2022] Open
Abstract
Key points Hyperekplexia or startle disease is a serious neurological condition affecting newborn children and usually involves dysfunctional glycinergic neurotransmission. Glycine receptors (GlyRs) are major mediators of inhibition in the spinal cord and brainstem. A missense mutation, replacing asparagine (N) with lysine (K), at position 46 in the GlyR α1 subunit induced hyperekplexia following a reduction in the potency of the transmitter glycine; this resulted from a rapid deactivation of the agonist current at mutant GlyRs. These effects of N46K were rescued by mutating a juxtaposed residue, N61 on binding Loop D, suggesting these two asparagines may interact. Asparagine 46 is considered to be important for the structural stability of the subunit interface and glycine binding site, and its mutation represents a new mechanism by which GlyR dysfunction induces startle disease.
Abstract Dysfunctional glycinergic inhibitory transmission underlies the debilitating neurological condition, hyperekplexia, which is characterised by exaggerated startle reflexes, muscle hypertonia and apnoea. Here we investigated the N46K missense mutation in the GlyR α1 subunit gene found in the ethylnitrosourea (ENU) murine mutant, Nmf11, which causes reduced body size, evoked tremor, seizures, muscle stiffness, and morbidity by postnatal day 21. Introducing the N46K mutation into recombinant GlyR α1 homomeric receptors, expressed in HEK cells, reduced the potencies of glycine, β‐alanine and taurine by 9‐, 6‐ and 3‐fold respectively, and that of the competitive antagonist strychnine by 15‐fold. Replacing N46 with hydrophobic, charged or polar residues revealed that the amide moiety of asparagine was crucial for GlyR activation. Co‐mutating N61, located on a neighbouring β loop to N46, rescued the wild‐type phenotype depending on the amino acid charge. Single‐channel recording identified that burst length for the N46K mutant was reduced and fast agonist application revealed faster glycine deactivation times for the N46K mutant compared with the WT receptor. Overall, these data are consistent with N46 ensuring correct alignment of the α1 subunit interface by interaction with juxtaposed residues to preserve the structural integrity of the glycine binding site. This represents a new mechanism by which GlyR dysfunction induces startle disease. Hyperekplexia or startle disease is a serious neurological condition affecting newborn children and usually involves dysfunctional glycinergic neurotransmission. Glycine receptors (GlyRs) are major mediators of inhibition in the spinal cord and brainstem. A missense mutation, replacing asparagine (N) with lysine (K), at position 46 in the GlyR α1 subunit induced hyperekplexia following a reduction in the potency of the transmitter glycine; this resulted from a rapid deactivation of the agonist current at mutant GlyRs. These effects of N46K were rescued by mutating a juxtaposed residue, N61 on binding Loop D, suggesting these two asparagines may interact. Asparagine 46 is considered to be important for the structural stability of the subunit interface and glycine binding site, and its mutation represents a new mechanism by which GlyR dysfunction induces startle disease.
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Affiliation(s)
- Megan E Wilkins
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Alex Caley
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Marc C Gielen
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Robert J Harvey
- Department of Pharmacology, UCL School of Pharmacy, 29-39, Brunswick Square, London, WC1N 1AX, UK
| | - Trevor G Smart
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
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16
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Cornelison GL, Pflanz NC, Tipps ME, Mihic SJ. Identification and characterization of heptapeptide modulators of the glycine receptor. Eur J Pharmacol 2016; 780:252-9. [PMID: 27038522 DOI: 10.1016/j.ejphar.2016.03.058] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 03/24/2016] [Accepted: 03/29/2016] [Indexed: 02/07/2023]
Abstract
The glycine receptor is a member of the Cys-loop receptor superfamily of ligand-gated ion channels and is implicated as a possible therapeutic target for the treatment of diseases such as alcoholism and inflammatory pain. In humans, four glycine receptor subtypes (α1, α2, α3, and β) co-assemble to form pentameric channel proteins as either α homomers or αβ heteromers. To date, few agents have been identified that can selectively modulate the glycine receptor, especially those possessing subtype specificity. We used a cell-based method of phage display panning, coupled with two-electrode voltage-clamp electrophysiology in Xenopus laevis oocytes, to identify novel heptapeptide modulators of the α1β glycine receptor. This involved a panning procedure in which the phage library initially underwent subtractive panning against Human Embryonic Kidney (HEK) 293 cells expressing alternative glycine receptor subtypes before panning the remaining library over HEK 293 cells expressing the target, the α1β glycine receptor. Peptides were identified that act with selectivity on α1β and α3β, compared to α2β, glycine receptors. In addition, peptide activity at the glycine receptor decreased when zinc was chelated by tricine, similar to previous observations of a decrease in ethanol's enhancing actions at the receptor in the absence of zinc. Comparisons of the amino acid sequences of heptapeptides capable of potentiating glycine receptor function revealed several consensus sequences that may be predictive of a peptide's enhancing ability.
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Affiliation(s)
- Garrett L Cornelison
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - Natasha C Pflanz
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - Megan E Tipps
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - S John Mihic
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA.
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17
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Allosteric modulation of the glycine receptor activated by agonists differing in efficacy. Brain Res 2015; 1606:95-101. [PMID: 25721789 DOI: 10.1016/j.brainres.2015.02.024] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Revised: 02/12/2015] [Accepted: 02/13/2015] [Indexed: 01/29/2023]
Abstract
The glycine receptor (GlyR) is the predominant inhibitory neurotransmitter receptor in the brainstem and spinal cord but is also found in higher brain regions. GlyR function is affected by a variety of allosteric modulators including drugs of abuse, such as ethanol and inhalants and the ubiquitous divalent cation zinc. Two-electrode voltage-clamp experiments were conducted on Xenopus laevis oocytes expressing wild-type α1 homomeric glycine receptors to compare the degree of enhancement produced by zinc on GlyR activated by two agonists (glycine vs. taurine) that vary markedly in their efficacies. Zinc potentiation of both glycine- and taurine-evoked currents was the same at the concentrations of agonists that produced the same currents, corresponding to 6% of the maximal effect of glycine compared to 23% of the maximal effect of taurine. Similar results were seen with 50 and 200 mM ethanol. A direct comparison of agonist concentration-response curves showed that zinc enhancement was greater, overall, for taurine-activated than glycine-activated receptors. In addition, zinc only enhanced taurine- but not glycine-activated GlyR when agonists were applied at saturating concentrations. These data suggest that zinc affects taurine affinity, as well as the probability of channel opening at sub-maximal taurine concentrations, and that the magnitude of allosteric modulation at the GlyR depends on the efficacy of the agonist tested. This has implications for mutagenesis studies in which changes in the degree of allosteric modulation observed may result from mutation-induced changes in agonist efficacy.
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18
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Zhang Y, Dixon CL, Keramidas A, Lynch JW. Functional reconstitution of glycinergic synapses incorporating defined glycine receptor subunit combinations. Neuropharmacology 2015; 89:391-7. [DOI: 10.1016/j.neuropharm.2014.10.026] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Revised: 10/16/2014] [Accepted: 10/26/2014] [Indexed: 10/24/2022]
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19
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Morud J, Adermark L, Ericson M, Söderpalm B. Alterations in ethanol-induced accumbal transmission after acute and long-term zinc depletion. Addict Biol 2015; 20:170-81. [PMID: 24102995 DOI: 10.1111/adb.12096] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Alcoholism is subject to extensive research, but the role of changes in metabolism caused by alcohol consumption has been poorly investigated. Zinc (Zn(2+) ) deficiency is a common metabolic aberration among alcoholics and Zn(2+) influences the function of ligand-gated ion channels, known pharmacological targets of ethanol (EtOH). Here, we investigate whether manipulation of extracellular levels of Zn(2+) modulates EtOH-induced increases of dopamine (DA) output, as measured by in vivo microdialysis in the rat, and whether voluntary EtOH consumption is altered by Zn(2+) deficiency. Our findings show that the Zn(2+) -chelating agent tricine slowly raises DA levels when perfused in the nucleus accumbens (nAc), whereas the more potent Zn(2+) chelator TPEN reduces DA levels. We also show that pre-treatment with either tricine or TPEN blocks the EtOH-induced DA elevation. Chronic Zn(2+) deficiency induced by a Zn(2+) -free diet did not affect EtOH consumption, but excitatory transmission, assessed by striatal field-potential recordings in the nAc shell, was significantly modulated both by Zn(2+) -free diet and by EtOH consumption, as compared with the EtOH naïve controls. The present study indicates that Zn(2+) influences EtOH's interaction with the brain reward system, possibly by interfering with glycine receptor and GABAA receptor function. This also implies that Zn(2+) deficiency among alcoholics may be important to correct in order to normalize important aspects of brain function.
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Affiliation(s)
- Julia Morud
- Addiction Biology Unit; Department of Psychiatry and Neurochemistry; Institute of Neuroscience and Physiology; The Sahlgrenska Academy at University of Gothenburg; Sweden
| | - Louise Adermark
- Addiction Biology Unit; Department of Psychiatry and Neurochemistry; Institute of Neuroscience and Physiology; The Sahlgrenska Academy at University of Gothenburg; Sweden
| | - Mia Ericson
- Addiction Biology Unit; Department of Psychiatry and Neurochemistry; Institute of Neuroscience and Physiology; The Sahlgrenska Academy at University of Gothenburg; Sweden
| | - Bo Söderpalm
- Addiction Biology Unit; Department of Psychiatry and Neurochemistry; Institute of Neuroscience and Physiology; The Sahlgrenska Academy at University of Gothenburg; Sweden
- Beroendekliniken; Sahlgrenska University Hospital; Sweden
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20
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Marger L, Schubert C, Bertrand D. Zinc: An underappreciated modulatory factor of brain function. Biochem Pharmacol 2014; 91:426-35. [DOI: 10.1016/j.bcp.2014.08.002] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Revised: 07/30/2014] [Accepted: 08/08/2014] [Indexed: 02/05/2023]
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21
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Malhotra A, Dhawan DK. Current view of zinc as a hepatoprotective agent in conditions of chlorpyrifos induced toxicity. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2014; 112:1-6. [PMID: 24974110 DOI: 10.1016/j.pestbp.2014.04.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 04/15/2014] [Accepted: 04/21/2014] [Indexed: 11/18/2022]
Affiliation(s)
- Anshoo Malhotra
- Department of Biophysics, Post Graduate Institute of Medical Education & Research, Chandigarh, India
| | - D K Dhawan
- Department of Biophysics, Panjab University, Chandigarh, India.
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22
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Cornelison GL, Mihic SJ. Contaminating levels of zinc found in commonly-used labware and buffers affect glycine receptor currents. Brain Res Bull 2013; 100:1-5. [PMID: 24177173 DOI: 10.1016/j.brainresbull.2013.10.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Revised: 10/18/2013] [Accepted: 10/21/2013] [Indexed: 11/18/2022]
Abstract
Zinc is an allosteric modulator of glycine receptor function, enhancing the effects of glycine at nM to low μM concentrations, and inhibiting its effects at higher concentrations. Because of zinc's high potency at the glycine receptor, there exists a possibility that effects attributed solely to exogenously-applied glycine in fact contain an undetected contribution of zinc acting as an allosteric modulator. We found that glycine solutions made up in standard buffers and using deionized distilled water produced effects that could be decreased by the zinc chelator tricine. This phenomenon was observed in three different vials tested and persisted even if vials were extensively washed, suggesting the zinc was probably present in the buffer constituents. In addition, polystyrene, but not glass, pipets bore a contaminant that enhanced glycine receptor function and that could also be antagonized by tricine. Our findings suggest that without checking for this effect using a chelator such as tricine, one cannot assume that responses elicited by glycine applied alone are not necessarily also partially due to some level of allosteric modulation by zinc.
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Affiliation(s)
- Garrett L Cornelison
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - S John Mihic
- Department of Neuroscience, Division of Pharmacology and Toxicology, Waggoner Center for Alcohol & Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA.
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23
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Physiological concentrations of zinc reduce taurine-activated GlyR responses to drugs of abuse. Neuropharmacology 2013; 75:286-94. [PMID: 23973295 DOI: 10.1016/j.neuropharm.2013.07.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Revised: 07/26/2013] [Accepted: 07/29/2013] [Indexed: 02/07/2023]
Abstract
Taurine is an endogenous ligand acting on glycine receptors in many brain regions, including the hippocampus, prefrontal cortex, and nucleus accumbens (nAcc). These areas also contain low concentrations of zinc, which is known to potentiate glycine receptor responses. Despite an increasing awareness of the role of the glycine receptor in the rewarding properties of drugs of abuse, the possible interactions of these compounds with zinc has not been thoroughly addressed. Two-electrode voltage-clamp electrophysiological experiments were performed on α1, α2 α1β and α2β glycine receptors expressed in Xenopus laevis oocytes. The effects of zinc alone, and zinc in combination with other positive modulators on the glycine receptor, were investigated when activated by the full agonist glycine versus the partial agonist taurine. Low concentrations of zinc enhanced responses of maximally-effective concentrations of taurine but not glycine. Likewise, chelation of zinc from buffers decreased responses of taurine- but not glycine-mediated currents. Potentiating concentrations of zinc decreased ethanol, isoflurane, and toluene enhancement of maximal taurine currents with no effects on maximal glycine currents. Our findings suggest that the concurrence of high concentrations of taurine and low concentrations of zinc attenuate the effects of additional modulators on the glycine receptor, and that these conditions are more representative of in vivo functioning than effects seen when these modulators are applied in isolation.
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24
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McCracken LM, Trudell JR, McCracken ML, Harris RA. Zinc-dependent modulation of α2- and α3-glycine receptor subunits by ethanol. Alcohol Clin Exp Res 2013; 37:2002-10. [PMID: 23895467 DOI: 10.1111/acer.12192] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Accepted: 04/09/2013] [Indexed: 11/28/2022]
Abstract
BACKGROUND Strychnine-sensitive glycine receptors (GlyRs) are expressed throughout the brain and spinal cord and are among the strongly supported protein targets of alcohol. This is based largely on studies of the α1-subunit; however, α2- and α3-GlyR subunits are as or more abundantly expressed than α1-GlyRs in multiple forebrain brain areas considered to be important for alcohol-related behaviors, and uniquely some α3-GlyRs undergo RNA editing. Nanomolar and low micromolar concentrations of zinc ions potentiate GlyR function, and in addition to zinc's effects on glycine-activated currents, we have recently shown that physiological concentrations of zinc also enhance the magnitude of ethanol (EtOH)'s effects on α1-GlyRs. METHODS Using 2-electrode voltage-clamp electrophysiology in oocytes expressing either α2- or α3-GlyRs, we first tested the hypothesis that the effects of EtOH on α2- and α3-GlyRs would be zinc dependent, as we have previously reported for α1-GlyRs. Next, we constructed an α3P185L-mutant GlyR to test whether RNA-edited and unedited GlyRs contain differences in EtOH sensitivity. Last, we built a homology model of the α3-GlyR subunit. RESULTS The effects of EtOH (20 to 200 mM) on both subunits were greater in the presence than in the absence of 500 nM added zinc. The α3P185L-mutation that corresponds to RNA editing increased sensitivity to glycine and decreased sensitivity to EtOH. CONCLUSIONS Our findings provide further evidence that zinc is important for determining the magnitude of EtOH's effects at GlyRs and suggest that by better understanding zinc/EtOH interactions at GlyRs, we may better understand the sites and mechanisms of EtOH action.
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Affiliation(s)
- Lindsay M McCracken
- The Waggoner Center for Alcohol and Addiction Research , The University of Texas at Austin, Austin, Texas
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25
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McCracken LM, Blednov YA, Trudell JR, Benavidez JM, Betz H, Harris RA. Mutation of a zinc-binding residue in the glycine receptor α1 subunit changes ethanol sensitivity in vitro and alcohol consumption in vivo. J Pharmacol Exp Ther 2012; 344:489-500. [PMID: 23230213 DOI: 10.1124/jpet.112.197707] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ethanol is a widely used drug, yet an understanding of its sites and mechanisms of action remains incomplete. Among the protein targets of ethanol are glycine receptors (GlyRs), which are potentiated by millimolar concentrations of ethanol. In addition, zinc ions also modulate GlyR function, and recent evidence suggests that physiologic concentrations of zinc enhance ethanol potentiation of GlyRs. Here, we first built a homology model of a zinc-bound GlyR using the D80 position as a coordination site for a zinc ion. Next, we investigated in vitro the effects of zinc on ethanol action at recombinant wild-type (WT) and mutant α1 GlyRs containing the D80A substitution, which eliminates zinc potentiation. At D80A GlyRs, the effects of 50 and 200 mM ethanol were reduced as compared with WT receptors. Also, in contrast to what was seen with WT GlyRs, neither adding nor chelating zinc changed the magnitude of ethanol enhancement of mutant D80A receptors. Next, we evaluated the in vivo effects of the D80A substitution by using heterozygous Glra1(D80A) knock-in (KI) mice. The KI mice showed decreased ethanol consumption and preference, and they displayed increased startle responses compared with their WT littermates. Other behavioral tests, including ethanol-induced motor incoordination and strychnine-induced convulsions, revealed no differences between the KI and WT mice. Together, our findings indicate that zinc is critical in determining the effects of ethanol at GlyRs and suggest that zinc binding at the D80 position may be important for mediating some of the behavioral effects of ethanol action at GlyRs.
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Affiliation(s)
- Lindsay M McCracken
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas, USA
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26
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Lemoine D, Jiang R, Taly A, Chataigneau T, Specht A, Grutter T. Ligand-gated ion channels: new insights into neurological disorders and ligand recognition. Chem Rev 2012; 112:6285-318. [PMID: 22988962 DOI: 10.1021/cr3000829] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Damien Lemoine
- Laboratoire de Biophysicochimie des Récepteurs Canaux, UMR 7199 CNRS, Conception et Application de Molécules Bioactives, Faculté de Pharmacie, Université de Strasbourg , 67400 Illkirch, France
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27
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Chen J, Winarski KL, Myerburg MM, Pitt BR, Sheng S. Probing the structural basis of Zn2+ regulation of the epithelial Na+ channel. J Biol Chem 2012; 287:35589-35598. [PMID: 22930753 DOI: 10.1074/jbc.m112.394734] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Extracellular Zn(2+) activates the epithelial Na(+) channel (ENaC) by relieving Na(+) self-inhibition. However, a biphasic Zn(2+) dose response was observed, suggesting that Zn(2+) has dual effects on the channel (i.e. activating and inhibitory). To investigate the structural basis for this biphasic effect of Zn(2+), we examined the effects of mutating the 10 extracellular His residues of mouse γENaC. Four mutations within the finger subdomain (γH193A, γH200A, γH202A, and γH239A) significantly reduced the maximal Zn(2+) activation of the channel. Whereas γH193A, γH200A, and γH202A reduced the apparent affinity of the Zn(2+) activating site, γH239A diminished Na(+) self-inhibition and thus concealed the activating effects of Zn(2+). Mutation of a His residue within the palm subdomain (γH88A) abolished the low-affinity Zn(2+) inhibitory effect. Based on structural homology with acid-sensing ion channel 1, γAsp(516) was predicted to be in close proximity to γHis(88). Ala substitution of the residue (γD516A) blunted the inhibitory effect of Zn(2+). Our results suggest that external Zn(2+) regulates ENaC activity by binding to multiple extracellular sites within the γ-subunit, including (i) a high-affinity stimulatory site within the finger subdomain involving His(193), His(200), and His(202) and (ii) a low-affinity Zn(2+) inhibitory site within the palm subdomain that includes His(88) and Asp(516).
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Affiliation(s)
- Jingxin Chen
- Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Katie L Winarski
- Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Mike M Myerburg
- Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Bruce R Pitt
- Department of Environmental and Occupational Health, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Shaohu Sheng
- Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
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28
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Weltzin MM, Huang Y, Schulte MK. Allosteric modulation of alpha4beta2 nicotinic acetylcholine receptors by HEPES. Eur J Pharmacol 2012; 732:159-68. [PMID: 22732654 DOI: 10.1016/j.ejphar.2012.06.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2011] [Revised: 05/29/2012] [Accepted: 06/05/2012] [Indexed: 11/28/2022]
Abstract
A number of new positive allosteric modulators (PAMs) have been reported that enhance responses of neuronal alpha7 and alpha4beta2 nicotinic acetylcholine receptor subtypes to orthosteric ligands. PAMs represent promising new leads for the development of therapeutic agents for disorders involving alterations in nicotinic neurotransmission including Autism, Alzheimer's and Parkinson's disease. During our recent studies of alpha4beta2 PAMs, we identified a novel effect of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). The effects of HEPES were evaluated in a phosphate buffered recording solution using two-electrode voltage clamp techniques and alpha4beta2 and alpha7 nicotinic acetylcholine receptor subtypes expressed in Xenopus laevis oocytes. Acetylcholine induced responses of high-sensitivity alpha4beta2 receptors were potentiated 190% by co-exposure to HEPES. Responses were inhibited at higher concentrations (bell-shaped concentration/response curve). Coincidentally, at concentrations of HEPES typically used in oocyte recording (5-10mM), the potentiating effects of HEPES are matched by its inhibitory effects, thus producing no net effect. Mutagenesis results suggest HEPES potentiates the high-sensitivity stoichiometry of the alpha4beta2 receptors through action at the beta2+/beta2- interface and is dependent on residue beta2D218. HEPES did not potentiate low-sensitivity alpha4beta2 receptors and did not produce any observable effect on acetylcholine induced responses on alpha7 nicotinic acetylcholine receptors.
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Affiliation(s)
- Maegan M Weltzin
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks Fairbank, AK 99775, USA
| | - Yanzhou Huang
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks Fairbank, AK 99775, USA
| | - Marvin K Schulte
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks Fairbank, AK 99775, USA.
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Abstract
Inhibitory (or strychnine sensitive) glycine receptors (GlyRs) are anion-selective transmitter-gated ion channels of the cys-loop superfamily, which includes among others also the inhibitory γ-aminobutyric acid receptors (GABA(A) receptors). While GABA mediates fast inhibitory neurotransmission throughout the CNS, the action of glycine as a fast inhibitory neurotransmitter is more restricted. This probably explains why GABA(A) receptors constitute a group of extremely successful drug targets in the treatment of a wide variety of CNS diseases, including anxiety, sleep disorders and epilepsy, while drugs specifically targeting GlyRs are virtually lacking. However, the spatially more restricted distribution of glycinergic inhibition may be advantageous in situations when a more localized enhancement of inhibition is sought. Inhibitory GlyRs are particularly relevant for the control of excitability in the mammalian spinal cord, brain stem and a few selected brain areas, such as the cerebellum and the retina. At these sites, GlyRs regulate important physiological functions, including respiratory rhythms, motor control, muscle tone and sensory as well as pain processing. In the hippocampus, RNA-edited high affinity extrasynaptic GlyRs may contribute to the pathology of temporal lobe epilepsy. Although specific modulators have not yet been identified, GlyRs still possess sites for allosteric modulation by a number of structurally diverse molecules, including alcohols, neurosteroids, cannabinoids, tropeines, general anaesthetics, certain neurotransmitters and cations. This review summarizes the present knowledge about this modulation and the molecular bases of the interactions involved.
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Affiliation(s)
- Gonzalo E Yevenes
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
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Zeilhofer HU, Wildner H, Yévenes GE. Fast synaptic inhibition in spinal sensory processing and pain control. Physiol Rev 2012; 92:193-235. [PMID: 22298656 DOI: 10.1152/physrev.00043.2010] [Citation(s) in RCA: 256] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The two amino acids GABA and glycine mediate fast inhibitory neurotransmission in different CNS areas and serve pivotal roles in the spinal sensory processing. Under healthy conditions, they limit the excitability of spinal terminals of primary sensory nerve fibers and of intrinsic dorsal horn neurons through pre- and postsynaptic mechanisms, and thereby facilitate the spatial and temporal discrimination of sensory stimuli. Removal of fast inhibition not only reduces the fidelity of normal sensory processing but also provokes symptoms very much reminiscent of pathological and chronic pain syndromes. This review summarizes our knowledge of the molecular bases of spinal inhibitory neurotransmission and its organization in dorsal horn sensory circuits. Particular emphasis is placed on the role and mechanisms of spinal inhibitory malfunction in inflammatory and neuropathic chronic pain syndromes.
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Abstract
Since the discovery of the major excitatory and inhibitory neurotransmitters and their receptors in the brain, many have deliberated over their likely structures and how these may relate to function. This was initially satisfied by the determination of the first amino acid sequences of the Cys-loop receptors that recognized acetylcholine, serotonin, GABA, and glycine, followed later by similar determinations for the glutamate receptors, comprising non-NMDA and NMDA subtypes. The last decade has seen a rapid advance resulting in the first structures of Cys-loop receptors, related bacterial and molluscan homologs, and glutamate receptors, determined down to atomic resolution. This now provides a basis for determining not just the complete structures of these important receptor classes, but also for understanding how various domains and residues interact during agonist binding, receptor activation, and channel opening, including allosteric modulation. This article reviews our current understanding of these mechanisms for the Cys-loop and glutamate receptor families.
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Affiliation(s)
- Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom.
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32
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Allosteric modulators of the α4β2 subtype of neuronal nicotinic acetylcholine receptors. Biochem Pharmacol 2011; 82:952-8. [PMID: 21596025 DOI: 10.1016/j.bcp.2011.04.020] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 04/28/2011] [Accepted: 04/29/2011] [Indexed: 02/07/2023]
Abstract
Nicotinic acetylcholine receptors are ligand-gated ion conducting transmembrane channels from the Cys-loop receptor super-family. The α4β2 subtype is the predominant heteromeric subtype of nicotinic receptors found in the brain. Allosteric modulators for α4β2 receptors interact at a site other than the orthosteric site where acetylcholine binds. Many compounds which act as allosteric modulators of the α4β2 receptors have been identified, with both positive and negative effects. Such allosteric modulators either increase or decrease the response induced by agonist on the α4β2 receptors. Here we discuss the concept of allosterism as it pertains to the α4β2 receptors and summarize the important features of allosteric modulators for this nicotinic receptor subtype.
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33
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Tian Y, Yang Z, Zhang T. Zinc ion as modulator effects on excitability and synaptic transmission in hippocampal CA1 neurons in Wistar rats. Neurosci Res 2010; 68:167-75. [DOI: 10.1016/j.neures.2010.07.2030] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2010] [Revised: 07/02/2010] [Accepted: 07/09/2010] [Indexed: 10/19/2022]
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34
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Zinc enhances ethanol modulation of the alpha1 glycine receptor. Neuropharmacology 2009; 58:676-81. [PMID: 19913039 DOI: 10.1016/j.neuropharm.2009.11.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Revised: 10/29/2009] [Accepted: 11/05/2009] [Indexed: 11/20/2022]
Abstract
Glycine receptor function mediates most inhibitory neurotransmission in the brainstem and spinal cord and is enhanced by alcohols, volatile anesthetics, inhaled drugs of abuse, and endogenous compounds including zinc. Because zinc exists ubiquitously throughout the brain, investigations of its effects on the enhancement of GlyR function by alcohols and anesthetics are important to understanding the effects of these agents in vivo. In the present study, the effects of zinc plus ethanol, pentanol, or isoflurane were tested on homomeric alpha1 glycine receptors to determine if concurrent applications of physiological concentrations of zinc with each of these modulators changed the magnitude of their effects. Homomeric alpha1 glycine receptors were expressed in Xenopus laevis oocytes, and the two-electrode voltage-clamp technique was used to measure glycine-mediated currents in the presence of combinations of zinc with ethanol, pentanol or isoflurane. The combined effects of zinc plus ethanol were greater than the sum of the effects produced by either compound alone. However, this was not seen when zinc was combined with either pentanol or isoflurane. Chelation of zinc by tricine decreased the effects of sub-maximal, but not maximal, concentrations of glycine, and diminished the magnitude of ethanol enhancement observed. These findings suggest a zinc/ethanol interaction at the alpha1 GlyR that results in the enhancement of the effects of ethanol action on GlyR function.
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Schumann T, Grudzinska J, Kuzmin D, Betz H, Laube B. Binding-site mutations in the α1 subunit of the inhibitory glycine receptor convert the inhibitory metal ion Cu2+ into a positive modulator. Neuropharmacology 2009; 56:310-7. [DOI: 10.1016/j.neuropharm.2008.08.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 07/31/2008] [Accepted: 08/08/2008] [Indexed: 10/21/2022]
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36
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Mapping a molecular link between allosteric inhibition and activation of the glycine receptor. Nat Struct Mol Biol 2008; 15:1084-93. [PMID: 18806798 DOI: 10.1038/nsmb.1492] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2008] [Accepted: 08/27/2008] [Indexed: 11/08/2022]
Abstract
Cys-loop ligand-gated ion channels mediate rapid neurotransmission throughout the central nervous system. They possess agonist recognition sites and allosteric sites where modulators regulate ion channel function. Using strychnine-sensitive glycine receptors, we identified a scaffold of hydrophobic residues enabling allosteric communication between glycine-agonist binding loops A and D, and the Zn(2+)-inhibition site. Mutating these hydrophobic residues disrupted Zn(2+) inhibition, generating novel Zn(2+)-activated receptors and spontaneous channel activity. Homology modeling and electrophysiology revealed that these phenomena are caused by disruption to three residues on the '-' loop face of the Zn(2+)-inhibition site, and to D84 and D86, on a neighboring beta3 strand, forming a Zn(2+)-activation site. We provide a new view for the activation of a Cys-loop receptor where, following agonist binding, the hydrophobic core and interfacial loops reorganize in a concerted fashion to induce downstream gating.
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Jenkins A, Lobo IA, Gong D, Trudell JR, Solt K, Harris RA, Eger EI. General anesthetics have additive actions on three ligand gated ion channels. Anesth Analg 2008; 107:486-93. [PMID: 18633027 DOI: 10.1213/ane.0b013e31817b70c1] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND The purpose of this study was to determine whether pairs of compounds, including general anesthetics, could simultaneously modulate receptor function in a synergistic manner, thus demonstrating the existence of multiple intraprotein anesthetic binding sites. METHODS Using standard electrophysiologic methods, we measured the effects of at least one combination of benzene, isoflurane (ISO), halothane (HAL), chloroform, flunitrazepam, zinc, and pentobarbital on at least one of the following ligand gated ion channels: N-methyl-D-aspartate receptors, glycine receptors and gamma-aminobutyric acid type A receptors. RESULTS All drug-drug-receptor combinations were found to exhibit additive, not synergistic modulation. ISO with benzene additively depressed N-methyl-D-aspartate receptors function. ISO with HAL additively enhanced glycine receptors function, as did ISO with zinc. ISO with HAL additively enhanced gamma-aminobutyric acid type A receptors function as did all of the following: HAL with chloroform, pentobarbital with ISO, and flunitrazepam with ISO. CONCLUSION The simultaneous allosteric modulation of ligand gated ion channels by general anesthetics is entirely additive. Where pairs of general anesthetic drugs interact synergistically to produce general anesthesia, they must do so on systems more complex than a single receptor.
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Affiliation(s)
- Andrew Jenkins
- Department of Anesthesiology, Emory University School of Medicine, 1462 Clifton Rd NE Suite 420, Atlanta, GA 30322, USA.
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38
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Hsiao B, Mihalak KB, Magleby KL, Luetje CW. Zinc potentiates neuronal nicotinic receptors by increasing burst duration. J Neurophysiol 2007; 99:999-1007. [PMID: 18094103 DOI: 10.1152/jn.01040.2007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Micromolar zinc potentiates neuronal nicotinic acetylcholine receptors (nAChRs) in a subtype-dependent manner. Zinc potentiates receptor function even at saturating agonist concentrations, without altering the receptor desensitization rate. Potentiation could occur through an increase in the number of available receptors, an increase in single-channel current amplitude, or an increase in single-channel open probability. To distinguish among these possibilities, we examined rat neuronal nAChRs expressed in Xenopus oocytes. Blockade of a large fraction of ACh activated alpha4beta4 or alpha4beta2 receptors by the open channel blocker hexamethonium failed to change the extent of potentiation by zinc, suggesting that zinc does not change the number of available receptors. The single-channel amplitudes of ACh (1 microM) activated alpha4beta4 receptors in outside-out patches were similar in the absence and the presence of 100 microM zinc (3.0 +/- 0.1 and 2.9 +/- 0.1 pA, respectively). To determine the effect of zinc on single-channel open probability, we examined alpha4beta4 receptors in cell-attached patches. The open probability at 100 nM ACh (0.011 +/- 0.002) was increased 4.5-fold by 100 microM zinc (0.050 +/- 0.008), accounting for most of the potentiation observed at the whole cell level. The increase in open probability was due to an increase in burst duration, which increased from 207 +/- 38 ms in the absence of zinc to 830 +/- 189 ms in the presence of zinc. Our results suggest that potentiation of neuronal nAChRs by zinc is due to a stabilization of the bursting states of the receptor.
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Affiliation(s)
- Bernard Hsiao
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33101, USA
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Huidobro-Toro JP, Lorca RA, Coddou C. Trace metals in the brain: allosteric modulators of ligand-gated receptor channels, the case of ATP-gated P2X receptors. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 37:301-14. [DOI: 10.1007/s00249-007-0230-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Revised: 10/10/2007] [Accepted: 10/11/2007] [Indexed: 01/26/2023]
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40
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Bhalla P, Chadha VD, Dhawan DK. Effectiveness of Zinc in Modulating Lithium Induced Biochemical and Behavioral Changes in Rat Brain. Cell Mol Neurobiol 2007; 27:595-607. [PMID: 17458692 DOI: 10.1007/s10571-007-9146-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Accepted: 03/29/2007] [Indexed: 11/30/2022]
Abstract
1. The purpose of the present study was to determine the effect of zinc on the status of various neurotransmitters as well as behavioral patterns of lithium-treated rats. The study was designed with a view to find out whether zinc affords protection to brain against lithium toxicity. 2. Animals were segregated into four different groups. Animals in group I were fed with standard laboratory feed and water ad libitum and served as normal controls. Animals in group II and IV were given lithium in the form of lithium carbonate in their diet at a dose level of 1.1 g/Kg diet. Animals in group III and IV were given zinc treatment in the form of zinc sulfate at a dose level of 227 mg/L mixed in drinking water of animals. 3. The effects of all the treatments were studied for a duration of 1, 2, and 4 months with regard to the parameters, which included estimation of serotonin and dopamine concentrations as well as the activity of acetylcholinesterase in cerebral cortex of rat brain. Further, passive avoidance, active avoidance, and behavior despair tests were conducted to assess the short-term memory, cognitive behavior, and psychomotor dysfunction of the animals, respectively. 4. Initially, a decrease in the acetylcholinesterase activity was reported in cerebral cortex followed by an increase in the enzyme activity after 2 and 4 months of lithium treatment. Serotonin concentration significantly decreased after 2 and 4 months of lithium treatment, whereas dopamine concentration increased significantly after 4 months of lithium treatment. Zinc administration to the lithium-treated group significantly improved the acetylcholinesterase activity as well as the concentration of dopamine and serotonin. Further, lithium-treated rats showed an increase in depression time as compared to normal controls both after 1 and 4 months of treatment. Short-term memory significantly improved in lithium-treated rats in all treatment groups. However, no change in the cognitive behavior of the animals was reported after lithium treatment. Zinc co-administration with lithium significantly improved the short-term memory and cognitive functions of the animals. From the above results it can be concluded that zinc proved beneficial in altering the status of neurotransmitters as well as the behavior patters of the animals treated with both short and long-term lithium therapy.
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Affiliation(s)
- Punita Bhalla
- Department of Biophysics, Panjab University, Chandigarh 160 014, India
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41
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Chen Z, Huang R. Identification of residues mediating inhibition of glycine receptors by protons. Neuropharmacology 2007; 52:1606-15. [PMID: 17459427 DOI: 10.1016/j.neuropharm.2007.03.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2006] [Revised: 02/14/2007] [Accepted: 03/12/2007] [Indexed: 11/23/2022]
Abstract
We previously identified H109 of the glycine alpha1 subunit as a putative proton binding site. In the present studies, we explored additional proton binding site(s) as well as the mechanism underlying modulation of glycine receptors by protons. Whole-cell glycine currents were recorded from HEK 293 cells transiently expressing wild type or mutant glycine receptors. Individual mutation of 3 of 4 remaining extracellular histidine residue into alanine (i.e., alpha1 H107A, H215A or H419A), reduced the receptor sensitivity to protons to a varying extent. In contrast, mutation of alpha1 H201A did not affect proton sensitivity. Double, triple or quadruple histidine mutation of these residues caused a further reduction of proton sensitivity, suggesting multiple binding sites for proton action on glycine receptors. Furthermore, the substitution T133A, which mediates Zn(2+) inhibition, virtually abolished the proton effect on peak amplitude and current kinetics of glycine response. Replacement of T with S on position 133 partially restored receptor sensitivity to protons, suggesting the hydroxyl group of residue T133 is essential for proton-mediated modulation. In heteromeric alpha1beta receptors, mutations beta H132A and S156A, which correspond to H109 and T133 of the alpha1 subunit, respectively, also affected proton inhibition. In conclusion, multiple extracellular histidine residues (H107, H109, H215 and H419) and threonine residues of the alpha1 and beta Zn(2+) coordination sites are critical for modulation of the glycine receptor by protons.
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Affiliation(s)
- Zhenglan Chen
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center at Fort Worth, Fort Worth, TX 76107, USA
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42
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Abstract
gamma-Aminobutyric acid (GABA) emerged as a potentially important brain chemical just over 50 years ago, but its significance as a neurotransmitter was not fully realized until over 16 years later. We now know that at least 40% of inhibitory synaptic processing in the mammalian brain uses GABA. Establishing its role as a transmitter was a lengthy process and it seems hard to believe with our current knowledge that there was ever any dispute about its role in the mammalian brain. The detailed information that we now have about the receptors for GABA together with the wealth of agents which facilitate or reduce GABA receptor mechanisms make the prospects for further research very exciting. The emergence of glycine as a transmitter seems relatively painless by comparison to GABA. Perhaps this is appropriate for the simplest of transmitter structures! Its discovery within the spinal cord and brainstem approximately 40 years ago was followed only 2 years later by the proposal that it be conferred with 'neurotransmitter' status. It was another 16 years before the receptor was biochemically isolated. Now it is readily accepted as a vital spinal and supraspinal inhibitory transmitter and we know many details regarding its molecular structure and trafficking around neurones. The pharmacology of these receptors has lagged behind that of GABA. There is not the rich variety of allosteric modulators that we have come to readily associate with GABA receptors and which has provided us with a virtual treasure trove of important drugs used in anxiety, insomnia, epilepsy, anaesthesia, and spasticity, all stemming from the actions of the simple neutral amino acid GABA. Nevertheless, the realization that glycine receptors are involved in motor reflexes and nociceptive pathways together with the more recent advent of drugs that exhibit some subtype selectivity make the goal of designing selective therapeutic ligands for the glycine receptor that much closer.
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Affiliation(s)
- N G Bowery
- GlaxoSmithKline, Biology, PsyCEDD, Verona 37135, Italy.
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Yang Z, Ney A, Cromer BA, Ng HL, Parker MW, Lynch JW. Tropisetron modulation of the glycine receptor: femtomolar potentiation and a molecular determinant of inhibition. J Neurochem 2006; 100:758-69. [PMID: 17181559 DOI: 10.1111/j.1471-4159.2006.04242.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The 5-hydroxytryptamine type-3 receptor antagonist tropisetron is in clinical use as an anti-emetic drug. This compound also exerts both potentiating and inhibitory effects on the glycine receptor chloride channel. The inhibitory effects occur at micromolar concentrations, whereas the potentiating effects are shown here to occur at femtomolar concentrations at the homomeric alpha1 receptor. Potentiation occurred only when tropisetron was applied in the presence of glycine. We also sought to identify molecular determinants of tropisetron inhibition at the alpha1 glycine receptor by serially mutating residues located in or near known ligand-binding sites. We discovered that conservative mutations to N102 ablated tropisetron inhibition without affecting the magnitude or sensitivity of tropisetron potentiation. Several lines of evidence, including a structure-activity analysis of tropisetron, atropine and SB203186, suggest that N102 may bind to the tropisetron tropane nitrogen via H-bonding. Mutation of the N125 residue in the beta subunit, which corresponds to N102 in the alpha1 subunit, had little effect on tropisetron inhibitory potency. These results show that N102 is required for tropisetron inhibition but not potentiation and that inhibitory tropisetron binds in different orientations at different subunit interfaces. To our knowledge, tropisetron is the most exquisitely sensitive modulator yet identified for a cys-loop receptor.
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Affiliation(s)
- Zhe Yang
- School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
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44
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Hirzel K, Müller U, Latal AT, Hülsmann S, Grudzinska J, Seeliger MW, Betz H, Laube B. Hyperekplexia Phenotype of Glycine Receptor α1 Subunit Mutant Mice Identifies Zn2+ as an Essential Endogenous Modulator of Glycinergic Neurotransmission. Neuron 2006; 52:679-90. [PMID: 17114051 DOI: 10.1016/j.neuron.2006.09.035] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2006] [Revised: 08/08/2006] [Accepted: 09/18/2006] [Indexed: 01/09/2023]
Abstract
Zn(2+) is thought to modulate neurotransmission by affecting currents mediated by ligand-gated ion channels and transmitter reuptake by Na(+)-dependent transporter systems. Here, we examined the in vivo relevance of Zn(2+) neuromodulation by producing knockin mice carrying the mutation D80A in the glycine receptor (GlyR) alpha1 subunit gene (Glra1). This substitution selectively eliminates the potentiating effect of Zn(2+) on GlyR currents. Mice homozygous for Glra1(D80A) develop a severe neuromotor phenotype postnatally that resembles forms of human hyperekplexia (startle disease) caused by mutations in GlyR genes. In spinal neurons and brainstem slices from Glra1(D80A) mice, GlyR expression, synaptic localization, and basal glycinergic transmission were normal; however, potentiation of spontaneous glycinergic currents by Zn(2+) was significantly impaired. Thus, the hyperekplexia phenotype of Glra1(D80A) mice is due to the loss of Zn(2+) potentiation of alpha1 subunit containing GlyRs, indicating that synaptic Zn(2+) is essential for proper in vivo functioning of glycinergic neurotransmission.
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Affiliation(s)
- Klaus Hirzel
- Abteilung Neurochemie, Max-Planck-Institut für Hirnforschung, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany
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Betz H, Laube B. Glycine receptors: recent insights into their structural organization and functional diversity. J Neurochem 2006; 97:1600-10. [PMID: 16805771 DOI: 10.1111/j.1471-4159.2006.03908.x] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Strychnine-sensitive glycine receptors (GlyRs) are known to mediate synaptic inhibition in spinal cord, brainstem and other regions of the CNS. During the past 5 years, considerable progress has been made in delineating structural determinants of ligand binding and channel activation in recombinant GlyRs. Furthermore, immunohistochemical and gene inactivation studies have disclosed distinct distributions and functions of differentially expressed GlyR subtypes in retina, hippocampus and the dorsal horn of the spinal cord. Accordingly, GlyRs regulate not only the excitability of motor and sensory neurones, but are also essential for the processing of photoreceptor signals, neuronal development and inflammatory pain sensitization. Hence, these receptors constitute promising targets for the development of clinically useful compounds.
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Affiliation(s)
- Heinrich Betz
- Abteilung Neurochemie, Max-Planck-Institut für Hirnforschung, Frankfurt am Main, Germany.
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46
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Thio LL, Zhang HX. Modulation of inhibitory glycine receptors in cultured embryonic mouse hippocampal neurons by zinc, thiol containing redox agents and carnosine. Neuroscience 2006; 139:1315-27. [PMID: 16515845 DOI: 10.1016/j.neuroscience.2006.01.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Revised: 01/04/2006] [Accepted: 01/21/2006] [Indexed: 11/24/2022]
Abstract
Modulation of inhibitory glycine receptors by zinc (Zn(2+)) and endogenous redox agents such as glutathione may alter inhibition in the mammalian brain. Despite the abundance of Zn(2+) in the hippocampus and its ability to modulate glycine receptors, few studies have examined Zn(2+) modulation of hippocampal glycine receptors. Whether redox agents modulate hippocampal glycine receptors also remains unknown. This study examined Zn(2+) and redox modulation of glycine receptor-mediated currents in cultured embryonic mouse hippocampal neurons using whole-cell recordings. Zn(2+) concentrations below 10 microM potentiated currents elicited by low glycine, beta-alanine, and taurine concentrations by 300-400%. Zn(2+) concentrations above 300 microM produced nearly complete inhibition. Potentiating Zn(2+) concentrations shifted the dose-response curves for the three agonists to the left and decreased the Hill coefficient for glycine and beta-alanine but not taurine. Inhibiting Zn(2+) concentrations shifted the dose-response curves for glycine and beta-alanine to the right but reduced the maximum taurine response. Histidine residues may participate in potentiation because diethyl pyrocarbonate and pH 5.4 diminished Zn(2+) enhancement of glycine currents. pH 5.4 diminished Zn(2+) block of glycine currents, but diethyl pyrocarbonate did not. These findings indicate that separate sites mediate Zn(2+) potentiation and inhibition. The redox agents glutathione, dithiothreitol, tris(2-carboxyethyl)phosphine, and 5,5'-dithiobis(2-nitrobenzoic acid) did not alter glycine currents by a redox mechanism. However, glutathione and dithiothreitol interfered with the effects of Zn(2+) on glycine currents by chelating it. Carnosine had similar effects. Thus, Zn(2+) and thiol containing redox agents that chelate Zn(2+) modulate hippocampal glycine receptors with the mechanism of Zn(2+) modulation being agonist dependent.
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Affiliation(s)
- L L Thio
- Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110, USA.
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47
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Liu Y, Teeter MM, DuRand CJ, Neve KA. Identification of a Zn2+-binding site on the dopamine D2 receptor. Biochem Biophys Res Commun 2006; 339:873-9. [PMID: 16332354 DOI: 10.1016/j.bbrc.2005.11.110] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Accepted: 11/19/2005] [Indexed: 11/21/2022]
Abstract
Zinc (II) modulates the function of many integral membrane proteins. To identify the Zn(2+)-binding site responsible for allosteric modulation of the D(2) dopamine receptor, we first demonstrated that the binding site is likely located in extracellular loops or in transmembrane regions that are accessible from the extracellular milieu. We mutated every histidine in these regions to alanine; two mutants, H394A and H399A, exhibited a reduced response to Zn(2+). Combined mutation of H394 and H399 caused a larger effect of zinc than did either single mutation. Mutation of other potential Zn(2+)-binding residues predicted to be in proximity to H394 or H399 did not substantially alter the potency of Zn(2+). The double mutant H394A/H399A was similar to D(2) in affinity for [(3)H]spiperone and ability to inhibit cyclic AMP accumulation. We conclude that binding of Zn(2+) to H394 and H399 on the dopamine D(2) receptor contributes to allosteric regulation of antagonist binding.
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Affiliation(s)
- Yong Liu
- Department of Behavioral Neuroscience, Oregon Health and Science University, Portland, OR 97239, USA
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48
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Miller PS, Da Silva HMA, Smart TG. Molecular basis for zinc potentiation at strychnine-sensitive glycine receptors. J Biol Chem 2005; 280:37877-84. [PMID: 16144831 DOI: 10.1074/jbc.m508303200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The divalent cation Zn(2+) is a potent potentiator at the strychnine-sensitive glycine receptor (GlyR). This occurs at nanomolar concentrations, which are the predicted endogenous levels of extracellular neuronal Zn(2+). Using structural modeling and functional mutagenesis, we have identified the molecular basis for the elusive Zn(2+) potentiation site on GlyRs and account for the differential sensitivity of GlyR alpha(1) and GlyR alpha(2) to Zn(2+) potentiation. In addition, juxtaposed to this Zn(2+) site, which is located externally on the N-terminal domain of the alpha subunit, another residue was identified in the nearby Cys loop, a region that is critical for receptor gating in all Cys loop ligand-gated ion channels. This residue acted as a key control element in the allosteric transduction pathway for Zn(2+) potentiation, enabling either potentiation or overt inhibition of receptor activation depending upon the moiety resident at this location. Overall, we propose that Zn(2+) binds to a site on the extracellular outer face of the GlyR alpha subunit and exerts its positive allosteric effect via an interaction with the Cys loop to increase the efficacy of glycine receptor gating.
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Affiliation(s)
- Paul S Miller
- Department of Pharmacology, University College London, UK
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Miller PS, Beato M, Harvey RJ, Smart TG. Molecular determinants of glycine receptor alphabeta subunit sensitivities to Zn2+-mediated inhibition. J Physiol 2005; 566:657-70. [PMID: 15905212 PMCID: PMC1464794 DOI: 10.1113/jphysiol.2005.088575] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Glycine receptors exhibit a biphasic sensitivity profile in response to Zn2+-mediated modulation, with low Zn2+ concentrations potentiating (< 10 microm), and higher Zn2+ concentrations inhibiting submaximal responses to glycine. Here, a substantial 30-fold increase in sensitivity to Zn2+-mediated inhibition was apparent for the homomeric glycine receptor (GlyR) alpha1 subunit compared to either GlyR alpha2 or alpha3 subtypes. Swapping the divergent histidine (H107) residue in GlyR alpha1, which together with the conserved H109 forms part of an intersubunit Zn2+-binding site, for the equivalent asparagine residue present in GlyR alpha2 and alpha3, reversed this phenotype. Co-expression of heteromeric GlyR alpha1 or alpha2 with the ancillary beta subunit yielded receptors that maintained their distinctive sensitivities to Zn2+ inhibition. However, GlyR alpha2beta heteromers were consistently 2-fold more sensitive to inhibition compared to the GlyR alpha2 homomer. Comparative studies to elucidate the specific residue in the beta subunit responsible for this differential sensitivity revealed instead threonine 133 in the alpha1 subunit as a new vital component for Zn2+-mediated inhibition. Further studies on heteromeric receptors demonstrated that a mutated beta subunit could indeed affect Zn2+-mediated inhibition but only from one side of the intersubunit Zn2+-binding site, equivalent to the GlyR alpha1 H107 face. This strongly suggests that the alpha subunit is responsible for Zn2+-mediated inhibition and that this is effectively transduced, asymmetrically, from the side of the Zn2+-binding site where H109 and T133 are located.
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Affiliation(s)
- Paul S Miller
- Department of Pharmacology, University College London, Medical Sciences Building, Gower Street, London WC1E 6BT, UK
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Nagaya N, Tittle RK, Saar N, Dellal SS, Hume RI. An intersubunit zinc binding site in rat P2X2 receptors. J Biol Chem 2005; 280:25982-93. [PMID: 15899882 PMCID: PMC1479454 DOI: 10.1074/jbc.m504545200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
P2X receptors are ATP-gated ion channels made up of three similar or identical subunits. It is unknown whether ligand binding is intersubunit or intrasubunit, either for agonists or for allosteric modulators. Zinc binds to rat P2X2 receptors and acts as an allosteric modulator, potentiating channel opening. To probe the location of this zinc binding site, P2X2 receptors bearing mutations of the histidines at positions 120 and 213 were expressed in Xenopus oocytes. Studies of H120C and H213C mutants produced five lines of evidence consistent with the hypothesis that the residues in these positions bind zinc. Mixing of subunits containing the H120A or H213A mutation generated receptors that showed zinc potentiation, even though neither of these mutant receptors showed zinc potentiation on its own. Furthermore, expression of trimeric concatamers with His --> Ala mutations at some but not all six positions showed that zinc potentiation correlated with the number of intersubunit histidine pairs. These results indicate that zinc potentiation requires an interaction across a subunit interface. Expression of the H120C/H213C double mutant resulted in the formation of ectopic disulfide bonds that could be detected by changes in the physiological properties of the receptors after treatment with reducing and oxidizing agents. Immunoblot analysis of H120C/H213C protein separated under nonreducing conditions demonstrated that the ectopic bonds were between adjacent subunits. Taken together, these data indicate that His120 and His213 sit close to each other across the interface between subunits and are likely to be key components of the zinc binding site in P2X2 receptors.
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Affiliation(s)
| | | | | | | | - Richard I. Hume
- Address correspondence to: Richard I. Hume, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 830 N. University Ave., Ann Arbor, MI 48109-1048, Tel. 734-764-7427 ; Fax: 734-647-0884 ; E-mail:
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