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Gimenez-Gomez P, Le T, Martin GE. Modulation of neuronal excitability by binge alcohol drinking. Front Mol Neurosci 2023; 16:1098211. [PMID: 36866357 PMCID: PMC9971943 DOI: 10.3389/fnmol.2023.1098211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 01/19/2023] [Indexed: 02/16/2023] Open
Abstract
Drug use poses a serious threat to health systems throughout the world. The number of consumers rises every year being alcohol the drug of abuse most consumed causing 3 million deaths (5.3% of all deaths) worldwide and 132.6 million disability-adjusted life years. In this review, we present an up-to-date summary about what is known regarding the global impact of binge alcohol drinking on brains and how it affects the development of cognitive functions, as well as the various preclinical models used to probe its effects on the neurobiology of the brain. This will be followed by a detailed report on the state of our current knowledge of the molecular and cellular mechanisms underlying the effects of binge drinking on neuronal excitability and synaptic plasticity, with an emphasis on brain regions of the meso-cortico limbic neurocircuitry.
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Affiliation(s)
- Pablo Gimenez-Gomez
- Department of Neurobiology, University of Massachusetts Chan Medical School, Worcester, MA, United States
- The Brudnick Neuropsychiatric Research Institute, Worcester, MA, United States
| | - Timmy Le
- Department of Neurobiology, University of Massachusetts Chan Medical School, Worcester, MA, United States
- The Brudnick Neuropsychiatric Research Institute, Worcester, MA, United States
- Graduate Program in Neuroscience, Morningside Graduate School of Biomedical Sciences, UMass Chan Medical School, Worcester, MA, United States
| | - Gilles E. Martin
- Department of Neurobiology, University of Massachusetts Chan Medical School, Worcester, MA, United States
- The Brudnick Neuropsychiatric Research Institute, Worcester, MA, United States
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Andrew RD, Hartings JA, Ayata C, Brennan KC, Dawson-Scully KD, Farkas E, Herreras O, Kirov SA, Müller M, Ollen-Bittle N, Reiffurth C, Revah O, Robertson RM, Shuttleworth CW, Ullah G, Dreier JP. The Critical Role of Spreading Depolarizations in Early Brain Injury: Consensus and Contention. Neurocrit Care 2022; 37:83-101. [PMID: 35257321 PMCID: PMC9259543 DOI: 10.1007/s12028-021-01431-w] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 12/29/2021] [Indexed: 02/02/2023]
Abstract
BACKGROUND When a patient arrives in the emergency department following a stroke, a traumatic brain injury, or sudden cardiac arrest, there is no therapeutic drug available to help protect their jeopardized neurons. One crucial reason is that we have not identified the molecular mechanisms leading to electrical failure, neuronal swelling, and blood vessel constriction in newly injured gray matter. All three result from a process termed spreading depolarization (SD). Because we only partially understand SD, we lack molecular targets and biomarkers to help neurons survive after losing their blood flow and then undergoing recurrent SD. METHODS In this review, we introduce SD as a single or recurring event, generated in gray matter following lost blood flow, which compromises the Na+/K+ pump. Electrical recovery from each SD event requires so much energy that neurons often die over minutes and hours following initial injury, independent of extracellular glutamate. RESULTS We discuss how SD has been investigated with various pitfalls in numerous experimental preparations, how overtaxing the Na+/K+ ATPase elicits SD. Elevated K+ or glutamate are unlikely natural activators of SD. We then turn to the properties of SD itself, focusing on its initiation and propagation as well as on computer modeling. CONCLUSIONS Finally, we summarize points of consensus and contention among the authors as well as where SD research may be heading. In an accompanying review, we critique the role of the glutamate excitotoxicity theory, how it has shaped SD research, and its questionable importance to the study of early brain injury as compared with SD theory.
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Affiliation(s)
- R. David Andrew
- grid.410356.50000 0004 1936 8331Queen’s University, Kingston, ON Canada
| | - Jed A. Hartings
- grid.24827.3b0000 0001 2179 9593University of Cincinnati, Cincinnati, OH USA
| | - Cenk Ayata
- grid.38142.3c000000041936754XHarvard Medical School, Harvard University, Boston, MA USA
| | - K. C. Brennan
- grid.223827.e0000 0001 2193 0096The University of Utah, Salt Lake City, UT USA
| | | | - Eszter Farkas
- grid.9008.10000 0001 1016 96251HCEMM-USZ Cerebral Blood Flow and Metabolism Research Group, and the Department of Cell Biology and Molecular Medicine, Faculty of Science and Informatics & Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Oscar Herreras
- grid.419043.b0000 0001 2177 5516Instituto de Neurobiologia Ramon Y Cajal (Consejo Superior de Investigaciones Científicas), Madrid, Spain
| | - Sergei. A. Kirov
- grid.410427.40000 0001 2284 9329Medical College of Georgia, Augusta, GA USA
| | - Michael Müller
- grid.411984.10000 0001 0482 5331University of Göttingen, University Medical Center Göttingen, Göttingen, Germany
| | - Nikita Ollen-Bittle
- grid.39381.300000 0004 1936 8884University of Western Ontario, London, ON Canada
| | - Clemens Reiffurth
- grid.7468.d0000 0001 2248 7639Center for Stroke Research Berlin, Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health; and the Department of Experimental Neurology, Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health., Berlin, Germany
| | - Omer Revah
- grid.168010.e0000000419368956School of Medicine, Stanford University, Stanford, CA USA
| | | | | | - Ghanim Ullah
- grid.170693.a0000 0001 2353 285XUniversity of South Florida, Tampa, FL USA
| | - Jens P. Dreier
- grid.7468.d0000 0001 2248 7639Center for Stroke Research Berlin, Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health; and the Department of Experimental Neurology, Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health., Berlin, Germany
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3
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Petzold GC, Dreier JP. Spreading depolarization evoked by endothelin-1 is inhibited by octanol but not by carbenoxolone. BRAIN HEMORRHAGES 2021. [DOI: 10.1016/j.hest.2020.08.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Morel C, Montgomery S, Han MH. Nicotine and alcohol: the role of midbrain dopaminergic neurons in drug reinforcement. Eur J Neurosci 2019; 50:2180-2200. [PMID: 30251377 PMCID: PMC6431587 DOI: 10.1111/ejn.14160] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2018] [Revised: 07/31/2018] [Accepted: 08/20/2018] [Indexed: 12/11/2022]
Abstract
Nicotine and alcohol addiction are leading causes of preventable death worldwide and continue to constitute a huge socio-economic burden. Both nicotine and alcohol perturb the brain's mesocorticolimbic system. Dopamine (DA) neurons projecting from the ventral tegmental area (VTA) to multiple downstream structures, including the nucleus accumbens, prefrontal cortex, and amygdala, are highly involved in the maintenance of healthy brain function. VTA DA neurons play a crucial role in associative learning and reinforcement. Nicotine and alcohol usurp these functions, promoting reinforcement of drug taking behaviors. In this review, we will first describe how nicotine and alcohol individually affect VTA DA neurons by examining how drug exposure alters the heterogeneous VTA microcircuit and network-wide projections. We will also examine how coadministration or previous exposure to nicotine or alcohol may augment the reinforcing effects of the other. Additionally, this review briefly summarizes the role of VTA DA neurons in nicotine, alcohol, and their synergistic effects in reinforcement and also addresses the remaining questions related to the circuit-function specificity of the dopaminergic system in mediating nicotine/alcohol reinforcement and comorbidity.
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Affiliation(s)
- Carole Morel
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Center for Affective Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Sarah Montgomery
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Center for Affective Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Ming-Hu Han
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Center for Affective Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
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5
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Segal D, Bale AS, Phillips LJ, Sasso A, Schlosser PM, Starkey C, Makris SL. Issues in assessing the health risks of n-butanol. J Appl Toxicol 2019; 40:72-86. [PMID: 31231852 DOI: 10.1002/jat.3820] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Revised: 04/18/2019] [Accepted: 04/18/2019] [Indexed: 01/25/2023]
Abstract
A literature review and health effects evaluation were conducted for n-butanol, a chemical that occurs naturally in some foods, which is an intermediate in the production of butyl esters and can be used as a gasoline additive or blend. Studies evaluating n-butyl acetate were included in the review as n-butyl acetate is rapidly converted to n-butanol following multiple routes of exposure. The primary n-butanol health effects identified were developmental and nervous system endpoints. In conducting the literature review and evaluating study findings, the following observations were made: (1) developmental findings were consistently identified; (2) neurodevelopmental findings were inconsistent; (3) evidence for nervous system effects was weak; (4) comparing internal doses from oral and inhalation exposures using physiologically based pharmacokinetic models introduces uncertainties; and (5) a lack of mechanistic information for n-butanol resulted in the reliance on mechanistic data for ethanol, which may or may not be applicable to n-butanol. This paper presents findings from a literature review on the health effects of n-butanol and proposes research to help reduce uncertainty that exists due to database limitations.
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Affiliation(s)
- Deborah Segal
- EPA Office of Research and Development (ORD), National Center for Environmental Assessment (NCEA), Washington, DC
| | - Ambuja S Bale
- EPA Office of Research and Development (ORD), National Center for Environmental Assessment (NCEA), Washington, DC
| | - Linda J Phillips
- EPA Office of Research and Development (ORD), National Center for Environmental Assessment (NCEA), Washington, DC
| | - Alan Sasso
- EPA Office of Research and Development (ORD), National Center for Environmental Assessment (NCEA), Washington, DC
| | | | - C Starkey
- Formerly ORISE Research Fellow at EPA,, Alexandria, Virginia
| | - Susan L Makris
- EPA Office of Research and Development (ORD), National Center for Environmental Assessment (NCEA), Washington, DC
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6
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Viswanathan A, Zhurina A, Assoah B, Paakkunainen A, Musa A, Kute D, Saravanan KM, Yli-Harja O, Candeias NR, Kandhavelu M. Decane-1,2-diol derivatives as potential antitumor agents for the treatment of glioblastoma. Eur J Pharmacol 2018; 837:105-116. [PMID: 30179612 DOI: 10.1016/j.ejphar.2018.08.041] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Revised: 08/29/2018] [Accepted: 08/30/2018] [Indexed: 12/20/2022]
Abstract
Glioblastoma remains the most common and aggressive type of malignant brain tumor among adults thus, considerable attention has been given to discovery of novel anti-tumor drugs for its treatment. This study reports the synthesis of a series of twelve novel decane-1,2-diol derivatives and evaluation of its anti-tumor activity in mammalian glioblastoma cell lines, U87 and LN229. Starting from decane-1,2-diol, several derivatives were prepared using a diversity oriented synthesis approach through which a small library composed of esters, silyl ethers, sulfonates, sulfites, sulfates, ketals, and phosphonates was built. The decane-1,2-diol ditosylated derivative, DBT, found to have higher cytotoxicity than the standard drug cisplatin, has IC50 value of 52 µM in U87 and 270 µM in LN229. Migration analysis of U87 cell line treated with the DBT indicated its ability to effectively suppress proliferation during initial hours of treatment and decrease anti-proliferative property over time. Additionally, DBT was assessed for its role in apoptosis, oxidative stress and caspase 3/7 activation in U87. Interestingly, our experiments indicated that its cytotoxicity is independent of Reactive oxygen species induced caspase 3/7 activity. The compound also exhibited caspase independent apoptosis activity in U87. DBT treatment led to G1/S cell cycle arrest and apoptosis induction of glioma cell lines. In addition, we identified 1533 genes with significant changes at the transcriptional level, in response to DBT. A molecular docking study accounting for the interaction of DBT with NMDA receptor disclosed several hydrogen bonds and charged residue interactions with 17 amino acids, which might be the basis of the DBT cytotoxicity observed. We conclude that this molecule exerts its cytotoxicity via caspase 3/7 independent pathways in glioblastoma cells. Concisely, simple decane-1,2-diol derivatives might serve as scaffolds for the development of effective anti-glioblastoma agents.
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Affiliation(s)
- Anisha Viswanathan
- Molecular Signaling Lab, Computational Systems Biology Research Group, BioMediTech and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland
| | - Anastasia Zhurina
- Molecular Signaling Lab, Computational Systems Biology Research Group, BioMediTech and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland
| | - Benedicta Assoah
- Laboratory of Chemistry and Bioengineering, Tampere University of Technology, Korkeakoulunkatu 8, 33101 Tampere, Finland
| | - Aleksi Paakkunainen
- Laboratory of Chemistry and Bioengineering, Tampere University of Technology, Korkeakoulunkatu 8, 33101 Tampere, Finland
| | - Aliyu Musa
- Predictive Medicine and Data Analytics Lab, Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland
| | - Dinesh Kute
- Molecular Signaling Lab, Computational Systems Biology Research Group, BioMediTech and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland
| | - Konda Mani Saravanan
- Centre of Advanced Study in Crystallography & Biophysics, University of Madras, Chennai 600025, India
| | - Olli Yli-Harja
- Molecular Signaling Lab, Computational Systems Biology Research Group, BioMediTech and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland; Institute for Systems Biology, 1441N 34th Street, Seattle, WA 98103-8904, USA
| | - Nuno R Candeias
- Laboratory of Chemistry and Bioengineering, Tampere University of Technology, Korkeakoulunkatu 8, 33101 Tampere, Finland.
| | - Meenakshisundaram Kandhavelu
- Molecular Signaling Lab, Computational Systems Biology Research Group, BioMediTech and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland.
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Li C, Dinu V. miR2Pathway: A novel analytical method to discover MicroRNA-mediated dysregulated pathways involved in hepatocellular carcinoma. J Biomed Inform 2018; 81:31-40. [PMID: 29578099 DOI: 10.1016/j.jbi.2018.03.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2017] [Revised: 02/10/2018] [Accepted: 03/21/2018] [Indexed: 10/17/2022]
Abstract
MicroRNAs (miRNAs) are small, non-coding RNAs involved in the regulation of gene expression at a post-transcriptional level. Recent studies have shown miRNAs as key regulators of a variety of biological processes, such as proliferation, differentiation, apoptosis, metabolism, etc. Aberrantly expressed miRNAs influence individual gene expression level, but rewired miRNA-mRNA connections can influence the activity of biological pathways. Here, we define rewired miRNA-mRNA connections as the differential (rewiring) effects on the activity of biological pathways between hepatocellular carcinoma (HCC) and normal phenotypes. Our work presented here uses a PageRank-based approach to measure the degree of miRNA-mediated dysregulation of biological pathways between HCC and normal samples based on rewired miRNA-mRNA connections. In our study, we regard the degree of miRNA-mediated dysregulation of biological pathways as disease risk of biological pathways. Therefore, we propose a new method, miR2Pathway, to measure and rank the degree of miRNA-mediated dysregulation of biological pathways by measuring the total differential influence of miRNAs on the activity of pathways between HCC and normal states. miR2Pathway proposed here systematically shows the first evidence for a mechanism of biological pathways being dysregulated by rewired miRNA-mRNA connections, and provides new insight into exploring mechanisms behind HCC. Thus, miR2Pathway is a novel method to identify and rank miRNA-dysregulated pathways in HCC.
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Affiliation(s)
- Chaoxing Li
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
| | - Valentin Dinu
- Department of Biomedical Informatics, Arizona State University, Scottsdale, AZ 85255, USA.
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8
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Raškevičius V, Jotautis V, Rimkutė L, Marandykina A, Kazokaitė M, Kairys V, Skeberdis VA. Molecular basis for potentiation of Cx36 gap junction channel conductance by n-alcohols and general anesthetics. Biosci Rep 2018; 38:BSR20171323. [PMID: 29298877 PMCID: PMC5803492 DOI: 10.1042/bsr20171323] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Revised: 12/22/2017] [Accepted: 01/01/2018] [Indexed: 01/01/2023] Open
Abstract
In our recent study, we have demonstrated that short carbon chain n-alcohols (up to octanol) stimulated while long carbon chain n-alcohols inhibited the conductance of connexin (Cx) 36 (Cx36) gap junction (GJ) channels. In contrast, GJ channels composed of other types of Cxs all were inhibited by n-alcohols independent of their carbon chain length. To identify the putative structural domains of Cx36, responsible for the dual effect of n-alcohols, we performed structural modeling of Cx36 protein docking with hexanol and isoflurane that stimulated as well as nonanol and carbenoxolone that inhibited the conductance of Cx36 GJs and revealed their multiple common docking sites and a single pocket accessible only to hexanol and isoflurane. The pocket is located in the vicinity of three unique cysteine residues, namely C264 in the fourth, and C92 and C87 in the second transmembrane domain of the neighboring Cx36 subunits. To examine the hypothesis that disulphide bonding might be involved in the stimulatory effect of hexanol and isoflurane, we generated cysteine substitutions in Cx36 and demonstrated by a dual whole-cell patch-clamp technique that in HeLa (human cervix carcinoma cell line) and N2A (mouse neuroblastoma cell line) cells these mutations reversed the stimulatory effect of hexanol and isoflurane to inhibitory one, typical of other Cxs that lack respective cysteines and a specific docking pocket for these compounds. Our findings suggest that the stimulatory effect of hexanol and isoflurane on Cx36 GJ conductance could be achieved by re-shuffling of the inter-subunit disulphide bond between C264 and C92 to the intra-subunit one between C264 and C87.
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Affiliation(s)
- Vytautas Raškevičius
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Vaidas Jotautis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Lina Rimkutė
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Alina Marandykina
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Mintautė Kazokaitė
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Visvaldas Kairys
- Institute of Biotechnology, Vilnius University, Vilnius LT-10257, Lithuania
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Chen YH, Ge CL, Wang H, Ge MH, He QQ, Zhang Y, Tian W, Wu ZX. GCY-35/GCY-36-TAX-2/TAX-4 Signalling in O 2 Sensory Neurons Mediates Acute Functional Ethanol Tolerance in Caenorhabditis elegans. Sci Rep 2018; 8:3020. [PMID: 29445226 PMCID: PMC5813177 DOI: 10.1038/s41598-018-20477-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 01/18/2018] [Indexed: 11/29/2022] Open
Abstract
Ethanol is a widely used beverage and abused drug. Alcoholism causes severe damage to human health and creates serious social problems. Understanding the mechanisms underlying ethanol actions is important for the development of effective therapies. Alcohol has a wide spectrum of effects on physiological activities and behaviours, from sensitization to sedation and even intoxication with increasing concentrations. Animals develop tolerance to ethanol. However, the underlying mechanisms are not well understood. In Caenorhabditis elegans, NPR-1 negatively regulates the development of acute tolerance to ethanol. Here, using in vivo Ca2+ imaging, behavioural tests and chemogenetic manipulation, we show that the soluble guanylate cyclase complex GCY-35/GCY-36-TAX-2/TAX-4 signalling pathway in O2 sensory neurons positively regulates acute functional tolerance in npr-1 worms.
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Affiliation(s)
- Yuan-Hua Chen
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
| | - Chang-Li Ge
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
| | - Hong Wang
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
| | - Ming-Hai Ge
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
| | - Qing-Qin He
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
| | - Yu Zhang
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
| | - Wei Tian
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
| | - Zheng-Xing Wu
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Department of Biophysics and Molecular Physiology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China.
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Chandler CM, Overton JS, Rüedi-Bettschen D, Platt DM. GABA A Receptor Subtype Mechanisms and the Abuse-Related Effects of Ethanol: Genetic and Pharmacological Evidence. Handb Exp Pharmacol 2018; 248:3-27. [PMID: 29204713 DOI: 10.1007/164_2017_80] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Ethanol's reinforcing and subjective effects, as well as its ability to induce relapse, are powerful factors contributing to its widespread use and abuse. A significant mediator of these behavioral effects is the GABAA receptor system. GABAA receptors are the target for γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the CNS. Structurally, they are pentameric, transmembrane chloride ion channels comprised of subunits from at least eight different families of distinct proteins. The contribution of different GABAA subunits to ethanol's diverse abuse-related effects is not clear and remains an area of research focus. This chapter details the clinical and preclinical findings supporting roles for different α, β, γ, and δ subunit-containing GABAA receptors in ethanol's reinforcing, subjective/discriminative stimulus, and relapse-inducing effects. The reinforcing properties of ethanol have been studied the most systematically, and convergent preclinical evidence suggests a key role for the α5 subunit in those effects. Regarding ethanol's subjective/discriminative stimulus effects, clinical and genetic findings support a primary role for the α2 subunit, whereas preclinical evidence implicates the α5 subunit. At present, too few studies investigating ethanol relapse exist to make any solid conclusions regarding the role of specific GABAA subunits in this abuse-related effect.
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Affiliation(s)
- Cassie M Chandler
- Graduate Program in Neuroscience, University of Mississippi Medical Center, Jackson, MS, USA
| | - John S Overton
- Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson, MS, USA
| | - Daniela Rüedi-Bettschen
- Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson, MS, USA
| | - Donna M Platt
- Graduate Program in Neuroscience, University of Mississippi Medical Center, Jackson, MS, USA.
- Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson, MS, USA.
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11
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Willebrords J, Maes M, Crespo Yanguas S, Vinken M. Inhibitors of connexin and pannexin channels as potential therapeutics. Pharmacol Ther 2017; 180:144-160. [PMID: 28720428 PMCID: PMC5802387 DOI: 10.1016/j.pharmthera.2017.07.001] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
While gap junctions support the exchange of a number of molecules between neighboring cells, connexin hemichannels provide communication between the cytosol and the extracellular environment of an individual cell. The latter equally holds true for channels composed of pannexin proteins, which display an architecture reminiscent of connexin hemichannels. In physiological conditions, gap junctions are usually open, while connexin hemichannels and, to a lesser extent, pannexin channels are typically closed, yet they can be activated by a number of pathological triggers. Several agents are available to inhibit channels built up by connexin and pannexin proteins, including alcoholic substances, glycyrrhetinic acid, anesthetics and fatty acids. These compounds not always strictly distinguish between gap junctions, connexin hemichannels and pannexin channels, and may have effects on other targets as well. An exception lies with mimetic peptides, which reproduce specific amino acid sequences in connexin or pannexin primary protein structure. In this paper, a state-of-the-art overview is provided on inhibitors of cellular channels consisting of connexins and pannexins with specific focus on their mode-of-action and therapeutic potential.
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Affiliation(s)
- Joost Willebrords
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium
| | - Michaël Maes
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium
| | - Sara Crespo Yanguas
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium
| | - Mathieu Vinken
- Department of In Vitro Toxicology and Dermato-cosmetology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Laarbeeklaan 103, Brussels, Belgium.
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Marin-Lahoz J, Gironell A. Linking Essential Tremor to the Cerebellum: Neurochemical Evidence. THE CEREBELLUM 2017; 15:243-52. [PMID: 26498765 DOI: 10.1007/s12311-015-0735-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The pathophysiology and the exact anatomy of essential tremor (ET) is not well known. One of the pillars that support the cerebellum as the main anatomical locus in ET is neurochemistry. This review examines the link between neurochemical abnormalities found in ET and cerebellum. The review is based on published data about neurochemical abnormalities described in ET both in human and in animal studies. We try to link those findings with cerebellum. γ-aminobutyric acid (GABA) is the main neurotransmitter involved in the pathophysiology of ET. There are several studies about GABA that clearly points to a main role of the cerebellum. There are few data about other neurochemical abnormalities in ET. These include studies with noradrenaline, glutamate, adenosine, proteins, and T-type calcium channels. One single study reveals high levels of noradrenaline in the cerebellar cortex. Another study about serotonin neurotransmitter results negative for cerebellum involvement. Finally, studies on T-type calcium channels yield positive results linking the rhythmicity of ET and cerebellum. Neurochemistry supports the cerebellum as the main anatomical locus in ET. The main neurotransmitter involved is GABA, and the GABA hypothesis remains the most robust pathophysiological theory of ET to date. However, this hypothesis does not rule out other mechanisms and may be seen as the main scaffold to support findings in other systems. We clearly need to perform more studies about neurochemistry in ET to better understand the relations among the diverse systems implied in ET. This is mandatory to develop more effective pharmacological therapies.
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Affiliation(s)
- Juan Marin-Lahoz
- Movement Disorders Unit, Department of Neurology, Hospital de la Santa Creu i Sant Pau, Autonomous University of Barcelona, Av.Sant Antoni Maria Claret, 167, 08025, Barcelona, Catalonia, Spain
| | - Alexandre Gironell
- Movement Disorders Unit, Department of Neurology, Hospital de la Santa Creu i Sant Pau, Autonomous University of Barcelona, Av.Sant Antoni Maria Claret, 167, 08025, Barcelona, Catalonia, Spain.
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Chen Q, Wells MM, Tillman TS, Kinde MN, Cohen A, Xu Y, Tang P. Structural Basis of Alcohol Inhibition of the Pentameric Ligand-Gated Ion Channel ELIC. Structure 2016; 25:180-187. [PMID: 27916519 DOI: 10.1016/j.str.2016.11.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 09/30/2016] [Accepted: 11/07/2016] [Indexed: 11/18/2022]
Abstract
The structural basis for alcohol modulation of neuronal pentameric ligand-gated ion channels (pLGICs) remains elusive. We determined an inhibitory mechanism of alcohol on the pLGIC Erwinia chrysanthemi (ELIC) through direct binding to the pore. X-ray structures of ELIC co-crystallized with 2-bromoethanol, in both the absence and presence of agonist, reveal 2-bromoethanol binding in the pore near T237(6') and the extracellular domain (ECD) of each subunit at three different locations. Binding to the ECD does not appear to contribute to the inhibitory action of 2-bromoethanol and ethanol as indicated by the same functional responses of wild-type ELIC and mutants. In contrast, the ELIC-α1β3GABAAR chimera, replacing the ELIC transmembrane domain (TMD) with the TMD of α1β3GABAAR, is potentiated by 2-bromoethanol and ethanol. The results suggest a dominant role of the TMD in modulating alcohol effects. The X-ray structures and functional measurements support a pore-blocking mechanism for inhibitory action of short-chain alcohols.
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Affiliation(s)
- Qiang Chen
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Marta M Wells
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Computational and System Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Tommy S Tillman
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Monica N Kinde
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Aina Cohen
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Yan Xu
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA; Department of Structural Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Pei Tang
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA; Department of Computational and System Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA.
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Desai R, Savechenkov PY, Zolkowska D, Ge RL, Rogawski MA, Bruzik KS, Forman SA, Raines DE, Miller KW. Contrasting actions of a convulsant barbiturate and its anticonvulsant enantiomer on the α1 β3 γ2L GABAA receptor account for their in vivo effects. J Physiol 2016; 593:4943-61. [PMID: 26378885 DOI: 10.1113/jp270971] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 09/11/2015] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Most barbiturates are anaesthetics but unexpectedly a few are convulsants whose mechanism of action is poorly understood. We synthesized and characterized a novel pair of chiral barbiturates that are capable of photolabelling their binding sites on GABAA receptors. In mice the S-enantiomer is a convulsant, but the R-enantiomer is an anticonvulsant. The convulsant S-enantiomer binds solely at an inhibitory site. It is both an open state inhibitor and a resting state inhibitor. Its action is pH independent, suggesting the pyrimidine ring plays little part in binding. The inhibitory site is not enantioselective because the R-enantiomer inhibits with equal affinity. In contrast, only the anticonvulsant R-enantiomer binds to the enhancing site on open channels, causing them to stay open longer. The enhancing site is enantioselective. The in vivo actions of the convulsant S-enantiomer are accounted for by its interactions with GABAA receptors. ABSTRACT Most barbiturates are anaesthetics but a few unexpectedly are convulsants. We recently located the anaesthetic sites on GABAA receptors (GABAA Rs) by photolabelling with an anaesthetic barbiturate. To apply the same strategy to locate the convulsant sites requires the creation and mechanistic characterization of a suitable agent. We synthesized enantiomers of a novel, photoactivable barbiturate, 1-methyl-5-propyly-5-(m-trifluoromethyldiazirinyl) phenyl barbituric acid (mTFD-MPPB). In mice, S-mTFD-MPPB acted as a convulsant, whereas R-mTFD-MPPB acted as an anticonvulsant. Using patch clamp electrophysiology and fast solution exchange on recombinant human α1 β3 γ2L GABAA Rs expressed in HEK cells, we found that S-mTFD-MPPB inhibited GABA-induced currents, whereas R-mTFD-MPPB enhanced them. S-mTFD-MPPB caused inhibition by binding to either of two inhibitory sites on open channels with bimolecular kinetics. It also inhibited closed, resting state receptors at similar concentrations, decreasing the channel opening rate and shifting the GABA concentration-response curve to the right. R-mTFD-MPPB, like most anaesthetics, enhanced receptor gating by rapidly binding to allosteric sites on open channels, initiating a rate-limiting conformation change to stabilized open channel states. These states had slower closing rates, thus shifting the GABA concentration-response curve to the left. Under conditions when most GABAA Rs were open, an inhibitory action of R-mTFD-MPPB was revealed that had a similar IC50 to that of S-mTFD-MPPB. Thus, the inhibitory sites are not enantioselective, and the convulsant action of S-mTFD-MPPB results from its negligible affinity for the enhancing, anaesthetic sites. Interactions with these two classes of barbiturate binding sites on GABAA Rs underlie the enantiomers' different pharmacological activities in mice.
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Affiliation(s)
- Rooma Desai
- Department of Anaesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Pavel Y Savechenkov
- Deparment of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Dorota Zolkowska
- Department of Neurology, School of Medicine, University of California, Davis, Sacramento, CA, 95817, USA
| | - Ri Le Ge
- Department of Anaesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Michael A Rogawski
- Department of Neurology, School of Medicine, University of California, Davis, Sacramento, CA, 95817, USA
| | - Karol S Bruzik
- Deparment of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Stuart A Forman
- Department of Anaesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Douglas E Raines
- Department of Anaesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Keith W Miller
- Department of Anaesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, 02115, USA
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15
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Heusser SA, Yoluk Ö, Klement G, Riederer EA, Lindahl E, Howard RJ. Functional characterization of neurotransmitter activation and modulation in a nematode model ligand-gated ion channel. J Neurochem 2016; 138:243-53. [PMID: 27102368 DOI: 10.1111/jnc.13644] [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: 11/20/2015] [Revised: 03/21/2016] [Accepted: 04/07/2016] [Indexed: 11/29/2022]
Abstract
The superfamily of pentameric ligand-gated ion channels includes neurotransmitter receptors that mediate fast synaptic transmission in vertebrates, and are targets for drugs including alcohols, anesthetics, benzodiazepines, and anticonvulsants. However, the mechanisms of ion channel opening, gating, and modulation in these receptors leave many open questions, despite their pharmacological importance. Subtle conformational changes in both the extracellular and transmembrane domains are likely to influence channel opening, but have been difficult to characterize given the limited structural data available for human membrane proteins. Recent crystal structures of a modified Caenorhabditis elegans glutamate-gated chloride channel (GluCl) in multiple states offer an appealing model system for structure-function studies. However, the pharmacology of the crystallographic GluCl construct is not well established. To establish the functional relevance of this system, we used two-electrode voltage-clamp electrophysiology in Xenopus oocytes to characterize activation of crystallographic and native-like GluCl constructs by L-glutamate and ivermectin. We also tested modulation by ethanol and other anesthetic agents, and used site-directed mutagenesis to explore the role of a region of Loop F which was implicated in ligand gating by molecular dynamics simulations. Our findings indicate that the crystallographic construct functionally models concentration-dependent agonism and allosteric modulation of pharmacologically relevant receptors. Specific substitutions at residue Leu174 in loop F altered direct L-glutamate activation, consistent with computational evidence for this region's role in ligand binding. These insights demonstrate conservation of activation and modulation properties in this receptor family, and establish a framework for GluCl as a model system, including new possibilities for drug discovery. In this study, we elucidate the validity of a modified glutamate-gated chloride channel (GluClcryst ) as a structurally accessible model for GABAA receptors. In contrast to native-like controls, GluClcryst exhibits classical activation by its neurotransmitter ligand L-glutamate. The modified channel is also sensitive to allosteric modulators associated with human GABAA receptors, and to site-directed mutations predicted to alter channel opening.
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Affiliation(s)
- Stephanie A Heusser
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Özge Yoluk
- Swedish e-Science Research Center, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Göran Klement
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Erika A Riederer
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, USA
| | - Erik Lindahl
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden.,Swedish e-Science Research Center, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Rebecca J Howard
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, USA
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Brosnan RJ, Pham TL. Hydrocarbon molar water solubility predicts NMDA vs. GABAA receptor modulation. BMC Pharmacol Toxicol 2014; 15:62. [PMID: 25410726 PMCID: PMC4247779 DOI: 10.1186/2050-6511-15-62] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 11/13/2014] [Indexed: 12/02/2022] Open
Abstract
Background Many anesthetics modulate 3-transmembrane (such as NMDA) and 4-transmembrane (such as GABAA) receptors. Clinical and experimental anesthetics exhibiting receptor family specificity often have low water solubility. We hypothesized that the molar water solubility of a hydrocarbon could be used to predict receptor modulation in vitro. Methods GABAA (α1β2γ2s) or NMDA (NR1/NR2A) receptors were expressed in oocytes and studied using standard two-electrode voltage clamp techniques. Hydrocarbons from 14 different organic functional groups were studied at saturated concentrations, and compounds within each group differed only by the carbon number at the ω-position or within a saturated ring. An effect on GABAA or NMDA receptors was defined as a 10% or greater reversible current change from baseline that was statistically different from zero. Results Hydrocarbon moieties potentiated GABAA and inhibited NMDA receptor currents with at least some members from each functional group modulating both receptor types. A water solubility cut-off for NMDA receptors occurred at 1.1 mM with a 95% CI = 0.45 to 2.8 mM. NMDA receptor cut-off effects were not well correlated with hydrocarbon chain length or molecular volume. No cut-off was observed for GABAA receptors within the solubility range of hydrocarbons studied. Conclusions Hydrocarbon modulation of NMDA receptor function exhibits a molar water solubility cut-off. Differences between unrelated receptor cut-off values suggest that the number, affinity, or efficacy of protein-hydrocarbon interactions at these sites likely differ.
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Affiliation(s)
- Robert J Brosnan
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
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17
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Franklin KM, Asatryan L, Jakowec MW, Trudell JR, Bell RL, Davies DL. P2X4 receptors (P2X4Rs) represent a novel target for the development of drugs to prevent and/or treat alcohol use disorders. Front Neurosci 2014; 8:176. [PMID: 25009459 PMCID: PMC4068020 DOI: 10.3389/fnins.2014.00176] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2014] [Accepted: 06/05/2014] [Indexed: 12/19/2022] Open
Abstract
Alcohol use disorders (AUDs) have a staggering socioeconomic impact. Few therapeutic options are available, and they are largely inadequate. These shortcomings highlight the urgent need to develop effective medications to prevent and/or treat AUDs. A critical barrier is the lack of information regarding the molecular target(s) by which ethanol (EtOH) exerts its pharmacological activity. This review highlights findings implicating P2X4 receptors (P2X4Rs) as a target for the development of therapeutics to treat AUDs and discusses the use of ivermectin (IVM) as a potential clinical tool for treatment of AUDs. P2XRs are a family of ligand-gated ion channels (LGICs) activated by extracellular ATP. Of the P2XR subtypes, P2X4Rs are expressed the most abundantly in the CNS. Converging evidence suggests that P2X4Rs are involved in the development and progression of AUDs. First, in vitro studies report that pharmacologically relevant EtOH concentrations can negatively modulate ATP-activated currents. Second, P2X4Rs in the mesocorticolimbic dopamine system are thought to play a role in synaptic plasticity and are located ideally to modulate brain reward systems. Third, alcohol-preferring (P) rats have lower functional expression of the p2rx4 gene than alcohol-non-preferring (NP) rats suggesting an inverse relationship between alcohol intake and P2X4R expression. Similarly, whole brain p2rx4 expression has been shown to relate inversely to innate 24 h alcohol preference across 28 strains of rats. Fourth, mice lacking the p2rx4 gene drink more EtOH than wildtype controls. Fifth, IVM, a positive modulator of P2X4Rs, antagonizes EtOH-mediated inhibition of P2X4Rs in vitro and reduces EtOH intake and preference in vivo. These findings suggest that P2X4Rs contribute to EtOH intake. The present review summarizes recent findings focusing on the P2X4R as a molecular target of EtOH action, its role in EtOH drinking behavior and modulation of its activity by IVM as a potential therapy for AUDs.
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Affiliation(s)
- Kelle M Franklin
- Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine Indianapolis, IN, USA
| | - Liana Asatryan
- Titus Family Department of Clinical Pharmacy and Pharmaceutical Economics and Policy, School of Pharmacy, University of Southern California Los Angeles, CA, USA
| | - Michael W Jakowec
- Department of Neurology, University of Southern California Los Angeles, CA, USA
| | - James R Trudell
- Beckman Program for Molecular and Genetic Medicine, Department of Anesthesia, Stanford University Palo Alto, CA, USA
| | - Richard L Bell
- Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine Indianapolis, IN, USA
| | - Daryl L Davies
- Titus Family Department of Clinical Pharmacy and Pharmaceutical Economics and Policy, School of Pharmacy, University of Southern California Los Angeles, CA, USA
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18
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An alcohol-sensing site in the calcium- and voltage-gated, large conductance potassium (BK) channel. Proc Natl Acad Sci U S A 2014; 111:9313-8. [PMID: 24927535 DOI: 10.1073/pnas.1317363111] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Ethanol alters BK (slo1) channel function leading to perturbation of physiology and behavior. Site(s) and mechanism(s) of ethanol-BK channel interaction are unknown. We demonstrate that ethanol docks onto a water-accessible site that is strategically positioned between the slo1 calcium-sensors and gate. Ethanol only accesses this site in presence of calcium, the BK channel's physiological agonist. Within the site, ethanol hydrogen-bonds with K361. Moreover, substitutions that hamper hydrogen bond formation or prevent ethanol from accessing K361 abolish alcohol action without altering basal channel function. Alcohol interacting site dimensions are approximately 10.7 × 8.6 × 7.1 Å, accommodating effective (ethanol-heptanol) but not ineffective (octanol, nonanol) channel activators. This study presents: (i) to our knowledge, the first identification and characterization of an n-alkanol recognition site in a member of the voltage-gated TM6 channel superfamily; (ii) structural insights on ethanol allosteric interactions with ligand-gated ion channels; and (iii) a first step for designing agents that antagonize BK channel-mediated alcohol actions without perturbing basal channel function.
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19
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Wyatt LR, Finn DA, Khoja S, Yardley MM, Asatryan L, Alkana RL, Davies DL. Contribution of P2X4 receptors to ethanol intake in male C57BL/6 mice. Neurochem Res 2014; 39:1127-39. [PMID: 24671605 DOI: 10.1007/s11064-014-1271-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Revised: 02/15/2014] [Accepted: 02/26/2014] [Indexed: 11/26/2022]
Abstract
P2X receptors (P2XRs) are a family of cation-permeable ligand-gated ion channels activated by synaptically released extracellular adenosine 5'-triphosphate. The P2X4 subtype is abundantly expressed in the central nervous system and is sensitive to low intoxicating ethanol concentrations. Genetic meta-analyses identified the p2rx4 gene as a candidate gene for innate alcohol intake and/or preference. The current study used mice lacking the p2rx4 gene (knockout, KO) and wildtype (WT) C57BL/6 controls to test the hypothesis that P2X4Rs contribute to ethanol intake. The early acquisition and early maintenance phases of ethanol intake were measured with three different drinking procedures. Further, we tested the effects of ivermectin (IVM), a drug previously shown to reduce ethanol's effects on P2X4Rs and to reduce ethanol intake and preference, for its ability to differentially alter stable ethanol intake in KO and WT mice. Depending on the procedure and the concentration of the ethanol solution, ethanol intake was transiently increased in P2X4R KO versus WT mice during the acquisition of 24-h and limited access ethanol intake. IVM significantly reduced ethanol intake in P2X4R KO and WT mice, but the degree of reduction was 50 % less in the P2X4R KO mice. Western blot analysis identified significant changes in γ-aminobutyric acidA receptor α1 subunit expression in brain regions associated with the regulation of ethanol behaviors in P2X4R KO mice. These findings add to evidence that P2X4Rs contribute to ethanol intake and indicate that there is a complex interaction between P2X4Rs, ethanol, and other neurotransmitter receptor systems.
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Affiliation(s)
- Letisha R Wyatt
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA, 90033, USA
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20
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Howard RJ, Trudell JR, Harris RA. Seeking structural specificity: direct modulation of pentameric ligand-gated ion channels by alcohols and general anesthetics. Pharmacol Rev 2014; 66:396-412. [PMID: 24515646 PMCID: PMC3973611 DOI: 10.1124/pr.113.007468] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Alcohols and other anesthetic agents dramatically alter neurologic function in a wide range of organisms, yet their molecular sites of action remain poorly characterized. Pentameric ligand-gated ion channels, long implicated in important direct effects of alcohol and anesthetic binding, have recently been illuminated in renewed detail thanks to the determination of atomic-resolution structures of several family members from lower organisms. These structures provide valuable models for understanding and developing anesthetic agents and for allosteric modulation in general. This review surveys progress in this field from function to structure and back again, outlining early evidence for relevant modulation of pentameric ligand-gated ion channels and the development of early structural models for ion channel function and modulation. We highlight insights and challenges provided by recent crystal structures and resulting simulations, as well as opportunities for translation of these newly detailed models back to behavior and therapy.
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Affiliation(s)
- Rebecca J Howard
- Department of Chemistry, Skidmore College, Saratoga Springs, NY 12866.
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21
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Structural basis for potentiation by alcohols and anaesthetics in a ligand-gated ion channel. Nat Commun 2013; 4:1697. [PMID: 23591864 DOI: 10.1038/ncomms2682] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 02/28/2013] [Indexed: 01/28/2023] Open
Abstract
Ethanol alters nerve signalling by interacting with proteins in the central nervous system, particularly pentameric ligand-gated ion channels. A recent series of mutagenesis experiments on Gloeobacter violaceus ligand-gated ion channel, a prokaryotic member of this family, identified a single-site variant that is potentiated by pharmacologically relevant concentrations of ethanol. Here we determine crystal structures of the ethanol-sensitized variant in the absence and presence of ethanol and related modulators, which bind in a transmembrane cavity between channel subunits and may stabilize the open form of the channel. Structural and mutagenesis studies defined overlapping mechanisms of potentiation by alcohols and anaesthetics via the inter-subunit cavity. Furthermore, homology modelling show this cavity to be conserved in human ethanol-sensitive glycine and GABA(A) receptors, and to involve residues previously shown to influence alcohol and anaesthetic action on these proteins. These results suggest a common structural basis for ethanol potentiation of an important class of targets for neurological actions of ethanol.
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Das J, Xu S, Pany S, Guillory A, Shah V, Roman GW. The pre-synaptic Munc13-1 binds alcohol and modulates alcohol self-administration in Drosophila. J Neurochem 2013; 126:715-26. [PMID: 23692447 DOI: 10.1111/jnc.12315] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Revised: 05/09/2013] [Accepted: 05/17/2013] [Indexed: 11/30/2022]
Abstract
Munc13-1 is a pre-synaptic active-zone protein essential for neurotransmitter release and involved in pre-synaptic plasticity in brain. Ethanol, butanol, and octanol quenched the intrinsic fluorescence of the C1 domain of Munc13-1 with EC₅₀ s of 52 mM, 26 mM, and 0.7 mM, respectively. Photoactive azialcohols photolabeled Munc13-1 C1 exclusively at Glu-582, which was identified by mass spectrometry. Mutation of Glu-582 to alanine, leucine, and histidine reduced the alcohol binding two- to five-fold. Circular dichroism studies suggested that binding of alcohol increased the stability of the wild-type Munc13-1 compared with the mutants. If Munc13-1 plays some role in the neural effects of alcohol in vivo, changes in the activity of this protein should produce differences in the behavioral responses to ethanol. We tested this prediction with a loss-of-function mutation in the conserved Dunc-13 in Drosophila melanogaster. The Dunc-13(P84200) /+ heterozygotes have 50% wild-type levels of Dunc-13 mRNA and display a very robust increase in ethanol self-administration. This phenotype is reversed by the expression of the rat Munc13-1 protein within the Drosophila nervous system. The present studies indicate that Munc13-1 C1 has binding site(s) for alcohols and Munc13-1 activity is sufficient to restore normal self-administration to Drosophila mutants deficient in Dunc-13 activity. The pre-synaptic Mun13-1 protein is a critical regulator of synaptic vesicle fusion and may be involved in processes that lead to ethanol abuse and addiction. We studied its interaction with alcohol and identified Glu-582 as a critical residue for ethanol binding. Munc13-1 can functionally complement the Dunc13 haploinsufficient ethanol self-administration phenotype in Drosophila melanogaster, indicating that this protein participates in alcohol-induced behavioral plasticity.
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Affiliation(s)
- Joydip Das
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas 77204, USA.
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Egawa K, Yamada J, Furukawa T, Yanagawa Y, Fukuda A. Cl⁻ homeodynamics in gap junction-coupled astrocytic networks on activation of GABAergic synapses. J Physiol 2013; 591:3901-17. [PMID: 23732644 PMCID: PMC3764636 DOI: 10.1113/jphysiol.2013.257162] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The electrophysiological properties and functional role of GABAergic signal transmission from neurons to the gap junction-coupled astrocytic network are still unclear. GABA-induced astrocytic Cl− flux has been hypothesized to affect the driving force for GABAergic transmission by modulating [Cl−]o. Thus, revealing the properties of GABA-mediated astrocytic responses will deepen our understanding of GABAergic signal transmission. Here, we analysed the Cl− dynamics of neurons and astrocytes in CA1 hippocampal GABAergic tripartite synapses, using Cl− imaging during GABA application, and whole cell recordings from interneuron–astrocyte pairs in the stratum lacunosum-moleculare. Astrocytic [Cl−]i was adjusted to physiological conditions (40 mm). Although GABA application evoked bidirectional Cl− flux via GABAA receptors and mouse GABA transporter 4 (mGAT4) in CA1 astrocytes, a train of interneuron firing induced only GABAA receptor-mediated inward currents in an adjacent astrocyte. A GAT1 inhibitor increased the interneuron firing-induced currents and induced bicuculline-insensitive, mGAT4 inhibitor-sensitive currents, suggesting that synaptic spillover of GABA predominantly induced the astrocytic Cl− efflux because GABAA receptors are localized near the synaptic clefts. This GABA-induced Cl− efflux was accompanied by Cl− siphoning via the gap junctions of the astrocytic network because gap junction inhibitors significantly reduced the interneuron firing-induced currents. Thus, Cl− efflux from astrocytes is homeostatically maintained within astrocytic networks. A gap junction inhibitor enhanced the activity-dependent depolarizing shifts of reversal potential of neuronal IPSCs evoked by repetitive stimulation to GABAergic synapses. These results suggest that Cl− conductance within the astrocytic network may contribute to maintaining GABAergic synaptic transmission by regulating [Cl−]o.
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Affiliation(s)
- Kiyoshi Egawa
- Department of Neurophysiology, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan
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Leishman E, Kokesh KJ, Bradshaw HB. Lipids and addiction: how sex steroids, prostaglandins, and cannabinoids interact with drugs of abuse. Ann N Y Acad Sci 2013; 1282:25-38. [PMID: 23510307 DOI: 10.1111/nyas.12081] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Lipidomics aims to identify and characterize all endogenous species of lipids and understand their roles in cellular signaling and, ultimately, the functioning of the organism. We are on the cusp of fully understanding the functions of many of the lipid signaling systems that have been identified for decades (e.g., steroids, prostaglandins), whereas our understanding of newer lipid signaling systems (e.g., endocannabinoids, N-acyl amides) still lags considerably behind. With an emphasis on their roles in the neurophysiology of addiction, we will examine three classes of lipids--sex steroids, prostaglandins, and cannabinoids--and how they work synergistically in the neurocircuitry of motivation. We will first give a brief overview of the biosynthesis for each class of lipid and its receptors, and then summarize what is known about the collective roles of the lipids in cocaine and alcohol abuse. This approach provides a novel view of lipid signaling as a class of molecules and their synergistic roles in addiction.
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Affiliation(s)
- Emma Leishman
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA
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Kako H, Kobayashi Y, Yokogoshi H. Dopamine release from rat pheochromocytoma (PC12) cells and rat brain striata induced by a series of straight carbon chain aldehydes with variations in carbon chain length and functional groups. Eur J Pharmacol 2012; 691:86-92. [DOI: 10.1016/j.ejphar.2012.07.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Revised: 06/27/2012] [Accepted: 07/02/2012] [Indexed: 11/15/2022]
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Krasowski MD, Hopfinger AJ. The discovery of new anesthetics by targeting GABAAreceptors. Expert Opin Drug Discov 2011; 6:1187-201. [DOI: 10.1517/17460441.2011.627324] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Kako H, Kobayashi Y, Yokogoshi H. Effects of n-hexanal on dopamine release in the striatum of living rats. Eur J Pharmacol 2011; 651:77-82. [DOI: 10.1016/j.ejphar.2010.11.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2010] [Revised: 09/22/2010] [Accepted: 11/07/2010] [Indexed: 10/18/2022]
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Mostile G, Jankovic J. Alcohol in essential tremor and other movement disorders. Mov Disord 2010; 25:2274-84. [DOI: 10.1002/mds.23240] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Chisari M, Shu HJ, Taylor A, Steinbach JH, Zorumski CF, Mennerick S. Structurally diverse amphiphiles exhibit biphasic modulation of GABAA receptors: similarities and differences with neurosteroid actions. Br J Pharmacol 2010; 160:130-41. [PMID: 20412070 DOI: 10.1111/j.1476-5381.2010.00679.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Some neurosteroids, notably 3alpha-hydroxysteroids, positively modulate GABA(A) receptors, but sulphated steroids negatively modulate these receptors. Recently, other lipophilic amphiphiles have been suggested to positively modulate GABA receptors. We examined whether there was similarity among the actions of these agents and the mechanisms of neurosteroids. Significant similarity would affect theories about the specificity of steroid actions. EXPERIMENTAL APPROACH Xenopus laevis oocytes were challenged with Triton X-100, octyl-beta-glucoside, capsaicin, docosahexaenoic acid and sodium dodecyl sulphate (SDS), along with different GABA concentrations. KEY RESULTS These compounds have both positive and negative effects on GABA currents, which can be accentuated according to the degree of receptor activation. A low GABA concentration (1 microM) promoted potentiation and a high concentration (20 microM) promoted inhibition of current, except for SDS that inhibited function even at low GABA concentrations. Amphiphile inhibition was characterized by enhanced apparent desensitization and by weak voltage dependence, similar to pregnenolone sulphate antagonism. We then tested amphiphile effects on mutated receptor subunits that are insensitive to negative (alpha1V256S) and positive (alpha1Q241L or alpha1N407A/Y410F) steroid modulation. Negative regulation by amphiphiles was nearly abolished in alpha1V256S-mutated receptors, but potentiation was unaffected. In alpha1Q241L- or alpha1N407A/Y410F-mutated receptors, potentiation by amphiphiles remained intact. CONCLUSIONS AND IMPLICATIONS Structurally diverse amphiphiles have antagonist actions at GABA(A) receptors very similar to those of sulphated neurosteroids, while the potentiating mechanisms of these amphiphiles are distinct from those of neurosteroid-positive modulators. Thus, such antagonism at GABA(A) receptors does not have a clear pharmacophore requirement.
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Affiliation(s)
- M Chisari
- Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA
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Handforth A, Homanics GE, Covey DF, Krishnan K, Lee JY, Sakimura K, Martin FC, Quesada A. T-type calcium channel antagonists suppress tremor in two mouse models of essential tremor. Neuropharmacology 2010; 59:380-7. [PMID: 20547167 DOI: 10.1016/j.neuropharm.2010.05.012] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 05/14/2010] [Accepted: 05/24/2010] [Indexed: 11/17/2022]
Abstract
Essential tremor is a common disorder that lacks molecular targets for therapeutic development. T-type calcium channel activation has been postulated to underlie rhythmicity in the olivo-cerebellar system that is implicated in essential tremor. We therefore tested whether compounds that antagonize T-type calcium channel currents suppress tremor in two mouse models that possess an essential tremor-like pharmacological response profile. Tremor was measured using digitized spectral motion power analysis with harmaline-induced tremor and in the GABA(A) receptor α1 subunit-null model. Mice were given ethosuximide, zonisamide, the neuroactive steroid (3β,5α,17β)-17-hydroxyestrane-3-carbonitrile (ECN), the 3,4-dihydroquinazoline derivative KYS05064, the mibefradil derivative NNC 55-0396, or vehicle. In non-sedating doses, each compound reduced harmaline-induced tremor by at least 50% (range of maximal suppression: 53-81%), and in the GABA(A) α1-null model by at least 70% (range 70-93%). Because the T-type calcium channel Cav3.1 is the dominant subtype expressed in the inferior olive, we assessed the tremor response of Cav3.1-deficient mice to harmaline, and found that null and heterozygote mice exhibit as much tremor as wild-type mice. In addition, ECN and NNC 55-0396 suppressed harmaline tremor as well in Cav3.1-null mice as in wild-type mice. The finding that five T-type calcium antagonists suppress tremor in two animal tremor models suggests that T-type calcium channels may be an appropriate target for essential tremor therapy development. It is uncertain whether medications developed to block only the Cav3.1 subtype would exhibit efficacy.
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Affiliation(s)
- Adrian Handforth
- Neurology Service (W127), Veterans Affairs Greater Los Angeles Healthcare System, 11301 Wilshire Blvd, Los Angeles, CA 90073, USA.
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Molecular targets and mechanisms for ethanol action in glycine receptors. Pharmacol Ther 2010; 127:53-65. [PMID: 20399807 DOI: 10.1016/j.pharmthera.2010.03.003] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Accepted: 03/23/2010] [Indexed: 11/23/2022]
Abstract
Glycine receptors (GlyRs) are recognized as the primary mediators of neuronal inhibition in the spinal cord, brain stem and higher brain regions known to be sensitive to ethanol. Building evidence supports the notion that ethanol acting on GlyRs causes at least a subset of its behavioral effects and may be involved in modulating ethanol intake. For over two decades, GlyRs have been studied at the molecular level as targets for ethanol action. Despite the advances in understanding the effects of ethanol in vivo and in vitro, the precise molecular sites and mechanisms of action for ethanol in ligand-gated ion channels in general, and in GlyRs specifically, are just now starting to become understood. The present review focuses on advances in our knowledge produced by using molecular biology, pressure antagonism, electrophysiology and molecular modeling strategies over the last two decades to probe, identify and model the initial molecular sites and mechanisms of ethanol action in GlyRs. The molecular targets on the GlyR are covered on a global perspective, which includes the intracellular, transmembrane and extracellular domains. The latter has received increasing attention in recent years. Recent molecular models of the sites of ethanol action in GlyRs and their implications to our understanding of possible mechanism of ethanol action and novel targets for drug development in GlyRs are discussed.
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Minami K, Sudo Y, Shiraishi S, Seo M, Uezono Y. Analysis of the effects of anesthetics and ethanol on mu-opioid receptor. J Pharmacol Sci 2010; 112:424-31. [PMID: 20379080 DOI: 10.1254/jphs.10003fp] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
Abstract
G protein-coupled receptors, in particular, Ca(2+)-mobilizing G(q)-coupled receptors have been reported to be targets for anesthetics. Opioids are commonly used analgesics in clinical practice, but the effects of anesthetics on the opioid mu-receptors (muOR) have not been systematically examined. We report here an electrophysiological assay to analyze the effects of anesthetics and ethanol on the functions of muOR in Xenopus oocytes expressing a muOR fused to chimeric Galpha protein G(qi5) (muOR-G(qi5)). Using this system, the effects of halothane, ketamine, propofol, and ethanol on the muOR functions were analyzed. In oocytes expressing muOR-G(qi5), the( )muOR agonist DAMGO ([D-Ala(2),N-MePhe(4),Gly-ol]-enkephalin) elicited Ca(2+)-activated Cl(-) currents in a concentration-dependent manner (EC(50) = 0.24 microM). Ketamine, propofol, halothane, and ethanol themselves did not elicit any currents in oocytes expressing muOR-G(qi5), whereas ketamine and ethanol inhibited the DAMGO-induced Cl(-) currents at clinically equivalent concentrations. Propofol and halothane inhibited the DAMGO-induced currents only at higher concentrations. These findings suggest that ketamine and ethanol may inhibit muOR functions in clinical practice. We propose that the electrophysiological assay in Xenopus oocytes expressing muOR-G(qi5) would be useful for analyzing the effects of anesthetics and analgesics on opioid receptor function.
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Affiliation(s)
- Kouichiro Minami
- Department of Anesthesiology and Critical Care Medicine, Jichi Medical University, Japan.
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Kobayashi Y, Kako H, Yokogoshi H. Contribution of Intracellular Ca2+ Concentration and Protein Dephosphorylation to the Induction of Dopamine Release from PC12 cells by the Green Odor Compound Hexanal. Cell Mol Neurobiol 2009; 30:173-84. [PMID: 19693664 DOI: 10.1007/s10571-009-9440-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2009] [Accepted: 07/30/2009] [Indexed: 11/28/2022]
Affiliation(s)
- Yoko Kobayashi
- Laboratory of Nutritional Biochemistry and Global COE (Center of Excellence) Program, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Yada 52-1, Suruga-ku, Shizuoka, Shizuoka, 422-8526, Japan.
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Abstract
Alcohols regulate the expression and function of PKC (protein kinase C), and it has been proposed that an alcohol-binding site is present in PKCα in its C1 domain, which consists of two cysteine-rich subdomains, C1A and C1B. A PKCϵ-knockout mouse showed a significant decrease in alcohol consumption compared with the wild-type. The aim of the present study was to investigate whether an alcohol-binding site could be present in PKCϵ. Here we show that ethanol inhibited PKCϵ activity in a concentration-dependent manner with an EC50 (equilibrium ligand concentration at half-maximum effect) of 43 mM. Ethanol, butanol and octanol increased the binding affinity of a fluorescent phorbol ester SAPD (sapintoxin-D) to PKCϵC1B in a concentration-dependent manner with EC50 values of 78 mM, 8 mM and 340 μM respectively, suggesting the presence of an allosteric alcohol-binding site in this subdomain. To identify this site, PKCϵC1B was photolabelled with 3-azibutanol and 3-azioctanol and analysed by MS. Whereas azibutanol preferentially labelled His236, Tyr238 was the preferred site for azioctanol. Inspection of the model structure of PKCϵC1B reveals that these residues are 3.46 Å (1 Å=0.1 nm) apart from each other and form a groove where His236 is surface-exposed and Tyr238 is buried inside. When these residues were replaced by alanine, it significantly decreased alcohol binding in terms of both photolabelling and alcohol-induced SAPD binding in the mutant H236A/Y238A. Whereas Tyr238 was labelled in mutant H236A, His236 was labelled in mutant Y238A. The present results provide direct evidence for the presence of an allosteric alcohol-binding site on protein kinase Cϵ and underscore the role of His236 and Tyr238 residues in alcohol binding.
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Aryal P, Dvir H, Choe S, Slesinger PA. A discrete alcohol pocket involved in GIRK channel activation. Nat Neurosci 2009; 12:988-95. [PMID: 19561601 PMCID: PMC2717173 DOI: 10.1038/nn.2358] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Accepted: 06/03/2009] [Indexed: 12/18/2022]
Abstract
Ethanol modifies neural activity in the brain by modulating ion channels. Ethanol activates G protein-gated inwardly rectifying K+ channels, but the molecular mechanism is not well understood. Here, we used a crystal structure of a mouse inward rectifier containing a bound alcohol and structure-based mutagenesis to probe a putative alcohol-binding pocket located in the cytoplasmic domains of GIRK channels. Substitutions with bulkier side-chains in the alcohol-binding pocket reduced or eliminated activation by alcohols. By contrast, alcohols inhibited constitutively open channels, such as IRK1 or GIRK2 that binds PIP2 strongly. Mutations in the hydrophobic alcohol-binding pocket of these channels had no effect on alcohol-dependent inhibition, suggesting an alternate site is involved in inhibition. Comparison of high-resolution structures of inwardly rectifying K+ channels suggests a model for activation of GIRK channels utilizing this hydrophobic alcohol-binding pocket. These results provide a tool for developing therapeutic compounds that could mitigate the effects of alcohol.
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Affiliation(s)
- Prafulla Aryal
- Peptide Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California, USA
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Juszczak GR, Swiergiel AH. Properties of gap junction blockers and their behavioural, cognitive and electrophysiological effects: animal and human studies. Prog Neuropsychopharmacol Biol Psychiatry 2009; 33:181-98. [PMID: 19162118 DOI: 10.1016/j.pnpbp.2008.12.014] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 12/22/2008] [Accepted: 12/22/2008] [Indexed: 10/21/2022]
Abstract
Gap junctions play an important role in brain physiology. They synchronize neuronal activity and connect glial cells participating in the regulation of brain metabolism and homeostasis. Gap junction blockers (GJBs) include various chemicals that impair gap junction communication, disrupt oscillatory neuronal activity over a wide range of frequencies, and decrease epileptic discharges. The behavioural and clinical effects of GJBs suggest that gap junctions can be involved in the regulation of locomotor activity, arousal, memory, and breathing. Severe neuropsychiatric side effects suggest the involvement of gap junctions in mechanisms of consciousness. Unfortunately, the available GJBs are not selective and can bind to targets other than gap junctions. Other problems in behavioural studies include the possible adverse effects of GJBs, for example, retinal toxicity and hearing disturbances, changes in blood-brain transport, and the metabolism of other drugs. Therefore, it is necessary to design experiments properly to avoid false, misleading or uninterpretable results. We review the pharmacological properties and electrophysiological, behavioural and cognitive effects of the available gap junction blockers, such as carbenoxolone, glycyrrhetinic acid, quinine, quinidine, mefloquine, heptanol, octanol, anandamide, fenamates, 2-APB, several anaesthetics, retinoic acid, oleamide, spermine, aminosulfonates, and sodium propionate. It is concluded that despite a number of different problems, the currently used gap junction blockers could be useful tools in pharmacology and neuroscience.
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Affiliation(s)
- Grzegorz R Juszczak
- Department of Animal Behaviour, Institute of Genetics and Animal Breeding, Jastrzebiec, ul. Postepu 1, 05-552 Wolka Kosowska, Poland.
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Ho C, Shanmugasundararaj S, Miller KW, Malinowski SA, Cook AC, Slater SJ. Interaction of anesthetics with the Rho GTPase regulator Rho GDP dissociation inhibitor. Biochemistry 2008; 47:9540-52. [PMID: 18702520 DOI: 10.1021/bi800544d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The physiological effects of anesthetics have been ascribed to their interaction with hydrophobic sites within functionally relevant CNS proteins. Studies have shown that volatile anesthetics compete for luciferin binding to the hydrophobic substrate binding site within firefly luciferase and inhibit its activity (Franks, N. P., and Lieb, W. R. (1984) Nature 310, 599-601). To assess whether anesthetics also compete for ligand binding to a mammalian signal transduction protein, we investigated the interaction of the volatile anesthetic, halothane, with the Rho GDP dissociation inhibitor (RhoGDIalpha), which binds the geranylgeranyl moiety of GDP-bound Rho GTPases. Consistent with the existence of a discrete halothane binding site, the intrinsic tryptophan fluorescence of RhoGDIalpha was quenched by halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) in a saturable, concentration-dependent manner. Bromine quenching of tryptophan fluorescence is short-range and W192 and W194 of the RhoGDIalpha are located within the geranylgeranyl binding pocket, suggesting that halothane binds within this region. Supporting this, N-acetyl-geranylgeranyl cysteine reversed tryptophan quenching by halothane. Short chain n-alcohols ( n < 6) also reversed tryptophan quenching, suggesting that RhoGDIalpha may also bind n-alkanols. Consistent with this, E193 was photolabeled by 3-azibutanol. This residue is located in the vicinity of, but outside, the geranylgeranyl chain binding pocket, suggesting that the alcohol binding site is distinct from that occupied by halothane. Supporting this, N-acetyl-geranylgeranyl cysteine enhanced E193 photolabeling by 3-azibutanol. Overall, the results suggest that halothane binds to a site within the geranylgeranyl chain binding pocket of RhoGDIalpha, whereas alcohols bind to a distal site that interacts allosterically with this pocket.
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Affiliation(s)
- Cojen Ho
- Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Abstract
Ethanol produces a wide variety of behavioral and physiological effects in the body, but exactly how it acts to produce these effects is still poorly understood. Although ethanol was long believed to act nonspecifically through the disordering of lipids in cell membranes, proteins are at the core of most current theories of its mechanisms of action. Although ethanol affects various biochemical processes such as neurotransmitter release, enzyme function, and ion channel kinetics, we are only beginning to understand the specific molecular sites to which ethanol molecules bind to produce these myriad effects. For most effects of ethanol characterized thus far, it is unknown whether the protein whose function is being studied actually binds ethanol, or if alcohol is instead binding to another protein that then indirectly affects the functioning of the protein being studied. In this Review, we describe criteria that should be considered when identifying alcohol binding sites and highlight a number of proteins for which there exists considerable molecular-level evidence for distinct ethanol binding sites.
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Affiliation(s)
- R Adron Harris
- Section of Neurobiology and Waggoner Center for Alcohol and Addiction Research, Institutes for Neuroscience and Cell & Molecular Biology, University of Texas, Austin, TX 78712, USA.
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Horishita T, Harris RA. n-Alcohols inhibit voltage-gated Na+ channels expressed in Xenopus oocytes. J Pharmacol Exp Ther 2008; 326:270-7. [PMID: 18434586 DOI: 10.1124/jpet.108.138370] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated sodium channels are essential for the initiation and propagation of action potentials in excitable cells and are known as a target of local anesthetics. In addition, inhibition of sodium channels by volatile anesthetics has been proposed as a mechanism of general anesthesia. The n-alcohols produce anesthesia, and their potency increases with carbon number until a "cut-off" is reached. In this study, we examined effects of a range of n-alcohols on Na(v)1.2 subunits to determine the alcohol cut-off for this channel. We also studied the effect of a short-chain alcohol (ethanol) and a long-chain alcohol (octanol) on Na(v)1.2, Na(v)1.4, Na(v)1.6, and Na(v)1.8 subunits, and we investigated the effects of alcohol on channel kinetics. Ethanol and octanol inhibited sodium currents of all subunits, and the inhibition of the Na(v)1.2 channel by n-alcohols indicated a cut-off at nonanol. Ethanol and octanol produced open-channel block, which was more pronounced for Na(v)1.8 than for the other sodium channels. Inhibition of Na(v)1.2 was due to decreased activation and increased inactivation. These results suggest that sodium channels may have a hydrophobic binding site for n-alcohols and demonstrate the differences in the kinetic mechanisms of inhibition for n-alcohols and inhaled anesthetics.
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Affiliation(s)
- Takafumi Horishita
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, TX 78712, USA
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Kako H, Fukumoto S, Kobayashi Y, Yokogoshi H. Effects of direct exposure of green odour components on dopamine release from rat brain striatal slices and PC12 cells. Brain Res Bull 2008; 75:706-12. [DOI: 10.1016/j.brainresbull.2007.11.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Revised: 11/27/2007] [Accepted: 11/27/2007] [Indexed: 11/27/2022]
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Abstract
BACKGROUND Numerous studies suggest that cAMP signaling pathways play important roles in the development of and predisposition to alcoholism. Our previous study showed that cAMP generation by various isoforms of adenylyl cyclase (AC) exhibits a broad spectrum of responses to ethanol in the human embryonic kidney (HEK) 293 cell system overexpressing individual AC isoforms. These findings suggest that the target of ethanol's action in the cAMP-generating system is AC. However, it is unknown if the action of ethanol is direct or indirect. METHODS The effect of a series of n-alkanols (ethanol to decanol) on dopamine (DA)-stimulated activity of AC isoforms type 6, 7, and 9 (AC6, AC7, and AC9) were examined in transfected HEK293 cells by cAMP accumulation assay. RESULTS n-Alkanols increased DA-stimulated cAMP production in an AC isoform-specific manner, and displayed the alcohol cutoff phenomenon (defined as the carbon chain length beyond which there is no further increase in the potency of an ascending series of n-alkanols). The n-alkanol cutoffs for AC6, AC7, and AC9 are butanol (C4), pentanol (C5), and equal to or greater than decanol (C10), respectively. CONCLUSION The results clearly indicate that, in the HEK293 expression system, the alcohol cutoff effect for n-alkanol potentiation of DA-stimulated AC activity is AC isoform specific. These results strongly suggest that alcohols interact directly with AC molecules.
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Affiliation(s)
- Jinghong Kou
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Minami K, Uezono Y, Sakurai T, Horishita T, Shiraishi M, Ueta Y. Effects of anesthetics on the function of orexin-1 receptors expressed in Xenopus oocytes. Pharmacology 2007; 79:236-42. [PMID: 17435392 DOI: 10.1159/000101713] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Accepted: 12/15/2006] [Indexed: 11/19/2022]
Abstract
Neurons in the hypothalamus containing the neuropeptide orexin have been implicated in the control of sleep and wakefulness and in the pathology of narcolepsy. In this study, we investigated the effects of volatile anesthetics, ethanol and intravenous anesthetics on orexin-A-induced Ca2+-activated Cl- currents using Xenopus oocytes expressing orexin-1 receptors (OX1Rs). The volatile anesthetics isoflurane, enflurane and halothane inhibited Cl- currents elicited by 1-micromol/l orexin-A. Ethanol and the intravenous anesthetics pentobarbital and ketamine also inhibited the action of orexin-A. The inhibitory effects of all of the compounds tested were shown to be caused by the inhibition of OX1R function. These results may, at least in part, explain their hypnotic effects.
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Affiliation(s)
- Kouichiro Minami
- Department of Anesthesiology, Jichi Medical University, Tochigi, Japan.
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Martin FC, Handforth A. Carbenoxolone and mefloquine suppress tremor in the harmaline mouse model of essential tremor. Mov Disord 2006; 21:1641-9. [PMID: 16773639 DOI: 10.1002/mds.20940] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Excessive olivo-cerebellar synchrony is implicated in essential tremor. Because synchrony in some networks is mediated by gap junctions, we examined whether the gap junction blockers heptanol, octanol, carbenoxolone, and mefloquine suppress tremor in the mouse harmaline model, and performed an open-treatment clinical study of mefloquine for essential tremor. Digitized motion was used to quantify tremor in mice administered harmaline, 20 mg/kg s.c. In mice the broad-spectrum gap junction blockers heptanol, octanol (350 mg/kg i.p. each), and carbenoxolone (20 mg/kg) suppressed harmaline tremor. Mefloquine (50 mg/kg), which blocks gap junctions containing connexin 36, robustly suppressed harmaline tremor. Glycyrrhizic acid (related to carbenoxolone) and chloroquine (related to mefloquine), which do not block gap junctions, failed to suppress harmaline tremor in mice. Clinically, tremor was assessed with standard rating scales, and subjects asked to take 62.5, 125, and 250 mg mefloquine weekly for 12 weeks at each dose. None of the four human subjects showed a meaningful tremor reduction with mefloquine, likely because clinical levels were below those required for efficacy. In view of recent genetic evidence, the anti-tremor mechanism of these compounds is uncertain but may represent a novel therapeutic target, possibly involving gap junctions other than those containing connexin 36.
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Affiliation(s)
- Fredricka C Martin
- Research Service, Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California, USA
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Ogata J, Shiraishi M, Namba T, Smothers CT, Woodward JJ, Harris RA. Effects of Anesthetics on Mutant N-Methyl-d-Aspartate Receptors Expressed in Xenopus Oocytes. J Pharmacol Exp Ther 2006; 318:434-43. [PMID: 16622040 DOI: 10.1124/jpet.106.101691] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Alcohols, inhaled anesthetics, and some injectable anesthetics inhibit the function of N-methyl-d-aspartate (NMDA) receptors, but the mechanisms responsible for this inhibition are not fully understood. Recently, it was shown that ethanol inhibition of NMDA receptors was reduced by mutation of residues in the transmembrane (TM) segment 3 of the NR1 subunit (F639A) or in TM4 of the NR2A subunit (A825W), suggesting putative ethanol binding sites. We hypothesized that the actions of other anesthetics might also require these amino acids and evaluated the effects of anesthetics on the NMDA receptors expressed in Xenopus oocytes with two-electrode voltage-clamp recording. Effects of hexanol, octanol, isoflurane, halothane, chloroform, cyclopropane, 1-chloro-1,2,2-trifluorocyclobutane, and xenon were reduced or eliminated in the mutant NMDA receptors, whereas the inhibitory effects of nitrous oxide, ketamine, and benzene were not affected by these mutations. Rapid applications of glutamate and glycine by a T-tube device provided activation time constants, which suggested different properties of ketamine and isoflurane inhibition. Thus, amino acids in TM3 and TM4 are important for the actions of many anesthetics, but nitrous oxide, benzene, and ketamine seem to have distinct mechanisms for inhibition of the NMDA receptors.
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Affiliation(s)
- Junichi Ogata
- University of Texas, Waggoner Center for Alcohol and Addiction Research, 1 University Station A4800, Austin, TX 78712-0159, USA, and Department of Anesthesia, Kyoto University Hospital, Japan
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Jung S, Harris RA. Sites in TM2 and 3 are critical for alcohol-induced conformational changes in GABA receptors. J Neurochem 2006; 96:885-92. [PMID: 16405501 DOI: 10.1111/j.1471-4159.2005.03617.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Abstract gamma-Aminobutyric acid type A (GABA(A)) receptors are molecular targets for alcohols. Previous work suggests that S270 and A291 residues in the transmembrane (TM) 2 and 3 domains of the GABA(A) receptor alpha subunit are components of an alcohol-binding pocket, and S270I and A291W mutants abolished ethanol potentiation. Our results showed that A295C and F296C residues in the TM3 of the GABA(A) receptor alpha1 subunit are accessible to hexylmethanethiosulfonate (HMTS) in the alcohol-bound state, but not in the resting state. Thus, the A295C and F296C sites become water-accessible as a result of alcohol-induced conformational changes. If S270 or A291 residues are sites of alcohol binding, then S270I or A291W mutations should prevent alcohol-induced conformational movements within the TM3 domain. To investigate this question, the accessibility of HMTS reagent to double mutants (A291W/A295C, A291W/F296C, S270I/A295C or S270I/F296C) in the presence of ethanol or hexanol was tested. The A291W or S270I mutations markedly reduced the accessibility of HMTS to all the double mutants in the ethanol-bound state, and to S270I/F296C, A291W/A295C and A291W/F296C double mutants in the hexanol-bound state, suggesting that the A291 or S270 residues are critical sites for alcohol binding and alcohol-induced conformational changes.
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Affiliation(s)
- Sangwook Jung
- Cell and Molecular Biology Program and Waggoner Center for Alcohol and Addiction Research, University of Texas at Austin, TX, USA.
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Lopreato GF, Banerjee P, Mihic SJ. Amino acids in transmembrane domain two influence anesthetic enhancement of serotonin-3A receptor function. ACTA ACUST UNITED AC 2004; 118:45-51. [PMID: 14559353 DOI: 10.1016/s0169-328x(03)00332-2] [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] [Indexed: 10/27/2022]
Abstract
Alcohols and volatile anesthetics affect the function of members of the nicotinic acetylcholine (nACh) superfamily of receptors. Studies on glycine and GABA(A) receptors implicate amino acid residues within transmembrane (TM) regions two and three of these receptors as critical for alcohol and anesthetic enhancement of receptor function. The serotonin-3 (5-HT(3)) receptor is a member of the nicotinic acetylcholine receptor superfamily, sharing sequence and structural homology with the other members. We tested the hypothesis that amino acids of the 5-HT(3) receptor homologous to those shown to affect alcohol and anesthetic potentiation in GABA(A) and glycine receptors also determine the effects of these compounds on the 5-HT(3) receptor. Six 5-HT(3A) mutant cDNAs were generated by site-directed mutagenesis of two amino acids, phenylalanine-269 (14') and lecucine-270 (15') in transmembrane domain two (TM2). When assayed electrophysiologically in Xenopus oocytes, wild-type 5-HT(3) receptors exhibit enhancement of function by enflurane, halothane, isoflurane, chloroform and ethanol, but not by decanol and propofol. Mutations in transmembrane domain two markedly affected alcohol and anesthetic enhancement of 5-HT(3) receptor function. Some mutations had differential effects on the abilities of the isomers enflurane and isoflurane to potentiate 5-HT(3) receptor function.
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MESH Headings
- Amino Acid Sequence/drug effects
- Amino Acid Sequence/genetics
- Amino Acids/chemistry
- Amino Acids/drug effects
- Anesthetics, Inhalation/pharmacology
- Animals
- Cell Membrane/chemistry
- Cell Membrane/drug effects
- Dose-Response Relationship, Drug
- Drug Synergism
- Ethanol/pharmacology
- Female
- Leucine/chemistry
- Leucine/drug effects
- Mutagenesis, Site-Directed
- Mutation/genetics
- Oocytes/metabolism
- Phenylalanine/chemistry
- Phenylalanine/drug effects
- Protein Structure, Tertiary/drug effects
- Protein Structure, Tertiary/physiology
- Receptors, Serotonin, 5-HT3/chemistry
- Receptors, Serotonin, 5-HT3/drug effects
- Receptors, Serotonin, 5-HT3/genetics
- Serotonin/metabolism
- Serotonin/pharmacology
- Xenopus laevis
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Affiliation(s)
- Gregory F Lopreato
- Section of Neurobiology, Waggoner Center for Alcohol and Addiction Research, Institute for Neuroscience, and the Institute for Cellular and Molecular Biology, University of Texas at Austin, 2500 Speedway, MBB 1.148, Austin, TX 78712, USA
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Abstract
For many years, the expression "cutoff effect of anesthesia," has been used to denote the failure of the higher alcohols or paraffins to produce anesthesia. As such, it is used to assess the plausibility of specific models, proposed for anesthesia. However, the uses were shown, in many respects, to be problematic. This article augments the notion of the cutoff to fit for all cases in which only some of the molecules in a homologous series are anesthetics. We find that the location of the cutoff points is affected by three free energy quantities: that of the adsorption of the agent to the anesthetic "site" (f(sl,site)), that of the perturbation of the site (f(ll,site)), and that of the evaporation of the agent from its pure condensed phase (Deltamu degrees (evaporation)). This outcome indicates that the cutoff cannot be attributed to a single parameter. In addition, the analyses that attribute the cutoff to the failure of compounds to obey the much-used Meyer-Overton correlation will have to be amended. This article shows that cutoff results can be used to elucidate the structure of a site.
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Affiliation(s)
- Y Katz
- The National Physical Laboratory of Israel, Givat Ram, Jerusalem 91904, Israel.
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Harris T, Graber AR, Covarrubias M. Allosteric modulation of a neuronal K+ channel by 1-alkanols is linked to a key residue in the activation gate. Am J Physiol Cell Physiol 2003; 285:C788-96. [PMID: 12958027 DOI: 10.1152/ajpcell.00113.2003] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The selective inhibition of neuronal Shaw2 K+ channels by 1-alkanols is conferred by the internal S4-S5 loop, a region that also contributes to the gating of voltage-gated K+ channels. Here, we applied alanine scanning mutagenesis to examine the contribution of the S5 and S6 segments to the allosteric modulation of Shaw2 K+ channels by 1-alkanols. The internal section of S6 is the main activation gate of K+ channels. While several mutations in S5 and S6 modulated the inhibition of the channels by 1-butanol and others had no effect, a single mutation at a key site in S6 (P410A) converted this inhibition into a dramatic dose-dependent potentiation (approximately 2-fold at 15 mM and approximately 6-fold at 50 mM). P410 is the second proline in the highly conserved PVP motif that may cause a significant alpha-helix kink. The P410A currents in the presence of 1-butanol also exhibited novel kinetics (faster activation and slow inactivation). Internal application of 15 mM 1-butanol to inside-out patches expressing P410A did not significantly affect the mean unitary currents (approximately 2 pA at 0 mV) or the mean open time (5-6 ms) but clearly increased the opening frequency and open probability (approximately 2- to 4-fold). All effects displayed a fast onset and were fully reversible upon washout. The results suggest that the allosteric modulation of the Shaw2 K+ channel by 1-alkanols depends on a critical link between the PVP motif and activation gating. This study establishes the Shaw2 K+ channel as a robust model to investigate the mechanisms of alcohol intoxication and general anesthesia.
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Affiliation(s)
- Thanawath Harris
- Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College of Thomas Jefferson University, 1020 Locust St., Philadelphia, PA 19107, USA
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Borghese CM, Wang L, Bleck V, Harris RA. Mutation in neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes blocks ethanol action. Addict Biol 2003; 8:313-8. [PMID: 13129833 DOI: 10.1080/13556210310001602220] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Amino acids (AAs) in the extracellular portion of the transmembrane domain of several inhibitory ligand-gated ion channels participate in an alcohol binding site. To extend these studies to neuronal nicotinic acetylcholine receptors (nAChRs), we focused on an AA (L262) located in the same region of the second transmembrane domain of the alpha2 subunit of neuronal nAChRs. Single-point mutation of alpha2L262 was carried out, the resulting alpha2 subunits co-expressed with wild-type beta4 subunits in Xenopus laevis oocytes, and studied using two-electrode voltage clamp. Ethanol enhancement of ACh responses was diminished [alpha2(L262F)beta4] or abolished [alpha2(L262G)beta4, alpha2(L2625)beta4 and alpha2(L262A)beta4]. Mutation of the homologous AA in beta4 [beta4(L258A)] did not modify the ethanol modulation and the mutation in alpha2 was dominant, because ethanol did not enhance ACh responses in alpha2(L262A)beta4(L258A) nAChRs. n-Alcohols (ethanol through octanol) were applied to alpha2(L262A)beta4 nAChRs. As described previously for other nAChRs, short-chain alcohols enhanced, intermediate-chain alcohols had no effect and long-chain alcohols inhibited ACh responses in the wild-type receptor. For alpha2(L262A)beta4 nAChRs the alcohol enhancing effect was absent, and the alcohol inhibitory action was increased. Although this suggests removal of an alcohol enhancing site through mutagenesis, we cannot rule out the enhancement of action at an alcohol inhibitory site.
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Affiliation(s)
- Cecilia M Borghese
- Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, TX 78712-0159, USA
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Davies M. The role of GABAA receptors in mediating the effects of alcohol in the central nervous system. J Psychiatry Neurosci 2003; 28:263-74. [PMID: 12921221 PMCID: PMC165791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 03/01/2023] Open
Abstract
Ethanol is a chemically simple compound that produces many well-known effects in humans. The prevailing idea for many years was that ethanol and other alcohols exerted their effects on the central nervous system (CNS) by non-selectively disrupting the lipid bilayers of neurons. However, in recent years, there has been an accumulation of evidence pointing to the importance of ligand-gated ion channels (LGICs) in mediating the effects of ethanol. Of these LGICs, gamma-aminobutyric acid type A (GABAA) receptors appear to occupy a central role in mediating the effects of ethanol in the CNS. GABA is the primary inhibitory neurotransmitter in the mammalian CNS, and activation of GABAA receptors by GABA tends to decrease neuronal excitability. This article reviews several aspects of GABAA receptor and ethanol interactions, including the evidence for short- and long-term modulation of GABAA receptors by ethanol and evidence for a GABAA receptor-related genetic component of alcoholism.
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Affiliation(s)
- Martin Davies
- Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alta.
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