1
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Danbolt NC, López-Corcuera B, Zhou Y. Reconstitution of GABA, Glycine and Glutamate Transporters. Neurochem Res 2021; 47:85-110. [PMID: 33905037 PMCID: PMC8763731 DOI: 10.1007/s11064-021-03331-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 04/13/2021] [Accepted: 04/15/2021] [Indexed: 10/25/2022]
Abstract
In contrast to water soluble enzymes which can be purified and studied while in solution, studies of solute carrier (transporter) proteins require both that the protein of interest is situated in a phospholipid membrane and that this membrane forms a closed compartment. An additional challenge to the study of transporter proteins has been that the transport depends on the transmembrane electrochemical gradients. Baruch I. Kanner understood this early on and first developed techniques for studying plasma membrane vesicles. This advanced the field in that the experimenter could control the electrochemical gradients. Kanner, however, did not stop there, but started to solubilize the membranes so that the transporter proteins were taken out of their natural environment. In order to study them, Kanner then had to find a way to reconstitute them (reinsert them into phospholipid membranes). The scope of the present review is both to describe the reconstitution method in full detail as that has never been done, and also to reveal the scientific impact that this method has had. Kanner's later work is not reviewed here although that also deserves a review because it too has had a huge impact.
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Affiliation(s)
- Niels Christian Danbolt
- Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317, Oslo, Norway.
| | - Beatriz López-Corcuera
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, Madrid, Spain.,Centro de Biología Molecular "Severo Ochoa" Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain.,IdiPAZ, Hospital Universitario La Paz, Madrid, Spain
| | - Yun Zhou
- Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317, Oslo, Norway
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2
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Affiliation(s)
- Christopher L. Cioffi
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences , Albany, NY, USA
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3
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Arribas-González E, de Juan-Sanz J, Aragón C, López-Corcuera B. Molecular basis of the dominant negative effect of a glycine transporter 2 mutation associated with hyperekplexia. J Biol Chem 2014; 290:2150-65. [PMID: 25480793 DOI: 10.1074/jbc.m114.587055] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hyperekplexia or startle disease is a rare clinical syndrome characterized by an exaggerated startle in response to trivial tactile or acoustic stimuli. This neurological disorder can have serious consequences in neonates, provoking brain damage and/or sudden death due to apnea episodes and cardiorespiratory failure. Hyperekplexia is caused by defective inhibitory glycinergic neurotransmission. Mutations in the human SLC6A5 gene encoding the neuronal GlyT2 glycine transporter are responsible for the presynaptic form of the disease. GlyT2 mediates synaptic glycine recycling, which constitutes the main source of releasable transmitter at glycinergic synapses. Although the majority of GlyT2 mutations detected so far are recessive, a dominant negative mutant that affects GlyT2 trafficking does exist. In this study, we explore the properties and structural alterations of the S512R mutation in GlyT2. We analyze its dominant negative effect that retains wild-type GlyT2 in the endoplasmic reticulum (ER), preventing surface expression. We show that the presence of an arginine rather than serine 512 provoked transporter misfolding, enhanced association to the ER-chaperone calnexin, altered association with the coat-protein complex II component Sec24D, and thereby impeded ER exit. The S512R mutant formed oligomers with wild-type GlyT2 causing its retention in the ER. Overexpression of calnexin rescued wild-type GlyT2 from the dominant negative effect of the mutant, increasing the amount of transporter that reached the plasma membrane and dampening the interaction between the wild-type and mutant GlyT2. The ability of chemical chaperones to overcome the dominant negative effect of the disease mutation on the wild-type transporter was demonstrated in heterologous cells and primary neurons.
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Affiliation(s)
- Esther Arribas-González
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain
| | - Jaime de Juan-Sanz
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain, and
| | - Carmen Aragón
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain, and
| | - Beatriz López-Corcuera
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain, and
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4
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López-Corcuera B, Geerlings A, Aragón C. Glycine neurotransmitter transporters: an update. Mol Membr Biol 2009. [DOI: 10.1080/09687680010028762] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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5
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Armsen W, Himmel B, Betz H, Eulenburg V. The C-terminal PDZ-ligand motif of the neuronal glycine transporter GlyT2 is required for efficient synaptic localization. Mol Cell Neurosci 2007; 36:369-80. [PMID: 17851090 DOI: 10.1016/j.mcn.2007.07.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Revised: 07/13/2007] [Accepted: 07/24/2007] [Indexed: 11/28/2022] Open
Abstract
The neuronal glycine transporter 2 (GlyT2) belongs to the large SLC6 family of Na+/Cl--dependent neurotransmitter transporters. At its extreme C-terminus, GlyT2 carries a type III PDZ domain binding motif (PDZ-ligand motif), which interacts with the PDZ domain protein syntenin-1. Here, we investigated the physiological role of the GlyT2 PDZ-ligand motif by a loss-of-function approach. Inactivation of the PDZ-ligand motif did not impair the localization, glycosylation and transport function of recombinant GlyT2 expressed in HEK293T cells. However, in transfected hippocampal neurons, the synaptic localization of GlyT2 was significantly reduced upon PDZ-ligand motif inactivation. Co-localization of GlyT2 with marker proteins of excitatory and inhibitory synapses was decreased by down to 50% upon PDZ-ligand motif deletion as compared to the wild-type protein. These data indicate that the C-terminal PDZ-ligand motif of GlyT2 plays an important role in transporter trafficking to and/or stabilization at synaptic sites.
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Affiliation(s)
- Wencke Armsen
- Department of Neurochemistry, Max-Planck Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany
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6
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Goracke-Postle CJ, Overland AC, Riedl MS, Stone LS, Fairbanks CA. Potassium- and capsaicin-induced release of agmatine from spinal nerve terminals. J Neurochem 2007; 102:1738-1748. [PMID: 17539920 DOI: 10.1111/j.1471-4159.2007.04647.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Agmatine (decarboxylated arginine) was originally identified in the CNS as an imidazoline receptor ligand. Further studies demonstrated that agmatine antagonizes NMDA receptors and inhibits nitric oxide synthase. Intrathecally administered agmatine inhibits opioid tolerance and hyperalgesia evoked by inflammation, nerve injury, and intrathecally administered NMDA. These actions suggest an anti-glutamatergic role for agmatine in the spinal cord. We have previously reported that radiolabeled agmatine is transported into spinal synaptosomes in an energy- and temperature-dependent manner. In the present study, we demonstrate that agmatine is releasable from purified spinal nerve terminals upon depolarization. When exposed to either elevated potassium or capsaicin, tritiated agmatine (but not its precursor L-arginine or its metabolite putrescine) is released in a calcium-dependent manner. Control experiments confirmed that the observed release was specific to depolarization and not due to permeabilization of or degradation of synaptosomes. That capsaicin-evoked stimulation results in agmatine release implicates the participation of primary afferent nerve terminals. Radiolabeled agmatine also accumulates in purified spinal synaptosomal vesicles in a temperature-dependent manner, suggesting that the source of releasable agmatine may be vesicular in origin. These results support the proposal that agmatine may serve as a spinal neuromodulator involved in pain processing.
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Affiliation(s)
- Cory J Goracke-Postle
- Department of Pharmaceutics, University of Minnesota, Minneapolis, Minnesota, USADepartment of Pharmacology, University of Minnesota, Minneapolis, Minnesota, USADepartment of Neuroscience, University of Minnesota, Minneapolis, Minnesota, USADepartment of Anesthesiology, University of Minnesota, Minneapolis, Minnesota, USACenter for Pain Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Aaron C Overland
- Department of Pharmaceutics, University of Minnesota, Minneapolis, Minnesota, USADepartment of Pharmacology, University of Minnesota, Minneapolis, Minnesota, USADepartment of Neuroscience, University of Minnesota, Minneapolis, Minnesota, USADepartment of Anesthesiology, University of Minnesota, Minneapolis, Minnesota, USACenter for Pain Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Maureen S Riedl
- Department of Pharmaceutics, University of Minnesota, Minneapolis, Minnesota, USADepartment of Pharmacology, University of Minnesota, Minneapolis, Minnesota, USADepartment of Neuroscience, University of Minnesota, Minneapolis, Minnesota, USADepartment of Anesthesiology, University of Minnesota, Minneapolis, Minnesota, USACenter for Pain Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Laura S Stone
- Department of Pharmaceutics, University of Minnesota, Minneapolis, Minnesota, USADepartment of Pharmacology, University of Minnesota, Minneapolis, Minnesota, USADepartment of Neuroscience, University of Minnesota, Minneapolis, Minnesota, USADepartment of Anesthesiology, University of Minnesota, Minneapolis, Minnesota, USACenter for Pain Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Carolyn A Fairbanks
- Department of Pharmaceutics, University of Minnesota, Minneapolis, Minnesota, USADepartment of Pharmacology, University of Minnesota, Minneapolis, Minnesota, USADepartment of Neuroscience, University of Minnesota, Minneapolis, Minnesota, USADepartment of Anesthesiology, University of Minnesota, Minneapolis, Minnesota, USACenter for Pain Research, University of Minnesota, Minneapolis, Minnesota, USA
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7
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Igartua I, Solís JM, Bustamante J. Glycine-induced long-term synaptic potentiation is mediated by the glycine transporter GLYT1. Neuropharmacology 2007; 52:1586-95. [PMID: 17462677 DOI: 10.1016/j.neuropharm.2007.03.003] [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: 11/24/2006] [Revised: 02/13/2007] [Accepted: 03/05/2007] [Indexed: 11/29/2022]
Abstract
The negative symptoms of schizophrenia are reverted by treatment with glycine or other agonists of the glycine-B site which facilitate NMDA receptor function. On the other hand, there are experimental observations showing that exogenous application of glycine (0.5-10mM) results in a long-lasting potentiation of glutamatergic synaptic transmission (LTP-GLY). The characterization of the mechanisms underlying LTP-GLY could be useful to develop new therapies for schizophrenia. The main goal of this work is to deepen the understanding of this potentiation phenomenon. The present study demonstrates in rat hippocampal slices that superfusion of glycine 1mM during 30 min produces a potentiation of excitatory postsynaptic potentials in CA3-CA1 pathway lasting at least 1h. Glycine application does not modify neither presynaptic fiber volley nor paired-pulse facilitation of synaptic potentials. This LTP-GLY is independent of both strychnine-sensitive glycine receptors and nifedipine-sensitive calcium channels. Interestingly, LTP-GLY is not inhibited but strengthened by NMDA receptors antagonists such as AP-5 or MK-801. In contrast, LTP-GLY is partially or totally blocked with the antagonists of glycine transporter GLYT1, sarcosine or ALX-5407, respectively. These results indicate that LTP-GLY requires the activation of GLYT1, a glycine transporter co-localized and associated to NMDA receptors. In addition, the fact that NMDA receptor inhibition increases LTP-GLY magnitude, opens the possibility that these receptors could have a negative control on GLYT1 activity.
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Affiliation(s)
- Itziar Igartua
- Servicio de Neurobiología-Investigación, Hospital Ramón y Cajal, 28034 Madrid, Spain
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8
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Rud E, Gederaas O, Høgset A, Berg K. 5-Aminolevulinic Acid, but not 5-Aminolevulinic Acid Esters, is Transported into Adenocarcinoma Cells by System BETA Transporters. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2000)0710640aabnaa2.0.co2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Abstract
Glycine has multiple neurotransmitter functions in the central nervous system (CNS). In the spinal cord and brainstem of vertebrates, it serves as a major inhibitory neurotransmitter. In addition, it participates in excitatory neurotransmission by modulating the activity of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. The extracellular concentrations of glycine are regulated by Na+/Cl(-)-dependent glycine transporters (GlyTs), which are expressed in neurons and adjacent glial cells. Considerable progress has been made recently towards elucidating the in vivo roles of GlyTs in the CNS. The generation and analysis of animals carrying targeted disruptions of GlyT genes (GlyT knockout mice) have allowed investigators to examine the different contributions of individual GlyT subtypes to synaptic transmission. In addition, they have provided animal models for two hereditary human diseases, glycine encephalopathy and hyperekplexia. Selective GlyT inhibitors have been shown to modulate neurotransmission and might constitute promising therapeutic tools for the treatment of psychiatric and neurological disorders such as schizophrenia and pain. Therefore, pharmacological and genetic studies indicate that GlyTs are key regulators of both glycinergic inhibitory and glutamatergic excitatory neurotransmission. This chapter describes our present understanding of the functions of GlyTs and their involvement in the fine-tuning of neuronal communication.
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Affiliation(s)
- J Gomeza
- Department of Pharmacology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
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10
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West M, Park D, Dodd JR, Kistler J, Christie DL. Purification and characterization of the creatine transporter expressed at high levels in HEK293 cells. Protein Expr Purif 2005; 41:393-401. [PMID: 15866727 DOI: 10.1016/j.pep.2005.02.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2004] [Revised: 02/22/2005] [Indexed: 11/23/2022]
Abstract
The bovine creatine transporter (CreaT) has been purified from membranes of HEK293 cells stably expressing high levels of the transporter. Membranes were solubilized with decyl maltoside and the CreaT was purified (90% pure) by affinity chromatography on wheat germ agglutinin (WGA)-Sepharose and gel-filtration. The CreaT was shown to be an approximately 70 kDa glycoprotein by SDS-polyacrylamide gel electrophoresis and Western blotting. Identification of the CreaT was confirmed by sequencing tryptic peptides by mass spectrometry. Laser light scattering showed the majority of the CreaT to be present as a 224 kDa species. Additional purification was obtained when the Creat was eluted from the WGA column and purified by gel-filtration in Fos-choline 12 instead of decyl maltoside, followed by a second WGA affinity step to exchange the detergent for sodium cholate. This resulted in a 30-fold purification (95% purity) of the approximately 70kDa CreaT, with a yield of 15%. From this, it is estimated that the CreaT comprises approximately 3% of total HEK293-CreaT membrane protein. Gel-filtration showed the transporter to migrate with an apparent molecular mass of 210 kDa. Circular dichroism showed a predominantly alpha-helical structure, consistent with the 12 transmembrane domains predicted for the transporter. This work has enabled the purification of the CreaT in amounts ( approximately 100 microg) that make it feasible to consider structural studies of a member of the Na(+)- and Cl(-)-dependent neurotransmitter transporter family.
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Affiliation(s)
- Mark West
- Biochemistry and Cell Biology Group, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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11
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Abstract
Glycine exerts multiple functions in the central nervous system, as an inhibitory neurotransmitter through activation of specific, Cl--permeable, ligand-gated ionotropic receptors and as an obligatory co-agonist with glutamate on the activation of N-methyl-D-aspartate (NMDA) receptors. In some areas of the central nervous system, glycine seems to be co-released with gamma-aminobutyric acid (GABA), the main inhibitory amino acid neurotransmitter. The synaptic action of glycine ends by active recapture through sodium- and chloride-coupled glycine transporters located in glial and neuronal plasma membranes, whose structure-function relationship is being studied. The trafficking and plasma membrane expressions of these proteins are controlled by regulatory mechanisms. Glycine transporter inhibitors may find application in the treatment of muscle tone defects, epilepsy, schizophrenia, pain and neurodegenerative disorders. This review deals on recent progress on localization, transport mechanisms, structure, regulation and pharmacology of the glycine transporters (GLYTs).
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Affiliation(s)
- Carmen Aragón
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
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12
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Tunnicliff G. Membrane glycine transport proteins. J Biomed Sci 2003; 10:30-6. [PMID: 12566983 DOI: 10.1007/bf02255994] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2002] [Accepted: 09/01/2002] [Indexed: 11/24/2022] Open
Abstract
Structurally, the simplest amino acid is glycine, and it has a number of important yet distinct functions in the body. This review focuses on the different transport systems and the associated carrier proteins for glycine that are responsible for its movement across biological membranes. Transport proteins in the class GLYT appear to be the most specific for glycine. However, the B0+ system also carries significant amounts of glycine. Other amino acid transport systems capable of carrying small amounts of glycine are ASC, asc and system L. In addition, an ATP-dependent transport process exists that takes up glycine into synaptic vesicles at nerve endings. This is known as the vesicular inhibitory amino acid transporter since, in addition to glycine, it can transport possibly two other inhibitory neurotransmitters.
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Affiliation(s)
- Godfrey Tunnicliff
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Evansville, Ind. 47712, USA.
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13
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Abstract
In the brain, neurons and glial cells compete for the uptake of the fast neurotransmitters, glutamate, GABA and glycine, through specific transporters. The relative contributions of glia and neurons to the neurotransmitter uptake depend on the kinetic properties, thermodynamic coupling and density of transporters but also on the intracellular metabolization or sequestration of the neurotransmitter. In the case of glycine, which is both an inhibitory transmitter and a neuromodulator of the excitatory glutamatergic transmission as a co-agonist of N-methyl D-aspartate receptors, the glial (GlyT1b) and neuronal (GlyT2a) transporters differ at least in three aspects: (i) stoichiometries, (ii) reverse uptake capabilities and (iii) pre-steady-state kinetics. A 3 Na(+)/1 Cl(-)/gly stoichiometry was established for GlyT2a on the basis of a 2 charges/glycine flux ratio and changes in the reversal potential of the transporter current as a function of the extracellular glycine, Na(+) and Cl(-) concentrations. Therefore, the driving force available for glycine uphill transport in neurons is about two orders of magnitude larger than for glial cells. In addition, GlyT2a shows a severe limitation for reverse uptake, which suggests an essential role of GlyT2a in maintaining a high intracellular glycine pool, thus facilitating the refilling of synaptic vesicles by the low affinity, low specificity vesicular transporter VGAT/VIAAT. In contrast, the 2 Na(+)/1 Cl(-)/gly stoichiometry and bi-directional transport properties of GlyT1b are appropriate for the control of the extracellular glycine concentration in a submicromolar range that can modulate N-methyl D-aspartate receptors effectively. Finally, analysis of the pre-steady-state kinetics of GlyT1b and GlyT2a revealed that at the resting potential neuronal transporters are preferentially oriented outward, ready to bind glycine, which suggests a kinetic advantage in the uptake contest.
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Affiliation(s)
- Stéphane Supplisson
- Laboratoire de Neurobiologie Moléculaire et Cellulaire, UMR8544, Ecole Normale Supérieure, 46 rue d'Ulm, 75005, Paris, France.
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Abstract
Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.
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Affiliation(s)
- N C Danbolt
- Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1105, Blindern, N-0317, Oslo, Norway
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15
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Martínez-Maza R, Poyatos I, López-Corcuera B, N úñez E, Giménez C, Zafra F, Aragón C. The role of N-glycosylation in transport to the plasma membrane and sorting of the neuronal glycine transporter GLYT2. J Biol Chem 2001; 276:2168-73. [PMID: 11036075 DOI: 10.1074/jbc.m006774200] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glycine transporter GLYT2 is an axonal glycoprotein involved in the removal of glycine from the synaptic cleft. To elucidate the role of the carbohydrate moiety on GLYT2 function, we analyzed the effect of the disruption of the putative N-glycosylation sites on the transport activity, intracellular traffic in COS cells, and asymmetrical distribution of this protein in polarized Madin-Darby canine kidney (MDCK) cells. Transport activity was reduced by 35-40% after enzymatic deglycosylation of the transporter reconstituted into liposomes. Site-directed mutagenesis of the four glycosylation sites (Asn-345, Asn-355, Asn-360, and Asn-366), located in the large extracellular loop of GLYT2, produced an inactive protein that was retained in intracellular compartments when transiently transfected in COS cells or in nonpolarized MDCK cells. When expressed in polarized MDCK cells, wild type GLYT2 localizes in the apical surface as assessed by transport and biotinylation assays. However, a partially unglycosylated mutant (triple mutant) was distributed in a nonpolarized manner in MDCK cells. The apical localization of GLYT2 occurred by a glycolipid rafts independent pathway.
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Affiliation(s)
- R Martínez-Maza
- Centro de Biologia Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Consejo Superior de Investigaciones Cientificas, 28049 Madrid, Spain
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16
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Rud E, Gederaas O, Høgset A, Berg K. 5-aminolevulinic acid, but not 5-aminolevulinic acid esters, is transported into adenocarcinoma cells by system BETA transporters. Photochem Photobiol 2000; 71:640-7. [PMID: 10818796 DOI: 10.1562/0031-8655(2000)071<0640:aabnaa>2.0.co;2] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
5-aminolevulinic acid (5-ALA) and its ester derivatives are used in photodynamic therapy as precursors for the formation of photosensitizers. This study relates to the mechanisms by which 5-ALA is transported into cells. The transport of 5-ALA has been studied in a human adenocarcinoma cell line (WiDr) by means of [14C]-labeled 5-ALA. The rate of uptake was saturable following Michaelis-Menten kinetics (K(m) = 8-10 mM and Vmax = 18-20 nmol.(mg protein x h)-1), and Arrhenius plot of the temperature-dependent uptake of 5-ALA was characterized by a single discontinuity at 32 degrees C. The activation energy was 112 kJ.mol-1 in the temperature range 15 degrees-32 degrees C and 26 kJ.mol-1 above 32 degrees C. Transport of 5-ALA was Na+ and partly Cl(-)-dependent. Stoichiometric analysis revealed a Na+:5-ALA coupling ratio of 3:1. With the exception of valine, methionine and threonine, zwitterionic and basic amino acids inhibited the transport of 5-ALA. 5-ALA methyl ester was not an inhibitor of 5-ALA uptake. The transport was most efficiently inhibited, i.e. by 65-75%, by the beta-amino acids, beta-alanine and taurine and by gamma-aminobutyric acid (GABA). Accordingly, 5-ALA, but not 5-ALA methyl ester, was found to inhibit cellular uptake of [3H]-GABA and [14C]-beta-alanine. Protoporphyrin IX (PpIX) accumulation in the presence of 5-ALA (0.3 mM) was attenuated 85% in the presence of 10 mM beta-alanine, while PpIX formation in cells treated with 5-ALA methyl ester (0.3 mM) or 5-ALA hexyl ester (4 microM) was not significantly influenced by beta-alanine. Thus, 5-ALA, but not 5-ALA esters, is transported by beta-amino acid and GABA carriers in this cell line.
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Affiliation(s)
- E Rud
- Department of Biophysics, Norwegian Radium Hospital, Montebello, Oslo, Norway
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17
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Abstract
It is known that channel catfish erythrocytes can take up glycine by several distinct transport systems. Further, glycine is an inhibitory neurotransmitter in mammalian brain and spinal cord. Consequently, the uptake of [(3)H]glycine by catfish brain was investigated and found to be a saturable process, dependent on the presence of Na(++) and Cl(--) and sensitive to temperature. A kinetic analysis of transport was performed at 22C. This showed that a high-affinity system existed which exhibited a K(m) of 5.1 (+/- 2. 1) microM. Several structural analogues of glycine were capable of inhibiting uptake in a competitive manner. The most effective inhibitor was sarcosine (IC(50) 5 36 microM). Uptake was also able to be inhibited by harmaline, a drug known to interfere with Na(+)-dependent transport processes. It is concluded that glycine transport by channel catfish brain has much in common with transport by mammalian nervous tissue which is carried out by the membrane carriers GLYT1 and GLYT2. On the other hand, synaptosomal transport differs somewhat from glycine transport by channel catfish erythrocytes.
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Affiliation(s)
- T R Wolf
- Laboratory of Neurochemistry, Indiana University School of Medicine, Evansville, IN 47712, USA
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18
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Affiliation(s)
- C G Tate
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
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19
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Aragón C, López-Corcuera B. Purification, hydrodynamic properties, and glycosylation analysis of glycine transporters. Methods Enzymol 1998; 296:3-17. [PMID: 9779437 DOI: 10.1016/s0076-6879(98)96003-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Affiliation(s)
- C Aragón
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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20
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Povlock SL, Amara SG. Vaccinia virus-T7 RNA polymerase expression system for neurotransmitter transporters. Methods Enzymol 1998; 296:436-43. [PMID: 9779465 DOI: 10.1016/s0076-6879(98)96031-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Affiliation(s)
- S L Povlock
- Vollum Institute for Advanced Biomedical Research, Oregon Health Sciences University, Portland 97201-3011, USA
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21
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Palacín M, Estévez R, Bertran J, Zorzano A. Molecular biology of mammalian plasma membrane amino acid transporters. Physiol Rev 1998; 78:969-1054. [PMID: 9790568 DOI: 10.1152/physrev.1998.78.4.969] [Citation(s) in RCA: 584] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Molecular biology entered the field of mammalian amino acid transporters in 1990-1991 with the cloning of the first GABA and cationic amino acid transporters. Since then, cDNA have been isolated for more than 20 mammalian amino acid transporters. All of them belong to four protein families. Here we describe the tissue expression, transport characteristics, structure-function relationship, and the putative physiological roles of these transporters. Wherever possible, the ascription of these transporters to known amino acid transport systems is suggested. Significant contributions have been made to the molecular biology of amino acid transport in mammals in the last 3 years, such as the construction of knockouts for the CAT-1 cationic amino acid transporter and the EAAT2 and EAAT3 glutamate transporters, as well as a growing number of studies aimed to elucidate the structure-function relationship of the amino acid transporter. In addition, the first gene (rBAT) responsible for an inherited disease of amino acid transport (cystinuria) has been identified. Identifying the molecular structure of amino acid transport systems of high physiological relevance (e.g., system A, L, N, and x(c)- and of the genes responsible for other aminoacidurias as well as revealing the key molecular mechanisms of the amino acid transporters are the main challenges of the future in this field.
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Affiliation(s)
- M Palacín
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Spain
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22
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Abstract
Glycine is a major inhibitory neurotransmitter in the spinal cord and brainstem of vertebrates. Glycine is accumulated into synaptic vesicles by a proton-coupled transport system and released to the synaptic cleft after depolarization of the presynaptic terminal. The inhibitory action of glycine is mediated by pentameric glycine receptors (GlyR) that belong to the ligand-gated ion channel superfamily. The synaptic action of glycine is terminated by two sodium- and chloride-coupled transporters, GLYT1 and GLYT2, located in the glial plasma membrane and in the presynaptic terminals, respectively. Dysfunction of inhibitory glycinergic neurotransmission is associated with several forms of inherited mammalian myoclonus. In addition, glycine could participate in excitatory neurotransmission by modulating the activity of the NMDA subtype of glutamate receptor. In this article, we discuss recent progress in our understanding of the molecular mechanisms that underlie the physiology and pathology of glycinergic neurotransmission.
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Affiliation(s)
- F Zafra
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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23
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Zafra F, Gomeza J, Olivares L, Aragón C, Giménez C. Regional distribution and developmental variation of the glycine transporters GLYT1 and GLYT2 in the rat CNS. Eur J Neurosci 1995; 7:1342-52. [PMID: 7582108 DOI: 10.1111/j.1460-9568.1995.tb01125.x] [Citation(s) in RCA: 204] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The high-affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. Previous molecular cloning studies have indicated heterogeneity of glycine transporters in the CNS. Here the distribution of glycine transporter GLYT1 and GLYT2 transcripts and proteins in different regions and developmental stages of the rat brain were analysed by Northern, Western and in situ hybridization techniques. Sequence-specific riboprobes and two specific antibodies raised against fusion proteins were used, containing either 76 or 193 amino acids of the C or N terminus of the GLYT1 and GLYT2 transporters respectively. High levels of GLYT1 transcripts were found in the spinal cord, brainstem and cerebellum, and moderate levels in forebrain regions such as the cortex or hippocampus. GLYT2 transcripts are restricted to the spinal cord, brainstem and cerebellum. The onset of both GLYT1 and GLYT2 expression in the brainstem occurred in late fetal life, and full expression of these proteins was observed before weaning. There was a stepwise increase in the levels of mRNA and protein for these two transporters, reaching a maximum by the second postnatal week, followed by a slight decrease until adult values were reached by the fourth postnatal week. These data reveal interesting parallelism between the distribution of different glycine transporters and glycine receptor subunits, and suggest discrete roles for distinct glycine transporters.
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Affiliation(s)
- F Zafra
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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24
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Olivares L, Aragón C, Giménez C, Zafra F. The role of N-glycosylation in the targeting and activity of the GLYT1 glycine transporter. J Biol Chem 1995; 270:9437-42. [PMID: 7721869 DOI: 10.1074/jbc.270.16.9437] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
To elucidate the role of N-glycosylation in the function of the high affinity glycine transporter GLYT1, we have investigated the effect of the glycosylation inhibitor tunicamycin as well as the effect of the disruption of the putative glycosylation sites by site-directed mutagenesis. SDS-polyacrylamide gel electrophoresis of proteins from GLYT1-transfected COS cells reveals a major band of 80-100 kDa and a minor one of 57 kDa. Treatment with tunicamycin produces a 40% inhibition in transport activity and a decrease in the intensity of the 80-100-kDa band, whereas the 57-kDa band decreases in size to yield a 47-kDa protein corresponding to the unglycosylated form of the transporter. Simultaneous mutation of Asn-169, Asn-172, Asn-182, and Asn-188 to Gln also produces the 47-kDa form of the protein, indicating that there are no additional sites for N-glycosylation. Progressive mutation of the potential glycosylation sites produces a progressive decrease in transport activity and in size of the protein, indicating that the four putative glycosylation sites are actually glycosylated. N-Glycosylation of the GLYT1 is not indispensable for the transport activity itself, as demonstrated by enzymatic deglycosylation of the transporter. Analysis of surface proteins by biotinylation and by immunofluorescence demonstrates that a significant portion of the unglycosylated GLYT1 mutant remains in the intracellular compartment. This suggests that the carbohydrate moiety of glycine transporter GLYT1 is necessary for the proper trafficking of the protein to the plasma membrane.
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Affiliation(s)
- L Olivares
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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25
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Gomeza J, Zafra F, Olivares L, Giménez C, Aragón C. Regulation by phorbol esters of the glycine transporter (GLYT1) in glioblastoma cells. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1233:41-6. [PMID: 7833348 DOI: 10.1016/0005-2736(94)00249-o] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The high-affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. The effects of 12-O-tetradecanoylphorbol ester (TPA), a potent activator of protein kinase C (PKC), on the high-affinity Na(+)-dependent glycine transport were investigated in C6 cells, a cell line of glial origin. Incubation of C6 cells with TPA led to concentration- and time-dependent decrease in the glycine transport that could be completely suppressed by the addition of the PKC inhibitor staurosporine. The TPA effect could be mimicked by oleoylacetylglycerol and exogenous phospholipase C. Northern and Western blot analysis indicate that C6 cells express the GLYT1 glycine transporter. Incubation of COS cells transiently transfected with a full-length clone of the GLYT1 transporter in the presence of TPA, produces a decrease in glycine uptake.
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Affiliation(s)
- J Gomeza
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, C.S.I.C., Spain
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26
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Affiliation(s)
- N C Danbolt
- Anatomical Institute, University of Oslo, Norway
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27
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Olivares L, Aragón C, Giménez C, Zafra F. Carboxyl terminus of the glycine transporter GLYT1 is necessary for correct processing of the protein. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)46941-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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28
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Núñez E, Aragón C. Structural analysis and functional role of the carbohydrate component of glycine transporter. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(19)89477-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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29
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Nakanishi M, Kagawa Y, Narita Y, Hirata H. Purification and reconstitution of an intestinal Na(+)-dependent neutral L-alpha-amino acid transporter. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37111-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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30
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Gomeza J, Giménez C, Zafra F. Cellular distribution and regulation by cAMP of the GABA transporter (GAT-1) mRNA. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1994; 21:150-6. [PMID: 8164515 DOI: 10.1016/0169-328x(94)90387-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The high-affinity GABA transporter in neurons and glial cells is the primary means of inactivating synaptic GABA. In the present study, a rat GABA transporter (GAT-1)-specific probe was used to quantitate GAT-1 mRNA in cultured neurons and glial cells from rat brain. GAT-1 mRNA is expressed in neurons but not in pure cultures of astrocytes. Incubation of neurons with forskolin led to concentration- and time-dependent decreases in GAT-1 mRNA. This effect could be also achieved by chronic exposure of neurons to 8-Br-cAMP and dib-cAMP but not with 1,9-dideoxyforskolin. This effect on the levels of GAT-1 mRNA correlates with a decrease in the Na(+)-dependent GABA transport activity in neurons. Treatment with agents that increase cellular levels of cAMP did not affect GABA transport or GAT-1 mRNA expression in glial cells.
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Affiliation(s)
- J Gomeza
- Departamento de Biología Molecular, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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31
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Cloning and expression of a spinal cord- and brain-specific glycine transporter with novel structural features. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)41598-0] [Citation(s) in RCA: 209] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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32
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Abstract
Our understanding of the plasma membrane and vesicular transport systems that mediate neurotransmitter re-uptake has been greatly enhanced in the past year by the cloning and characterization of two additional gene families involved in this process, the excitatory amino acid transporters and the vesicular amine transporters. Additional members of the previously defined family of Na+/Cl(-)-dependent transporters continue to be identified.
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Affiliation(s)
- S G Amara
- Vollum Institute, Oregon Health Sciences University, Portland
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33
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Clark JA, Amara SG. Amino acid neurotransmitter transporters: structure, function, and molecular diversity. Bioessays 1993; 15:323-32. [PMID: 8102052 DOI: 10.1002/bies.950150506] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Many biologically active compounds including neurotransmitters, metabolic precursors, and certain drugs are accumulated intracellularly by transporters that are coupled to the transmembrane Na+ gradient. Amino acid neurotransmitter transporters play a key role in the regulation of extracellular amino acid concentrations and termination of neurotransmission in the CNS section. Transporters for the major amino acid neurotransmitters glutamate, GABA, and glycine are found in both neurons and glial cells. Recent work has resulted in the identification of cDNAs encoding several amino acid neurotransmitter transport proteins, all of which belong to the Na(+)- and Cl(-)-dependent transporter gene family. The diversity of this family suggests a degree of transporter heterogeneity that is greater than that indicated by biochemical and pharmacological studies.
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Affiliation(s)
- J A Clark
- Department of Pharmacology, Yale University, New Haven, CT 06510
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34
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Levy LM, Lehre KP, Rolstad B, Danbolt NC. A monoclonal antibody raised against an [Na(+)+K+]coupled L-glutamate transporter purified from rat brain confirms glial cell localization. FEBS Lett 1993; 317:79-84. [PMID: 7679083 DOI: 10.1016/0014-5793(93)81495-l] [Citation(s) in RCA: 107] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A monoclonal antibody (9C4) shows that an [Na(+)+K+]coupled glutamate transporter protein purified from rat brain runs electrophoretically as a wide band and is localized in neuroglial cell bodies and processes, but not in neurons. This confirms the findings with polyclonal antibodies [Neuroscience 51 (1992) 295-310], and shows that the apparent heterogeneity in relative molecular mass is accounted for by a single antigenic epitope. By testing several synthetic peptides derived from the deduced amino acid sequences of two cloned rat brain glutamate transporters, the antigenic epitope was identified as residing within the peptide TQSVYDDTKNHRESNSNQC (residues 518-536) of one of these [Nature 360 (1992) 464-467].
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Affiliation(s)
- L M Levy
- Anatomical Institute, University of Oslo, Norway
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35
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Hydrodynamic properties and immunological identification of the sodium- and chloride-coupled glycine transporter. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53987-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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36
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Danbolt NC, Storm-Mathisen J, Kanner BI. An [Na+ + K+]coupled L-glutamate transporter purified from rat brain is located in glial cell processes. Neuroscience 1992; 51:295-310. [PMID: 1465194 DOI: 10.1016/0306-4522(92)90316-t] [Citation(s) in RCA: 331] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Polyclonal antibodies were generated against the major polypeptide (73,000 mol. wt) present in a highly purified preparation of the [Na+ + K+]coupled L-glutamate transporter from rat brain. These antibodies were able to selectively immunoprecipitate the 73,000 mol. wt polypeptide as well as most of the L-glutamate transport activity--as assayed upon reconstitution--from crude detergent extracts of rat brain membranes. The immunoreactivity in the various fractions obtained during the purification procedure [Danbolt et al. (1990) Biochemistry 29, 6734-6740] closely correlated with the L-glutamate transport activity. Immunoblotting of a crude sodium dodecyl sulphate brain extract, separated by two-dimensional isoelectric focusing-sodium dodecyl sulphate-polyacrylamide gel electrophoresis, showed that the antibodies recognized one 73,000 mol. wt protein species only. Deglycosylation of the protein gave a 10,000 reduction in molecular mass, but no reduction in immunoreactivity. These findings establish that the 73,000 mol. wt polypeptide represents the L-glutamate transporter or a subunit thereof. The antibodies also recognize a 73,000 mol. wt polypeptide and immunoprecipitate L-glutamate transport activity in extracts of brain plasma membranes from rabbit, pig, cow, cat and man. Using the antibodies, the immunocytochemical localization of the transporter was studied at the light and electron microscopic levels in rat central nervous system. In all regions examined (including cerebral cortex, caudatoputamen, corpus callosum, hippocampus, cerebellum, spinal cord) it was found to be located in glial cells rather than in neurons. In particular, fine astrocytic processes were strongly stained. Putative glutamatergic axon terminals appeared non-immunoreactive. The uptake of glutamate by such terminals (for which there is strong previous evidence) therefore may be due to a subtype of glutamate transporter different from the glial transporter demonstrated by us.
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Affiliation(s)
- N C Danbolt
- Anatomical Institute, University of Oslo, Norway
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37
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Alcántara R, Casado M, Olivares L, Giménez C, Aragón C. L-glutamate transporter derived from mRNAs of primary glial cultures: expression in Xenopus laevis oocytes. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1992; 15:167-70. [PMID: 1331663 DOI: 10.1016/0169-328x(92)90166-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A high-affinity sodium-dependent L-glutamate transporter was expressed in Xenopus oocytes after microinjection of poly(A)+ RNA from primary astrocyte cultures from rat brain cortex. mRNA-induced L-glutamate transport was saturable by substrate and shows kinetic features similar to those found in intact glial cell preparations. L-Glutamate accumulation was prevented by rising the external K+ concentration or by coincubation with L-, D-aspartate or D-glutamate. After fractionation by sucrose density gradient, the mRNA encoding for the expressed L-glutamate transporter from glial cells was found in fractions containing messages of 2.05-2.9 kilobases (kb) in length.
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Affiliation(s)
- R Alcántara
- Centro de Biología Molecular, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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38
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Liu QR, Nelson H, Mandiyan S, López-Corcuera B, Nelson N. Cloning and expression of a glycine transporter from mouse brain. FEBS Lett 1992; 305:110-4. [PMID: 1618338 DOI: 10.1016/0014-5793(92)80875-h] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We have isolated a cDNA clone from a mouse brain library encoding the glycine transporter (GLYT). Xenopus oocytes injected with a synthetic mRNA accumulated [3h]glycine to levels of up to 80-fold above control values. The uptake was specific for glycine and dependent on the presence of Na+ and Cl- in the medium. The cDNA sequence predicts a highly hydrophobic protein of 633 amino acids with 12 potential transmembrane helices. The predicted amino acid sequence has 40-45% identity to the GABA, noradrenaline, serotonin and dopamine transporters. This implies that all of these neurotransmitter transporters may have evolved from a common ancestral gene that diverged into the GABA, glycine and catecholamine subfamilies at nearly the same time.
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Affiliation(s)
- Q R Liu
- Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110
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