Inhibitory neurotransmitter receptors: The GABA receptor family, molecular properties and regulation
Professor Trevor G. Smart, FRPharmS, FMedSci
|Schild Professor of Pharmacology|
|Tel: +44 (0) 20 7679 3770|
Professor Trevor G. Smart graduated in 1977 with a B. Pharm and worked in the NHS until 1978 returning to study for a PhD in receptor pharmacology at The School of Pharmacy, University of London. He obtained a teaching fellowship at The School and also postdoctoral experience at Sandoz, Basel, before securing a New Blood Lectureship at The School and remained there as a Wellcome Trust Research Leave Fellow, Reader in Molecular Neuropharmacology, eventually becoming the Wellcome Professor of Pharmacology and Head of Department in 1996. In 2002, he moved to the Schild Chair in Pharmacology and Head of Department at UCL. He has been an editor of Journal of Physiology and Neuropharmacology and is a Senior Editor of Br. J. Pharmacology. He serves on the MRC Neurosciences and Mental Health Board in addition to the MRC JREI and TSE panels and chairs the MRC ESS panel. He has been previously awarded the Sandoz prize in Pharmacology, the Lilly Award for Pharmaceutical Sciences and the RSPGB Conference Science Medal. In 2000, he became an FRPharmS and in 2006 he was made a Fellow of the Academy of Medical Sciences.
Securing a ‘peaceful, quiet, even calm’ nervous system requires nerve cells and their natural excitability to be controlled continuously. There are various ways of achieving this aim, but by far the most important route involves the operation of ligand-gated ion channels that are activated by the inhibitory transmitter, GABA. Fast synaptic inhibition is achieved by rapid activation of GABAA receptors whilst longer term modulatory affects on excitability is accomplished by GABAB receptor activation. What has become increasingly clear is that there are many different isoforms of GABAA receptors and these appear, in particular examples, to be targeted to discrete areas of the brain, and even within single neurones, to discrete synapses. Given the critical role these receptors play in neuronal function, they form a logical target for therapeutic agents principally designed to ameliorate neuronal excitability in disease states such as epilepsy and anxiety. These receptors are also increasingly involved in the action of selected general anaesthetic agents.
The areas of our research are supported by long-term programme grant support from the Medical Research Council and the Wellcome Trust, benefiting also from the MRC Cooperative centred at UCL on ‘Receptors, Ion Channels and Transporters’. We are using a combined approach to elucidate the molecular properties of GABA receptors employing electrophysiological techniques at both whole-cell, synaptic and single channel levels, using both native neurones in dissociated culture or sliced preparations. We also use concurrent expression of recombinant receptors in Xenopus oocytes and suitable cell lines for functional analyses. The techniques we use to enable DNA or RNA to gain access to cells and allow receptor expression includes, transfection, viral infection, direct microinjection and lipofection, depending on the cell type. In addition, we are also using imaging techniques, with various fluorophores, to enable the tracking in live cells of receptor subunits in real time and also in fixed tissue into and out of various structures of the nervous system. All of these techniques are supported by modern, well-equipped laboratories, housing continuously updated equipment.
The major thrusts of our work include understanding how endogenous regulators in the nervous system can modulate the function of GABA receptors and inhibitory synapses. This leads to detailed, rationale structure-function studies using molecular biological approaches to understand where ligands bind to the receptors and how they affect function. In addition, we also wish to understand how intracellular processes can affect receptor targeting to synapses and long-term function. This involves analysing how accessory proteins on the intracellular surface of the cell may affect receptor functional properties including cell-surface expression levels at synaptic and extrasynaptic sites. This approach also incorporates the role of receptor phosphorylation in controlling receptor ion channel coupling and long-term changes in inhibitory synaptic efficacy/plasticity. These techniques benefit from the use of using internally perfused peptides to interfere with protein-protein associations in neurones and also the use of particular knock-out/in receptor/protein models. Overall, our major objective is to provide a complete molecular description of the therapeutically important GABA receptor classes that will enable a deeper understanding of their role in both healthy and diseased states.
- Duguid, IC, Pankratov, Y, Moss, GWJ & Smart ,TG (2007). Somatodendritic Release of Glutamate Regulates Synaptic Inhibition in Cerebellar Purkinje Cells via Autocrine mGluR1 Activation. J. Neurosci.; 27, 12464-12474.
- Mortensen M, Smart TG (2007). Single-channel recording of ligand-gated ion channels. Nature Protocols. 2, 2826-2841.
- Kuramoto N, Wilkins ME, Fairfax BP, Revilla-Sanchez R, Terunuma M, Tamaki K, Iemata M, Warren N, Couve A, Calver A, Horvath Z, Freeman K, Carling D, Huang L, Gonzales C, Cooper E, Smart TG, Pangalos MN & Moss SJ (2007). Phospho-Dependent Functional Modulation of GABAB Receptors by the Metabolic Sensor AMP-Dependent Protein Kinase. Neuron. 53, 233-247.
- Hosie AM, Wilkins ME, da Silva HM & Smart TG. (2006). Endogenous neurosteroids regulate GABAA receptors through two discrete transmembrane sites. Nature.444, 486-489.
- Thomas, P., Mortensen, M., Hosie, A.M. and Smart, T.G. (2005) Dynamic mobility of functional GABAA receptors at inhibitoty synapses. Nat. Neurosci. 8 (7), 889-897.
- Duguid I & Smart TG (2004). Retrograde activation of presynaptic NMDA receptors enhances GABA release at cerebellar interneuron-Purkinje cell synapses. Nature Neuroscience, in press.
- Mortensen M, Kristiansen U, Ebert B, Frølund B, Krogsgaard-Larsen P & Smart TG (2004). Activation of single heteromeric GABAA receptor ion channels by full and partial agonists. J. Physiol. In press.
- Smart et al. (2004) Twenty questions, the state of ion channel research in 2004. Nature Reviews Drug discovery 3, 237-278.
- Hosie AM, Dunne EL, Harvey RJ, Smart TG. (2003). Zinc-mediated inhibition of GABAA receptors: discrete binding sites underlie subtype specificity. Nature Neuroscience 6, 362-369.
- Wilkins, M.E. & Smart, T.G. (2002). Redox modulation of GABAA receptors obscured by Zn2+ complexation. Neuropharmacology 43, 938-944.
- Dunne, E.L., Hosie, A.M., Wooltorton, J.R.A., Duguid, I.C., Harvey , K., Moss, S.J., Harvey., R.J. & Smart, T.G.(2002). An N-terminal histidine regulates Zn2+ inhibition on the murine GABAA receptor 3 subunit. Brit. J. Pharmacol. 137 (1), 29-38.
- Wilkins , M.E. , Hosie, A.M. & Smart, T.G. (2002). Identification of a subunit TM2 residue mediating proton modulation of GABAA receptors. J. Neuroscience 22(13), 5328-5333.
- Couve A, Thomas P, Calver AR, Hirst WD, Pangalos MN Walsh FS,Smart TG, Moss SJ. (2002). Cyclic AMP-dependent protein kinase phosphorylation facilitates GABAB receptor-effector coupling. Nature Neuroscience 5(5),415-424.
- Moss S,J. & Smart, T.G. (2001). Constructing inhibitory synapses. Nature Reviews Neuroscience, 2, 240-250.
- Krishek, B.J. & Smart, T.G. (2001). Proton sensitivity of cerebellar granule cell GABAA receptors: Dependence on neuronal development. J. Physiol. 530.2, 219-233.
- Bedford FK, Kittler JT, Muller E, Thomas P, Uren JM, Merlo D,Wisden W, Triller A, Smart TG, Moss SJ. (2001). GABAA receptor cell surface number and subunit stability are regulated by the ubiquitin-like protein Plic-1. Nature Neuroscience. 4,908-16.
Current and former:-
Dr Damian Bright: Examining the trafficking of GABAA receptors involved in tonic inhibition and how this is altered in diseases such as epilepsy.
Dr Saad Hannan: Using novel tracking methods to monitor the movement of GABAB receptors in heterologous expression systems and neurones and deduce how this is regulated.
Dr Catriona Houston: Investigating the regulation of GABAA receptor function by Ca2+/calmodulin-dependent protein kinase II and how this affects inhibitory synaptic plasticity.
Dr Paul Miller: Studies the glycine receptor in neurones and expression systems. Paul aims to explain why Zn2+ can potentiate receptor function and examine whether this is physiologically relevant at glycinergic synapses in the spinal cord.
Dr Martin Mortensen: Studying the kinetics of synaptic and extrasynaptic GABAA receptor subtypes/populations in cultured hippocampal neurones using whole-cell and single channel patch clamp electrophysiology. He is also developing several single channel mechanisms which can describe the precise kinetic behaviour of recombinant and neuronal single GABAA receptor channels.
Dr Philip Thomas: Working on the trafficking of GABAA receptors into and out of synaptic compartments in cultured neurones by devising novel electrophysiological tracking methods.
Dr Megan Wilkins: Examining the regulation of GABAB receptors by phosphorylation and developing novel methods to monitor the trafficking of these receptors in live neuronal tissues.
Ms Joanna Adams: Studying the interaction of neurosteroids and protein phosphorylation on the regulation of GABAA receptor function.
Ms Qionger He: Researching the underling molecular mechanisms responsible for inhibitory synaptic plasticity at the interneuronal-Purkinje cell synapses in the cerebellum using both imaging and patch clamp electrophysiology.
Helena da Silva: Using expression systems to evaluate the interaction of therapeutically active drugs with the GABAA receptor.