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Encyclopedia > GABA A receptor

The GABAA receptor is one of the three ligand-gated ion channels responsible for mediating the effects of Gamma-AminoButyric Acid (GABA), the major inhibitory neurotransmitter in the brain. Ligand-gated ion channel is a broad term that refers to any ion channel that is gated (i. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... Gaba may refer to: Gabâ or gabaa (Philippines), the concept of negative karma of the Cebuano people GABA, the gamma-amino-butyric acid neurotransmitter GABA receptor, in biology, receptors with GABA as their endogenous ligand Gaba 1 to 1, an English conversational school in Japan Marianne Gaba, a US model... Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ...

Contents

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Structure and function

The receptor is a multimeric transmembrane receptor that consists of five subunits arranged around a central pore. The receptor sits in the membrane of its neuron at a synapse. The ligand GABA is the endogenous compound that causes this receptor to open; once bound to GABA, the protein receptor changes conformation within the membrane, opening the pore in order to allow chloride ions (Cl-) to pass down an electrochemical gradient. Because the [reversal potential] for chloride in most neurons is close to the resting membrane potential, activation of GABAA receptors tends to stabilize the resting potential, and can make it more difficult for excitatory neurotransmitters to depolarize the neuron and generate an action potential. The net effect is typically inhibitory, reducing the activity of the neuron. The GABAA channel opens quickly and thus contributes to the early part of the inhibitory postsynaptic potential (IPSP) (Siegel et al., 1999; Chen et al., 2005). Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ... A pore, in general, is some form of opening, usually very small. ... It has been suggested that Net flux be merged into this article or section. ... Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. ... Illustration of the major elements in a prototypical synapse. ... In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... The chloride ion is formed when the element chlorine picks up one electron to form an anion (negatively-charged ion) Cl−. The salts of hydrochloric acid HCl contain chloride ions and are also called chlorides. ... An ion is an atom or group of atoms that normally are electrically neutral and achieve their status as an ion by loss (or addition) of an electron. ... Membrane potential (or transmembrane potential or transmembrane potential difference or transmembrane potential gradient), is the electrical potential difference (voltage) across a cells plasma membrane. ... Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... In biology, depolarization is the event a cell undergoes when its membrane potential grows more positive with respect to the extracellular solution. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... Inhibitory Postsynaptic Potential is commonly abbreviated to Impulses are transmitted from neuron to neuron by the release of a chemical transmitter across synaptic clefts from the synaptic vesicles along the axon to the postsynaptic receptors of another neuron. ...

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Subunits

GABAA receptors are members of the large "Cys-loop" superfamily of evolutionarily related and structurally similar ligand-gated ion channels that also includes nicotinic acetylcholine receptors, glycine receptors, and the 5HT3 serotonin receptor. There are numerous subunit isoforms for the GABAA receptor, which determine the receptor’s agonist affinity, chance of opening, conductance, and other properties (Cossart et al., 2005). There are six types of α subunits, three β's, three γ's, as well as a δ, an ε, a π, a θ, and three ρs (Martin and Dunn, 2002; Sieghart et al., Neurochem Int 1999;34:379–85). Five subunits can combine in different ways to form GABAA channels, but the most common type in the brain has two α's, two β's, and a γ (Martin and Dunn, 2002). The receptor binds two GABA molecules (Siegel et al., 1999; Colquhoun and Sivilotti, 2004), somewhere between an α and a β subunit (Martin and Dunn, 2002). Ligand-gated ion channel is a broad term that refers to any ion channel that is gated (i. ... Nicotinic acetylcholine receptors, or nAChRs, are ionotropic receptors that form ion channels in cells plasma membranes. ... The Glycine receptor is one of the most widely distributed inhibitory receptors in the Central nervous system. ... Serotonin (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract. ... In biology, a protein isoform is a version of a protein with some small differences, usually a splice variant or the product of some posttranslational modification. ...

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Agonists and antagonists

Other ligands (besides GABA) interact with the GABAA receptor to activate it (agonists), to inhibit its activation (antagonists) or to increase or decrease its response to an agonist (positive and negative allosteric modulators). Such other ligands include benzodiazepines (increase pore opening frequency; often the ingredient of sleep pills and anxiety medications), imidazopyridines (newer class of sleep medications), barbiturates (increase pore opening duration; used as sedatives), and certain steroids, called neuroactive steroids. alprazolam 2mg tablets The benzodiazepines (pronounced , which are considered minor tranquilizers) are a class of drugs with sedative, hypnotic, anxiolytic, anticonvulsant, amnestic and muscle relaxant properties. ... The imidazopyridines are a class of drugs related to benzodiazepines. ... Barbiturates are drugs that act as central nervous system (CNS) depressants, and by virtue of this they produce a wide spectrum of effects, from mild sedation to anesthesia. ... In chemistry and biology, Steroids are a type of lipid, characterized by a carbon skeleton with four fused rings. ... Apart from exerting effects on the genome via intracellular steroid receptors, neuroactive steroids (or neurosteroids) rapidly alter neuronal excitability through interaction with neurotransmitter-gated ion channels. ...


Among antagonists are picrotoxin (which blocks the channel pore) and bicuculline (which occupies the GABA site and prevents GABA from activating the receptor). The antagonist flumazenil is used medically to reverse the effects of the benzodiazepines. Flumazenil (flumazepil, Anexate®, Lanexat®, Mazicon®, Romazicon®) is a benzodiazepine antagonist, used as an antidote in the treatment of benzodiazepine overdose. ...


A useful property of the many agonists and some antagonists is that they often have a greater interaction with GABAA receptors which contain specific subunits. This allows one to determine which GABAA receptor subunit combinations are prevalent in particular brain areas and provides a clue as to which subunit combinations may be responsible for behavioral effects of drugs acting at GABAA receptors. Among the behavioral effects of such drugs are relief of anxiety (anxiolysis), muscle relaxation, sedation, anticonvulsion, and anesthesia. Sedation is a medical procedure involving administration of sedative drugs, generally to facilitate a medical procedure, such as endoscopy, vasectomy, or minor surgery with local anaesthesia. ... The anticonvulsants, sometimes also called antiepileptics, belong to a diverse group of pharmaceuticals used in prevention of the occurrence of epileptic seizures. ... Anesthesia or anaesthesia (see spelling differences) has traditionally meant the process of blocking the perception of pain and other sensations. ...

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See also

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The GABA receptors are a group of receptors with γ-aminobutyric acid (GABA) as their endogenous ligand. ... GABAB receptors (GABABR) are metabotropic transmembrane receptors that are linked via G-proteins to potassium channels (Chen et al. ... The GABAC receptor is also linked to chloride channels, with distinct physiological and pharmacological properties. ...

References

  • Chen K., Lia H.Z., Yea N., Zhanga J., and Wang J.J. 2005. Role of GABAB receptors in GABA and baclofen-induced inhibition of adult rat cerebellar interpositus nucleus neurons in vitro. Brain Research Bulletin, 67(4), 310-318.
  • Colquhoun D. and Sivilotti L.G. 2004. Function and structure in glycine receptors and some of their relatives. Trends in Neurosciences, 27(6), 337-344.
  • Martin I.L., and Dunn S.M.J. 2002. "GABA Receptors". Tocris Cookson Ltd.
  • Siegel G.J., Agranoff B.W., Fisher S.K., Albers R.W., and Uhler M.D. 1999. Basic Neurochemistry: Molecular, Cellular and Medical Aspects, Sixth Edition. GABA Receptor Physiology and Pharmacology. American Society for Neurochemistry. Lippincott Williams and Wilkins.
  • Cossart R, Bernard C, Ben-Ari Y. 2005. Multiple facets of GABAergic neurons and synapses: multiple fates of GABA signalling in epilepsies. TRENDS in Neurosciences, 28(2), 108-115
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External links

  • Basic Neurochemistry: GABA Receptor Physiology and Pharmacology
  • Dr. Dreyer's GABA-R webpage (University of Fribourg, Switzerland)


  Results from FactBites:
 
GABA receptor - Wikipedia, the free encyclopedia (1143 words)
GABA is the chief inhibitory neurotransmitter in the mammalian brain.
receptors were initially distinguished by their sensitivity to the ligand bicuculline with the former being antagonized by it while the latter were insensitive.
The GABA A receptor is a member of the Cys-loop ligand-gated ion channel superfamily which also includes the glycine, 5-hydroxytryptamine (5-HT, serotonin), and nicotinic acetylcholine receptors.
GABA A receptor - Wikipedia, the free encyclopedia (600 words)
The receptor is a multimeric transmembrane receptor that consists of five subunits arranged around a central pore.
The ligand GABA is the endogenous compound that causes this receptor to open; once bound to GABA, the protein receptor changes conformation within the membrane, opening the pore in order to allow chloride ions (Cl-) to pass down an electrochemical gradient.
receptors in GABA and baclofen-induced inhibition of adult rat cerebellar interpositus nucleus neurons in vitro.
  More results at FactBites »

 
 

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