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Gamma-aminobutyric acid
Gamma-aminobutyric acid

The GABA receptors are a class of receptors that respond to the neurotransmitter γ-aminobutyric acid (GABA), the chief inhibitory neurotransmitter in the vertebrate central nervous system. Gamma-aminobutyric acid (GABA is the chief inhibitory Neurotransmitter in the Mammalian Central nervous system. In Biochemistry, a receptor is a Protein molecule embedded in either the Plasma membrane or Cytoplasm of a cell to which a mobile signaling See Chemical synapse for an introduction to concepts and terminology used in this article Gamma-aminobutyric acid (GABA is the chief inhibitory Neurotransmitter in the Mammalian Central nervous system. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. There are three classes of GABA receptors: GABAA, GABAB, and GABAС. The GABAA receptor is one of two ligand-gated Ion channels responsible for mediating the effects of Gamma-aminobutyric acid (GABA the major GABAB receptors (GABABR are Metabotropic Transmembrane receptors for Gamma-aminobutyric acid (GABA that are linked via G-proteins The GABAC receptor is one of two Ligand-gated ion channels responsible for mediating the effects of Gamma-Amino Butyric Acid ( GABA) the major inhibitory

GABAA and GABAС receptors are ligand-gated ion channels (also known as ionotropic receptors), whereas GABAB receptors are G protein-coupled receptors (also known as metabotropic receptors). The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are G protein-coupled receptors ( GPCRs) also known as seven transmembrane domain receptors, 7TM receptors, heptahelical receptors, and Metabotropic receptor is a subtype of membrane receptors at the surface or in vesicles of Eukaryotic cells

Contents

Ligand-gated ion channels

GABAA

It has long been recognized that the fast response of neurons to GABA that is blocked by bicuculline and picrotoxin is due to direct activation of an anion channel. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information Bicuculline (BIC is a light-sensitive competitive antagonist of GABAA receptors Picrotoxin, also known as cocculin, is a poisonous crystalline plant alkaloid first isolated by Boullay in 1812 An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge [1][2][3][4][5]

This channel was subsequently termed the GABAA receptor. The GABAA receptor is one of two ligand-gated Ion channels responsible for mediating the effects of Gamma-aminobutyric acid (GABA the major [1] Fast-responding GABA receptors are members of family of Cys-loop ligand-gated ion channels. The Cys-loop Ligand-gated ion channel superfamily is comprised of Nicotinic Acetylcholine, GABAA, GABAC, The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are Ion channels are pore-forming Proteins that help establish and control the small Voltage Gradient across the Plasma membrane of all living [6][7][8] Members of this superfamily, which includes nicotinic acetylcholine receptors, GABAA and GABAС receptors, glycine and 5-HT3 receptors, possess a characteristic loop formed by a disulfide bond between two cysteine residues. Structure Nicotinic receptors with a molecular mass of 290 kDa, are made up of five subunits arranged symmetrically around the central pore. The GABAC receptor is one of two Ligand-gated ion channels responsible for mediating the effects of Gamma-Amino Butyric Acid ( GABA) the major inhibitory The glycine receptor, or GlyR, is the receptor for the Amino acid Neurotransmitter Glycine. The 5-HT3 receptor is a member of the superfamily of Ligand-gated ion channels a superfamily that also includes the neuronal Nicotinic acetylcholine receptors In Chemistry, a disulfide bond is a single Covalent bond derived from the coupling of Thiol groups Not to be confused with Cystine, its oxidized dimer Cysteine (abbreviated as Cys or C) is an α- Amino acid with

GABAС

A second type of ionotropic GABA receptors, insensitive to typical allosteric modulators of GABAA receptor channels such as benzodiazepines and barbiturates,[9][10][11] was designated GABAС receptor. The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are In Biochemistry, allosteric regulation is the regulation of an Enzyme or other Protein by binding an effector molecule at the protein's allosteric The benzodiazepines (pronounced, often abbreviated to "benzos") are a class of Psychoactive drugs with varying Hypnotic Barbiturates are drugs that act as central nervous system Depressants and by virtue of this they produce a wide spectrum of effects from mild Sedation [12][13]

Native responses of the GABAС receptor type occur in retinal bipolar or horizontal cells across vertebrate species. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. [14][15][16][17] GABAС receptors are exclusively composed of ρ subunits that are related to GABAA receptor subunits. [18][19][20]

Although the term "GABAС receptor" is frequently used, GABAС may be viewed as a variant within the GABAA receptor family. [6] However others have argued that the differences between GABAС and GABAA receptors are large enough to justify maintaining the distinction between these two subclasses of GABA receptors. [21]

Common characteristics

In ionotropic GABAA and GABAС receptors, binding of GABA molecules to their binding sites in the extracellular part of receptor triggers opening of a chloride ion-selective pore. The chloride Ion is formed when the element Chlorine picks up one Electron to form an Anion (negatively-charged ion Cl&minus The increased chloride conductance drives the membrane potential towards the reversal potential of the Cl¯ ion which is about –80 mV in neurons, inhibiting the firing of new action potentials. Membrane potential (or transmembrane potential) is the Voltage difference (or Electrical potential difference between the interior and exterior of a mv (short for m o' v' e is a Unix command that moves one or more files or directories from one place to another In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal

However, there are numerous reports of excitatory GABAA receptors. This phenomenon is due to increased intracellular concentration of Cl¯ ions either during development of the nervous system[22][23] or in certain cell populations. [24][25][26]

After this period of development, a Chloride pump is upregulated and inserted into the cell membrane, pumping Cl- ions into the extracellular space of the cell. Further openings via GABA binding to the receptor then produce inhibitory responses. Over-excitation of this receptor induces receptor remodeling and the eventual invagination of the GABA receptor. As a result, further GABA binding becomes inhibited and IPSPs are no longer relevant.

G protein coupled receptor: GABAB

A slow response to GABA is mediated by GABAB receptors,[27] originally defined on the basis of pharmacological properties. GABAB receptors (GABABR are Metabotropic Transmembrane receptors for Gamma-aminobutyric acid (GABA that are linked via G-proteins [28]

In studies focused on the control of neurotransmitter release, it was noted that a GABA receptor was responsible for modulating evoked release in a variety of isolated tissue preparations. This ability of GABA to inhibit neurotransmitter release from these preparations was not blocked by bicuculline, was not mimicked by isoguvacine, and was not dependent on Cl¯, all of which are characteristic of the GABAA receptor. The GABAA receptor is one of two ligand-gated Ion channels responsible for mediating the effects of Gamma-aminobutyric acid (GABA the major The most striking discovery was the finding that baclofen (β-parachlorophenyl GABA), a clinically employed spasmolytic[29][30] mimicked, in a stereoselective manner, the effect of GABA. Baclofen (brand names Kemstro and Lioresal) is a derivative of gamma-aminobutyric acid (GABA primarily used to treat Spasticity. In Chemistry, stereoselectivity is the property of a Chemical reaction that yields an unequal mixture of stereoisomers from a single Reactant

Later ligand-binding studies provided direct evidence of binding sites for baclofen on central neuronal membranes. [31] cDNA cloning confirmed that the GABAB receptor belongs to the family of G-protein coupled receptors. In Genetics, complementary DNA ( cDNA) is DNA synthesized from a mature MRNA template in a reaction catalyzed by the enzyme Reverse G protein-coupled receptors ( GPCRs) also known as seven transmembrane domain receptors, 7TM receptors, heptahelical receptors, and [32] Additional information on GABAB receptors has been reviewed elsewhere. [33][34][35][36][37][38][39][40]

Summary

Thus, GABAA and GABAС receptors are ligand-gated ion channels, whereas GABAB receptors are G protein-coupled receptors. The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are G protein-coupled receptors ( GPCRs) also known as seven transmembrane domain receptors, 7TM receptors, heptahelical receptors, and

This has a parallel to several other systems in the body, where a single molecule binds to receptors which function in completely different ways:

References

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