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The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid (GABA), the chief inhibitory neurotransmitter in the mature vertebrate central nervous system. There are two classes of GABA receptors: GABAA and GABAB. GABAA receptors are ligand-gated ion channels (also known as ionotropic receptors), whereas GABAB receptors are G protein-coupled receptors (also known as metabotropic receptors). == 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. This channel was subsequently termed the GABAA receptor. Fast-responding GABA receptors are members of family of Cys-loop ligand-gated ion channels. Members of this superfamily, which includes nicotinic acetylcholine receptors, GABAA receptors, glycine and 5-HT3 receptors, possess a characteristic loop formed by a disulfide bond between two cysteine residues. In ionotropic GABAA receptors, binding of GABA molecules to their binding sites in the extracellular part of the receptor triggers opening of a chloride ion-selective pore. The increased chloride conductance drives the membrane potential towards the reversal potential of the Cl¯ ion which is about –65 mV in neurons, inhibiting the firing of new action potentials. This mechanism is responsible for the sedative effects of GABAA allosteric agonists. 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 or in certain cell populations. 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 tissue. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「GABA receptor」の詳細全文を読む スポンサード リンク
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