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G protein-gated ion channels are a family of transmembrane ion channels in neurons and atrial myocytes that are directly gated by G proteins. == Overview of mechanisms and function == Generally, G protein-gated ion channels are specific ion channels located in the plasma membrane of cells that are directly activated by a family of associated proteins. Ion channels allow for the selective movement of certain ions across the plasma membrane in cells. More specifically, in nerve cells, along with ion transporters, they are responsible for maintaining the electrochemical gradient across the cell. G proteins are a family of intracellular proteins capable of mediating signal transduction pathways. Each G protein is a heterotrimer of three subunits: α-, β-, and γ- subunits. The α-subunit (Gα) typically binds the G protein to a transmembrane receptor protein known as a G protein-coupled receptor, or GPCR. This receptor protein has a large, extracellular binding domain which will bind its respective ligands (e.g. neurotransmitters and hormones). Once the ligand is bound to its receptor, a conformational change occurs. This conformational change in the G protein allows Gα to bind GTP. This leads to yet another conformational change in the G protein, resulting in the separation of the βγ-complex (Gβγ) from Gα.〔 At this point, both Gα and Gβγ are active and able to continue the signal transduction pathway. Different classes of G protein-coupled receptors have many known functions including the cAMP and Phosphatidylinositol signal transduction pathways. A class known as metabotropic glutamate receptors play a large role in indirect ion channel activation by G proteins. These pathways are activated by second messengers which initiate signal cascades involving various proteins which are important to the cell's response. G protein-gated ion channels are associated with a specific type of G protein-coupled receptor. These ion channels are transmembrane ion channels with selectivity filters and a G protein binding site. The GPCRs associated with G protein-gated ion channels are not involved in signal transduction pathways. They only directly activate these ion channels using effector proteins or the G protein subunits themselves (see picture). Unlike most effectors, not all G protein-gated ion channels have their activity mediated by Gα of their corresponding G proteins. For instance, the opening of inwardly rectifying K+ (GIRK) channels is mediated by the binding of Gβγ. G protein-gated ion channels are primarily found in CNS neurons and atrial myocytes, and affect the flow of potassium (K+), calcium (Ca2+), sodium (Na+), and chloride (Cl−) across the plasma membrane.〔 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「G protein-gated ion channel」の詳細全文を読む スポンサード リンク
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