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ATP-sensitive potassium channel
An ATP-sensitive potassium channel (or KATP channel) is a type of potassium channel that is gated by intracellular nucleotides, ATP and ADP. ATP-sensitive potassium channels are composed of Kir6.x-type subunits and sulfonylurea receptor (SUR) subunits, along with additional components. KATP channels are found in the plasma membrane; however some may also be found on subcellular membranes. These latter classes of KATP channels can be classified as being either sarcolemmal ("sarcKATP"), mitochondrial ("mitoKATP"), or nuclear ("nucKATP").
== Discovery and structure ==
KATP channels were first identified in cardiac myocytes by the Akinori Noma group in Japan. They have also been found in pancreas where they control insulin secretion, but are in fact widely distributed in plasma membranes. SarcKATP are composed of eight protein subunits (octamer). Four of these are members of the inward-rectifier potassium ion channel family Kir6.x (either Kir6.1 or Kir6.2), while the other four are sulfonylurea receptors (SUR1, SUR2A, and SUR2B). The Kir subunits have two transmembrane spans and form the channel’s pore. The SUR subunits have three additional transmembrane domains, and contain two nucleotide-binding domains on the cytoplasmic side. These allow for nucleotide-mediated regulation of the potassium channel, and are critical in its roles as a sensor of metabolic status. These SUR subunits are also sensitive to sulfonylureas, MgATP, and some other pharmacological channel openers. While all sarcKATP are constructed of eight subunits in this 4:4 ratio, their precise composition varies with tissue type.
MitoKATP were first identified in 1991 by single-channel recordings of the inner mitochondrial membrane. The molecular structure of mitoKATP is less clearly understood than that of sarcKATP. Some reports indicate that cardiac mitoKATP consist of Kir6.1 and Kir6.2 subunits, but neither SUR1 nor SUR2. More recently, it was discovered that certain multiprotein complexes containing succinate dehydrogenase can provide activity similar to that of KATP channels.
The presence of nucKATP was confirmed by the discovery that isolated patches of nuclear membrane possess properties, both kinetic and pharmacological, similar to plasma membrane KATP channels.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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