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Inwardly rectifying potassium channels (Kir, IRK) are a specific subset of potassium selective ion channels. To date, seven subfamilies have been identified in various mammalian cell types and they are also found in plants. They are the targets of multiple toxins, and malfunction of the channels has been implicated in several diseases. ==Overview of inward rectification== A channel that is "inwardly-rectifying" is one that passes current (positive charge) more easily in the inward direction (into the cell) than in the outward direction (out of the cell). It is thought that this current may play an important role in regulating neuronal activity, by helping to stabilise the resting membrane potential of the cell. By convention, inward current is displayed in voltage clamp as a downward deflection, while an outward current (positive charge moving out of the cell) is shown as an upward deflection. At membrane potentials negative to potassium's reversal potential, inwardly rectifying K+ channels support the flow of positively charged K+ ions into the cell, pushing the membrane potential back to the resting potential. This can be seen in figure 1: when the membrane potential is clamped negative to the channel's resting potential (e.g. -60 mV), inward current flows (i.e. positive charge flows into the cell). However, when the membrane potential is set positive to the channel's resting potential (e.g. +60 mV), these channels pass very little charge out of the cell. Simply put, this channel passes much more current in the inward direction than the outward one. Note that these channels are not perfect rectifiers, as they can pass some outward current in the voltage range up to about 30 mV above resting potential. These channels differ from the potassium channels that are typically responsible for repolarizing a cell following an action potential, such as the delayed rectifier and A-type potassium channels. Those more "typical" potassium channels preferentially carry outward (rather than inward) potassium currents at depolarized membrane potentials, and may be thought of as "outwardly rectifying." When first discovered, inward rectification was named "anomalous rectification" to distinguish it from outward potassium currents.〔Bertil Hille (2001). ''Ion Channels of Excitable Membranes'' 3rd ed. (Sinauer: Sunderland, MA), p. 151. ISBN 0-87893-321-2.〕 Inward rectifiers also differ from tandem pore domain potassium channels, which are largely responsible for "leak" K+ currents.〔Hille, p. 155.〕 Some inward rectifiers, termed "weak inward rectifiers", carry measurable outward K+ currents at voltages positive to the K+ reversal potential (corresponding to, but larger than, the small currents above the 0 nA line in figure 1). They, along with the "leak" channels, establish the resting membrane potential of the cell. Other inwardly rectifying channels, termed "strong inward rectifiers," carry very little outward current at all, and are mainly active at voltages negative to the reversal potential, where they carry inward current (the much larger currents below the 0 nA line in figure 1).〔Hille, p. 153.〕 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「Inward-rectifier potassium ion channel」の詳細全文を読む スポンサード リンク
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