WordNet

direct the flow of; "channel information towards a broad audience" (同)canalize, canalise
a television station and its programs; "a satellite TV channel"; "surfing through the channels"; "they offer more than one hundred channels" (同)television channel, TV channel
a passage for water (or other fluids) to flow through; "the fields were crossed with irrigation channels"; "gutters carried off the rainwater into a series of channels under the street"
(often plural) a means of communication or access; "it must go through official channels"; "lines of communication were set up between the two firms" (同)communication channel, line
a path over which electrical signals can pass; "a channel is typically what you rent from a telephone company" (同)transmission channel
a deep and relatively narrow body of water (as in a river or a harbor or a strait linking two larger bodies) that allows the best passage for vessels; "the ship went aground in the channel"
supply with a gate; "The house was gated"
restrict (school boys'
total admission receipts at a sports event
a computer circuit with several inputs but only one output that can be activated by particular combinations of inputs (同)logic gate
a movable barrier in a fence or wall
passageway (as in an air terminal) where passengers can embark or disembark
control with a valve or other device that functions like a gate
the rate at which energy is drawn from a source that produces a flow of electricity in a circuit; expressed in volts (同)electromotive_force, emf
a gangsters pistol (同)rod
official routes of communication; "you have to go through channels"

PrepTutorEJDIC

〈C〉『水路』(川・湾・運河の船の通行ができる深い部分) / 〈U〉河床・川底 / 〈C〉『海峡』 / 〈C〉みぞ(groove),(道路の)水渠(すいきょ) / 《複数形で》(運搬・伝達の)正式の経路(手続き);(一般に)経路 / 〈C〉(テレビ・ラジオの)チャンネル / …‘に'水路を開く / …‘に'みぞを堀る / …'を'伝える,流す
(…への)『門』,通用門《+『to』(『of』)+『名』》;(門の)とびら / (ダム・運河などの)水門 / (競技場・劇場などの)[有料]入場者数 / (またgate money)総入場料
電圧,電圧量,ボルト数
ピストル,はじき

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/07/05 14:40:59」(JST)

wiki en

Voltage-gated ion channels are a class of transmembrane ion channels that are activated by changes in electrical membrane potential near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cells.

They have a crucial role in excitable neuronal and muscle tissues, allowing a rapid and co-ordinated depolarization in response to triggering voltage change. Found along the axon and at the synapse, voltage-gated ion channels directionally propagate electrical signals.

Structure

They generally are composed of several subunits arranged in such a way that there is a central pore through which ions can travel down their electrochemical gradients. The channels tend to be ion-specific, although similarly sized and charged ions may sometimes travel through them.

Examples include:

the sodium and potassium voltage-gated channels of nerve and muscle.
the voltage-gated calcium channels that play a role in neurotransmitter release in pre-synaptic nerve endings.

Mechanism

From crystallographic structural studies of a potassium channel, assuming that this structure remains intact in the corresponding plasma membrane, it is possible to surmise that when a potential difference is introduced over the membrane, the associated electric field induces a conformational change in the potassium channel. The conformational change distorts the shape of the channel proteins sufficiently such that the cavity, or channel, opens to admit ion influx or efflux to occur across the membrane, down its electrochemical gradient. This subsequently generates an electric current sufficient to depolarise the cell membrane.

Voltage-gated sodium channels and calcium channels are made up of a single polypeptide with four homologous domains. Each domain contains 6 membrane spanning alpha helices. One of these helices, S4, is the voltage sensing helix.^[1] It has many positive charges such that a high positive charge outside the cell repels the helix, keeping the channel in its closed state. Depolarization of the cell interior causes the helix to move, inducing a conformational change such that ions may flow through the channel (the open state). Potassium channels function in a similar way, with the exception that they are composed of four separate polypeptide chains, each comprising one domain.

The voltage-sensitive protein domain of these channels (the "voltage sensor") generally contains a region composed of S3b and S4 helices, known as the "paddle" due to its shape, which appears to be a conserved sequence, interchangeable across a wide variety of cells and species. A similar voltage sensor paddle has also been found in a family of voltage sensitive phosphatases in various species.^[2] Genetic engineering of the paddle region from a species of volcano-dwelling archaebacteria into rat brain potassium channels results in a fully functional ion channel, as long as the whole intact paddle is replaced.^[3] This "modularity" allows use of simple and inexpensive model systems to study the function of this region, its role in disease, and pharmaceutical control of its behavior rather than being limited to poorly characterized, expensive, and/or difficult to study preparations.^[4]

Although voltage-gated ion channels are typically activated by membrane depolarization, some channels, such as inward-rectifier potassium ion channels, are activated instead by hyperpolarization.

References

^ Voltage sensor in the voltage gated sodium and potassium channels | PharmaXChange.info
^ Murata, Y.; Iwasaki, H.; Sasaki, M.; Inaba, K.; Okamura, Y. (2005). "Phosphoinositide phosphatase activity coupled to an intrinsic voltage sensor". Nature 435 (7046): 1239–1243. doi:10.1038/nature03650. PMID 15902207.
^ Alabi AA, Bahamonde MI, Jung HJ, Kim JI, Swartz KJ (November 2007). "Portability of paddle motif function and pharmacology in voltage sensors". Nature 450 (7168): 370–5. doi:10.1038/nature06266. PMC 2709416. PMID 18004375.
^ Long SB, Tao X, Campbell EB, MacKinnon R (November 2007). "Atomic structure of a voltage-dependent K+ channel in a lipid membrane-like environment". Nature 450 (7168): 376–82. doi:10.1038/nature06265. PMID 18004376.

External links

IUPHAR-DB Voltage-gated ion channel subunits
The IUPHAR Compendium of Voltage-gated Ion Channels 2005
Voltage-Dependent Anion Channels at the US National Library of Medicine Medical Subject Headings (MeSH)

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