Canle iónica regulada por voltaxe: Diferenzas entre revisións

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{{further|Cation channel superfamily}}

Voltage-gated ion channels are generally composed of several subunits arranged in such a way that there is a central pore through which ions can travel down their [[electrochemical gradient]]s. The channels tend to be ion-specific, although similarly sized and charged ions may sometimes travel through them. The functionality of voltage-gated ion channels is attributed to its three main discrete units: the voltage sensor, the pore or conducting pathway, and the gate.<ref name="Bezanilla_2005">{{cite journal | vauthors = Bezanilla F | title = Voltage-gated ion channels | journal = IEEE Transactions on NanoBioscience | volume = 4 | issue = 1 | pages = 34–48 | date = March 2005 | pmid = 15816170 | doi=10.1109/tnb.2004.842463}}</ref> Na⁺, K⁺, and Ca²⁺ channels are composed of four transmembrane domains arranged around a central pore; these four domains are part of a single α-subunit in the case of most Na⁺ and Ca²⁺ channels, whereas there are four α-subunits, each contributing one transmembrane domain, in most K⁺ channels.<ref name="MCB_2000">{{cite book | first1 = Harvey | last1 = Lodish | first2 = Arnold | last2 = Berk | first3 = S Lawrence | last3 = Zipursky | first4 = Paul | last4 = Matsudaira | first5 = David | last5 = Baltimore | first6 = James | last6 = Darnell | name-list-format = vanc | title = Molecular Cell Biology | date = 2000 | publisher = Scientific American Books | location = New York | isbn = 978-0-7167-3136-8 | edition = 4th | chapter = Section 21.3, Molecular Properties of Voltage-Gated Ion Channels | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK21608/ }}</ref> The membrane-spanning segments, designated S1-S6, all take the form of [[alpha helix|alpha helices]] with specialized functions. The fifth and sixth transmembrane segments (S5 and S6) and pore loop serve the principal role of ion conduction, comprising the gate and pore of the channel, while S1-S4 serve as the voltage-sensing region.<ref name="Bezanilla_2005" /> The four subunits may be identical, or different from one another. In addition to the four central α-subunits, there are also regulatory β-subunits, with [[oxidoreductase]] activity, which are located on the inner surface of the cell membrane and do not cross the membrane, and which are coassembled with the α-subunits in the [[endoplasmic reticulum]].<ref>{{cite journal | vauthors = Gulbis JM, Mann S, MacKinnon R | title = Structure of a voltage-dependent K⁺ channel beta subunit | journal = Cell | volume = 97 | issue = 7 | pages = 943–52 | date = June 1999 | pmid = 10399921 | doi=10.1016/s0092-8674(00)80805-3}}</ref>

 

 

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== Notas ==

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