Canle iónica regulada por voltaxe: Diferenzas entre revisións
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Liña 40:
Aínda que as canles iónicas reguladas por voltaxe son activadas normalmente pola despolarización da membrana, algunhas canles, como as [[canle de ión potasio rectificador interno|canles de ión potasio rectificador interno]] son activados por [[hiperpolarización (bioloxía)|hiperpolarización]].
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The gate is thought to be coupled to the voltage sensing regions of the channels and appears to contain a mechanical obstruction to ion flow.<ref>{{cite journal | vauthors = Yellen G | title = The moving parts of voltage-gated ion channels | journal = Quarterly Reviews of Biophysics | volume = 31 | issue = 3 | pages = 239–95 | date = August 1998 | pmid = 10384687 | doi=10.1017/s0033583598003448}}</ref> While the S6 domain has been agreed upon as the segment acting as this obstruction, its exact mechanism is unknown. Possible explanations include: the S6 segment makes a scissor-like movement allowing ions to flow through,<ref>{{cite journal | vauthors = Perozo E, Cortes DM, Cuello LG | title = Structural rearrangements underlying K<sup>+</sup>-channel activation gating | journal = Science | volume = 285 | issue = 5424 | pages = 73–8 | date = July 1999 | pmid = 10390363 | doi=10.1126/science.285.5424.73}}</ref> the S6 segment breaks into two segments allowing of passing of ions through the channel,<ref name="Jiang_2002">{{cite journal | vauthors = Jiang Y, Lee A, Chen J, Cadene M, Chait BT, MacKinnon R | title = Crystal structure and mechanism of a calcium-gated potassium channel | journal = Nature | volume = 417 | issue = 6888 | pages = 515–22 | date = May 2002 | pmid = 12037559 | doi = 10.1038/417515a | bibcode = 2002Natur.417..515J }}</ref> or the S6 channel serving as the gate itself.<ref>{{cite journal | vauthors = Webster SM, Del Camino D, Dekker JP, Yellen G | title = Intracellular gate opening in Shaker K<sup>+</sup> channels defined by high-affinity metal bridges | journal = Nature | volume = 428 | issue = 6985 | pages = 864–8 | date = April 2004 | pmid = 15103379 | doi = 10.1038/nature02468 | bibcode = 2004Natur.428..864W }}</ref> The mechanism by which the movement of the S4 segment affects that of S6 is still unknown, however it is theorized that there is a S4-S5 linker whose movement allows the opening of S6.<ref name="Bezanilla_2005" />▼
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Inactivation of ion channels occurs within milliseconds after opening. Inactivation is thought to be mediated by an intracellular gate that controls the opening of the pore on the inside of the cell.<ref>{{cite journal | vauthors = Armstrong CM | title = Sodium channels and gating currents | journal = Physiological Reviews | volume = 61 | issue = 3 | pages = 644–83 | date = July 1981 | pmid = 6265962 }}</ref> This gate is modeled as a [[ball and chain inactivation|ball tethered to a flexible chain]]. During inactivation, the chain folds in on itself and the ball blocks the flow of ions through the channel.<ref>{{cite journal | vauthors = Vassilev P, Scheuer T, Catterall WA | title = Inhibition of inactivation of single sodium channels by a site-directed antibody | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 86 | issue = 20 | pages = 8147–51 | date = October 1989 | pmid = 2554301 | doi=10.1073/pnas.86.20.8147 | pmc=298232| bibcode = 1989PNAS...86.8147V }}</ref> Fast inactivation is directly linked to the activation caused by intramembrane movements of the S4 segments,<ref name="Bénitah_1999">{{cite journal | vauthors = Bénitah JP, Chen Z, Balser JR, Tomaselli GF, Marbán E | title = Molecular dynamics of the sodium channel pore vary with gating: interactions between P-segment motions and inactivation | journal = The Journal of Neuroscience | volume = 19 | issue = 5 | pages = 1577–85 | date = March 1999 | pmid = 10024345 }}</ref> though the mechanism linking movement of S4 and the engagement of the inactivation gate is unknown.
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