Editing Repolarization (section)

== Voltage gated K<sup>+</sup> mechanisms ==
The structure of the voltage gated K<sup>+</sup> channel is that of six [[transmembrane helices]] along the [[lipid bilayer]]. The selectivity of this channel to voltage is mediated by four of these transmembrane domains (S1–S4) – the voltage sensing domain. The other two domains (S5, S6) form the pore by which ions traverse.<ref name="pmid26070303">{{cite journal | vauthors = Kuang Q, Purhonen P, Hebert H | title = Structure of potassium channels | journal = Cellular and Molecular Life Sciences | volume = 72 | issue = 19 | pages = 3677–93 | date = October 2015 | pmid = 26070303 | pmc = 4565861 | doi = 10.1007/s00018-015-1948-5 }}</ref> Activation and deactivation of the voltage gated K<sup>+</sup> channel is triggered by conformational changes in the voltage sensing domain. Specifically, the S4 domain moves such that it activates and deactivates the pore. During activation, there is outward S4 motion, causing tighter VSD-pore linkage. Deactivation is characterized by inward S4 motion.<ref name="Jensen_2012">{{cite journal |vauthors=Jensen MØ, Jogini V, Borhani DW, Leffler AE, Dror RO, Shaw DE |date=April 2012 |title=Mechanism of voltage gating in potassium channels |url=https://www.researchgate.net/publication/224006426 |journal=Science |volume=336 |issue=6078 |pages=229–33 |bibcode=2012Sci...336..229J |doi=10.1126/science.1216533 |pmid=22499946 |s2cid=2340286}}</ref>

The switch from depolarization into repolarization is dependent on the kinetic mechanisms of both voltage gated K<sup>+</sup> and [[Sodium channel|Na<sup>+</sup> channels]]. Although both voltage gated Na<sup>+</sup> and K<sup>+</sup> channels activate at roughly the same voltage (−50 [[Millivolt|mV]]), Na<sup>+</sup> channels have faster kinetics and activate/deinactivate much more quickly.<ref name=":2">{{cite web | first = John H. | last = Byrn | name-list-style = vanc |url=https://nba.uth.tmc.edu/neuroscience/m/s1/chapter02.html|title=Chapter Two: Ionic Mechanisms and Action Potentials|work = Neuroscience Online | publisher = University of Texas Medical School }}</ref> Repolarization occurs as the influx of Na<sup>+</sup> decreases (channels deinactivate) and the efflux of K<sup>+</sup> ions increases as its channels open.<ref>{{cite book | vauthors = Striedter GF | date = 2016 | title = Neurobiology: A Functional Approach | location = New York, NY | publisher = Oxford University Press }}</ref> The decreased conductance of sodium ions and increased conductance of potassium ions cause the cell's membrane potential to very quickly return to, and past the resting membrane potential, which causes the hyperpolarization due to the potassium channels closing slowly, allowing more potassium to flow through after the resting membrane potential has been reached.<ref name=":2" />