Editing Repolarization (section)

== Type of K<sup>+</sup> channels in repolarization ==
Following the action potential, characteristically generated by the influx of Na<sup>+</sup> through voltage gated Na<sup>+</sup> channels, there is a period of repolarization in which the Na<sup>+</sup> channels are inactivated while K<sup>+</sup> channels are activated.  Further study of K<sup>+</sup> channels shows that there are four types which influence the repolarization of the cell membrane to re-establish the resting potential.  The four types are K<sub>v</sub>1, K<sub>v</sub>2, K<sub>v</sub>3 and K<sub>v</sub>4. The K<sub>v</sub>1 channel primarily influences the repolarization of the axon.  The K<sub>v</sub>2 channel is characteristically activated slower.  The K<sub>v</sub>4 channels are characteristically activated rapidly.  When K<sub>v</sub>2 and K<sub>v</sub>4 channels are blocked, the action potential predictably widens.<ref name=":3">{{cite journal | vauthors = Pathak D, Guan D, Foehring RC | title = Roles of specific K<sub>v</sub> channel types in repolarization of the action potential in genetically identified subclasses of pyramidal neurons in mouse neocortex | journal = Journal of Neurophysiology | volume = 115 | issue = 5 | pages = 2317–29 | date = May 2016 | pmid = 26864770 | pmc = 4922457 | doi = 10.1152/jn.01028.2015 }}</ref> The K<sub>v</sub>3 channels open at a more positive membrane potential and deactivate 10 times faster than the other K<sub>v</sub> channels. These properties allow for the high-frequency firing that mammalian [[neuron]]s require. Areas with dense K<sub>v</sub>3 channels include the [[neocortex]], [[basal ganglia]], [[brain stem]] and [[hippocampus]] as these regions create microsecond action potentials that requires quick repolarization.<ref>{{cite journal | vauthors = Kaczmarek LK, Zhang Y | title = K<sub>v</sub>3 Channels: Enablers of Rapid Firing, Neurotransmitter Release, and Neuronal Endurance | journal = Physiological Reviews | volume = 97 | issue = 4 | pages = 1431–1468 | date = October 2017 | pmid = 28904001 | pmc = 6151494 | doi = 10.1152/physrev.00002.2017 }}</ref>

Utilizing voltage-clamp data from experiments based on rodent neurons, the K<sub>v</sub>4 channels are associated with the primary repolarization conductance following the depolarization period of a neuron.  When the K<sub>v</sub>4 channel is blocked, the action potential becomes broader, resulting in an extended repolarization period, delaying the neuron from being able to fire again.  The rate of repolarization closely regulates the amount of Ca<sup>2+</sup> ions entering the cell.  When large quantities of Ca<sup>2+</sup> ions enter the cell due to extended repolarization periods, the neuron may die, leading to the development of stroke or seizures.<ref name=":3" />

The K<sub>v</sub>1 channels are found to contribute to repolarization of [[Pyramidal cell|pyramidal neurons]], likely associated with an upregulation of the K<sub>v</sub>4 channels.  The K<sub>v</sub>2 channels were not found to contribute to repolarization rate as blocking these channels did not result in changes in neuron repolarization rates.<ref name=":3" />