Editing Cardiac action potential (section)

===Potassium channels===
{{main|Potassium channel}}

The two main types of potassium channels in cardiac cells are inward rectifiers and voltage-gated potassium channels.{{cn|date=April 2024}}

[[Inward-rectifier potassium ion channel|Inwardly rectifying potassium channels]] (K<sub>ir)</sub> favour the flow of K<sup>+</sup> into the cell. This influx of potassium, however, is larger when the membrane potential is more negative than the [[Reversal potential|equilibrium potential]] for K<sup>+</sup> (~-90 mV). As the membrane potential becomes more positive (i.e. during cell stimulation from a neighbouring cell), the flow of potassium into the cell via the K<sub>ir</sub> decreases. Therefore, K<sub>ir</sub> is responsible for maintaining the resting membrane potential and initiating the depolarization phase. However, as the membrane potential continues to become more positive, the channel begins to allow the passage of K<sup>+</sup> ''out'' of the cell. This outward flow of potassium ions at the more positive membrane potentials means that the K<sub>ir</sub> can also aid the final stages of repolarisation.<ref>{{Cite journal |last=Hibino |first=Hiroshi |last2=Inanobe |first2=Atsushi |last3=Furutani |first3=Kazuharu |last4=Murakami |first4=Shingo |last5=Findlay |first5=Ian |last6=Kurachi |first6=Yoshihisa |date=2010-01-01 |title=Inwardly rectifying potassium channels: their structure, function, and physiological roles |journal=Physiological Reviews |volume=90 |issue=1 |pages=291–366 |doi=10.1152/physrev.00021.2009 |issn=1522-1210 |pmid=20086079 |s2cid=472259}}</ref><ref>{{Cite journal |last=Dhamoon |first=Amit S. |last2=Jalife |first2=José |date=2005-03-01 |title=The inward rectifier current (IK1) controls cardiac excitability and is involved in arrhythmogenesis |journal=Heart Rhythm |volume=2 |issue=3 |pages=316–324 |doi=10.1016/j.hrthm.2004.11.012 |issn=1547-5271 |pmid=15851327}}</ref>

The [[voltage-gated potassium channel]]s (K<sub>v</sub>) are activated by depolarization. The currents produced by these channels include the transient out potassium current [[Cardiac transient outward potassium current|''I''<sub>to1</sub>]]. This current has two components. Both components activate rapidly, but ''I''<sub>to,fast</sub> inactivates more rapidly than ''I''<sub>to, slow</sub>. These currents contribute to the early repolarization phase (phase 1) of the action potential.{{cn|date=April 2024}}

Another form of voltage-gated potassium channels are the delayed rectifier potassium channels. These channels carry potassium currents which are responsible for the plateau phase of the action potential, and are named based on the speed at which they activate: slowly activating ''I''<sub>Ks</sub>, rapidly activating ''I''<sub>Kr</sub> and ultra-rapidly activating ''I''<sub>Kur</sub>.<ref>{{Cite journal |last=Snyders |first=D. J. |date=1999-05-01 |title=Structure and function of cardiac potassium channels |journal=Cardiovascular Research |volume=42 |issue=2 |pages=377–390 |doi=10.1016/s0008-6363(99)00071-1 |issn=0008-6363 |pmid=10533574 |doi-access=free}}</ref>