Editing Ventricular action potential

[[Image:Action potential ventr myocyte.gif|thumb|right|The action potential of a ventricular myocyte]]
In [[electrocardiography]], the ventricular [[cardiomyocyte]] [[membrane potential]] is about −90&nbsp;mV at rest,<ref name=":0">{{Cite journal |last=Grant |first=Augustus O. |date=2009 |title=Cardiac Ion Channels |url=https://www.ahajournals.org/doi/10.1161/CIRCEP.108.789081 |journal=Circulation: Arrhythmia and Electrophysiology |language=en |volume=2 |issue=2 |pages=185–194 |doi=10.1161/CIRCEP.108.789081 |issn=1941-3149|doi-access=free |url-access=subscription }}</ref> which is close to the [[potassium]] [[reversal potential]]. When an [[action potential]] is generated, the membrane potential rises above this level in five distinct phases.<ref name=":0" />

# Phase 4: Resting membrane potential remains stable at ≈−90 mV.<ref name=":0" />
# Phase 0: Rapid depolarisation, shifting the voltage to positive. Specialised [[integral membrane protein|membrane proteins]] ([[ion channel|voltage-gated sodium channels]]) in the [[cell membrane]] selectively allow [[sodium]] [[ion]]s to enter the cell. This causes the membrane potential to rise at a rate of about 300&nbsp;V/s. As the membrane voltage rises (to about 40&nbsp;mV) sodium channels close due to a process called inactivation.
# Phase 1: Rapid repolarisation.
# Phase 2: Plateau, the longest phase, approximately 100ms.<ref name=":0" />
# Phase 3: Rapid repolarisation, which returns the membrane potential to resting potential.<ref name=":0" />

The Na<sup>+</sup> channel opening is followed by inactivation. Na<sup>+</sup> inactivation comes with slowly activating Ca<sup>2+</sup> channels at the same time as a few fast K<sup>+</sup> channels open. There is a balance between the outward flow of K<sup>+</sup> and the inward flow of Ca<sup>2+</sup> causing a plateau of length in variables. The delayed opening of more Ca<sup>2+</sup>-activated K<sup>+</sup> channels, which are activated by build-up of Ca<sup>2+</sup> in the sarcoplasm, while the Ca<sup>2+</sup> channels close, ends the plateau. This leads to repolarization.

The depolarization of the membrane allows [[calcium]] channels to open as well. As sodium channels close calcium provides current to maintain the potential around 20&nbsp;mV. The plateau lasts on the order of 100&nbsp;ms. At the time that calcium channels are getting activated, channels that mediate the transient outward potassium current open as well. This outward potassium current causes a small dip in membrane potential shortly after [[action potential|depolarization]]. This current is observed in human and dog action potentials, but not in guinea pig action potentials.

[[action potential|Repolarization]] is accomplished by channels that open slowly and are mostly activated at the end of the action potential ([[KvLQT1|slow delayed-rectifier channels]]) and channels that open quickly but are inactivated until the end of the action potential ([[hERG|rapid delayed rectifier channels]]). Fast delayed rectifier channels open quickly but are shut by inactivation at high membrane potentials. As the membrane voltage begins to drop the channels recover from inactivation and carry current.

==See also==
* [[Cardiac action potential]]

==References==
{{Reflist}}

{{Cardiovascular physiology}}

{{DEFAULTSORT:Ventricular Action Potential}}
[[Category:Cardiac electrophysiology]]
[[Category:Action potentials]]