# M current

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'''M current''' is a type of noninactivating potassium current first discovered in bullfrog sympathetic ganglion cells.<ref name="pmid6965523">{{cite journal | vauthors = Brown DA, Adams PR | title = Muscarinic suppression of a novel voltage-sensitive K+ current in a vertebrate neurone | journal = Nature | volume = 283 | issue = 5748 | pages = 673–6 | date = February 1980 | pmid = 6965523 | doi = 10.1038/283673a0| bibcode = 1980Natur.283..673B | s2cid = 4238485 }}</ref>

The ''M-channel'' is a voltage-gated K+ channel ([Kv7/KCNQ family](/source/voltage-gated_potassium_channel)) that is named after the receptor it is influenced by. The M-channel is important in raising the threshold for firing an action potential. It is unique because it is open at rest and even more likely to be open during depolarization. Furthermore, when the muscarinic acetylcholine receptor ([MAChR](/source/MAChR)) is activated, the channel closes. The M-channel is a PIP<sub>2</sub>-regulated ion channel.<ref name="Nicholls">{{cite book |first1=John G. |last1= Nicholls |first2= A. Robert |last2= Martin |first3= Paul A. |last3= Fuchs |first4=David A. |last4=Brown |first5=Mathew E. |last5=Diamond |last6= Weisblat |first6=David A. | name-list-style = vanc |year= 2012 |title= From Neuron to Brain |edition= Fifth |pages= 229, 342}}</ref> Kv7 channels have a prominent expression throughout the brain.<ref>{{cite journal | vauthors = Greene DL, Hoshi N | title = Modulation of Kv7 channels and excitability in the brain | journal = Cellular and Molecular Life Sciences | volume = 74 | issue = 3 | pages = 495–508 | date = February 2017 | pmid = 27645822 | pmc = 5243414 | doi = 10.1007/s00018-016-2359-y }}</ref>

== Function ==

===Actions of M-currents: "phasic-firing"===
M-channels are the reason for slow depolarizations produced by ACh and LHRH in the autonomic ganglia and other specified areas. 
1. Initial depolarization of a neuron increases likelihood that M-channels will open.
2. M-channels generate an outward potassium current (I<sub>K</sub>).
3. Potassium efflux counteracts sodium influx in [action potential (AP)](/source/Action_potential).
Overall result: full action potential is prevented.
<ref name="Nicholls" /> {{rp|343}}

===Inhibition of M-current: "tonic-firing"===
1 molecule of [Acetylcholine (Ach)](/source/Acetylcholine) binds to [mAchR](/source/mAchR). Potassium (K+) channels become more likely to be closed. Neuron becomes ''tonic-firing''.
<ref name="Nicholls" /> {{rp|343}}
This reduction in M-current is coupled with the actions of the [G<sub>q</sub>](/source/Gq_alpha_subunit) [G-protein](/source/G-protein). Specifically, the hydrolysis of PIP<sub>2</sub> to IP<sub>3</sub>. This hydrolysis causes PIP<sub>2</sub>, which is bound to the membrane, to become IP<sub>3</sub> and dissociate from the membrane into the cytoplasm. When M-current is restored, it moves back to the membrane. There is some evidence for different theories of how M-channel activity is directly affected by PIP<sub>2</sub>.<ref name="Nicholls" /> {{rp|229}}

==Clinical implications==
{{Expand section|date=June 2019}}
[Benign familial neonatal seizures](/source/Benign_familial_neonatal_seizures) (BFNE) is an [autosomal dominant](/source/autosomal_dominant) inherited form of [seizures](/source/seizures). There are three known genetic causes of BFNE, two being in the channels [KCNQ2](/source/KCNQ2) and [KCNQ3](/source/KCNQ3).

[Valproic acid](/source/Valproate) and [retigabine](/source/retigabine) are examples of medications used to treat epilepsy which are known to mediate their anti-seizure activity partly through enhancement of the M-current.

== References ==
{{reflist|colwidth=30em}}

Category:Electrophysiology
Category:Neurophysiology

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Adapted from the Wikipedia article [M current](https://en.wikipedia.org/wiki/M_current) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/M_current?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.