Muscarinic acetylcholine receptor M2

The muscarinic acetylcholine receptor M₂, also known as the cholinergic receptor, muscarinic 2, is a muscarinic acetylcholine receptor that in humans is encoded by the CHRM2 gene. Multiple alternatively spliced transcript variants have been described for this gene.

Function

Heart

The M₂ muscarinic receptors are located in the heart, where they act to slow the heart rate down to normal sinus rhythm after positive stimulatory actions of the sympathetic nervous system, by slowing the speed of depolarization. They also reduce contractile forces of the atrial cardiac muscle, and reduce conduction velocity of the atrioventricular node (AV node). However, they have no effect on the contractile forces of the ventricular muscle.

IQ

A Dutch family study found that there is "a highly significant association" between the CHRM2 gene and intelligence as measured by the Wechsler Adult Intelligence Scale-Revised. A similar association was found independently in the Minnesota Twin and Family Study.

However, a larger 2009 study attempting to replicate this claim instead found no significant association between the CHRM2 gene and intelligence.

Olfactory behavior

Mediating olfactory guided behaviors (e.g odor discrimination, aggression, mating)

Mechanism of action

M₂ muscarinic receptors act via a G_i type receptor, which causes a decrease in cAMP in the cell, generally leading to inhibitory-type effects. They appear to serve as autoreceptors.

In addition, they modulate muscarinic potassium channels. In the heart, this contributes to a decreased heart rate. They do so by the G beta gamma subunit of the G protein coupled to M₂. This part of the G protein can open K⁺ channels in the parasympathetic notches in the heart, which causes an outward current of potassium, which slows down the heart rate.

Ligands

Few highly selective M₂ agonists are available at present, although there are several non-selective muscarinic agonists that stimulate M₂, and a number of selective M₂ antagonists are available.

Agonists

• Bethanechol (nonselective muscarinic agonist)
• (2S,2'R,3'S,5'R)-1-methyl-2-(2-methyl-1,3-oxathiolan-5-yl)pyrrolidine 3-sulfoxide methyl iodide (selective for M₂ but only partial agonist)
• Berberine

Antagonists

• Atropine
• Hyoscyamine
• Dimethindene - N,N-Dimethyl-3-[(1S)-1-(2-pyridinyl)ethyl]-1H-indene-2-ethanamine, CAS# 121367-05-3, mixed M₂ / histamine H₁ antagonist
• Otenzepad - 11-([2-[(Diethylamino)methyl]-1-piperidinyl]acetyl)-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one, CAS# 102394-31-0
• AQRA-741 - 11-([4-[4-(Diethylamino)butyl]-1-piperidinyl]acetyl)-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one, CAS# 123548-16-3
• AFDX-384 (mixed M2/M4 antagonist) - N-[2-[2-[(Dipropylamino)methyl]-1-piperidinyl]ethyl]-5,6-dihydro-6-oxo-11H-pyrido[2,3-b][1,4]benzodiazepine-11-carboxamide, CAS# 118290-27-0
• dicycloverine
• Thorazine
• Diphenhydramine
• Dimenhydrinate
• tolterodine
• oxybutynin
• ipratropium
• methoctramine
• tripitramine
• gallamine
• chlorpromazine

See also

• Muscarinic acetylcholine receptor

External links

• CHRM2 protein, human at the US National Library of Medicine Medical Subject Headings (MeSH)

This article incorporates text from the United States National Library of Medicine, which is in the public domain.