Muscarinic acetylcholine receptors

Muscarinic acetylcholine receptors (mAChRs) are a type of receptor that play several roles in the body, including in the central nervous system, the peripheral nervous system, and various other tissues. They are named for their ability to be activated by the alkaloid muscarine and are part of the larger family of G protein-coupled receptors (GPCRs).

Structure and Function

Muscarinic acetylcholine receptors are metabotropic, meaning they act through a secondary messenger system. They are composed of five subtypes, named M1 through M5. Each subtype has a different distribution within the body and has different effects upon activation.

Subtypes

M1

The M1 receptors are found in the brain, autonomic ganglia, and gastric parietal cells. They are involved in cognitive functions such as learning and memory.

M2

M2 receptors are located in the heart and act to slow the heart rate down. They also play a role in the functioning of smooth muscles and the central nervous system.

M3

M3 receptors are found in many places in the body, including the lungs, glands, and gastrointestinal tract. They are involved in the contraction of smooth muscles, the production of saliva, and other secretions.

M4

M4 receptors are located in the striatum, a part of the brain involved in movement. They are thought to play a role in the regulation of dopamine pathways in the brain.

M5

M5 receptors are the least understood of the muscarinic acetylcholine receptors. They are found in the brain and peripheral tissues.

Pharmacology

Muscarinic acetylcholine receptors are the target of a number of drugs, including anticholinergics, which block the action of acetylcholine at the muscarinic receptor, and cholinergic drugs, which enhance the action of acetylcholine.

See Also

• Acetylcholine
• Nicotinic acetylcholine receptor
• G protein-coupled receptor

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