How does acetylcholine bind to its receptors

Acetylcholine receptor

Synonym: cholino receptor
English: acetylcholine receptor

1 definition

Acetylcholine receptors are specific receptors for acetylcholine (ACh) on the cell membrane. They belong to the transmembrane receptors.

2 classification

A distinction is made pharmacologically:

They are named after the agonists (nicotine or muscarine) that bind to the respective receptor type.

2.1 Nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors are ionotropic receptors, i.e. they are ion channels ("first messengers"). They consist of 5 symmetrically arranged protein subunits, the arrangement of which (and thus the ion permeability) changes when acetylcholine binds. Nicotinic acetylcholine receptors can be activated by nicotine or physostigmine (acetylcholinesterase inhibitors) and are therefore also referred to as n-acetylcholine receptors. Their effect is mostly excitatory. The antagonist is the parasympatholytic tubocurarine, a component of the arrow poison curare.

A distinction is made between the following subtypes:

  • n1 (motorized end plate)
  • n2 (neuronal, pre- to postsynaptic)

2.2 Muscarinic acetylcholine receptors

Muscarinic acetylcholine receptors are metabotropic, i.e. G-protein coupled. They activate other ion channels through a second messenger cascade. They can be activated by the agonistic acting muscarin, which is why they are also called m-acetylcholine receptors. They are inhibited by the antagonistic atropine.

A distinction is made as subtypes:

  • m1, m3, m5: Effect on the IP3-DAG cascade
  • m2, m4: The M2-Subtype is expressed on the pacemaker cells of the heart. It is a G protein-coupled receptor, more precisely a Gi-Receptor. Its alpha subunit inhibits adenylate cyclase, while its beta and gamma subunits open a potassium channel that hyperpolarizes the cell. Also m4 is Gi-coupled and is found in the neostriate.