What are the muscarinic cholinergic receptors

Muscarinic receptor

Synonyms: muscarinic receptor, muscarinic acetylcholine receptor, muscarinic acetylcholine receptor, mACh receptor, mAChR, m-choline receptor, M-cholino receptor

1 definition

Muscarinic receptors or mACh receptors are membrane-bound acetylcholine receptors that use the intracellular messenger substance cGMP when activated. Its name is based on its substrate acetylcholine and its ability to be activated by the mushroom poison muscarin.

2 physiology

In contrast to nicotine receptors, muscarinic receptors do not form ion channels, i.e. the binding site for the neurotransmitter and the possibly activated ion channel are not in the same membrane protein. They develop their effect indirectly by activating the second messenger systems (G proteins). They are therefore also referred to as metabotropic receptors. This type of receptor can be found:

The effects mediated by muscarinic receptors depend on whether agonists or antagonists bind to the receptor:

The acetylcholine effect is terminated in the synaptic cleft via transmitter cleavage by the acetylcholinesterase, so that 50% are taken up again in the presynapse. In contrast to acetylcholine, muscarine is not broken down and therefore leads to permanent stimulation of the receptors. Atropine has an antagonistic effect on all mACh receptors.

3 classification

One can distinguish 5 subtypes of muscarinic receptors (M.1-M5). Although they all have a binding specificity for acetylcholine and are inhibited by antagonists such as atropine, the effects they trigger follow two different second messenger paths. M.1-, M3- and M5Receptors stimulate intracellular IP3 signal transduction metabolism (Gq-coupled), M2- and M4Receptors inhibit adenylate cyclase (Gi-coupled).

The different types of receptors can be found in different target tissues: