The ion-channel-coupled receptors, also called ligand-gated ion channels, are one of the three main cell membrane receptor. They play an important role in the transmission of neuronal signals at the synapses and the neuromuscular junctions (NMJ).
Depending upon which neurotransmitter they bind, these receptors can be classified as excitatory and inhibitory.
They are cation channels that depolarize the membrane towards the action potential.
Nicotinic Acetylcholine receptor (nAChR)
This cholinergic receptor was the first receptor in history to be indentified and named. It binds the excitatory neurotrasmitter acetylcholine (ACh). They can be found in neurons of the CNS and the ANS ganglia, as well as in the muscle cells at the NMJ. The receptor is composed of five subunits (heteropentamer) and each subunit has 4 transmembrane domians.
The receptors at the NMJ are composed of 2α, 1β, 1γ, 1δ subunits, whereas the ones in the ganglia and CNS have 2α, 3β subunits. The α-subunit has the binding-site for ACh.