Ligand-gated ion channel

Suppose the channels are opened or closed by ligands binding to a receptor channel's extracellular domain. In that case, they are called ligand-gated ion channels or ionotropic receptors.

The nicotine receptor is shown as an example. The ion channel is a pentamer with two binding sites in the alfa subunit for the transmitter acetylcholine (Ach). This causes a conformational change, and the channel opens. The influx of Na+ ions occurs along the diffusion gradient, which is promoted by negatively charged amino acids on the inside of the channel opening. In the middle of the channel pore, there is a selectivity filter to prefer the incoming cations.…