Ligand-gated Ion Channel

Cross reference: 

Ion channel (Wiki) 
"Ligand-gated ion channels are also known as ionotropic receptors, this group of channels open in response to specific ligand molecules binding to the extracellular domain of the receptor protein. Ligand binding causes a conformational change in the structure of the channel protein that ultimately leads to the opening of the channel gate and subsequent ion flux across the plasma membrane.

Examples of such channels include the cation-permeable "nicotinic" Acetylcholine receptor, ionotropic glutamate-gated receptors and ATP-gated P2X receptors, and the anion-permeable γ-aminobutyric acid-gated GABAA receptor.

Ion channels activated by second messengers may also be categorized in this group, although ligands and second messengers are otherwise distinguished from each other."  

Ligand-gated ion channel (Wiki) 

Neurotransmitter-gated ion-channel transmembrane region

"Ligand-gated ion channels (LGICs) are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger (i.e., a ligand),[1] such as a neurotransmitter.[2]

Neurotransmitter-gated ion-channel ligand binding domain 

File:2bg9 opm.gif

The table, below, is just a summary of more detailed tables given in the Wiki article. 

ligand-gated ion channels

Cys-loop receptors
5-HT3 (A, B, C, D, E)

GABAA (α1, α2, α3, α4, α5, α6, β1, β2, β3, γ1, γ2, γ3, δ, ε, π, θ) · GABAA (ρ1, ρ2, ρ3)

α1 · α2 · α3 · α4 · β

monomers: α1 · α2 · α3 · α4 · α5 · α6 · α7 · α9 · α10 · β1 · β2 · β3 · β4 · δ · ε
pentamers: (α3)2(β4)3 · (α4)2(β2)3 · (α7)5 · (α1)2(β4)3 - Ganglion type · (α1)2β1δε - Muscle type


Ionotropic glutamates
Ligand-gated only
AMPA (1, 2, 3, 4) · Kainate (1, 2, 3, 4, 5)

Voltage- and ligand-gated
NMDA (1, 2A, 2B, 2C, 2D, 3A, 3B, L1A, L1B)

GluD (δ1, δ2)

ATP-gated channels
P2X (1, 2, 3, 4, 5, 6, 7)