ABSTRACT
Most ligand-gated ion channel (ionotropic) receptors are members of two families (Table 1), the cys-loop family (containing the nicotinic cholinergic, GABAA, glycine, and 5-hydroxytryptamine (5-HT3) receptors), and the ionotropic glutamate receptor family. The cys-loop receptors have a pentameric subunit structure; the glutamate receptors have four subunits. In both families the subunits are clustered around a central pore, like staves around a barrel. Because there are numerous subunit isoforms, receptors can be assembled from several subunit combinations. Each combination results in a receptor with distinct physiology and pharmacology, and is typically expressed in a specific population of cell types.
