ABSTRACT
Many ligand-gated ion channel receptors have had their primary structures determined by cloning and sequencing their DNA. The nicotinic receptor family members are pentamers, with the five subunits clustered around a central pore. GABAA receptors have much in common with nicotinic receptors. The ionotropic glutamate receptors (iGluRs) share only weak homologies with the other types of ligand-gated ion channels such as the nicotinic receptor superfamily. There are two populations of iGluRs, defined by selective agonists: α-amino-3-hydroxy-5-methyl-4-isoxazole-proprionic acid (AMPA)/kainate receptors and N-methyl-d-aspartate (NMDA) receptors. Six subunits that belong to the AMPA/kainate population have been cloned and sequenced (GluR1–GluR6). NMDA receptors are targets for a number of drugs including dissociative anesthetics that produce altered consciousness rather than unconsciousness and the hallucinogenic phencyclidine. G protein-linked receptors members include receptors for slow neurotransmitters, many hormones, and sensory transduction molecules mediating the responses to light by photoreceptors in the retina, and the chemical senses of smell and taste.
