Ligand-gated glutamate receptors

Figure 11.2 The Ca2+ influx channels of the plasma membrane, (a) A voltage-gated channel—the membrane topography of the al-subunit, which forms the channel proper, (b) Membrane topography of TRP channels, homologous to the SOC channels, (c) Membrane topography of the ligand-gated glutamate NMDA receptor. (From Carafoli, 2005. Reproduced with permission from Blackwell...

For differentiation of G-protein-coupled receptor sub-types from subtypes permanently linked to ion channels (ligand-gated ion channels) the terms metabotropic versus ionotropic receptors, respectively, are used. Prime examples of metabotropic receptors are given by the lnGlu receptor family of G-protein-coupled glutamate receptors. 

Ionotropic receptors (bottom left) are ligand-gated ion channels. When they open as a result of the transmitter s influence, ions flow in due to the membrane potential (see p. 126). If the inflowing ions are cations (Na"", C, Ca ""), depolarization of the membrane occurs and an action potential is triggered on the surface of the postsynaptic cell. This is the way in which stimulatory transmitters work (e.g., acetylcholine and glutamate). By contrast, if anions flow in (mainly Cl ), the result is hyperpolarization of the postsynaptic membrane, which makes the production of a postsynaptic action potential more dif cult. The action of inhibitory transmitters such as glycine and GABA is based on this effect. 

There are two main families of ligand-gated ion channel proteins that act as ionotropic receptors. One family includes the nicotinic acetylcholine receptor, the GABA-A receptor, the glycine receptor, and a class of serotonin receptor. The other family comprises various types of ionotropic glutamate receptors. Since these various ligand gated ion channels are activated by neurotransmitters, the medicinal chemistry of these proteins is presented in detail in chapter 4. 

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