Types
Glutamate receptors can be divided into two groups according to the mechanism by which their activation gives rise to a postsynaptic current. Ionotropic glutamate receptors (iGluRs) form the ion channel pore that activates when glutamate binds to the receptor. Metabotropic glutamate receptors (mGluRs) indirectly activate ion channels on the plasma membrane through a signaling cascade that involves G proteins. Ionotropic receptors tend to be quicker in relaying information, but metabotropic ones are associated with a more prolonged stimulus. This is due to the usage of many different messengers to carry out the signal, but since there is a cascade, just one activation of a G-protein can lead to multiple activations. Glutamate receptors are usually not specifically geared towards glutamate exclusively as the ligand and sometimes even requires another agonist.
Of the many specific subtypes of glutamate receptors, it is customary to refer to primary subtypes by a chemical which binds to it more selectively than glutamate. The research, though, is ongoing, as subtypes are identified and chemical affinities measured. Several compounds are routinely used in glutamate receptor research and associated with receptor subtypes:
| Type | Name | Agonist(s) |
| ionotropic | NMDA receptor | NMDA |
| Kainate receptor | Kainate | |
| AMPA receptor | AMPA | |
| metabotropic | mGluR | L-AP4, ACPD, L-QA |
Due to the diversity of glutamate receptors, their subunits are encoded by numerous gene families. Sequence similarities between mammals show a common evolutionary origin for many mGluR and all iGluR genes. Conservation of reading frames and splice sites of GluR genes between chimpanzees and humans is complete, suggesting no gross structural changes after humans diverged from the human-chimpanzee common ancestor. However, there is a possibility that two human-specific "fixed" amino acid substitutions, D71G in GRIN3A and R727H in GRIN3B, are specifically associated with human brain function.
Read more about this topic: Glutamate Receptor
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