Ligand-gated ion channel
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The Ligand-gated ion channels, also referred to as LGICs, or ionotropic receptors, are a group of intrinsic transmembrane ion channels that are opened or closed in response to binding of a chemical messenger, as opposed to voltage-gated ion channels or stretch-activated ion channels.
Regulation
The ion channel is regulated by a ligand and is usually very selective to one or more ions like Na+, K+, Ca2+, or Cl-. Such receptors located at synapses convert the chemical signal of presynaptically released neurotransmitter directly and very quickly into a postsynaptic electrical signal.
Many LGICs are additionally modulated by allosteric ligands, by channel blockers, ions, or the membrane potential.
Example: nicotinic acetylcholine receptor
The prototypic ligand-gated ion channel is the nicotinic acetylcholine receptor. It consists of a pentamer of protein subunits, with two binding sites for acetylcholine, which, when bound, alter the receptor's configuration and cause an internal pore to open. This pore, permeable to Na+, allows Na+ ions to flow down their electrochemical gradient into the cell. With a sufficient number of channels opening at once, the intracellular Na+ concentration rises to the point at which the positive charge within the cell is enough to depolarize the membrane, and an action potential is initiated.
Classification and examples
Many important ion channels are ligand-gated, and they show a great degree of homology at the genetic level. The Ligand-gated ion channels are classified into three superfamilies:
The Cys-loop receptors
- anionic
- cationic
The ionotropic glutamate receptors
The ATP-gated channels
Clinical relevance
Ligand-gated ion channels are likely to be the major site at which anaesthetic agents have their effects, although unequivocal evidence of this is yet to be established. In particular, the GABA and NMDA receptors are affected by anaesthetic agents at concentrations similar to those used in clinical anaesthesia.
See also
References
- Connolly, CN; Wafford KA (2004). "The Cys-loop superfamily of ligand-gated ion channels: the impact of receptor structure on function". Biochem. Soc. Trans 32 (3): 529-534. ISSN 0300-5127. PMID 15157178. Retrieved on 2007-06-08.
External links
- Ligand-Gated Ion Channel database at European Bioinformatics Institute. Verified availability April 11, 2007.
Membrane transport protein: ion channels | |
|---|---|
| Ca2+: Calcium channel | Voltage-dependent calcium channel (L-type/Cav1.2, Cav2.1, N-type, P-type, Q-type, R-type, T-type) - Inositol triphosphate receptor - Ryanodine receptor - Cation channels of sperm - Two-pore channel |
| Na+: Sodium channel | Nav1.4 - Nav1.5 - Nav1.7- Nav1.9 - Epithelial sodium channel |
| K+: Potassium channel | Voltage-gated (Kv1.1, KvLQT1, KvLQT2, KvLQT3, HERG, Shaker gene, KCNE1) - Calcium-activated (BK channel, SK channel, SK3) - Inward-rectifier (ROMK, Kir2.1, KCNJ11) - Tandem pore domain |
| Cl-: Chloride channel | Cystic fibrosis transmembrane conductance regulator |
| Porin | Aquaporin (1, 2, 3, 4) - Voltage-dependent anion channel |
| Cations: TRP | TRPA - TRPC (TRPC6) - TRPM (TRPM6) - TRPML (Mucolipin-1) - TRPP - TRPV (TRPV1, TRPV6) |
| Other/general | Voltage-gated ion channel - Ligand-gated ion channel - Cyclic nucleotide-gated ion channel - Stretch-activated ion channel |
Ion channel, receptor: ligand-gated ion channels | |
|---|---|
| Cys-loop receptors | 5-HT receptor (5-HT3 serotonin receptor (A)) - GABA receptor (GABA A (α1, α2, α3, α5, α6, β1, β2, β3, γ2, ε), GABA C (ρ1)) - Glycine receptor (α1) - Nicotinic acetylcholine receptor (α1, α2, α3, α4, α5, α7, β2, β3, β4, δ, ε, (α4)2(β2)3, (α7)5, Ganglion type, Muscle type) |
| Ionotropic glutamate receptors | AMPA (1, 2, 3, 4) - Kainate (1, 2) - NMDA (1, 2A, 2B, 2C, 2D) |
| ATP-gated channels | Purinergic receptors (P2X (1, 4, 5, 7)) |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
