Ligand - gated ion channel - wikipedia Ligand - gated ion channel `` Ionotropic '' redirects here, not to be confused with inotropic. Neurotransmitter - gated ion - channel transmembrane region Ligand - gated ion channel Identifiers Symbol Neur_chan_memb Pfam PF02932 InterPro IPR006029 PROSITE PDOC00209 SCOP 1cek SUPERFAMILY 1cek TCDB 1. A. 9 OPM superfamily 14 OPM protein 2bg9 show Available protein structures : Pfam structures PDB RCSB PDB ; PDBe ; PDBj PDBsum structure summary Ion - channel - linked receptor Ions Ligand ( such as acetylcholine ) When ligands bind to the receptor, the ion channel portion of the receptor opens, allowing ions to pass across the cell membrane. Ligand - gated ion channels ( LICs, LGIC ), also commonly referred as ionotropic receptors, are a group of transmembrane ion - channel proteins which open to allow ions such as Na, K, Ca, and / or Cl to pass through the membrane in response to the binding of a chemical messenger ( i.e. a ligand ), such as a neurotransmitter. When a presynaptic neuron is excited, it releases a neurotransmitter from vesicles into the synaptic cleft. The neurotransmitter then binds to receptors located on the postsynaptic neuron. If these receptors are ligand - gated ion channels, a resulting conformational change opens the ion channels, which leads to a flow of ions across the cell membrane. This, in turn, results in either a depolarization, for an excitatory receptor response, or a hyperpolarization, for an inhibitory response. These proteins are typically composed of at least two different domains : a transmembrane domain which includes the ion pore, and an extracellular domain which includes the ligand binding location ( an allosteric binding site ). This modularity has enabled a ' divide and conquer ' approach to finding the structure of the proteins ( crystallising each domain separately ). The function of such receptors located at synapses is to convert the chemical signal of presynaptically released neurotransmitter directly and very quickly into a postsynaptic electrical signal. Many LICs are additionally modulated by allosteric ligands, by channel blockers, ions, or the membrane potential. LICs are classified into three superfamilies which lack evolutionary relationship : cys - loop receptors, ionotropic glutamate receptors and ATP - gated channels. Contents 1 Cys - loop receptors 1.1 Structure 1.2 Cationic cys - loop receptors 1.3 Anionic cys - loop receptors 2 Ionotropic glutamate receptors 2.1 AMPA receptor 2.2 NMDA receptors 3 GABA receptors 3.1 GABA receptor 4 5 - HT3 receptor 5 ATP - gated channels 6 PIP - gated channels 7 Indirect modulation 7.1 G - protein - linked receptors 7.1. 1 GABA receptor 7.1. 2 Gα signaling 7.1. 3 Gβγ signaling 8 Clinical relevance 9 See also 10 References 11 External links Cys - loop receptors Nicotinic acetylcholine receptor in closed state with predicted membrane boundaries shown, PDB 2BG9 The cys - loop receptors are named after a characteristic loop formed by a disulfide bond between two cysteine residues in the N terminal extracellular domain. They are part of a larger family of pentameric ligand - gated ion channels that usually lack this disulfide bond, hence the tentative name `` Pro-loop receptors ''. A binding site in the extracellular N - terminal ligand - binding domain gives them receptor specificity for ( 1 ) acetylcholine ( AcCh ), ( 2 ) serotonin, ( 3 ) glycine, ( 4 ) glutamate and ( 5 ) γ - aminobutyric acid ( GABA ) in vertebrates. The receptors are subdivided with respect to the type of ion that they conduct ( anionic or cationic ) and further into families defined by the endogenous ligand. They are usually pentameric with each subunit containing 4 transmembrane helices constituting the transmembrane domain, and a beta sheet sandwich type, extracellular, N terminal, ligand binding domain. Some also contain an intracellular domain like shown in the image. The prototypic ligand - gated ion channel is the nicotinic acetylcholine receptor. It consists of a pentamer of protein subunits ( typically ααβγδ ), with two binding sites for acetylcholine ( one at the interface of each alpha subunit ). When the acetylcholine binds it alters the receptor 's configuration ( twists the T2 helices which moves the leucine residues, which block the pore, out of the channel pathway ) and causes the constriction in the pore of approximately 3 angstroms to widen to approximately 8 angstroms so that ions can pass through. This pore allows Na ions to flow down their electrochemical gradient into the cell. With a sufficient number of channels opening at once, the inward flow of positive charges carried by Na ions depolarizes the postsynaptic membrane sufficiently to initiate an action potential. While single - cell organisms like bacteria would have little apparent need for the transmission of an action potential, a bacterial homologue to an LIC has been identified, hypothesized to act nonetheless as a chemoreceptor. This prokaryotic nAChR variant is known as the GLIC receptor, after the species in which it was identified ; Gloeobacter Ligand - gated Ion C channel. Structure Cys - loop receptors have structural elements that are well conserved, with a large extracellular domain ( ECD ) harboring an alpha - helix and 10 beta - strands. Following the ECD, four transmembrane segments ( TMSs ) are connected by intracellular and extracellular loop structures. Except the TMS 3 - 4 loop, their lengths are only 7 - 14 residues. The TMS 3 - 4 loop forms the largest part of the intracellular domain ( ICD ) and exhibits the most variable region between all of these homologous receptors. The ICD is defined by the TMS 3 - 4 loop together with the TMS 1 - 2 loop preceding the ion channel pore. Crystallization has revealed structures for some members of the family, but to allow crystallization, the intracellular loop was usually replaced by a short linker present in prokaryotic cys - loop receptors, so their structures as not known. Nevertheless, this intracellular loop appears to function in desensitization, modulation of channel physiology by pharmacological substances, and posttranslational modifications. Motifs important for trafficking are therein, and the ICD interacts with scaffold proteins enabling inhibitory synapse formation. Cationic cys - loop receptors Type Class IUPHAR - recommended protein name Gene Previous names Serotonin ( 5 - HT ) 5 - HT 5 - HT3A 5 - HT3B 5 - HT3C 5 - HT3D 5 - HT3E HTR3A HTR3B HTR3C HTR3D HTR3E 5 - HT 5 - HT 5 - HT 5 - HT 5 - HT Nicotinic acetylcholine ( nAChR ) alpha α1 α2 α3 α4 α5 α6 α7 α9 α10 CHRNA1 CHRNA2 CHRNA3 CHRNA4 CHRNA5 CHRNA6 CHRNA7 CHRNA9 CHRNA10 ACHRA, ACHRD, CHRNA, CMS2A, FCCMS, SCCMS beta β1 β2 β3 β4 CHRNB1 CHRNB2 CHRNB3 CHRNB4 CMS2A, SCCMS, ACHRB, CHRNB, CMS1D EFNL3, nAChRB2 gamma γ CHRNG ACHRG delta δ CHRND ACHRD, CMS2A, FCCMS, SCCMS epsilon ε CHRNE ACHRE, CMS1D, CMS1E, CMS2A, FCCMS, SCCMS Zinc - activated ion channel ( ZAC ) ZAC ZACN ZAC1, L2m LICZ, LICZ1 Anionic cys - loop receptors Type Class IUPHAR - recommended protein name Gene Previous names GABA alpha α1 α2 α3 α4 α5 α6 GABRA1 GABRA2 GABRA3 GABRA4 GABRA5 GABRA6 EJM, ECA4 beta β1 β2 β3 GABRB1 GABRB2 GABRB3 ECA5 gamma γ1 γ2 γ3 GABRG1 GABRG2 GABRG3 CAE2, ECA2, GEFSP3 delta δ GABRD epsilon ε GABRE pi π GABRP theta θ GABRQ rho ρ1 ρ2 ρ3 GABRR1 GABRR2 GABRR3 GABA Glycine ( GlyR ) alpha α1 α2 α3 α4 GLRA1 GLRA2 GLRA3 GLRA4 STHE beta β GLRB Ionotropic glutamate receptors The AMPA receptor bound to a glutamate antagonist showing the amino terminal, ligand binding, and transmembrane domain, PDB 3KG2 The ionotropic glutamate receptors bind the neurotransmitter glutamate. They form tetramers with each subunit consisting of an extracellular amino terminal domain ( ATD, which is involved tetramer assembly ), an extracellular ligand binding domain ( LBD, which binds glutamate ), and a transmembrane domain ( TMD, which forms the ion channel ). The transmembrane domain of each subunit contains three transmembrane helices as well as a half membrane helix with a reentrant loop. The structure of the protein starts with the ATD at the N terminus followed by the first half of the LBD which is interrupted by helices 1, 2 and 3 of the TMD before continuing with the final half of the LBD and then finishing with helix 4 of the TMD at the C terminus. This means there are three links between the TMD and the extracellular domains. Each subunit of the tetramer has a binding site for glutamate formed by the two LBD sections forming a clamshell like shape. Only two of these sites in the tetramer need to be occupied to open the ion channel. The pore is mainly formed by the half helix 2 in a way which resembles an inverted potassium channel. Type Class IUPHAR - recommended protein name Gene Previous names AMPA GluA GluA1 GluA2 GluA3 GluA4 GRIA1 GRIA2 GRIA3 GRIA4 GLU, GluR1, GluRA, GluR - A, GluR - K1, HBGR1 GLU, GluR2, GluRB, GluR - B, GluR - K2, HBGR2 GLU, GluR3, GluRC, GluR - C, GluR - K3 GLU, GluR4, GluRD, GluR - D Kainate GluK GluK1 GluK2 GluK3 GluK4 GluK5 GRIK1 GRIK2 GRIK3 GRIK4 GRIK5 GLU, GluR5, GluR - 5, EAA3 GLU, GluR6, GluR - 6, EAA4 GLU, GluR7, GluR - 7, EAA5 GLU, KA1, KA - 1, EAA1 GLU, KA2, KA - 2, EAA2 NMDA GluN GluN1 NRL1A NRL1B GRIN1 GRINL1A GRINL1B GLU, NMDA - R1, NR1, GluRξ1 GluN2A GluN2B GluN2C GluN2D GRIN2A GRIN2B GRIN2C GRIN2D GLU, NMDA - R2A, NR2A, GluRε1 GLU, NMDA - R2B, NR2B, hNR3, GluRε2 GLU, NMDA - R2C, NR2C, GluRε3 GLU, NMDA - R2D, NR2D, GluRε4 GluN3A GluN3B GRIN3A GRIN3B GLU, NMDA - R3A, NMDAR - L, chi - 1 GLU, NMDA - R3B ' Orphan ' ( GluD ) GluD1 GluD2 GRID1 GRID2 GluRδ1 GluRδ2 AMPA receptor The AMPA receptor bound to a glutamate antagonist showing the amino terminal, ligand binding, and transmembrane domain, PDB 3KG2 The α - amino - 3 - hydroxy - 5 - methyl - 4 - isoxazolepropionic acid receptor ( also known as AMPA receptor, or quisqualate receptor ) is a non-NMDA - type ionotropic transmembrane receptor for glutamate that mediates fast synaptic transmission in the central nervous system ( CNS ). Its name is derived from its ability to be activated by the artificial glutamate analog AMPA. The receptor was first named the `` quisqualate receptor '' by Watkins and colleagues after a naturally occurring agonist quisqualate and was only later given the label `` AMPA receptor '' after the selective agonist developed by Tage Honore and colleagues at the Royal Danish School of Pharmacy in Copenhagen. AMPARs are found in many parts of the brain and are the most commonly found receptor in the nervous system. The AMPA receptor GluA2 ( GluR2 ) tetramer was the first glutamate receptor ion channel to be crystallized. AMPA receptor trafficking Ligands : Agonists : Glutamate, AMPA, 5 - Fluorowillardiine, Domoic acid, Quisqualic acid, etc. Antagonists : CNQX, Kynurenic acid, NBQX, Perampanel, Piracetam, etc. Positive allosteric modulators : Aniracetam, Cyclothiazide, CX - 516, CX - 614, etc. Negative allosteric modulators : Ethanol, Perampanel, Talampanel, GYKI - 52,466, etc. NMDA receptors Stylized depiction of an activated NMDAR The N - methyl - D - aspartate receptor ( NMDA receptor ) -- a type of ionotropic glutamate receptor -- is a voltage - dependent ligand - gated ion channel that is gated by the simultaneous binding of glutamate and a co-agonist ( i.e., either D - serine or glycine ). Studies show that the NMDA receptor is involved in regulating synaptic plasticity and memory. The name `` NMDA receptor '' is derived from the ligand N - methyl - D - aspartate ( NMDA ), which acts as a selective agonist at these receptors. When the NMDA receptor is activated by the binding of two co-agonists, the cation channel opens, allowing Na and Ca to flow into the cell, in turn raising the cell 's electric potential. Thus, the NMDA receptor is an excitatory receptor. At resting potentials, the binding of Mg or Zn at their extracellular binding sites on the receptor blocks ion flux through the NMDA receptor channel. `` However, when neurons are depolarized, for example, by intense activation of colocalized postsynaptic AMPA receptors, the voltage - dependent block by Mg is partially relieved, allowing ion influx through activated NMDA receptors. The resulting Ca influx can trigger a variety of intracellular signaling cascades, which can ultimately change neuronal function through activation of various kinases and phosphatases ''. Ligands : Primary endogenous co-agonists : glutamate and either D - serine or glycine Other agonists : aminocyclopropanecarboxylic acid ; D - cycloserine ; L - aspartate ; quinolinate, etc. Partial agonists : N - methyl - D - aspartic acid ( NMDA ) ; NRX - 1074 ; 3, 5 - dibromo - L - phenylalanine, etc. Antagonists : ketamine, PCP, dextropropoxyphene, ketobemidone, tramadol, kynurenic acid ( endogenous ), etc. GABA receptors GABA receptors are major inhibitory neurotransmitter expressed in the major interneurons in animal cortex. GABA receptor GABA receptor schematic GABA receptors are ligand - gated ion channels. GABA ( gamma - aminobutyric acid ), the endogenous ligand for these receptors, is the major inhibitory neurotransmitter in the central nervous system. When activated, it mediates Cl flow into the neuron, hyperpolarizing the neuron. GABA receptors occur in all organisms that have a nervous system. Due to their wide distribution within the nervous system of mammals, they play a role in virtually all brain functions. Various ligands can bind specifically to GABA receptors, either activating or inhibiting the Cl channel. Ligands : Agonists : GABA, muscimol, progabide, gaboxadol Antagonists : bicuculine, gabazine Partial agonist : piperidine - 4 - sulfonic acid 5 - HT3 receptor 5 - HT3 receptor The pentameric 5 - HT3 receptor is permeable to sodium ( Na ), potassium ( K ), and calcium ( Ca ) ions. ATP - gated channels Figure 1. Schematic representation showing the membrane topology of a typical P2X receptor subunit. First and second transmembrane domains are labeled TM1 and TM2. Main article : P2X receptor ATP - gated channels open in response to binding the nucleotide ATP. They form trimers with two transmembrane helices per subunit and both the C and N termini on the intracellular side. Type Class IUPHAR - recommended protein name Gene Previous names P2X N / A P2X1 P2X2 P2X3 P2X4 P2X5 P2X6 P2X7 P2RX1 P2RX2 P2RX3 P2RX4 P2RX5 P2RX6 P2RX7 P2X P2X P2X P2X P2X P2X P2X PIP - gated channels Phosphatidylinositol 4, 5 - bisphosphate ( PIP ) binds to and directly activates inwardly rectifying potassium channels ( K ). PIP is a cell membrane lipid, and its role in gating ion channels represents a novel role for the molecule. Indirect modulation In contrast to ligand - gated ion channels, there are also receptor systems in which the receptor and the ion channel are separate proteins in the cell membrane, instead of a single molecule. In this case, ion channels are indirectly modulated by activation of the receptor, instead of being gated directly. G - protein - linked receptors G - protein - coupled receptor mechanism Also called G protein - coupled receptor, seven - transmembrane domain receptor, 7 TM receptor, constitute a large protein family of receptors that sense molecules outside the cell and activate inside signal transduction pathways and, ultimately, cellular responses. They pass through the cell membrane 7 times. G - protein - Linked receptors are a huge family that have hundreds of members identified. Ion - channel - linked receptors ( e.g. GABAB, NMDA, etc. ) are only a part of them. Table 1. Three major families of Trimeric G Proteins FAMILY SOME FAMILY MEMBERS ACTION MEDIATED BY FUNCTIONS GS α Activate adenylyl cyclase activates Ca2+ channels Golf α Activates adenylyl cyclase in olfactory sensory neurons II Gi α Inhibits adenylyl cyclase βɣ Activates K+ channels G0 βɣ Activates K+ channels ; inactivate Ca2+ channels α and βɣ Activates phospholipase C - β Gt ( transducin ) α Activate cyclic GMP phosphodiesterase in vertebrate rod photoreceptors III Gq α Activates phospholipase C - β GABA receptor GABAB receptors are metabotropic transmembrane receptors for gamma - aminobutyric acid. They are linked via G - proteins to K+ channels, when active, they create hyperpolarized effect and lower the potential inside the cell. Ligands : Agonists : GABA, Baclofen, gamma - Hydroxybutyrate, Phenibut etc. Positive Allosteric Modulators : CGP - 7930, Fendiline, BSPP, etc. Antagonists : 2 - OH - saclofen, Saclofen, SCH - 50911 Gα signaling The cyclic - adenosine monophosphate ( cAMP ) - generating enzyme adenylate cyclase is the effector of both the G and G pathways. Ten different AC gene products in mammals, each with subtle differences in tissue distribution and / or function, all catalyze the conversion of cytosolic adenosine triphosphate ( ATP ) to cAMP, and all are directly stimulated by G - proteins of the G class. Interaction with Gα subunits of the G type, on the contrary, inhibits AC from generating cAMP. Thus, a GPCR coupled to G counteracts the actions of a GPCR coupled to G, and vice versa. The level of cytosolic cAMP may then determine the activity of various ion channels as well as members of the ser / thr - specific protein kinase A ( PKA ) family. As a result, cAMP is considered a second messenger and PKA a secondary effector. The effector of the G pathway is phospholipase C - β ( PLCβ ), which catalyzes the cleavage of membrane - bound phosphatidylinositol 4, 5 - biphosphate ( PIP2 ) into the second messengers inositol ( 1, 4, 5 ) trisphosphate ( IP3 ) and diacylglycerol ( DAG ). IP3 acts on IP3 receptors found in the membrane of the endoplasmic reticulum ( ER ) to elicit Ca release from the ER, DAG diffuses along the plasma membrane where it may activate any membrane localized forms of a second ser / thr kinase called protein kinase C ( PKC ). Since many isoforms of PKC are also activated by increases in intracellular Ca, both these pathways can also converge on each other to signal through the same secondary effector. Elevated intracellular Ca also binds and allosterically activates proteins called calmodulins, which in turn go on to bind and allosterically activate enzymes such as Ca / calmodulin - dependent kinases ( CAMKs ). The effectors of the G pathway are three RhoGEFs ( p115 - RhoGEF, PDZ - RhoGEF, and LARG ), which, when bound to G allosterically activate the cytosolic small GTPase, Rho. Once bound to GTP, Rho can then go on to activate various proteins responsible for cytoskeleton regulation such as Rho - kinase ( ROCK ). Most GPCRs that couple to G also couple to other sub-classes, often G. Gβγ signaling The above descriptions ignore the effects of Gβγ -- signalling, which can also be important, in particular in the case of activated G - coupled GPCRs. The primary effectors of Gβγ are various ion channels, such as G - protein - regulated inwardly rectifying K channels ( GIRKs ), P / Q - and N - type voltage - gated Ca channels, as well as some isoforms of AC and PLC, along with some phosphoinositide - 3 - kinase ( PI3K ) isoforms. Clinical relevance Ligand - gated ion channels are likely to be the major site at which anaesthetic agents and ethanol 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. By understanding the mechanism and exploring the chemical / biological / physical component that could function on those receptors, more and more clinical applications are proven by preliminary experiments or FDA. Memantine Memantine is approved by the U.S.F.D.A and the European Medicines Agency for the treatment of moderate - to - severe Alzheimer 's disease, and has now received a limited recommendation by the UK 's National Institute for Health and Care Excellence for patients who fail other treatment options. Antidepressant treatment Agomelatine, is a type of drug that acts on a dual melatonergic - serotonergic pathway, which have shown its efficacy in the treatment of anxious depression during clinical trails, study also suggests the efficacy in the treatment of atypical and melancholic depression. See also MCB portal Neuroscience portal Biology portal Receptor ( biochemistry ) Action potential Voltage - dependent calcium channel Calcium - activated potassium channel Cyclic nucleotide - gated ion channel Acid - sensing ion channel Ryanodine receptor Inositol trisphosphate receptor References Jump up ^ `` Gene Family : Ligand gated ion channels ''. HUGO Gene Nomenclature Committee. 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A randomized, double - blind study vs placebo ''. European Psychiatry. 28 ( Suppl 1 ) : 1. doi : 10.1016 / S0924 - 9338 ( 13 ) 76634 - 3. Jump up ^ Brunton, L ; Chabner, B ; Knollman, B ( 2010 ). Goodman and Gilman 's The Pharmacological Basis of Therapeutics ( 12th ed. ). New York : McGraw - Hill Professional. ISBN 978 - 0 - 07 - 162442 - 8. Jump up ^ Avedisova, A ; Marachev, M ( 2013 ). `` 2639 -- The effectiveness of agomelatine ( valdoxan ) in the treatment of atypical depression ''. European Psychiatry. 28 ( Suppl 1 ) : 1. doi : 10.1016 / S0924 - 9338 ( 13 ) 77272 - 9. External links Ligand - Gated Ion Channel database at European Bioinformatics Institute. Verified availability April 11, 2007. `` Revised Recommendations for Nomenclature of Ligand - Gated Ion Channels ''. IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. http://www.esf.edu/efb/course/EFB325/lectures/29HormoneSignals.htm https://www.genenames.org/ As of this edit, this article uses content from `` 1. A. 9 The Neurotransmitter Receptor, Cys loop, Ligand - gated Ion Channel ( LIC ) Family '', which is licensed in a way that permits reuse under the Creative Commons Attribution - ShareAlike 3.0 Unported License, but not under the GFDL. All relevant terms must be followed. Membrane transport protein : ion channels ( TC 1A ) Ca : Calcium channel Ligand - gated Inositol trisphosphate receptor Ryanodine receptor Voltage - gated L - type / Ca α 1.1 1.2 1.3 1.4 N - type / Ca α2. 2 P - type / Ca α 2.1 Q - type / Ca α2. 1 R - type / Ca α2. 3 T - type / Ca α 3.1 3.2 3.3 α δ - subunits β - subunits β1 β2 β3 β4 γ - subunits γ1 γ2 γ3 γ4 Cation channels of sperm Two - pore channel Na : Sodium channel Constitutively active Epithelial sodium channel α β γ δ Proton - gated Amiloride - sensitive cation channel Voltage - gated Na α 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 7A Na β K : Potassium channel Calcium - activated BK channel α1 β1 β2 β3 β4 SK channel SK1 SK2 SK3 IK channel IK1 1.1 2.1 2.2 2.3 3.1 4.1 4.2 5.1 Inward - rectifier 1.1 2.1 2.2 2.3 2.4 2.6 GIRK / K 3.1 3.2 3.3 3.4 4.1 4.2 5.1 6.1 6.2 7.1 Tandem pore domain K2P 5 6 7 9 10 12 13 15 16 17 18 Voltage - gated K α1 - 6 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 2.1 2.2 3.1 3.2 3.3 3.4 4.1 4.2 4.3 5.1 6.1 6.2 6.3 6.4 K α7 - 12 7.1 7.2 7.3 7.4 7.5 8.1 8.2 9.1 9.2 9.3 10.1 10.2 11.1 / hERG 11.2 11.3 12.1 12.2 12.3 K β KCNIP minK / ISK minK / ISK - like MiRP Shaker gene Miscellaneous Cl : Chloride channel Calcium - activated chloride channels Anoctamin ANO1 Bestrophin Chloride Channel Accessory CFTR CLCN 5 6 7 KA KB CLIC 5 6 L1 CLNS 1A 1B H : Proton channel HVCN1 M : CNG cation channel α β HCN FC M : TRP cation channel TRPA ( 1 ) TRPC 4AP 5 6 7 TRPM 5 6 7 8 TRPML TRPN TRPP TRPV 5 6 H O ( + solutes ) : Porin Aquaporin 0 5 6 7 8 9 Voltage - dependent anion channel General bacterial porin family Cytoplasm : Gap junction Connexin GJA1 GJA3 GJA4 GJA5 GJA8 GJA9 GJA10 GJB1 GJB2 GJB3 GJB4 GJB5 GJB6 GJB7 GJC1 GJC2 GJC3 GJD2 GJD3 GJD4 Innexin By gating mechanism Ion channel class Ligand - gated Light - gated Voltage - gated Stretch - activated see also disorders Ion channel, cell surface receptor : ligand - gated ion channels Cys - loop receptors 5 - HT / serotonin 5 - HT GABA GABA α α α α α α β β β γ γ γ δ ε π θ GABA - ρ ρ ρ ρ Glycine α α α α β Nicotinic acetylcholine monomers : α1 α2 α3 α4 α5 α6 α7 α9 α10 β1 β2 β3 β4 δ ε pentamers : ( α3 ) ( β4 ) ( α4 ) ( β2 ) ( α7 ) ( α1 ) ( β4 ) - Ganglion type ( α1 ) β1δε - Muscle type Zinc Zinc - activated Ionotropic glutamates Ligand - gated only AMPA ( 1 4 ) Kainate 5 Voltage - and ligand - gated NMDA 2A 2B 2C 2D 3A 3B L1A L1B ' Orphan ' GluD δ δ ATP - gated channels Purinergic receptors P2X 5 6 7 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Ligand-gated_ion_channel&oldid=856188737 '' Categories : Cell biology Electrophysiology Ion channels Ionotropic receptors Membrane biology Molecular neuroscience Neurochemistry Protein families Membrane proteins Transmembrane proteins Transmembrane transporters Transport proteins Integral membrane proteins Hidden categories : CS1 maint : Multiple names : authors list Articles with imported Creative Commons Attribution - ShareAlike 3.0 text Talk Contents About Wikipedia Català Čeština Deutsch Español فارسی Français 한국어 Italiano Latviešu Magyar Nederlands Norsk Polski Português Русский Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Svenska Türkçe Українська 13 more Edit links This page was last edited on 23 August 2018, at 13 : 36 ( UTC ). 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Question: where are ligand-gated ion channels found in cells
Answer: cell membrane