Pharmacology

• Ligand-gated ion channel
  Ligand-gated ion channel
  Ligand-gated ion channels are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger , such as a neurotransmitter.The binding site of endogenous ligands on LGICs...
  
  s such as the nicotinic acetylcholine receptor
  Nicotinic acetylcholine receptor
  Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...
  
   and GABA_A receptor are composed of five subunits arranged around a central pore that opens to allow ions to pass through. There are a large number of different subunits available, which can come together in a wide variety of combinations to form different subtypes of the ion channel. Sometimes the channel can be made from only one type of subunit, such as the α7 nicotinic receptor
  Alpha-7 nicotinic receptor
  The alpha-7 nicotinic receptor, also known as the α7 receptor, is a type of nicotinic acetylcholine receptor, consisting entirely of α7 subunits....
  
   which is made up from five α7
  CHRNA7
  Neuronal acetylcholine receptor subunit alpha-7 is a protein that in humans is encoded by the CHRNA7 gene.-See also:* Alpha-7 nicotinic receptor* Nicotinic acetylcholine receptor* Acetylcholine receptor...
  
   subunits, and so is a homomer rather than a heteromer, but more commonly several different types of subunit will come together to form a heteromeric complex (e.g. the α4β2 nicotinic receptor
  Alpha-4 beta-2 nicotinic receptor
  The alpha-4 beta-2 nicotinic receptor, also known as the α4β2 receptor, is a type of nicotinic acetylcholine receptor, consisting of α4 and β2 subunits...
  
   which is made up from two α4
  CHRNA4
  Neuronal acetylcholine receptor subunit alpha-4 is a protein that in humans is encoded by the CHRNA4 gene....
  
   subunits and three β2
  CHRNB2
  Neuronal acetylcholine receptor subunit beta-2 is a protein that in humans is encoded by the CHRNB2 gene....
  
   subunits). Because the different ion channel subtypes are expressed to different extents in different tissues, this allows selective modulation of ion transport and means that a single neurotransmitter
  Neurotransmitter
  Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
  
   can produce varying effects depending on where in the body it is released.

• G protein-coupled receptor
  G protein-coupled receptor
  G protein-coupled receptors , also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors , comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal...
  
  s are composed of seven membrane-spanning alpha-helical segments, which are usually linked together into a single folded chain to form the receptor complex. However research has demonstrated that a number of GPCRs are also capable of forming heteromers from a combination of two or more individual GPCR subunits under some circumstances, especially where several different GPCRs are densely expressed in the same neuron. Such heteromers may be between receptors from the same family (e.g. adenosine A₁/A_2A
  Adenosine A2A receptor
  The adenosine A2A receptor, also known as ADORA2A, is an adenosine receptor, but also denotes the human gene encoding it.-Structure:This protein is a member of the G protein-coupled receptor family which possess seven transmembrane alpha helices...
  
   heteromers and dopamine D₁
  Dopamine receptor D1
  Dopamine receptor D1, also known as DRD1, is a protein that in humans is encoded by the DRD1 gene.- Function :This gene encodes the D1 subtype of the dopamine receptor. The D1 subtype is the most abundant dopamine receptor in the central nervous system. This G-protein-coupled receptor stimulates...
  
  /D₂
  Dopamine receptor D2
  Dopamine receptor D2, also known as D2R, is a protein that, in humans, is encoded by the DRD2 gene.- Function :This gene encodes the D2 subtype of the dopamine receptor. This G protein-coupled receptor inhibits adenylyl cyclase activity...
  
   and D₁
  Dopamine receptor D1
  Dopamine receptor D1, also known as DRD1, is a protein that in humans is encoded by the DRD1 gene.- Function :This gene encodes the D1 subtype of the dopamine receptor. The D1 subtype is the most abundant dopamine receptor in the central nervous system. This G-protein-coupled receptor stimulates...
  
  /D₃
  Dopamine receptor D3
  D dopamine receptor is a protein that in humans is encoded by the DRD3 gene.This gene encodes the D3 subtype of the dopamine receptor. The D3 subtype inhibits adenylyl cyclase through inhibitory G-proteins. This receptor is expressed in phylogenetically older regions of the brain, suggesting that...
  
   heteromers) or between entirely unrelated receptors such as CB₁/A_2A, glutamate mGluR₅
  Metabotropic glutamate receptor 5
  Metabotropic glutamate receptor 5 is a protein that in humans is encoded by the GRM5 gene.- Function :The amino acid L-glutamate is the major excitatory neurotransmitter in the central nervous system and activates both ionotropic and metabotropic glutamate receptors...
  
   / adenosine A_2A heteromers, cannabinoid CB₁ / dopamine D₂ heteromers, and even CB₁/A_2A/D₂ heterotrimers where three different receptors have come together to form a heteromer. The ligand binding properties and intracellular trafficking pathways
  Second messenger system
  Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm or nucleus. They relay the signals of hormones like epinephrine , growth factors, and others, and cause some kind of change in the activity of the cell...
  
  of GPCR heteromers usually show elements from both parent receptors, but may also produce quite unexpected pharmacological effects, making such heteromers an important focus of current research.