Editing Inhibitory postsynaptic potential (section)

== Inhibitory receptors ==
There are two types of inhibitory receptors:

===Ionotropic receptors===
[[Ionotropic receptors]] (also known as ligand-gated ion channels) play an important role in inhibitory postsynaptic potentials.<ref name=neurobook/> A neurotransmitter binds to the extracellular site and opens the ion channel that is made up of a membrane-spanning domain that allows ions to flow across the membrane inside the postsynaptic cell.  This type of receptor produces very fast postsynaptic actions within a couple of milliseconds of the presynaptic terminal receiving an action potential.  These channels influence the amplitude and time-course of postsynaptic potentials as a whole. 

Ionotropic GABA receptors ([[GABAA receptor|GABA<sub>A</sub> receptors]]) are pentamers most commonly composed of three different subunits (α, β, γ), although several other subunits (δ,ε, θ, π, ρ) and conformations exist.  The open channels are selectively permeable to chloride or potassium ions (depending on the type of receptor) and allow these ions to pass through the membrane.  If the electrochemical potential of the ion is more negative than that of the action potential threshold then the resultant conductance change that occurs due to the binding of GABA to its receptors keeps the postsynaptic potential more negative than the threshold and decreases the probability of the postsynaptic neuron completing an action potential. 

Ionotropic GABA receptors are used in binding for various drugs such as [[barbiturates]] ([[Phenobarbital]], [[pentobarbital]]), steroids, and [[picrotoxin]]. [[Benzodiazepines]] (Valium) bind to the α and γ subunits of GABA receptors to improve GABAergic signaling.  Alcohol also modulates ionotropic GABA receptors.

===Metabotropic receptors===
[[Metabotropic receptors]] are often G-protein-coupled receptors such as [[GABAB receptor|GABA<sub>B</sub> receptors]]. These do not use ion channels in their structure; instead they consist of an extracellular domain that binds to a neurotransmitter and an intracellular domain that binds to [[G-protein]].<ref name=neurobook/> This begins the activation of the G-protein, which then releases itself from the receptor and interacts with ion channels and other proteins to open or close ion channels through intracellular messengers.  They produce slow postsynaptic responses (from milliseconds to minutes) and can be activated in conjunction with ionotropic receptors to create both fast and slow postsynaptic potentials at one particular synapse. Metabotropic GABA receptors, heterodimers of R1 and R2 subunits, use potassium channels instead of chloride.  They can also block calcium ion channels to hyperpolarize postsynaptic cells.