Editing Hyperpolarization (biology) (section)

==Examples==
[[Image:IPSPsummation.JPG|thumb|right|500px|An example of inhibitory postsynaptic potentials (IPSPs), excitatory postsynaptic potentials (EPSPs), and their summation.]]

[[GABA|GABA receptors]] are commonly known to downregulate neuronal activity by various means. 

# [[GABAA receptor|GABA<sub>A</sub>]] can induce hyperpolarization through an influx of Cl<sup>&ndash;</sup> ions. [[GABAA receptor|GABA<sub>A</sub>]] itself is a [[chloride channel|chloride ion channel]]. <ref name="GABAA1">{{cite journal| author=Luscher B, Fuchs T, Kilpatrick CL| title=GABAA receptor trafficking-mediated plasticity of inhibitory synapses. | journal=Neuron | year= 2011 | volume= 70 | issue= 3 | pages= 385-409 | pmid=21555068 | doi=10.1016/j.neuron.2011.03.024 | pmc=3093971 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21555068  }} </ref> This process of hyperpolarization is highly dependent on which direction Cl<sup>&ndash;</sup> flows. If Cl<sup>&ndash;</sup> travels into the cell, the flow of ions increases the voltage gradient. If Cl<sup>&ndash;</sup> flows out of the cell, the voltage gradient will decrease.
# [[GABAB receptor|GABA<sub>B</sub>]] induces hyperpolarization through K<sup>+</sup> ion influx into the neuron. Unlike GABA<sub>A</sub>, GABA<sub>B</sub> is a [[G protein-coupled receptor|G-Protein Coupled Receptor]] that activates [[potassium channels]] via [[Protein kinase A|Protein Kinase A]] (PKA) activation. <ref name="GABAB1">{{cite journal| author=Bowery NG, Bettler B, Froestl W, Gallagher JP, Marshall F, Raiteri M | display-authors=etal| title=International Union of Pharmacology. XXXIII. Mammalian gamma-aminobutyric acid(B) receptors: structure and function. | journal=Pharmacol Rev | year= 2002 | volume= 54 | issue= 2 | pages= 247-64 | pmid=12037141 | doi=10.1124/pr.54.2.247 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12037141  }} </ref> Potassium typically has a higher concentration inside the cell, while sodium typically has a higher concentration outside. When potassium channels open, K<sup>+</sup> ions flow out of the cell and cause the cell's internal potential to become more negative. GABA<sub>B</sub> activation of PKA also leads to Ca channel inactivation in presynaptic neurons. This likely leads to inhibited synaptic transmission. 
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have been identified as channels that mediate hyperpolarization. They were initially discovered in pacemaker cells of the heart. <ref name="HCNd1">{{cite journal| author=DiFrancesco D| title=Pacemaker mechanisms in cardiac tissue. | journal=Annu Rev Physiol | year= 1993 | volume= 55 | issue=  | pages= 455-72 | pmid=7682045 | doi=10.1146/annurev.ph.55.030193.002323 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7682045  }} </ref> These channels are controlled by cAMP, and activated by a hyperpolarized membrane. They allow the flow of Na<sup>+</sup> and K<sup>+</sup> ions, typically leading to a slight depolarization.