Cyclic nucleotide-gated ion channel 1349300 221016118 2008-06-22T17:51:18Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. [[Image:Cyclic-adenosine-monophosphate-2D-skeletal.png|thumb|[[Cyclic adenosine monophosphate]]]] [[Image:CGMP.png|thumb|[[Cyclic guanosine monophosphate]]]] A '''cyclic nucleotide-gated ion channel''' is any [[ion channel]] that opens in the presence of [[cyclic nucleotide]]s. ==Mechanism== The channels are gated by a chemical ligand (the cyclic nucleotide), but they are more similar in structure to the family of [[voltage-gated ion channel]]s than to the [[ligand-gated ion channel|ligand gated]] ones. In fact, the cyclic nucleotide-gated channels often have positively- or negatively-charged areas that may respond to changes in [[membrane potential]]. The purpose and function of these charged areas are not yet fully understood. ==Functions== Cyclic nucleotide-gated channels are particularly important in several systems: * The mammalian [[olfactory system|olfactory]] system.<ref name="pmid16782012">{{cite journal |author=Jenkins PM, Hurd TW, Zhang L, ''et al'' |title=Ciliary targeting of olfactory CNG channels requires the CNGB1b subunit and the kinesin-2 motor protein, KIF17 |journal=Curr. Biol. |volume=16 |issue=12 |pages=1211–6 |year=2006 |pmid=16782012 |doi=10.1016/j.cub.2006.04.034}}</ref> * In the [[visual system|visual]] system, a [[cyclic GMP|cGMP]]- (cyclic guanosine monophosphate-) gated channel is found in the outer membrane of [[retina|retinal]] [[photoreceptor cell]]s. In response to high levels of cGMP, the channels are open and allow positively-charged ions to flow into the cell, causing [[depolarization]]. This is the state of the cell in the dark (called the dark current), but a photon striking a [[photoreceptor]] in the cell causes a chain reaction that results in lower levels of cGMP and therefore [[hyperpolarization (biology)|hyperpolarization]]. Thus, these cells are actually more active in dark than in light. * [[Funny current]]s have been associated with the [[HCN channel]]s.<ref name="pmid15975637">{{cite journal |author=DiFrancesco D |title=Serious workings of the funny current |journal=Prog. Biophys. Mol. Biol. |volume=90 |issue=1-3 |pages=13–25 |year=2006 |pmid=15975637 |doi=10.1016/j.pbiomolbio.2005.05.001}}</ref> * cGMP-gated cation channels are present in the [[inner medullary collecting duct]]s of the [[kidney]]. They promote [[sodium|Na<sup>+</sup>]] reabsorption. A part of the [[atrial natriuretic peptide]] mechanism of action is inhibition of these channels<ref name=boron875/>, just as the [[diuretic]] drug [[amiloride]]<ref name=boron875/>. [[Aldosterone]] has an opposite effect.<ref name=boron875> {{cite book |author=Walter F., PhD. Boron |title=Medical Physiology: A Cellular And Molecular Approaoch |publisher=Elsevier/Saunders |location= |year= |pages= |isbn=1-4160-2328-3 |oclc= |doi=}} Page 875 </ref> ==Examples== ===Alpha=== "Cyclic nucleotide gated channel alpha" subunits include *[[Cyclic nucleotide-gated channel alpha 1]] ({{gene|CNGA1}}) *[[Cyclic nucleotide-gated channel alpha 2]] ({{gene|CNGA2}}) *[[Cyclic nucleotide-gated channel alpha 3]] ({{gene|CNGA3}}) *[[Cyclic nucleotide-gated channel alpha 4]] ({{gene|CNGA4}}) Beta-subunits include: *[[Cyclic nucleotide-gated channel beta 1]] ({{gene|CNGB1}}) *[[Cyclic nucleotide-gated channel beta 3]] ({{gene|CNGB3}}) ===Hyperpolarization-activated=== Other examples include the following "[[hyperpolarization]]-activated cyclic nucleotide-gated [[potassium channel]]s" ([[HCN channel]]s): [[HCN1]], [[HCN2]], [[HCN3]], [[HCN4]] ==References== <references/> ==External links== * {{MeshName|cyclic-nucleotide-gated+ion+channels}} * [http://www.neuro.wustl.edu/neuromuscular/mother/chan.html#cationcng Overview] at wustl.edu [[Category:Ion channels]] [[Category:Membrane biology]] {{membrane-protein-stub}} {{neuroscience-stub}} {{Ion channels}} [[de:HCN-Kanal]] [[et:Tsükliliste nukleotiidide poolt avatavad ioonikanalid]] [[fr:Protéine-canal HCN]]