This MedLibrary.org supplementary page on Cyclic nucleotide-gated ion channel is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
A cyclic nucleotide-gated (CNG) ion channel is any ion channel that opens in the presence of cyclic nucleotides.
Contents |
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 channels than to the 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:
- In the visual system, a cGMP- (cyclic guanosine monophosphate-) gated channel is found in the outer membrane of retinal photoreceptor cells. 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. Thus, these cells are actually more active in dark than in light.
- Funny currents have been associated with the HCN channels.2
- cGMP-gated cation channels are present in the inner medullary collecting ducts of the kidney. They promote Na+ reabsorption. A part of the atrial natriuretic peptide mechanism of action is inhibition of these channels3, just as the diuretic drug amiloride3. Aldosterone has an opposite effect.3
Examples
Alpha
"Cyclic nucleotide gated channel alpha" subunits include
- Cyclic nucleotide-gated channel alpha 1 (CNGA1)
- Cyclic nucleotide-gated channel alpha 2 (CNGA2)
- Cyclic nucleotide-gated channel alpha 3 (CNGA3)
- Cyclic nucleotide-gated channel alpha 4 (CNGA4)
Beta-subunits include:
Hyperpolarization-activated
Other examples include the following "hyperpolarization-activated cyclic nucleotide-gated potassium channels" (HCN channels): HCN1, HCN2, HCN3, HCN4
References
- ^ Jenkins PM, Hurd TW, Zhang L, et al (2006). "Ciliary targeting of olfactory CNG channels requires the CNGB1b subunit and the kinesin-2 motor protein, KIF17". Curr. Biol. 16 (12): 1211–6. doi:. PMID 16782012.
- ^ DiFrancesco D (2006). "Serious workings of the funny current". Prog. Biophys. Mol. Biol. 90 (1-3): 13–25. doi:. PMID 15975637.
- ^ a b c Walter F., PhD. Boron. Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 875
External links
- MeSH cyclic-nucleotide-gated+ion+channels
- Overview at wustl.edu
 |
This membrane protein-related article is a stub. You can help Wikipedia by expanding it. |
 |
This neuroscience article is a stub. You can help Wikipedia by expanding it. |
|
|||||||||||||||||||||||||||||||||||||||||||||||
Wikipedia content modification information:
- This page was last modified on 22 July 2008, at 01:24.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Cyclic nucleotide-gated ion channel".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.