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Cyclic nucleotide-gated ion channel: Wikis

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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:

  • The mammalian olfactory system.[1] It may also involved in insect olfactory system(doi:10.1038/nature06861)
  • 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.

Examples

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Alpha

"Cyclic nucleotide gated channel alpha" subunits include

Beta-subunits include:

Hyperpolarization-activated

Other examples include the following "hyperpolarization-activated cyclic nucleotide-gated potassium channels" (HCN channels): HCN1, HCN2, HCN3, HCN4

References

  1. ^ 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:10.1016/j.cub.2006.04.034. PMID 16782012. 
  2. ^ DiFrancesco D (2006). "Serious workings of the funny current". Prog. Biophys. Mol. Biol. 90 (1-3): 13–25. doi:10.1016/j.pbiomolbio.2005.05.001. PMID 15975637. 
  3. ^ a b c Walter F., PhD. Boron (2005). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3.  Page 875

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