Cyclic nucleotide-gated ion channel
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Overview
A cyclic nucleotide-gated ion channel is any ion channel that opens in the presence of cyclic nucleotides.
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]
Examples
Alpha
"Cyclic nucleotide gated channel alpha" subunits include CNGA1, CNGA2, CNGA3, and CNGA4. "Beta" subunits include CNGB1 and CNGB3.
Hyperpolarization-activated
Other examples include the following "hyperpolarization activated cyclic nucleotide-gated potassium channels" (HCN): 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:10.1016/j.cub.2006.04.034. PMID 16782012.
- ↑ 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.
External links
- MeSH cyclic-nucleotide+gated+ion+channels
- Overview at wustl.edu
Membrane transport protein: ion channels | |
|---|---|
| Ca2+: Calcium channel | Voltage-dependent calcium channel (L-type/Cav1.2, Cav2.1, N-type, P-type, Q-type, R-type, T-type) - Inositol triphosphate receptor - Ryanodine receptor - Cation channels of sperm - Two-pore channel |
| Na+: Sodium channel | Nav1.4 - Nav1.5 - Nav1.7- Nav1.9 - Epithelial sodium channel |
| K+: Potassium channel | Voltage-gated (Kv1.1, KvLQT1, KvLQT2, KvLQT3, HERG, Shaker gene, KCNE1) - Calcium-activated (BK channel, SK channel, SK3) - Inward-rectifier (ROMK, Kir2.1, KCNJ11) - Tandem pore domain |
| Cl-: Chloride channel | Cystic fibrosis transmembrane conductance regulator |
| Porin | Aquaporin (1, 2, 3, 4) - Voltage-dependent anion channel |
| Cations: TRP | TRPA - TRPC (TRPC6) - TRPM (TRPM6) - TRPML (Mucolipin-1) - TRPP - TRPV (TRPV1, TRPV6) |
| Other/general | Voltage-gated ion channel - Ligand-gated ion channel - Cyclic nucleotide-gated ion channel - Stretch-activated ion channel |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
