Cyclic nucleotide-gated ion channel

Overview

Cyclic adenosine monophosphate

Cyclic guanosine monophosphate

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:

• The mammalian olfactory system.

• 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.

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

External links

• cyclic-nucleotide+gated+ion+channels at the US National Library of Medicine Medical Subject Headings (MeSH)
• Overview at wustl.edu