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What Are C-Type Inactivation Ion Channels?

Transmitting messages down the axons of your nerve cells requires controlling the flow of charged ions across the membrane. Ion channels are central to this process. One especially important kind of channel is a voltage-gated potassium ion channel, which exists in one of three different states -- activated, deactivated and inactivated. C-type inactivation is an important mechanism for transition between two of these states in potassium ion channels.

Features
- Potassium ion channels are proteins embedded into the cell's membrane. At their center, they contain a pore through which water and potassium ions can flow. They are selective for potassium ions and will not permit other ions like sodium to cross. When the protein is in its ordinary deactivated state, the pore is closed like a locked gateway so that potassium cannot pass. Changes in the voltage across the membrane cause the channel to activate and force the pore open.
Deactivation
- Shortly after they open, voltage-gated potassium ion channels close again and re-enter the deactivated state. They do so through a mechanism called N-type inactivation, where a "ball" attached to a "chain" formed from amino acids in the protein is sucked into the pore, blocking it and thereby preventing further flow of ions. C-type inactivation, by contrast, causes the channel to enter the inactivated state and involves a more dramatic change in the structure of the protein.
Inactivation
- C-type inactivation is typically a much slower process. The mechanism of C-type inactivation is still the subject of ongoing research. According to a 2010 paper in the journal "Nature," it's currently believed that the process involves the selectivity filter, the part of the channel that ensures potassium ions can pass while sodium ions cannot. Alterations to the shape and geometry of this filter block the passage of potassium ions. In experiments, scientists have found that inactivated potassium ion channels also permit sodium ions to cross at a small though appreciable rate, although this only occurs in the absence of potassium ions.
Effects
- Aside from the mechanism, the most important distinction between N-type and C-type inactivation is that C-type inactivation is more long-lasting. Both N-type and C-type are reversible. The different names derive from the parts of the protein that are involved. Each protein is a string of amino acids; the C-terminal is the end with a chemical group called a carboxyl group, while the N-terminal has an amino group. The N-terminal region is involved in N-terminal inactivation, in contrast to C-type inactivation, which involves a different part of the protein.

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