Ion channels

Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane, controlling the flow of ions across secretory and epithelial cells, and regulating cell volume. Ion channels are present in the membranes of all cells. They are often described as narrow, water-filled tunnels that allow only ions of a certain size and/or charge to pass through. This characteristic is called selective permeability.

Structure

The basic structure of an ion channel is a single subunit that is repeated around the central water-filled pore. The subunit is usually composed of 5-6 transmembrane alpha helices. Some of these helices may be involved in the formation of the pore, and others may be involved in gating the channel.

Function

Ion channels have two main functions: establishing a resting membrane potential, and shaping action potentials and other electrical signals. The resting membrane potential is established by the concentration gradient of different ions across the membrane. The action potential is shaped by the time course of voltage-gated ion channel opening and closing.

Types

There are many types of ion channels, including voltage-gated ion channels, ligand-gated ion channels, and mechanically-gated ion channels. Voltage-gated ion channels open or close in response to changes in membrane potential. Ligand-gated ion channels open or close in response to specific ligand molecules binding to the channel protein. Mechanically-gated ion channels open or close in response to mechanical deformation of the cell membrane.

Role in disease

Ion channels are involved in a variety of diseases, including cystic fibrosis, epilepsy, and various cardiac diseases. In cystic fibrosis, a mutation in the CFTR chloride channel causes a buildup of thick mucus in the lungs. In epilepsy, mutations in sodium channels can lead to seizures. In cardiac diseases, mutations in potassium channels can lead to arrhythmias.

See also

• Voltage-gated ion channel
• Ligand-gated ion channel
• Mechanically-gated ion channel
• Cystic fibrosis
• Epilepsy
• Cardiac diseases

Ion channels Resources
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