Ion channel

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. The types of ion channels include those that are directly gated by an electrical potential, ligand-gated, mechanically-gated, and thermally-gated channels.

Structure

Ion channels may be composed of several different types of proteins. For example, potassium and sodium channels are known to have six transmembrane proteins. The protein subunit that forms the actual pore is called the P domain. The P domain connects the transmembrane domain with the extracellular domain. Different ion channels have different P domains.

Function

Ion channels have two main functions: they establish a resting membrane potential, and they create a change in membrane potential. The resting membrane potential is established by the concentration gradient of the ion and the ion's permeability through the membrane. Changes in the membrane potential are created by the opening and closing of ion channels. This can be due to changes in the environment, such as the binding of a ligand, a change in the voltage across the membrane, or a mechanical deformation of the channel.

Types

There are several types of ion channels, including voltage-gated ion channels, ligand-gated ion channels, and others. Voltage-gated ion channels open and close in response to changes in membrane potential. Ligand-gated ion channels open and close in response to specific ligand molecules binding to the channel protein.

Clinical significance

Ion channels are crucial for life, and defects in ion channels can lead to a variety of diseases, known collectively as channelopathies. These include cystic fibrosis, epilepsy, and many others. Ion channels are also the target of a number of drugs, including local anesthetics, antiepileptics, and antiarrhythmics.

See also

• Voltage-gated ion channel
• Ligand-gated ion channel
• Channelopathy

References

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