Sodium channel

A sodium channel is a type of ion channel that is selective for the passage of sodium ions (Na+) into cells. These channels are vital for the proper functioning of many biological processes, including the propagation of action potentials in neurons and muscle cells.

Structure

Sodium channels are integral membrane proteins and are composed of a large α subunit that associates with proteins, such as β subunits. The α subunit forms the actual pore through which ions pass into the cell. The α subunit is composed of four homologous domains (I–IV), each containing six transmembrane segments (S1–S6) for a total of 24 transmembrane segments.

Function

The main function of the sodium channel is to allow the passage of sodium ions through the cell membrane. This movement of ions creates an electrical current that can change the voltage across the cell membrane, a process known as depolarization. This is crucial for the propagation of action potentials in neurons and muscle cells.

Types

There are nine known isoforms of the sodium channel, each with distinct properties and tissue distribution. These include Nav1.1, Nav1.2, Nav1.3, Nav1.4, Nav1.5, Nav1.6, Nav1.7, Nav1.8, and Nav1.9.

Clinical significance

Mutations in sodium channels can lead to a variety of diseases, known as channelopathies. These include various forms of epilepsy, cardiac arrhythmias, myotonia, and periodic paralysis.

See also

• Potassium channel
• Calcium channel
• Ion channel
• Action potential
• Channelopathy

References

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  Membrane permeability of a neuron during an action potential
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  Sodium channel structure