Sodium channel

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Voltage activated sodium channel
Identifier
Gene name (s) SCN1A , SCN2A , SCN3A , SCN4A , SCN5A , SCN7A , SCN8A , SCN9A , SCN10A , SCN11A
Transporter classification
TCDB 1.A.1.10.1
designation Voltage gated ion channels

non-voltage activated sodium channel
Identifier
Gene name (s) SCNN1A , SCNN1B , SCNN1D , SCNN1G
Transporter classification
TCDB 1.A.6.1.1
designation Epithelial sodium channels
Occurrence
Parent taxon Vertebrates

In physiology and cell biology, sodium channels are ion channels that have a specific and more or less selective conductivity for sodium ions.

Like other ion channels, sodium channels can be voltage activated or not voltage activated. Nine different subtypes of voltage-activated sodium channels are currently known. According to the usual nomenclature, they are referred to as Na v 1.1 to Na v 1.9. The index v stands for voltage-activated , the first digit indicates the gene family (so far only one known), the second digit stands for a known gene (currently 1 to 9, arranged in the order in which it was discovered) .

Voltage-activated sodium channels are particularly densely expressed in electrically excitable cells . There their activation is responsible for the generation of action potentials . Under physiological conditions, the electrochemical driving force for sodium ions is directed in such a way that sodium ions from the extracellular space flow into the cell through opened sodium channels , about 10,000 per ms per channel. The simultaneous opening of many voltage-activated sodium channels when the potential threshold is reached intensifies the depolarization due to the resulting inward current , which leads to a rapid rise in the membrane potential (called “spread”). The voltage-dependent sodium channel has an inactivation domain (the so-called ball-and-chain mechanism), which, after the sodium channel has opened and sodium ions have passed through it, shifts it (1–2 ms) to an inactive state in which none further sodium ions can pass through. The voltage-dependent domain of the sodium channel is closed again and after a further 2-5 ms the inactivation domain also opens, whereby the channel is returned to the closed-resting state in which it can be excited by electrical stimuli.

An example of a non-voltage activated sodium channel is the epithelial sodium channel ( epithelial Na channel , ENaC). For example, it is responsible for the reabsorption of sodium ions from the primary urine in the collecting tube and in the proximal tubular cells of the kidney. Pharmacological inhibitors of the ENaC are used therapeutically as diuretics to flush out edema and to treat arterial hypertension . Since they do not lead to an increased excretion of potassium, such diuretics are also referred to as "potassium-sparing" diuretics.

Antiepileptic drugs and local anesthetics block the sodium channels and thus prevent the triggering of an action potential. Also riluzole is a sodium channel blocker and is neuroprotective.

literature

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  • J. Srinivasan, M. Schachner, WA Catterall: Interaction of voltage-gated sodium channels with the extracellular matrix molecules tenascin-C and tenascin-R. In: Proc. Natl. Acad. Sci. USA 95 (26), December 1998, pp. 15753-15757. doi: 10.1073 / pnas.95.26.15753 . PMC 28116 (free full text). PMID 9861042 .
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