Sodium Channels
Sodium channels are integral membrane proteins that form a Na+ permeable pore through the plasma membrane and allow ion flux. There are two very different types of sodium channels: voltage-gated sodium channels (NaV) and epithelial sodium channels (ENaC). NaV are present in the membrane of most excitable cells and exist as heterodimers or heterotrimers of 1 α- and 1 or 2 β-subunits. ENaC are present in absorptive epithelia, such as the distal kidney tubule, alveolar epithelium and distal colon, and are responsible for sodium reabsorption. They exist as heterotetramers of α-, β- and γ-subunits, the predominant one being 2α:1β:1γ.
Acid-Sensing Ion Channels (ASIC) | Epithelial Sodium Channels (ENaC) | Voltage-gated Sodium (NaV) Channels (NaV Channels) |
Properties of Voltage-Gated Sodium Channels
| Location | Subtype | TTX Sensitive? | Conductance (pS) |
|---|---|---|---|
| Brain | I, II, IIA, III, VI | Yes | 2.5-25 |
| Skeletal muscle | μ1 | Yes | 2.5-25 |
| Sympathetic ganglia | PN1 | Yes | 6.3-10.7 |
| Heart | h1 | No (IC50 6 μM) | 2.5-25 |
| Dorsal root ganglia | PN3/SNS | No (IC50 ~ 60 μM) | 3.4-6.3 |
References
Catterall (1992) Cellular and molecular biology of voltage-gated sodium channels. Physiol.Rev. 72 S15. Gordon (1997) Sodium channels as targets for neurotoxins. Mode of action and interaction of neurotoxins with receptor sites on sodium channels. Toxins and Signal Transduction. Eds. Gutman and Lazarovici, pp119-153, Harwood Academic Publishers.