sodium channel
(= sodium gate)
The protein responsible for electrical excitability of neurons. A multi-subunit transmembrane ion channel, containing an aqueous pore around 0.4nm diameter, with a negatively charged region internally (the "selectivity filter") to block passage of anions. The channel is voltage-gated: it opens in response to a small depolarization of the cell (usually caused by an approaching action potential), by a multistep process. Around 1000 sodium ions pass in the next millisecond, before the channel spontaneously closes (an event with single-step kinetics). The channel is then refractory to further depolarizations until returned to near the resting potential. There are around 100 channels per m m2 in unmyelinated axons; in myelinated axons, they are concentrated at the nodes of Ranvier. The sodium channel is the target of many of the deadliest neurotoxins.

Dictionary of molecular biology. 2004.

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