| Modification Notes |
Voltage-gated Na+ channels regulate the permeability of excitable cells to sodium ions. During the propagation of an action potential, Na+ channels allow an influx of sodium ions, which rapidly depolarize the cell. The sodium channel protein is comprised of one å subunit and two ∫ subunits. The Na+ CP type I and Na+ CP type IIå subunits are expressed in adult brain. Na+ CP type IIIå is expressed in embryonic brain, but not in adult brain. Na+ CP type III∫ is a 215 amino acid, single-pass type I membrane protein that modulates sodium channel gating kinetics and inactivates the channel opening more slowly than the I∫ subunit. It has an extracellular N-terminal domain, an N-terminal signal sequence, a single membrane-spanning region and a C-terminal cytoplasmic region. Expression of Na+ CP type III∫ is upregulated in response to DNA damage. In association with Neurofascin, Na+ CP type III∫ may target the sodium channels to nodes of Ranvier of developing axons and retain these channels at the nodes in mature myelinated axons. |