Fig. 4

Transmembrane organization of sodium channel α subunit. The alpha subunit of the channel comprises four repeat domains (I–IV), each containing six membrane-spanning segments (1–6). The highly conserved segment 4 acts as the voltage sensor of the channel close to the pore for ion entry. After Na+ has entered the cell and the membrane’s potential reached its maximum, the channel inactivate by closing the inactivation loop. Mutation M1500V could abolish channel inactivation and lead to its constitutive activity and firing of the synapses; however, further functional studies are needed to verify this assumption. Adapted from Brackenbury and Isom [29]