Alpha toxins bind voltage-independently at site-3 of sodium channels (Nav) and inhibit the inactivation of the activated channels, thereby blocking neuronal transmission. This recombinant toxin selectively inhibits the fast inactivation of mNav1.4/SCN4A (EC(50)=82.3 nM) (tested in HEK293 cells). Expressed by the venom gland. Has the structural arrangement of an alpha-helix connected to antiparallel beta-sheets by disulfide bonds (CS-alpha/beta). Does not inhibit rNav1.2/SCN2A (EC(50) is >30000 nM) channels. Belongs to the long (4 C-C) scorpion toxin superfamily. Sodium channel inhibitor family. Alpha subfamily.