Mu-conotoxins block voltage-gated sodium channels (Nav). This synthetic toxin reversibly and potently blocks rNav1.4/SCN4A (IC(50) is 9 nM) and rNav1.2/SCN2A (IC(50) is 40 nM). It also moderately blocks rNav1.1/SCN1A, rNav1.3/SCN3A, and rNav1.6/SCN8A. The block of SCN1A and SCN2A is modified when beta-subunits are coexpressed with alpha subunits. Hence, blocks of channels containing beta-1 and beta-3 subunits are more potent (compared to channels without beta subunits), whereas blocks of channels containing beta-2 and beta-4 subunits are less potent (compared to channels without beta subunits). Expressed by the venom duct. The cysteine framework is III (CC-C-C-CC). Classified in the M-4 branch, since 4 residues stand between the fourth and the fifth cysteine residues. Does not block Nav1.5/SCN5A, Nav1.7/SCN9A, and Nav1.8/SCN10A. No cis-trans isomerization is found. Belongs to the conotoxin M superfamily. Native TIIIA is not detected in crude venom.