Mu-conotoxins block voltage-gated sodium channels (Nav). This synthetic toxin potently blocks rNav1.4/SCN4A (Kd=0.34-3.6 nM), rNav1.2/SCN2A (Kd=13 nM), rNav1.3/SCN3A (Kd=200 nM), rNav1.1/SCN1A (Kd=360 nM), mNav1.6/SCN8A (IC(50)=1.8 uM), rNav1.5/SCN5A (IC(50)=9 uM), rNav1.6/SCN8A (IC(50)>30 uM) (PubMed:18950653, PubMed:21652775, PubMed:25632083, PubMed:23557677). It is noteworthy that the toxin is 50-fold more potent on mouse Nav1.6 than on rat Nav1.6 (PubMed:25632083). The block of SCN4A is very slowly reversible (PubMed:18950653). Expressed by the venom duct. The cysteine framework is III (CC-C-C-CC). Classified in the M-5 branch, since 5 residues stand between the fourth and the fifth cysteine residues. Does not or very weakly inhibits rNav1.7 and rNav1.8. Belongs to the conotoxin M superfamily.