Mu-conotoxins block voltage-gated sodium channels (Nav). This toxin potently inhibits hNav1.4/SCN4A (IC(50)=15.11 nM). It also displays lower activities on other human subtypes (Nav1.1/SCN1A; IC(50)=132 nM, Nav1.2/SCN2A; IC(50)=363.8, Nav1.3/SCN3A; IC(50)=89.4, Nav1.6/SCN3A; IC(50)=124.9, Nav1.7/SCN7A; IC(50)=152.2). At Nav1.7/SCN9A, it does not elicit change in channel voltage-dependence of fast inactivation or activation, suggesting it acts as a pore blocker. Interestingly, it blocks current inhibition in an irreversible manner (tested during 35 minutes). 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 show activity on hNav1.5/SCN5A and hNav1.8/SCN10A (tested at 1 uM). Belongs to the conotoxin M superfamily.