Mu-conotoxins block voltage-gated sodium channels. This synthetic peptide reversibly inhibits the brain sodium channel rNav1.2/SCN2A (IC(50) is 40 nM) and the skeletal muscle sodium channel rNav1.4/SCN4A (IC(50) is 9 nM). 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. No cis-trans isomerization is found. Belongs to the conotoxin M superfamily.