Mu-conotoxins block voltage-gated sodium channels (VGSC). Potently displaces (125)I-TIIIA from native rat brain Nav1.2/SCN2A (IC(50) is 5 nM) and muscle Nav1.4/SCN4A (IC(50) is 3 nM) VGSCs. Potently and irreversibly inhibits current through Xenopus oocyte-expressed Nav1.2/SCN2A and Nav1.4/SCN4A. 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. Belongs to the conotoxin M superfamily.