Mu-conotoxins block voltage-gated sodium channels (Nav). This toxin reversibly blocks voltage-gated sodium channel in cephalopods (tested on squid giant-fiber-lobe neurons) with an inhibitor constant (Ki) of 15 nmol/l, with no alteration in the voltage dependence of sodium conductance or on the kinetics of inactivation. Has no effect on sodium channels of the two gastropod S.luhuanus and A.californica (which are not natural prey). Expressed by the venom duct. The cysteine framework is XII (C-C-C-C-CC-C-C). Belongs to the conotoxin O1 superfamily.