Mu-conotoxins block voltage-gated sodium channels (Nav). This toxin potently blocks rat Nav1.4/SCN4A (IC(50)= 19-110 nM) (PubMed:1654319, PubMed:1326324, PubMed:10627583, PubMed:21652775, PubMed:30360356). It also moderately blocks rNav1.1/SCN1A (Kd=260 nM), rNav1.2/SCN2A (IC(50)=2.7-17.8 uM), and mNav1.6/SCN8A (IC(50)=680 nM) (PubMed:10627583, PubMed:21652775). The inhibition is reversible. In vivo, induces paralysis to an isolated skeletal muscle preparation from frog (cutaneous pectoralis) within a few minutes (PubMed:2410412). 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. Hydroxylated; hydroxylations improve the ability to block Nav1.4/SCN4A sodium channels but does not affect folding. This toxin does not or only weakly blocks rNav1.3/SCN3A, rNav1.5/SCN5A, rNav1.7/SCN9A (IC(50)=6.0 uM and >100 uM), and rNav1.8/SCN10A (PubMed:10627583, PubMed:21652775). Belongs to the conotoxin M superfamily.