Mu-conotoxins block voltage-gated sodium channels (Nav). This toxin potently blocks rNav1.4/SCN4A (IC(50)=36-41 nM) (PubMed:10627583, PubMed:21652775). It also moderately blocks rNav1.1/SCN1A (IC(50)=120 nM), rNav1.2/SCN2A (IC(50)=620 nM), rNav1.3/SCN3A (IC(50)=3.2 uM), mNav1.6/SCN8A (IC(50)=100 nM) (PubMed:10627583, PubMed:21652775). This inhibition is reversible. The block of Nav1.1, Nav1.2, and Nav1.6 is modified when beta-subunits are coexpressed with alpha subunits. Hence, blocks of channels containing the beta-1 and beta-3 subunits are more potent (compared to channels without beta subunits), whereas blocks of channels containing the beta-2 and beta-4 are less potent (compared to channels without beta subunits). In vivo, this peptide causes flaccid paralysis in both mice and fish. 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. 3D-structure of 3 disulfide-bond connectivities isomers is described (PIIIA-1 (C1-C5, C2-C6, C3-C4), PIIIA-2 (C1-C4, C2-C5, C3-C6) and PIIIA-3 (C1-C2, C3-C4, C5-C6)) (PubMed:22407516). Only PIIIA-2 contains the cysteine connectivity described as typical for native mu-conotoxins. However, PIIIA-1 is more potent than PIIIA-2, suggesting another possible disulfid connectivity. For this reason, both connectivities have been indicated in features. Exists in two forms, due to cis-trans isomerization at Hyp-57. Adopts a predominately trans conformation (Probable). This toxin does not or only weakly blocks rNav1.5/SCN5A, rNav1.7/SCN9A (IC(50)=3.1-6.2 uM and >100 uM), and rNav1.8/SCN10A. Belongs to the conotoxin M superfamily.