MuO-conotoxins are gating-modifier toxins that inhibit sodium current by trapping the domain II voltage sensor in the closed position to prevent opening of the sodium channel. This toxin shows high activity on Nav1.4/SCN4A (IC(50)=81 nM) and Nav1.8/SCN10A (IC(50)=96-529 nM). It also shows low activity on other sodium channels (Nav1.5/SCN5A, IC(50)=431-3900 nM > Nav1.1/SCN1A, IC(50)=3.3 uM; Nav1.2/SCN2A, IC(50)=5.1-6.3 uM; Nav1.3/SCN3A, IC(50)=2.2 uM; Nav1.6/SCN8A, IC(50)=1.2-4.6 uM; Nav1.7/SCN9A, IC(50)=2.3-5.5 uM) (PubMed:22609441). On Nav1.8/SCN10A, it causes a small left shift in the voltage dependence of activation and the voltage dependence of inactivation (PubMed:27026701). In addition, it has been shown to interact with lipid membranes (PubMed:27026701). Expressed by the venom duct. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. The cysteine framework is VI/VII (C-C-CC-C-C). Average mass. On Nav1.8/SCN10A, the mutant (E5K,E8K)MfVIA causes a small left shift in the voltage dependence of activation and the voltage dependence of inactivation (PubMed:27026701). In addition, it inserts more deeply into the membranes than the wild-type toxin (PubMed:27026701). In vivo, the mutant (E5K,E8K)MfVIA is analgesic in a formalin-induced mouse pain model (PubMed:27026701).