Binds voltage-dependently at site 3 of sodium channels (Nav) and inhibits the inactivation of the activated channels, thereby blocking neuronal transmission. Possesses the highest efficacy for the insect sodium channel para/tipE (EC(50)=5.5 nM) (PubMed:12459477), and has effect on Nav1.2/SCN2A (in complex with SCN1B), Nav1.4/SCN4A (in complex with SCN1B) and Nav1.5/SCN5A (in complex with SCN1B) (PubMed:12459477). Also interacts with sodium channels in cardiac cells (PubMed:11704639). Shows lethality to crabs (PubMed:22015268). LD(50) is 0.4 ug/kg by intracerebroventricular injection into mice. Has no effect on voltage-gated sodium channel Nav1.8/SCN10A (in complex with SCN1B). Belongs to the sea anemone sodium channel inhibitory toxin family. Type I subfamily.