Binds specifically to voltage-gated sodium channels (Nav), thereby delaying their inactivation. This toxin is active on a variety of voltage-gated sodium channels (Nav1.1/SCN1A, Nav1.2/SCN2A, Nav1.3/SCN3A, Nav1.4/SCN4A, Nav1.5/SCN5A and Nav1.6/SCN8A). Belongs to the sea anemone sodium channel inhibitory toxin family. Type I subfamily.