Binds specifically to voltage-gated sodium channels (Nav), thereby delaying their inactivation during signal transduction. It strongly stimulates mammalian cardiac muscle contraction. Paralyzes the shore crab (C.maenas) by tetanic contractions after intramuscular injection. Expressed in ectodermal glands. Not expressed in nematocytes. LD(50) is 1 ug/kg by intramuscular injection into crabs (C.maenas). Belongs to the sea anemone sodium channel inhibitory toxin family. Type I subfamily.