Binds specifically to voltage-gated sodium channels (Nav) (site 3), thereby delaying their inactivation. This toxin has moderate activity on Nav1.1/SCN1A (EC(50)=about 300 nM) and Nav1.5/SCN5A (EC(50)=307.00 nM). It less potent on Nav1.4/SCN4A (EC(50)=820.84 nM), Nav1.6/SCN8A (EC(50)=about 900 nM), Nav1.2/SCN2A (EC(50)=1449.17 nM) and Nav1.3/SCN3A (EC(50)=1458.42 nM) (when measured as the increase in the slow component). LD(50) is 600 ug/kg by intraperitoneal injection into mice. Belongs to the sea anemone sodium channel inhibitory toxin family. Type I subfamily.