Inhibits selectively tetrodotoxin-sensitive voltage-gated sodium channels (Nav). Does not act by binding to receptor site 3 to slow the inactivation kinetics of sodium currents. Monomer. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. IC(50) is 42.3 nM on rat neurons. Belongs to the neurotoxin 10 (Hwtx-1) family. 22 (Htx-4) subfamily.