Inhibits tetrodotoxin-sensitive sodium channels by binding to site 3. It slows the inactivation, causes a prolongation of action potential duration resulting in repetitive firing in autonomic and motor nerve fibers. Does not depolarize the resting potential. Does not affect tetrodotoxin-resistant sodium channels. This lethal neurotoxin is active on both insect and mammalian voltage-gated sodium channels (Nav). Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Belongs to the neurotoxin 06 (delta-actx) family.