Lethal neurotoxin. Slows the inactivation of tetrodotoxin-sensitive voltage-gated sodium channels (Nav) by binding to site 3 of the channel, resulting in repetitive firing in autonomic and motor nerve fibers. 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.