Inhibits preferentially tetrodotoxin-insensitive sodium currents (Nav) on rat cardiac myocytes (IC(50) is 0.26 uM) and has weaker inhibition activity toward tetrodotoxin-sensitive sodium currents on rat dorsal root ganglion (DRG) sensory neurons (IC(50) is 0.83 uM) and on cockroach dorsal unpaired median (DUM) neurons (IC(50) is 1.19 uM). Has no significant effect on potassium currents on DRG neurons. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Belongs to the neurotoxin 10 (Hwtx-1) family. 36 (Jztx-2) subfamily.