Agonist of rat Nav1.3/SCN3A. This toxin increases the peak current amplitude, and potently inhibits the fast inactivation of the channel (EC(50)=120 nM). The inhibition of fast inactivation is voltage-independent (depolarizing voltages ranging from 220 mV to 130 mV). The toxin might bind to the domain IV of the Nav1.3 channel, while domain II might not participate in interacting with the toxin but could determine the efficacy of RTX-VII. In vivo, when intracerebroventricularly injected into mice, the toxin causes involuntary body twitching (seizure-like symptoms). Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Belongs to the rTX family.