Inhibits voltage-gated potassium and sodium channels. It potently inhibits human Kv10.1/KCNH1/EAG1 (IC(50)=1.1 uM) and Kv1.4/KCNA4, and moderately inhibits rat Kv1.3/KCNA3, human Kv1.5/KCNA5 and human Kv2.1/KCNB1. Likely to act as a gating-modifier toxin that binds to closed Kv10.1 channels and reduces their activation by shifting their voltage-dependence in the positive direction and suppressing their current amplitudes elicited by strong depolarizing pulses. On sodium channels, it blocks rat Nav1.4/SCN4A, human Nav1.5/SCN5A and displays relatively weak inhibition of mouse Nav1.6/SCN8A. Has the CSbeta/beta fold, which comprises anti-parallel beta-sheets stabilized by three or four disulfide bonds. Does not block human Kv11.1/KCNH2/ERG1, Xenopus laevis Kv11.1/KCNH2/ERG1 and human Kv1.1/KCNA1. Belongs to the sea anemone type 3 (BDS) potassium channel toxin family.