Scorpion toxins that affect sodium channel (NaCh) gating in excitable cells are divided into a-andb-classes. Whereas a-toxinshavebeen found inscorpions throughout theworld, anti-mammalianb-toxins have been assigned, thus far, to New World scorpions while anti-insect selective b-toxins (depressant and excitatory) have been described only in the Old World . 2 This distribution suggested that diversification ofb-toxins into distinct pharmacological groups occurred after the separation of the continents, 150 million years ago
