A new class of scorpion toxin binding sites related to an A-type K+ channel: pharmacological characterization and localization in rat brain

A new scorpion toxin (3751.8 Da) was isolated from the Buthus martensi veno m, sequenced and chemically synthesized (sBmTX3), The A-type current of str iatum neurons in culture completely disappeared when 1 muM sBmTX3 was appli ed (K-d = 54 nM), whereas the sustained K+ current was unaffected. I-125-sB mTX3 specifically bound to rat brain synaptosomes (maximum binding = 14 fmo l mg(-1) of protein, K-d = 0.21 nM). A panel of toxins yet described as spe cific ligands for K+ channels were unable to compete with I-125-sBmTX3. A h igh density of I-125-sBmTX3 binding sites was found in the striatum, hippoc ampus, superior colliculus, and cerebellum in the adult rat brain. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.