Iberiotoxin, a peptide purified from venom of the scorpion B. tamulus, is a selective blocker of large-conductance calcium ion-activated potassium ion channels (BKCa). In single channel recordings, iberiotoxin can reversibly block outward currents mediated by BKCa in excised membrane patches from bovine aortic smooth muscle with an IC50 value of 250 pM. It is also a noncompetitive, partial inhibitor of charybdotoxin binding in bovine aortic sarcolemmal membrane vesicles (Ki = 250 pM).
