Charybdotoxin

Charybdotoxin (ChTx) is a 37 amino acid peptide isolated from the venom of the scorpion Leiurus quinquestriatus hebraeus that blocks voltage-gated and large conductance Ca2+ activated K+ channels KCa1.1 in nanomolar concentrations (IC50~ 3 nM) . This blockade causes hyperexcitability of the nervous system. The toxin reversibly blocks channel activity by interacting at the external pore of the channel protein with an apparent Kd of 2.1 nM. ChTX also blocks KCa3.1 (IC50 5 nM), Kv1.2 (IC50 14 nM), Kv1.3 (IC50 2.6 nM) and Kv1.6 (IC50 2 nM) channels.