Margatoxin is a Nonselective Inhibitor of Kv1.3 Channels - A Comprehensive Study

Ion channel inhibitor peptide toxins have become lead compounds for potential therapeutic use in the last decade. In the case of Kv1.3, the voltage-gated K+ channel responsible for membrane potential control in lymphocytes, high affinity and selectivity toxins have been used to demonstrate therapeutic application of peptide inhibitors in vitro as well as in vivo. Margatoxin (MgTx) is often considered as a high affinity and selective inhibitor of the Kv1.3 channel. MgTx consists of 39 amino acids stabilized by 3 disulfide bridges isolated from the venom of the scorpion Centruroides margaritatus. This peptide is widely used in the area of ion channel research, often to verify Kv1.3 expression in the plasma membrane. However, a comprehensive study of its selectivity with electrophysiological methods has not been published yet.We conducted electrophysiological measurements with the patch-clamp technique in voltage clamp mode to test the selectivity of MgTx. Measurements were carried out on L929 cells expressing mKv1.1 channels, human peripheral lymphocytes expressing Kv1.3 channels and transiently transfected tsA201 cells with the following ion channels: hKv1.1, hKv1.2, hKv1.3, hKv1.4-IR, hKv1.5, hKv1.6, hKv1.7, hKv2.1, Shaker-IR, hERG, hKCa1.1, hKCa3.1 and hNav1.5.Margatoxin is indeed a high affinity inhibitor of the Kv1.3 channel (Kd = 11.7 pM) but is not selective, since it inhibited Kv1.2 channel with similarly high affinity (Kd = 6.4 pM) and Kv1.1 in the nanomolar range (Kd = 4.2 nM and 1.7 nM for human and murine Kv1.1 respectively).Based on our comprehensive data MgTX has to be considered a non-selective Kv1.3 inhibitor, and thus, experiments aiming at elucidating the significance of Kv1.3 in in vitro or in vivo physiological responses using MgTx need to be carefully evaluated.