Electrophysiological characterization of BmK I, an α-like scorpion toxin, on rNav1.5 expressed in HEK293t cells

A recent study described the pharmacological properties of BmK I, an α-like toxin from the Chinese scorpion Buthus martensi Karsch, on the cardiac sodium channel (hH1) expressed in Xenopus oocytes. Considering that α-like toxins are unique in their inability to bind to rat synaptosomes despite a high toxicity by intravenous injection, the present study investigated the pharmacological properties of BmK I on rNav1.5 expressed in a mammalian HEK293t cell line. The results include: (1) BmK I slowed and partially inhibited the inactivation of rNav1.5, produced a substantial persistent current and increased peak current (the EC50 for increasing peak current by BmK I was 99.4 ± 20.1 nM); (2) BmK I delayed the recovery of the sodium channel from inactivation; (3) after exposure to 300 nM BmK I, the steady-state activation curve of rNav1.5 was negatively shifted by about 19 mV; and (4) the association of BmK I and rNav1.5 was faster than their dissociation. The results show that BmK I displayed the pharmacological characteristics of an α-like toxin on rNav1.5 channels expressed in HEK293t cells, and suggested that the host expression system should be taken into consideration when characterizing the pharmacological properties of toxins.