Effect of sibutramine HCl on cardiac hERG K⁺ channel

Common clinically used drugs block the delayed rectifier K⁺ channels and prolong the cardiac action potential duration associated with long QT syndrome. Here, we investigated the mechanism of hERG K⁺ channel current (I_hERG) blockade expressed in HEK-293 cells by sibutramine HCl, a serotonin-norepinephrine reuptake inhibitor. Sibutramine HCl inhibited I_hERG in a concentration-dependent manner with the half-maximal inhibitory concentration (IC₅₀) value of 2.5 μM at 40 mV. I_hERG inhibition by sibutramine HCl showed weak voltage dependency, but the time-dependence of I_hERG inhibition was developed relatively rapidly on membrane depolarization. On hERG channel gating for the S6 and pore regions, the S6 residue hERG mutant Y652A and F656A largely reduced the blocking potency of I_hERG, unlike the pore-region mutants T623A and S624A. These results indicate that sibutramine HCl preferentially inhibits the hERG potassium channel through the residue Y652 and F656, in a supratherapeutic concentration should be avoided by patients with high susceptibility for cardiac arrhythmia.