Scorpion Toxin BeKm‐1 Blocks Low K ⁺ ‐induced Endocytosis of Cell‐surface Human Ether‐a‐go‐go Related Gene (hERG) Channels

The human ether‐a‐go‐go related gene ( hERG )‐encoded potassium channel conducts an important current for the repolarization of cardiac action potentials. hERG channel dysfunction leads to abnormal cardiac electrical activities characterized by a prolonged QT interval. We have previously shown that exposure of hERG‐expressing HEK cells to a 0 mM K + medium induces vigorous internalization of hERG but not ether‐a‐go‐go (EAG) channels from the plasma membrane. To investigate the mechanisms of 0 mM K + ‐induced hERG endocytosis, we used a chimerical channel model constructed by combining hERG and EAG, as well as drugs that bind to either the internal pore mouth of the hERG channel (E‐4031) or the extracellular edge of the pore entrance (BeKm‐1). Using Western blot analysis and whole‐cell patch clamp, our data show that replacing the S5‐S6 linker of hERG with that of bovine EAG prevented 0 mM K + ‐induced hERG endocytosis. Moreover, BeKm‐1 prevented 0 mM K + ‐induced hERG internalization. Under the whole‐cell voltage clamp configuration, acute exposure of hERG‐expressing HEK cells to 0 mM K + solution eliminated hERG conductance within 5 minutes, and the hERG conductance recovered slowly upon re‐exposure to 5 mM K + solution. The 0 mM K + exposure‐induced conductance loss was completely prevented by the application of BeKm‐1 (1 µM). We conclude that a conformational change in the outer pore‐mouth of hERG occurs upon removal of extracellular K + , which triggers hERG internalization. BeKm‐1 prevents such conformational change and the subsequent internalization of hERG channels under 0 mM K + culture conditions. (Supported by the Canadian Institutes of Health Research and the Heart and Stroke Foundation of Ontario)​

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