Biophysical properties of concatenated FL_n/WT_4−n tetrameric hERG1 channels. (A) Representative current traces for concatenated tetramers containing zero to three WT subunits together with one to four F557L subunits. Pulses were applied to V_t of −70 to 30 mV in 20-mV increments. V_h was −80 mV and V_ret was −70 mV. (B) I_test-V_t relationships for FL_n/WT_4−n tetrameric hERG1 channels. (C) Voltage dependence of activation. (D) Fully activated I_tail-V_ret relationships. (E) Voltage dependence of inactivation. The symbol legend refers to B–E. Data are expressed as mean ± SEM (n = 3–12). Values for V_0.5 and z for activation and inactivation are presented in Table S2.