Concatenated tetrameric hERG1 (WT₄) channels have similar biophysical and pharmacological properties as channels formed by coassembly of single WT hERG1 subunits. (A) Representative WT and WT₄ hERG1 channel currents recorded at the indicated V_t (−70 to 30 mV stepped in 20-mV increments). (B) The voltage dependence of WT channel gating (upright green triangles, activation; sideways green triangles, C-type inactivation) is similar to WT₄ channels (upside-down black triangles, activation [n = 6]; sideways black triangles, C-type inactivation [n = 8]). Data were fitted to Boltzmann function (smooth curves) to determine V_0.5act and z values (presented in Table 1). (C) Time constants (τ deact) for fast and slow components of current deactivation for WT (green triangles, n = 10) and WT₄ (black triangles, n = 11) channels at the indicated return potential (V_ret). (D) Effect of 10 µM PD on WT and WT₄ hERG1 channel currents elicited by 4-s step to 0 mV. I_tail was measured at −70 mV. (E and F) I_test-V_t relationships in the absence (black triangles) and presence of 10 µM PD (red triangles) for oocytes injected with cRNA encoding single WT subunits (E, n = 10) or WT₄ channels (F, n = 7). Currents were normalized to peak I_test (at −20 mV) measured under control conditions. (G) Effect of 10 µM ICA on currents for WT and WT₄ channels. (H and I) I_test-V_t relationships in the absence (black triangles) and presence of 10 µM ICA (blue triangles) for oocytes injected with cRNA encoding single WT subunits (H, n = 5) or WT₄ channels (I, n = 10). Data are expressed as mean ± SEM (n = number of oocytes).