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. 2017 Jan 24;112(2):300–312. doi: 10.1016/j.bpj.2016.12.021

Figure 4.

Figure 4

Measurement of “true” mode-shift in WT hERG channels. (A) Plot of mean WT hERG GV relationships for activation and deactivation measured with voltage steps of physiological duration. For activation, oocytes were held at −100 mV and subjected to 250 ms depolarizing steps to +100 mV in 10 mV increments followed by a repolarizing voltage step to −110 mV. For deactivation, oocytes were held at −100 mV and subjected to a 250 ms depolarizing step +60 mV and then to 750 ms voltage steps to −110 mV in 10 mV increments followed by a repolarizing voltage step to −110 mV. Data were fitted with a Boltzmann function. (B and C) (Top) Typical WT ionic current traces recorded during protocols to measure activation (B) and deactivation (C) at steady state. For activation, oocytes were held at −100 mV and subjected to 8 s voltage steps to +60 mV in 10 mV increments, followed by a 3.5 s repolarizing step to −110 mV. For deactivation, oocytes were held at −100 mV and subjected to a 15 s depolarizing step +60 mV followed by 8 s repolarizing voltage steps from −110 mV to +40 mV in 10 mV increments and then a 100 ms repolarizing step to −110 mV. (Inset) Currents on an expanded timescale to highlight the peak tail current. (Bottom) Plot of WT hERG mean GV relationships for activation (B) and deactivation (C) constructed from normalized peak tail currents (n = 6) following the different prepulse durations. For both activation and deactivation, the protocols were repeated in the same cell with different Δt durations and the mean Vh and k values were obtained by fitting each data set to a Boltzmann function (see Table 1). These data demonstrate the approach toward steady-state activation and deactivation GV relations with increasing Δt duration. The dashed line in (C) represents the steady-state activation GV relation of WT hERG shown in (B). (D) Relationship between Vh of activation and deactivation with the Δt duration, as determined from the data presented in (B) and (C). Data are fitted with extrapolated single (solid line) or double (dotted line) exponential functions. Single exponential extrapolated steady-state values for activation and deactivation Vh were −33 and −48 mV. The equivalent values for double exponential fits were −38 and −45 mV, respectively.