Figure 5.

Uncoupling of the voltage sensor from the pore during deactivation. (A and B) (Top) Typical WT on-gating (A) and off-gating (B) currents. For on-gating currents, oocytes were held at −100 mV and subjected to 4 s voltage steps to +60 mV in 10 mV increments. Gating charge moved was determined from the integral of the off-gating current measured during the 500 ms step back to −100 mV. (A, inset) Off-gating currents are enlarged for clarity. For off-gating currents, oocytes were held at 0 mV and subjected to 4 s repolarizing steps to −160 mV in 10 mV increments. Gating charge moved was determined from the integral of the on-gating currents measured during the 500 ms step back to 0 mV. (B, inset), On-gating currents are enlarged for clarity. (Bottom) Plots of mean WT hERG QV relationships for on-gating (A) and off-gating (B) measured with varying depolarizing or repolarizing pulse durations (Δt). For both on- and off-gating, mean V_h and k values were obtained by fitting to a Boltzmann function (see Table 1). The dashed line in (B) represents the steady-state on-gating QV relation shown in (A). (C) Relationship between V_h of on- and off-gating with Δt duration, as determined from (A) and (B). Data are fitted with extrapolated single (solid line) or double (dotted line) exponential functions. Single exponential extrapolated steady-state values for on- and off-gating V_h were −40 and −77 mV. The equivalent values for double exponential fits were −45 and −77 mV, respectively. (D) Summary of the steady-state GV and QV relations highlighting the uncoupling of voltage sensor return from pore closure.