Bulky, aromatic substitutions of hERG F463 alter voltage-dependent gating. (A) Typical current traces recorded from WT and mutant hERG channels. Oocytes were held at −80 mV and subjected to either 2- or 15-s depolarizing steps to +60 V in 10-mV increments. Tail currents were recorded during a 2-s pulse to −60 mV. Arrows indicate the zero current level. Note the change in scale for F463W. (B) Effects of the F463 mutations on the G-V relationship. Peak tail currents from experiments such as those in A were normalized to the maximum peak tail current to provide a measure of conductance. WT data recorded using both 2- and 15-s pulses are shown to allow for comparisons with mutant G-V curves obtained using different pulse durations. Data points represent means ± SEM (error bars). Solid and broken lines indicate fits of the data to a Boltzmann function (see Materials and methods). n values and parameters from the Boltzmann fits are summarized in Table 1.