Voltage-dependent activation of KCNQ1 T312C mutant. (A) Exemplary current traces of the T312C mutant in response to stepwise depolarizing pulses from a holding potential of −100 mV to +60 mV in 20-mV increments. Dashed line corresponds to 0 current. (B) Conductance–voltage relationship of the T312C mutant after correction for inactivation. Tail currents were fitted with a double-exponential function and extrapolated back to the beginning of the segment. Values were normalized to current at +60 mV. The average leak currents, estimated in parallel batches of oocytes, were subtracted. Solid curve represents the fit of the data to a Boltzmann function of the form G/Gmax = (1 − Gmin)/{1 + exp[(V1/2 − V)ZF/RT]} + Gmin, where Gmin is fraction of the voltage-independent conductance component given by the horizontal asymptote of the function. Z, F, R, T, and V1/2 have their usual meanings. Gmin = 0.20 ± 0.04, V1/2 = −1.56 ± 0.14, n = 8, error bars represent ±SEM.