Atypical residues at two positions in S4 of N.at-Kv3.2 are responsible for the omega current. A. Representative traces from single mutants H325R and G331R and the unmutated N.at-K
3.2 channel. Both mutants express delayed-rectifying phenotypes through 'rescue' of the canonical pore pathway, with outward current increasing monotonically with more positive voltages. The unmutated channel currents plateau and then decrease with more positive voltages. B. Fitted conductance-voltage relationships for the delayed-rectifier mutant channels. The individual data points are not shown, to avoid obscuring the fitted curves. The H325 single mutants are shown in black (H325A solid; H325R dashed), the G331 single mutants are shown in red (G331R solid; G331K dashed) and the double mutant H325R+G331K is shown in grey. The vertical dashed line indicates the upper limit (+90 mV) of stimulation voltages; the portions of the curves to the right are extrapolations.