Induction of current decay of KCNQ2/3 channels occurs at lower membrane potential in D164N/D186N A, representative traces of KCNQ2/3 potassium currents in the presence of Ci-VSP (black traces), D151N (red) or D164N/D186N (blue). Current traces were elicited by a depolarizing step to between −20 mV and 60 mV. At a higher voltage level, endogenous outward current was activated and superimposed. B, the magnitude of the residual component of KCNQ2/3 current during a 4 s step pulse was normalized by the peak amplitude at each membrane potential level. Data were recorded from a single batch of oocytes. The proportion of residual current was calculated for each trace as the ratio of the minimum current amplitude following the peak timing against the maximum amplitude. When there is no decay, the maximum magnitude during a 4 s step pulse was divided by the amplitude at the end of the pulse. Expression level of Ci-VSPs was estimated by the total moved charges, Qoff, of OFF-‘gating’ currents measured from another batch of oocytes that were microinjected with the same concentration of cRNA as for the measurement of KCNQ2/3 currents. Qoff values (nC) were −51.5 ± 12.2 (Ci-VSP), −39.6 ± 8.2 (D151N), −45.8 ± 11.4 (D164N/D186N), respectively. The numbers of cells were 5, 4, 4 for Ci-VSP, D151N and D164N/D186N, respectively. Similar results of the current decay of KCNQ2/3 channel were obtained from two other experiments.