Fig. 1: A resonance-like frequency-dependent response is observed in Kcnq2/3-expressing HEK293 cells.

a (Top) Depolarizing voltage protocol for activating Kcnq2/3 currents in Kcnq2/3-expressing HEK293 cells. Voltage steps of 10 mV for 1 s were applied from −80 to 0 mV of membrane potentials. Representative traces in the absence (middle) and presence (bottom) of XE991 (20 μM). For recordings traces in the presence of XE991, a depolarizing prepulse of over −30 mV for more than 30 s was applied to block Kcnq2/3 channels. b Conductance plots of Kcnq2/3-expressing HEK293 cells at each holding membrane potential. Conductance was calculated using the theoretical equilibrium potential of K⁺ (−98 mV). Square symbols and bars represent the mean ± standard error of the mean (SEM; n = 88). c Pharmacological effects of XE991 on Kcnq2/3 conductance evoked by a membrane potential depolarization to 0 mV. Square symbols and bars represent the mean ± SEM (n = 26). ***P < 0.001 (paired t-test). d Waveform of the chirp current consisting of a sinusoidal current with a constant amplitude (50 pA) but a linearly altered frequency ranging from 0–40 Hz over 40 s. e, g, i Representative voltage traces in response to the chirp currents at individual membrane potentials in control (e), Kcnh7-expressing (g), and Kcnq2/3-expressing (i) HEK293 cells. f, h, j Averaged Z-F plot of control (f, n = 14–16), Kcnh7-expressing (h, n = 9–19), and Kcnq2/3-expressing (j, n = 37–58) HEK293 cells. Shaded areas indicate the mean ± SEM. k, l Membrane potential dependence of the resonant frequency (k) and resonant strength (l) in control (–75 mV, n = 16; –60 mV, n = 14; –40 mV, n = 16; –30 mV, n = 17; –20 mV, n = 15, gray), Kcnh7-expressing (–75 mV, n = 9; –60 mV, n = 9; –40 mV, n = 19; –30 mV, n = 17, green), and Kcnq2/3-expressing (–75 mV, n = 38; –60 mV, n = 38; –40 mV, n = 55; –30 mV, n = 37; –20 mV, n = 14, orange) HEK293 cells. The resonance could not be examined over −30 mV in Kcnh7-expressing cells because of membrane potential oscillations. The resonant frequency and strength at individual membrane potentials were compared with those at -75 mV. ***P < 0.001, **P < 0.01, *P < 0.05 (Kruskal-Wallis test; post-hoc Holm–Šidák test). Small dots represent individual data, and squares with bars present the mean ± SEM. m Average Z-F plots of Kcnq2/3 and Kcnh7 channels at −40 mV (those in h and j) are normalized by peak magnitudes. Kcnq2/3 channels showed a gentler frequency dependence than Kcnh7 channels. In contrast, the impedance at 0.5 Hz was higher for Kcnh7 channels, resulting in lower resonant strength. Scale bars, 0.5 nA, 0.2 s (a), 10 mV, 2 s (e), 5 mV, 2 s, (g, i).