Kcnq (Kv7) channels exhibit frequency-dependent responses via partial inductor-like gating dynamics

Kcnq channels are low-threshold voltage-dependent K⁺ channels that generate M-currents, which regulate the peri-threshold membrane potential. Kcnq channels reportedly participate in band-pass frequency responses (i.e., resonance), but it remains largely unclear how they contribute to generating resonance. We examined resonance in HEK293 cells expressing mouse Kcnq2 and Kcnq3 (Kcnq2/3) using whole-cell recording. Kcnq2/3-expressing cells generated resonance-like frequency-dependent responses. Kcnh7 channels displayed a rapid opposing conductance change followed by slow activation in response to a depolarizing voltage step, properties thought to be necessary for inductor-like activity. However, Kcnq2/3 channels exhibited only slow activation. The lack of an opposing conductance change was caused by the absence of rapid Kcnq2/3 channel inactivation. These data suggest that core ion channel characteristics that cause resonance-like frequency responses are not uniform among ion channels. The opposing conductance change is not necessary for resonance-like frequency responses but is crucial for fine frequency tuning and oscillation.