Inhibition of the NMDG⁺ currents by 4-AP. Top traces of A and B illustrate the pulse protocols used to record the currents shown below. The cells were held at −100 mV and depolarized for 12 ms to +80 mV (A) or +40 mV (B). The pulse frequency was 0.5 Hz. The current recordings were obtained from a cell transiently expressing Kv3.2b channels (A) or a cell stably expressing Kv3.1 channels (B) with 140 mM of symmetrical NMDG⁺ solutions in the presence of 0 or 5 mM 4-AP in the bathing solutions. Note that the application of 5 mM 4-AP in the bathing solutions significantly inhibited the inward NMDG⁺ currents both in Kv3.2b and Kv3.1 channels.