Fig. 9.
4-AP (0.25 mM) blocks a rapidly activating and inactivating current and reduces firing frequency. A: control current in response to a +21-mV voltage pulse and current in the presence of 0.25 mM 4-AP in a CZ calyx. The 4-AP-sensitive current (Isubtracted) showed a rapidly activating and inactivating component as well as a sustained component. B: I-V plot for the same cell as in A. Current amplitude was measured at the end of the 40-ms voltage pulse. C: action potentials under control conditions (left) and in the presence of 4-AP (right) (same cell as A). 4-AP increased action potential width and decreased firing frequency.