Effects of ZD7288 on calyx action potentials. Traces for control (orange, n = 5) and ZD7288-treated (green, n = 5) calyx terminals. Action potentials were generated by injecting a hyperpolarizing current sufficient to hold the membrane potential near −100 mV for 300 ms and then stepping back to the zero current level. In each case, a rebound action potential fired without additional current injection. (A) In control cells, action potentials occurred with shorter latencies, whereas in the presence of ZD7288 the latencies were longer. There was no difference in amplitude, which confirms that there is no effect of ZD7288 on Na⁺ channels. During the afterhyperpolarization (AHP), control calyx terminals reached hyperpolarized potentials and then quickly returned to rest. In ZD7288-treated calyx terminals, the AHP was very slow to return to rest. (B) Two representative traces from A are shown on an expanded time scale. Note the long latency of the action potential in the presence of ZD7288. (C) The traces shown in B were aligned at their peaks to highlight differences in the AHP. Note that the ZD7288-treated calyx terminal took longer to return to rest.