FIG. 5.
4-AP blocks a rapidly activating and inactivating outward current in calyx terminals. A Effect of different concentrations of 4-AP on outward currents. Control current during a step to +6 mV and currents during perfusion of 0.25, 0.75, and 1.25 mM 4-AP are shown. BIV relation showing reduction in peak currents with increasing 4-AP concentrations. Control (filled circles), 0.25 mM 4-AP (open squares), 0.75 mM 4-AP (filled diamonds), and 1.25 mM 4-AP (open triangles). C The 4-AP-sensitive current (I4-AP) in another cell was obtained by subtracting the currents in response to voltage steps (120-ms duration) in 1.25 mM 4-AP from control currents. The rise time (activation) and decay (inactivation) of subtracted currents were each fitted with a single exponential (gray lines, Eq. 2). D The time constants of activation (mean ± SEM, filled symbols, n = 7) and inactivation of I4-AP (unfilled symbols, n = 5) are shown at five different voltages between −20 and +30 mV.