The brief (0.1 ms) and strong (−1.0 µA) prepulse does not admit Ca²⁺. (A) The rate of release during a train (150 Hz, 100 s) of brief “prepulses” (dashed bar) was similar to that of spontaneous release before the train (■, compare rate before and during the train; n = 5). (B) Representative (n = 4) Ca²⁺ currents derived from ENTCs without (solid line) and with (dashed line) the brief prepulse preceding the ENTC. Inset shows experimental protocol. (C) Representative traces (without selection) showing evoked release (*) produced by a wider (0.2 ms, −1.0 µA) prepulse. (D) Representative (n = 4) Ca²⁺ currents derived from ENTCs without (solid line), with the wider prepulse (long dashed line), and with the wider prepulse followed immediately by even stronger (−2.0 µA, 0.1 ms) depolarization (short dashed line). Here and in B the prepulses were given such that they terminated 0.15 ms before the ENTC. Inset shows experimental protocols.