The waveform of action potentials (APs) plays a central role in regulating presynaptic Ca2+ currents (ICa) and neurotransmitter release from nerve terminals, but the elements that govem timing of Ca2+ influx during an AP remain unclear.By voltage-clamp recordings of presynaptic Ica and excitatory postsynaptic currents (IEPSC) at the mouse calyx of Held synapse, we systematically examined effects of amplitude,depolarization and/or repolarization duration of pseudo-and real-APs on the magnitude and onset timing of ICa and IEPSC.