Latency of transmitter release at crayfish motor nerve endings examined by intracellular depolarization

Latency of release of individual quanta of transmitter was studied at neuromuscular junctions of a crayfish (Procambarus clarkii). Postsynaptic quantal currents were recorded at individual motor nerve endings with a macropatch electrode while the subterminal axon branch was depolarized by current passed through an intracellular microelectrode. For depolarizing currents of moderate size, the latency of transmitter release did not change when the duration of the depolarizing current was altered. Previous studies in which a contrary result was obtained may have been compromised by artefacts or by the sampling methods employed. The present results do not support the hypothesis of a depolarization-induced "repressor" of quantal release.