Fig. 1.

Kinetics of the fast component of synaptic vesicle exocytosis. (A) Ca²⁺ current (I) recorded from the synaptic terminal of a zebrafish bipolar neuron in response to a voltage-clamp pulse (V) from −60 mV to 0 mV for 10 ms. The sinusoidal voltage stimulus used to monitor membrane capacitance (C_m) and series conductance (G_s) is visible at the beginning and end of the voltage trace. The resulting values of C_m (circles) and G_s (diamonds) before and after activation of Ca²⁺ current are shown below the traces. (B) The average increase in C_m (± SEM) evoked by voltage-clamp pulses of varying duration in 16 synaptic terminals, measured as demonstrated for a 10-ms pulse in A. The solid line is an exponential rise with a time constant of 2.3 ms. (B, Inset) A similar experiment using longer pulses to measure the release of the slow component (n = 8–17 terminals), reflecting exocytosis of the entire readily releasable pool of synaptic vesicles.