Phasic release of resupplied vesicles on ribbons underlies the off response of postsynaptic neurons. (a) Light-evoked voltage responses from a cone, a HBC and a DBC recorded from salamander retinal slices. Postsynaptic cells, but not the cone, showed a marked overshoot of the dark membrane potential at light offset. (b) Predicted changes in vesicle occupancy on the ribbon before, during, and after a light flash (top). A synaptic current response to a light flash in a voltage-clamped HBC (middle) is shown. Bottom, the time course of presynaptic release from the group of cones driving this HBC. Release was calculated by deconvolving the EPSC with the waveform of the averaged mEPSC. The dotted line is fit to tonic release before the light flash.