Figure 6.

Effects of stimulation on FM4-64 fluorescence at synaptic ribbons. A, Voltage-dependent calcium current recorded from dissociated retinal bipolar cells before and after photobleaching. The gray trace is the average calcium current evoked by a 500 ms depolarizing pulse from −60 to 0 mV, recorded from five cells before photobleaching. The black trace is the average calcium current, recorded from the same five cells, after photobleaching FM4-64 fluorescence in a ribbon-containing region of the cell to ∼25% of its initial intensity. Calcium current amplitude ranged from 40 to 100 pA, and bleaching had no effect on the current. B, Recovery of fluorescence at ribbon locations after photobleaching at t = 0 (n = 8). The arrow marks timing of a 500 ms depolarizing pulse, which elicited a stable increase in mobile fraction from 0.19 to 0.36.