Fig. 5.

The effect of 0.5 mm EGTA on release rates per vesicle. A, The same protocols as described in Figure 3 were used. However, the presynaptic patch pipette contained 0.5 mm EGTA. Release rates observed during the depleting pulse are shown at two different magnifications. Note that the Ca²⁺ tail current at the end of the depleting pulse (indicated by a short artifact in the inset) does not lead to any changes in release rate. B, The relationship between the peak release rate per vesicle and the amplitude of the Ca²⁺ current. The data are from the cell pair shown in A. The peak values of release rate per vesicle during the first (continuous line), second (broken line), and third (dotted line) pulses were plotted against the amplitude of Ca²⁺ current. First pulses could be fitted with a power relationship (Eq. 8) withn = 2.43. Second and third pulses were fitted with a Hill function (second pulse: ξ_max = 0.12 msec⁻¹; K = 739 pA; n = 3.42; third pulse: ξ_max = 0.13 msec⁻¹; K = 204 pA; n = 0.916). C, Summary of the relationship between the peak release rate per vesicle during the first (continuous line), second (broken line), and third (dotted line) pulses and the amplitude of Ca²⁺ current. The presynaptic patch pipette contained 0.5 mm EGTA (n = 4 cell pairs).