Figure 5. Estimation of the size of the readily releasable pool (RRP) at individual boutons.

A, postsynaptic responses to first 15 stimuli of a 50 Hz train. B, peak eIPSC amplitude values were summed to determine the cumulative eIPSC amplitude during trains of different frequencies. Evoked IPSCs were normalised to the mean dIPSC amplitude. Each data point is an average of three trials. Data from the same cell. Data points during a steady state phase (from the 10th to the 20th pulse) were fitted by linear regression (dotted lines), and back-extrapolated to time 0. The intersects provide an estimate of the number of available vesicles. C, RRP size does not depend on stimulation frequency. Shown data are from seven cells. D, the ARR is not modified by the substitution of Sr²⁺ (thick line) for extracellular Ca²⁺ (thin line). Each trace is an average of five responses.