Fig. 6
EGTA sensitivity of the Pr and size of RRP is heterogeneous in mature calyces. a Average traces (mean ± SEM) show amplitudes (left panels) and cumulative amplitudes (cuEPSC, right panels) of action potential (AP) train-evoked EPSCs (300 Hz, 200 ms) in simple (black, upper) and complex (red, lower) calyces before and after EGTA loading (blue, 10 mM, 3–5 min). Insets: representative pre-IAP 1–5 (presynaptic compound AP currents) and EPSC1–5. Gray trace (last panel): cuEPSC of simple calyces after EGTA injection for comparison (mean ± SEM). b Bar graphs show release probability (Pr) and readily releasable pool (RRP) before and after EGTA loading. (Pr, simple, control, 0.208 ± 0.016, EGTA, 0.191 ± 0.017, n = 8/7, t = 2.211, p = 0.0627, df = 7, paired t-test [p.t.t.]; complex, control, 0.157 ± 0.007, EGTA, 0.125 ± 0.005, n = 8/8, t = 3.53, p = 0.0096, df = 7, p.t.t.; RRP, simple, control, 49.32 ± 3.56 nA, EGTA, 43.56 ± 3.904 nA, n = 8/7, t = 3.412, p = 0.0113, df = 7, p.t.t.; complex, control, 90.64 ± 8.13 nA, EGTA, 70.32 ± 7.97 nA, n = 8/8, t = 9.363, p < 0.0001, df = 7, p.t.t.). The difference in EGTA effect on simple and complex calyces was quantified as EGTA/control (Pr, simple, 0.917 ± 0.035, n = 8/7, complex, 0.813 ± 0.052, n = 8/8, t = 1.664, p = 0.118, df = 14, unpaired t-test [u.t.t.]; RRP, simple, 0.881 ± 0.037, n = 8/7, complex, 0.762 ± 0.036, n = 8/8, t = 2.305, p = 0.037, df = 14, u.t.t.). c Pr and RRP size for all EGTA loaded synapses were plotted against the number of swellings (black triangles, control; blue dots, EGTA) and linearly fitted (mean ± 95% confidence interval). The y-intercept of the RRP fit gives RRP size in stalk (39.30 ± 10.08 nA), the slope determines RRP per swelling (1.74 ± 0.55 nA). R demonstrates correlation strength. Bar graphs summarize mean ± SEM (*p < 0.05, **p < 0.01, ***p < 0.001). See Supplementary Figure 6
