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FIG. 8. MLCK inhibition increases the RRP of vesicles. A1: graph summarizing the EPSC amplitudes during trains of stimulation (100 Hz; 50 stimuli) before (control; black circles) and after (red circles) ML-9 (25 µM) application at P15–P16 (n = 5 cells) in 2 mM extracellular calcium ([Ca2+]e). B1: graph summarizing the EPSC amplitudes during trains of stimulation (300 Hz; 50 stimuli) before (control; black circles) and after (red circles) ML-9 (25 µM) application at P17–P18 (n = 5 cells) in 4 mM [Ca2+]e and 2 mM gamma-D-glutamylglycine. Inset shows enlarged first few EPSC amplitudes for clarity. The difference between the EPSC amplitudes under control and ML-9 application is shown in green circles. A2 and B2: cumulative amplitudes of the EPSCs shown above under control conditions and on ML-9 application. Amplitudes of the EPSCs from 200 to 500 ms were fitted with a linear regression line and extrapolated to time 0 for estimating the RRP size. Note that the B2 regression line is significantly more shallower than for A2. A3 and B3: mean number of releasable vesicles (N) multiplied by mean quantal size (q), as estimated earlier, significantly increased after ML-9 application. Values from individual cells were shown. A4 and B4: the mean release probability (Pr) for individual cells, which was estimated from the ratio of the first EPSC amplitude divided by Nq. Note that Pr was not significantly (n.s.) increased after ML-9 application. Asterisks indicate a significant difference between the indicated pairwise comparisons (*P < 0.05; **P < 0.01; paired t-test).
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