Reduced size of the functional vesicle pool within motor-nerve terminals contributes to lowered quantal content of MuSK-MG-affected TS preparations.

<p>(A) Representative time course of quantal content for EPCs in control or MuSK-MG-affected TS muscles that were stimulated at 50 Hz; X axis is the stimulus number (log 2 scale). (B) Representative graph showing the summation of quantal content during the 2 minute, 50 Hz train. The Y axis value is the summation of all quantal contents prior to the EPC number plotted on the X axis. The final value, or Y axis endpoint, of each curve is the total number of vesicles released during the 2 minute, 50 Hz stimulus train. (C) The total number of quanta released during the 2 minute, 50 Hz stimulus train is significantly (* P<0.05) less for MuSK-MG-affected (8 NMJs, 4 mice) muscles than that for vehicle-injected control muscles (7 NMJs, 3 mice). (D) Distribution of mEPC amplitudes as a percent of the total mEPCs used to calculate the mean amplitude shown in (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110571#pone-0110571-g002" target="_blank">Figure 2B</a>). While the modal value remains equivalent to that of control, reduced numbers of mEPCs larger than 2–3 nA accounts for the decline of mean mEPC of MuSK-MG-affected TS preparations.