Failure analysis: SL- and RQ,SL-expressing NMJs show elevated release probability at very low extracellular calcium.

<p><b>(A, B)</b> Frequencies of evoked amplitudes at very low extracellular Ca²⁺ (0.14 mM) for <b>(A)</b> WT-expressing NMJs and <b>(B)</b> RQ,SL-expressing NMJs. For the RQ,SL-expressing NMJs, there is a clear rightward shift in the size distribution of RQ,SL-expressing events, as well as a marked decrease in the frequency of failures (categorized as 0 mV events). <b>(C)</b> For WT-, SL-, and RQ,SL-expressing NMJs, the average EPSP size for successfully evoked events, as well as estimated QC by failure analyses (0.14 mM Ca²⁺) (* <i>p</i> < 0.05; ** <i>p</i> < 0.01 by one-way ANOVA with Tukey’s post-hoc compared to WT). <b>(D)</b> Further lowering extracellular Ca²⁺ (0.1 mM) for RQ,SL reveals a leftward shift in size distribution and an increase in failure percentage compared to (B). <b>(E)</b> Box and whisker data are presented as in Figs <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007577#pgen.1007577.g005" target="_blank">5</a> and <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007577#pgen.1007577.g006" target="_blank">6</a> –this time showing the size distributions of spontaneous mEPSP events (WT, RQ,SL, and SL), as well as failure analysis (FA) evoked events for the same genotypes (failures excluded). <b>(F, G)</b> Box and whisker plots for mEPSP rise times (0.5 mM Ca²⁺, see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007577#pgen.1007577.g005" target="_blank">Fig 5D</a>) show a significant increase only for RQ,SL-expressing NMJs (F), as well as a dramatic slowdown for events > 2 mV in size, regardless of genotype (G).