(A) Representative eEJCs recorded in 2 mM extracellular calcium at 3rd instar larval muscle 6 NMJs for the indicated genotypes (control, overexpression of WT or I426K DSYT1 with elavC155-GAL4). (B) Quantification of mean eEJC amplitude in the indicated genotypes: control elavC155-GAL4, 293.3 ± 34.2 nA, n = 10; elavC155-GAL4; UAS-SYT1, 223.9 ± 11.7 nA, n = 12; elavC155-GAL4; UAS-SYT1 I426K#1, 92.4 ± 15.9 nA, n = 9; elavC155-GAL4; UAS-SYT1 I426K#2, 103.2 ± 12.2 nA, n = 10). (C) Representative eEJCs during a 10 Hz tetanic nerve stimulation in 2 mM external calcium for the indicated genotypes. (D) The average eEJC for the first 10 responses normalized to the amplitude of the first response during a 10-Hz tetanus is shown for control (black), elavC155-GAL4; UAS-WT DSYT 1 (blue), elavC155-GAL4; UAS-DSYT1 I426K #1 (green) and elavC155-GAL4; and UAS-DSYT1 I426K #2 (magenta). Statistical significance was determined using 1-way analysis of variance (nonparametric) with post hoc Sidak multiple comparisons test. N.S. = no significant change (p > 0.05), ***p < 0.001, ****p < 0.0001. All error bars are SEM. eEJC = excitatory junctional current; NMJ = neuromuscular junction.