Mutant Synaptotagmin Disrupts Neurotransmitter Release in the Presence of Endogenous Synaptotagmin
(A) Representative EPSCs recorded in 0.2 mM extracellular Ca2+ at third instar larval muscle 6 synapses for the indicated genotypes (control, induction of WT or p.Asp362Ala DSYT1 by elavC155-GAL4).
(B) Quantification of mean eEJC amplitudes in the indicated genotypes (w−/−, 120.5 ± 5.3 nA, n = 16; elavC155-GAL4; UAS-SYT1, 117.5 ± 11 nA, n = 15; elavC155-GAL4; UAS-SYT1 p.Asp362Ala#1, 26.6 ± 4.7 nA, n = 16; elavC155-GAL4; UAS-SYT1 p.Asp362Ala#2, 17.3 ± 3.2 nA, n = 16).
(C) Postsynaptic current recordings of spontaneous release for the indicated genotypes.
(D) Quantification of average mini frequency for the indicated genotypes (w−/−, 1.6 ± 0.1 Hz, n = 10; elavC155-GAL4; UAS-SYT1, 2.1 ± 0.2 Hz, n = 10; elavC155-GAL4; UAS-SYT1 p.Asp362Ala#1, 6.3 ± 0.5 Hz, n = 16; elavC155-GAL4; UAS-SYT1 p.Asp362Ala#2, 8.2 ± 0.7 Hz, n = 13).
Student’s t test: ∗p < 0.05; ∗∗∗∗p < 0.0001. Error bars represent SEM.
(E) Representative EPSCs during a short 10 Hz tetanic stimulation of the nerve in 0.2 mM external Ca2+ for the indicated genotypes.
(F) The average for the first ten responses normalized to the first response during the tetanus is shown following induction of WT DSYT 1 (blue), DSYT1 p.Asp362Ala #1 (green), and DSYT1 p.Asp362Ala #2 (red). The average fast tetanic facilitation after ten responses for each genotype is: WT DSYT1 = 0.94 ± 0.02; DSYT1 p.Asp362Ala#1 = 1.29 ± 0.03; DSYT1 p.Asp362Ala#2 = 1.49 ± 0.04. Student’s t test revealed significant differences between WT and p.Asp362Ala (p < 0.0001).