Figure 4.

Depletion of ER Ca²⁺ stores prevents peptide-induced modulation. Drosophila larvae with a conditional dominant negative temperature-sensitive SERCA mutation were used to test for a role of intracellular Ca²⁺ stores in DPKQDFMRFamide-induced modulation of evoked Ca²⁺ release. A, Normalized amplitude of evoked Ca²⁺ responses in CaP60A^Kum170 mutants under control conditions (black) and with inactivated SERCA (red) following an 8 min heat shock (HS) at 40°C. Each trace is the average of four consecutive responses during a 2 Hz train and averaged every 20 ms. B, Following inactivation of SERCA function, normalized amplitude increased dramatically (p < 0.001; n = 5). ER Ca²⁺ stores were depleted after ∼2 min of 30 Hz stimulation. Following this depletion, response amplitudes reduced to control levels (p = 0.001). Subsequent application of DPKQDFMRFamide did not significantly alter the amplitude of evoked responses (p = 0.9). C, The decay constant was significantly increased following inactivation of SERCA but was restored to control levels following the depletion of calcium stores from the ER. Application of the peptide had no effect on decay constant in terminals with depleted ER calcium stores. pre, Pre-DPKQDFMRFamide. Asterisks (*) indicate significant difference.