Figure 4.

ER store depletion in dissociated ommatidia in Ca²⁺-free solutions. A, Normalized ER-150 fluorescence in response to blue excitation control bath and in the same ommatidia perfused for ∼30 s with Ca²⁺-free bath (0 Ca²⁺, 1 mm EGTA). Average traces from five ommatidia in three otherwise wild-type flies. Inset (right), Expanded scale to show increase in latency (arrows). B, Time constants (tau) of rapid depletion from exponential fits to decay. C, Store depletion (ER-150 fluorescence, blue trace, expressed as F/F_max) and cytosolic Ca²⁺ (RGECO1 fluorescence; green trace expressed as ΔF/F₀) measured from the same ommatidia (average of 17 ommatidia from 5 otherwise wild-type flies). Stippled green trace: RGECO1 data replotted after inverting and rescaling to compare time courses. D, Peak RGECO1 ΔF/F₀ values (cytosolic Ca²⁺) from these ommatidia correlated strongly with the extent of store depletion (ER-150 F_min/F_max values) in the same ommatidium. E, Time to 50% depletion (t_1/2 ER-150) in these ommatidia also correlated with the t_1/2 for the rise in cytosolic Ca²⁺. F, Store depletion (ER-150 fluorescence): averaged from 10 ommatidia from 2 wild-type flies in control bath and during 0 Ca²⁺ perfusion, monitored over 30 s. G, Store depletion (ER-150 fluorescence) measured from wild-type ommatidia over 30 s in control bath, and same ommatidia during perfusion with 0 Na (130NMDG, 1.5 Ca, 4 Mg; n = 8) and 0Ca/0Na (130NMDG, 0Ca 1 mm EGTA, 4 Mg; n = 3). H, ER-150 fluorescence (normalized to fluorescence at time 0) measured continuously during perfusion with 0 Ca²⁺ (1 mm EGTA) in a wild-type background; the ER stores depleted almost completely within ∼3 min and then rapidly refilled on re-exposure to normal Ca²⁺ containing bath. I, During 0 Ca²⁺ perfusion in a PLC-null (norpA^P24) background, store Ca²⁺ declined more slowly, recovering partially on reperfusion with Ca²⁺ containing bath.