Figure 8.

Intensity dependence of store depletion in vivo measured from DPP. Flies were pre-illuminated with green light (540 nm) of various intensities for either 2, 4, or 30 s and store Ca²⁺ measured from ER-150 fluorescence immediately afterward. A, ER-150 fluorescence traces from wild-type fly with 30 s green pre-illumination. Blue trace shows initial dark-adapted fluorescence traces (no green pre-illumination). B, intensity dependence of depletion derived from such traces after both 4 s pre-illumination (i.e., monitoring the rapid, Calx-dependent store depletion) and after 30 s (predominantly non-CalX-dependent depletion); intensity expressed in effectively absorbed photons/microvillus/s. Note there was significant store depletion under intensities equivalent to bright daylight (dotted arrow): but at relatively dim intensities there was a slight filling of stores above the dark-adapted levels. C, Traces from fly overexpressing CalX (pCalX) with 2 s green pre-illumination. D, intensity dependence of rapid depletion from such traces was sensitized by several orders of magnitude in pCalx (pCalX 2 s); but after 30 s pre-illumination (which allows for rapid refilling phase; Fig. 7) pCalX flies appeared as resistant to depletion as wild-type. calx^A mutants showed behavior broadly similar to wild-type for long (30 s) pre-illumination protocols.