Figure 6.

Ca²⁺ is a limiting factor, which determines the maximal ERG amplitude when reduced IP₃R levels were combined with reduced catalytic activity of PLCβ. A, Intensity–response relationship of peak ERG responses to increasing intensities of light stimulations of WT (redrawn from Fig. 2), norpA^H43, and norpA^H43;IP₃R-RNAi flies. B, Traces of ERG recordings of norpA^H43 and norpA^H43;IP₃R-RNAi in response to maximal intensity light pulses (open bar) before and after application of anoxia (see D below), which is known to robustly increase cellular Ca²⁺. C, A histogram comparing the peak amplitude of the ERG light responses of norpA^H43 and norpA^H43;IP₃R-RNAi before and after anoxia (mean ± SEM, t test, p = 0.0014 and p = 0.00035 for norpA^H43 and norpA^H43;IP₃R-RNAi, respectively; n = 10). D, Traces showing the entire experiments from which the ERG traces of B were taken. Traces of prolonged ERG recordings of norpA^H43 (top trace) and norpA^H43;IP₃R-RNAi (bottom trace) in response to maximal intensity light pulses (arrows) followed by N₂ application. Anoxia was obtained by blowing N₂ on the intact fly as indicated by the horizontal line. The additional light pulses (3rd and 4th), tested the effects of cellular Ca²⁺ elevation by the anoxia on the ERG. The amplitudes of the ERG responses to the first and the third light pulses in each trace should be compared. The light pulses applied during anoxia (2 unmarked arrows) induced only very small light responses because most TRP and TRPL channels were already open by the anoxia.