“…This holds particularly for insect photoreceptor cells, where Ca i has been shown to play a key role in the regulation of the light sensitivity (Bader et al, 1976; Autrum, 1979; Muijser, 1979; Tsukahara, 1980; Walz, 1992). More specifically, Ca i has been implicated in the control of numerous cellular processes in fly photoreceptors; e.g., in the modulation of the light-activated ion channels (Hardie, 1991, 1995 a , 1995 b ; Hardie and Minke, 1994), the activation of the Na + /Ca 2+ exchanger (Hardie, 1995 a , 1995 b ), the regulation of many enzymes involved in the transduction cascade (Selinger et al, 1993; Minke and Selinger, 1996), the activation of mitochondria (Fein and Tsacopoulos, 1988; Mojet et al, 1991), and the migration of pigment granules in the photoreceptor cells (Kirschfeld and Vogt, 1980; Howard, 1984; Hofstee and Stavenga, 1996).…”