Spectral sensitivity of light induced respiratory activity of photoreceptor mitochondria in the intact fly

Fly Calliphora erythrocephala (white eyed) photoreceptors were investigated in intact, living animals by microspectrofluorometry in vivo. The fluorescence of mitochondrial flavoproteins was used to monitor transient changes in oxidative metabolism, which were induced by a test light following a stimulus of variable intensity. Two stimulus types were applied, a brief, activating illumination and a prolonged, adapting illumination, respectively. The intensity ranges of activation and adaptation appear to be separated by ca. 3 log units. Action spectra for inducing a criterion activation or adaptation of the light-dependent mitochondrial system are virtually indistinguishable and closely resemble the spectral sensitivity measured electrophysiologically, thus reinforcing the hypothesis that the light-induced changes in oxidative metabolism in fly photoreceptors are closely linked to the phototransduction process. On the basis of the literature we conclude that a light-induced rise in cytosolic calcium concentration is the likely cause for enhancing mitochondrial activity.