Photoreceptor Redox State Monitored In Vivo by Transmission and Fluorescence Microspectrophotometry in Blowfly Compound Eyes

The transmission and fluorescence of the compound eye of living, intact blowflies Calliphora erythrocephala, mutant chalky, were studied microspectrophotometrically. Transmission spectra were recorded under four conditions. The fly was either in the normal air environment or in a nitrogen atmosphere, and in both cases the investigated eye was adapted to red and blue light, respectively. The absorbance difference spectra obtained from the two chromatic adapted conditions showed the clear characteristics of the main visual pigment; the difference spectra for the air and the N2 case were virtually identical. The absorbance difference spectrum obtained from the air vs N2 case was very similar to the redox difference spectrum of the pigments in the mitochondrial chain. The redox difference spectra obtained for the two photosteady states were essentially the same. The fluorescence emission spectra induced by UV and blue excitation were measured with the fly in air and in a nitrogen atmosphere, respectively. The UV-induced blue emission increased under hypoxia, whereas the blue-induced green emission dropped. The changes are typical for a reduction of mitochondrial NADH and flavoproteins, respectively. The transmission and fluorescence measurements corroborate each other and demonstrate mitochondrial activity in photoreceptors in vivo and non-invasively.