Dependence of receptor potential and redox state of mitochondrial cytochromes on oxygen fraction measured in the blowfly eye in vivo

1. The dependence of dark-adapted fly (Calliphora vicina) photoreceptors on oxygen was investigated by measuring the electroretinogram (ERG), the receptor potential, and the redox states of the mitochondrial cytochromes. The redox states were determined via reflection microspectrophotometry on white-eyed fly mutants.

2. The light sensitivity of the photoreceptors at oxygen fractions above approximate to 2% is identical to that in the normal (air) environment, as judged from both ERG and receptor potential. Light sensitivity is rather abruptly and strongly reduced at oxygen fractions lower than approximate to 1% and vanishes at anoxia (0%).

3. The redox state of the mitochondrial cytochromes also changes around oxygen fractions of 1-2%, but the dependence on oxygen fraction is less abrupt than that of ERG and receptor potential.

4. The mitochondrial activity of dark-adapted fly photoreceptors appears to be well-buffered, to warrant ample supply of metabolic energy for unimpaired photoreceptor function down to extremely low oxygen levels.