Receptor potential and light-induced mitochondrial activation in blowfly photoreceptor mutants

1. Simultaneous measurements of the receptor potential and the light-induced mitochondrial activation were performed in white-eyed blowflies Calliphora vicina, mutant chalky, and Lucilia cuprina, mutants w(F) and w'nss. The intensity dependence and the temporal dynamics were investigated.

2. The characteristic curve of the light-induced mitochondrial activation vs. log intensity has an S-like shape, which is much steeper than the characteristic curve of the receptor potential (the V/log I curve). The threshold intensity of mitochondrial activation elicits about a half-maximal receptor potential, while mitochondrial activation and photoreceptor potential saturate at about the same intensity.

3. The time course of the mitochondrial activation induced by a light flash, i.e. the pulse-response curve, is biphasic in both mutants with normal phototransduction properties, Calliphora chalky and Lucilia w(F); the shape is slightly species dependent.

4. In the phototransduction mutant Lucilia w'nss the step-responses of both the (bright) light-induced mitochondrial activation and receptor potential are quite different from the corresponding signals in Lucilia w(F). The striking resemblance of the step-response of the mitochondrial activation to its pulse-response indicates that mitochondrial activation and receptor potential are intimately linked.