Properties of Ca ²⁺ transport in mitochondria of Drosophila melanogaster

We have studied the pathways for Ca ²⁺ transport in mitochondria of the fruit fly Drosophila melanogaster. We demonstrate the presence of ruthenium red (RR)-sensitive Ca ²⁺ uptake, of RR-insensitive Ca ²⁺ release, and of Na ⁺-stimulated Ca ²⁺ release in energized mitochondria, which match well characterized Ca ²⁺ transport pathways of mammalian mitochondria. Following larger matrix Ca ²⁺ loading Drosophila mitochondria underwent spontaneous RR-insensitive Ca ²⁺ release, an event that in mammals is due to opening of the permeability transition pore (PTP). Like the PTP of mammals, Drosophila Ca ²⁺-induced Ca ²⁺ release could be triggered by uncoupler, diamide, and N-ethylmaleimide, indicating the existence of regulatory voltage- and redox-sensitive sites and was inhibited by tetracaine. Unlike PTP-mediated Ca ²⁺ release in mammals, however, it was (i) insensitive to cyclosporin A, ubiquinone 0, and ADP; (ii) inhibited by Pi, as is the PTP of yeast mitochondria; and (iii) not accompanied by matrix swelling and cytochrome c release even in KCl-based medium. We conclude that Drosophila mitochondria possess a selective Ca ²⁺ release channel with features intermediate between the PTP of yeast and mammals.