Exogenous Phospholipids Specifically Affect Transmembrane Potential of Brain Mitochondria and Cytochrome cRelease

Release of cytochrome c , a decrease of membrane potential (Δψ m ), and a reduction of cardiolipin (CL) of rat brain mitochondria occurred upon incubation in the absence of respiratory substrates. Since CL is critical for mitochondrial functioning, CL enrichment of mitochondria was achieved by fusion with CL liposomes. Fusion was triggered by potassium phosphate at concentrations producing mitochondrial permeability transition pore opening but not cytochrome c release, which was observed only at >10 m m . Cyclosporin A inhibited phosphate-induced CL fusion, whereas Pronase pretreatment of mitochondria abolished it, suggesting that mitochondrial permeability transition pore and protein(s) are involved in the fusion process. Phosphate-dependent fusion was enhanced in respiratory state 3 and influenced by phospholipid classes in the order CL > phosphatidylglycerol (PG) > phosphatidylserine. The probe 10-nonylacridine orange indicated that fused CL had migrated to the inner mitochondrial membrane. In state 3, CL enrichment of mitochondria resulted in a pH decrease in the intermembrane space. Cytofluorimetric analysis of mitochondria stained with 3,3′-diexyloxacarbocyanine iodide and 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzymidazolylcarbocyanine iodide showed Δψ m increase upon fusion with CL or PG. In contrast, phosphatidylserine fusion required Δψ m consumption, suggesting that Δψ m is the driving force in mitochondrial phospholipid importation. Moreover, enrichment with CL and PG brought the low energy mitochondrial population to high Δψ m values and prevented phosphate-dependent cytochrome c release.