High cyclophilin D content of synaptic mitochondria results in increased vulnerability to permeability transition - PubMed (original) (raw)

Greater cyclosporine A concentrations are required to increase Ca2+ uptake capacity in synaptic versus nonsynaptic mitochondrial fractions. Isolated synaptic or nonsynaptic mitochondria, in the presence or absence of 1 or 5 μ

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CsA, were placed in a constantly stirred, temperature-controlled, cuvette. CaG5N fluorescence was monitored continuously. Malate and pyruvate (M/P) and ADP were provided. Oligomycin (O), an ATP synthase inhibitor, was then added to ensure that the mitochondria were at maximal ΔΨm. Ca2+ infusion began at 5 min (160 nmol Ca2+/mg protein per minute), causing a small, initial increase in CaG5N fluorescence until the mitochondria were able to sequester the added Ca2+. The subsequent sharp rise in CaG5N fluorescence signifies mitochondrial permeability transition and the release of Ca2+ from the mitochondria into the surrounding buffer. A, B, In the absence of cyclosporine, synaptic mitochondria (A) sequestered much less Ca2+ than nonsynaptic mitochondria (B) before undergoing permeability transition, as reported previously (Brown et al., 2006). AU, Arbitrary units. Arrows indicate the onset (On) and termination (Off) of CaCl2 infusion. C, Quantitative estimates of the nanomoles of Ca2+ infused per milligram of mitochondrial protein before permeability transition; n = 4 per group. One micromolar cyclosporine A significantly increased the Ca2+ uptake capacity of nonsynaptic mitochondria before permeability transition but did not influence the Ca2+ uptake capacity of synaptic mitochondria. Increasing the cyclosporine A concentration to 5 μ

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significantly increased the Ca2+ uptake capacity of synaptic mitochondria compared with both 0 and 1 μ

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cyclosporine A. In contrast, the higher cyclosporine A concentration did not further improve the Ca2+ uptake capacity of nonsynaptic mitochondria compared with results obtained with 1 μ

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cyclosporine A. In the presence of 5 μ

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cyclosporine A, the Ca2+ uptake capacity of nonsynaptic mitochondria remained greater than that of synaptic mitochondria. *p < 0.05.