Mitochondrial Physiology Network 10.9: 80-81 (2005) - download pdf

Brain mitochondrial production of reactive oxygen species is increased by calcium-induced permeability transition.

Magnus J Hansson¹, R Mansson^1,2, E Elmér¹

¹Lab. Experimental Brain Research, Lund University, Lund; ²Dept. Neurology, Malmo University Hospital, Malmo, Sweden. – magnus.hansson@med.lu.se

    Non-physiological increases in mitochondrial production of reactive oxygen species (ROS) are considered to be essential in the pathogenesis of several acute and chronic neurodegenerative diseases. Pathological calcium fluxes in neuronal cell death has been extensively investigated, but the role of calcium in mitochondrial ROS production is currently unresolved and both increases and decreases of the detection of ROS by calcium-loading in mitochondria have been reported [1,2].

    In the present study, we demonstrate that the production of ROS, as detected by Amplex Red oxidation in isolated rat brain mitochondria respiring on complex I substrates, is increased by calcium if the mitochondria undergo permeability transition (mPT) and large amplitude swelling. In contrast, the detection of ROS was decreased by the same dose of calcium if the mPT was blocked with cyclosporin A and its cofactor ADP. Unspecific permeabilization by the ionophore alamethicin produced a similar increase of ROS. Alamethicin permeabilization and mPT induced an immediate loss of NAD(P)H fluorescence and membrane potential, diminished respiration, release of cytochrome c and reduced levels of GSH. The ROS production following permeabilization was dependent on availability of respiratory substrates, and improved accessibility of electron donors increased the O₂ utilization and ROS detection.

    The mPT dependent increase of ROS can likely be attributed to both the loss of endogenous oxidant scavenging systems and escape of cytochrome c. However, challenging mitochondria with 1.4 and 8 µmol/mg calcium produced a similar extensive level of swelling but the latter dose led to a substantially greater ROS burst and to a significant inhibition of mitochondrial O₂ consumption following permeabilization. Thus, calcium overload combined with mPT is suggested to directly affect redox centers in the respiratory complexes. As the calcium-triggered ROS generation is dependent on inner membrane permeabilization it may be subject to pharmacological modulation of the mPT.

     Funded by the Swedish Research Council (Project No. 08644), the Laerdal and the Bergvall foundations.

1. Brustovetsky N, Brustovetsky T, Purl KJ, Capano M, Crompton M, Dubinsky JM (2003) Increased susceptibility of striatal mitochondria to calcium-induced permeability transition. J. Neurosci. 23: 4858-4867.

2. Maciel EN, Vercesi AE, Castilho RF (2001) Oxidative stress in Ca²⁺-induced membrane permeability transition in brain mitochondria. J. Neurochem. 79: 1237-1245.