(30) EVIDENCE THAT BRAIN MITOCHONDRIA DO NOT READILY UNDERGO PERMEABILITY TRANSITION

T.G. Hastings (1,3), S.W. Watkins (2) and S.B. Berman (3)
Departments of (1) Neurology,(2) Cell Biology and Physiology, and (3) Neuroscience, University of Pittsburgh, Pittsburgh, PA 15261

Opening of the mitochondrial permeability transition pore has increasingly been implicated in excitotoxic, ischemic, and apoptotic cell death, as well as in several neurodegenerative disease processes. However, most studies relating the transition pore to neuronal death have either utilized liver mitochondria or based findings on assumptions about properties that were developed in liver. It has largely been assumed that properties in brain mitochondria are similar to liver mitochondria, but this critical assumption has never been tested. Therefore, in this study, we directly compared isolated brain mitochondria with liver mitochondria. As expected, exposure of liver mitochondria to CaCl2 (70 uM) followed by inorganic phosphate (3 mM), phenylarsenoxide (10 uM), or tert-butylhydroperoxide (1 mM), led to a large, cyclosporin A-inhibitable decrease in spectrophotometric absorbance (-0.82 +/- 0.07; mean +/- SEM), indicative of mitochondrial swelling. Additionally, exposure of liver mitochondria to CaCl2 and phosphate led to the loss of mitochondrial glutathione (-82%) and morphologic evidence of matrix swelling and disruption. In contrast, we found that identically isolated and treated brain mitochondria showed very little absorbance change (10-14% of liver) and no loss of glutathione. The absence of a response in brain was not simply due to structural limitations, since large-amplitude swelling and release of glutathione occurred when membrane pores unrelated to the transition pore were formed by high concentrations of mastoparan. In addition, electron microscopy revealed that the majority of brain mitochondria appeared morphologically unchanged following treatment to induce permeability transition. These findings show that isolated brain mitochondria are more resistant to induction of permeability transition than mitochondria from liver and suggest that assumptions about pore function in brain that are based on observations in other tissues may not be valid.

(Supported in part by USPHS grants NS19068 and DA09601).