Characteristics of the permeability transition pore in brain cortex mitochondria.

BUSTAMANTE, J.; LORES-ARNAIZ, S.

Buenos Aires

Simposio; Simposio-Workshop OXIDATIVE STRESS AND ANTIOXIDANTS.; 2009

Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires.

Characteristics of the permeability transition pore in brain cortex mitochondria   Juanita Bustamante and Silvia Lores Arnaiz Laboratory of Free Radical Biology, School of Pharmacy and Biochemistry, University of Buenos Aires, Junın 956, 1113 Buenos Aires, Argentina   Mitochondria help to shape intracellular Ca2+ signalling by taking up cytosolic Ca2+ through an uniporter located on the inner membrane. However, their uptake capacity is finite, and when exceeded, mitochondrial Ca2+ efflux occurs rapidly by a change in the permeability of the mitochondrial inner membrane resulting from the opening of a non-specific mega channel called mitochondrial permeability transition pore or mitochondrial permeability transition (MPT). In this work we studied the effect of high Ca2+ exposure in the functions of non synaptic brain cortex mitochondria.. MPT was analysed through its two main characteristics mitochondrial swelling and depolarization after a single pulse of 100 mM Ca2+ (corresponding to 400 nmol/mg protein). In these conditions, H2O2 and NO production, mitochondrial respiratory function and the activity of the monoamine oxidase (MAO), an outer mitochondrial membrane enzyme, were determined. Energized organelles in the presence of 100 mM Ca2+, showed partial swelling and depolarization, being maximal after addition of alamethicin. An impaired respiratory function, with 47% increase in state 4 respiratory rate and 59% decrease in state 3 respiratory rate was also observed after 100 mM Ca2+. Increased hydrogen peroxide (H2O2) production was observed, being restored after CsA pretreatment to those levels observed in untreated mitochondria. Additionally, NO production was decreased by 51% and 73% after 3 and 7 min of 100 mM Ca2+ addition respectively and by 80% after alamethicin. Similarly, marked decreases of 38% and  60% in MAO activity were observed 7 minutes after Ca2+ and alamethicin respectively as compared with untreated mitochondria. Mitochondrial pretreatment with CsA, an inhibitor of MPT, before 100 mM Ca2+, protect against calcium induced swelling, and restored NO production and MAO activity to the levels observed in untreated mitochondria. We conclude that during Ca2+ or alamethicin induced swelling a marked increase in H2O2 leads to a structurally compromised mitochondria with disrupted antioxidant pathways, and that the typical modulation of MAO activity and NO production could be closely related with the topological alterations induced in the inner and outer mitochondrial membranes during MPT.