Inhibition of brain mitochondrial nitric oxide production during permeability transition.

BUSTAMANTE, J.; CZERNICZYNIEC, A.; LORES-ARNAIZ, S.

Montevideo, Uruguay

Congreso; V Meeting of SFRBM – South American Group, V International Conference on Peroxynitrite and Reactive Nitrogen Species.; 2007

Society for Free Radical Biology and Medicine

Increased and sustained cytosolic Ca2+ concentrations are predominantly coped by mitochondria, which are able to accumulate this cation in high concentrations. In this way, mitochondria protect astrocytes and neurons, from the deleterious effects of abnormal Ca2+ influx. In this work, we analyze how non synaptic mouse brain cortex mitochondria modulate his own NO synthesis during Ca2+-induced-permeability transition (MPT). Respiratory function and membrane potential were evaluated during Ca2+-induced MPT, simultaneously with mitochondrial NO production. Mitochondrial endogenous NO was registered immediately after mitochondrial incubation with 200 mM Ca2+, in these conditions a 65% increase in NO production was observed. Time course of mitochondrial NO production after alamethicin and Ca2+-induced-MPT was studied, being 33% decreased after 3.5 min, and 69% decreased after 7 min alamethicin incubation. When NO was registered during Ca2+-induced permeability transition (MPT), decreases of 48% and 58% were observed after 3.5 and 7 min respectively.  These results were associated with changes in the respiratory function and in the maintenance of a membrane potential. After Ca2+ addition and alamethicin-induced MPT, 39% and 80% of mitochondrial depolarization was observed respectively. Similarly, an impaired respiratory function was observed with increases of 60% and 75% in state 4 respiratory rate after Ca2+ and alamethicin-induced MPT respectively. These results show that physiological mitochondrial NO production, sustained by the endogenous Ca2+ concentration was associated with a closed pore condition. This mitochondrial NO production was stimulated by a mitochondrial Ca2+ entrance due to the supplementation of mitochondria with 200 mM Ca2+ and was decreased during MPT indicating that the mitochondrial NOS isoform is inactivated by the presence of an open pore due to a massive mitochondrial  calcium release.