RESUMO
Ischemic preconditioning, or the protective effect of short ischemic episodes on a longer, potentially injurious, ischemic period, is prevented by antagonists of mitochondrial ATP-sensitive K+ channels (mitoKATP) and involves changes in mitochondrial energy metabolism and reactive oxygen release after ischemia. However, the effects of ischemic preconditioning itself on mitochondria are still poorly understood. We determined the effects of ischemic preconditioning on isolated heart mitochondria and found that two brief (5 min) ischemic episodes are sufficient to induce a small but significant decrease ( approximately 25%) in mitochondrial NADH-supported respiration. Preconditioning also increased mitochondrial H2O2 release, an effect related to respiratory inhibition, because it is not observed in the presence of succinate plus rotenone and can be mimicked by chemically inhibiting complex I in the presence of NADH-linked substrates. In addition, preconditioned mitochondria presented more substantial ATP-sensitive K+ transport, indicative of higher mitoKATP activity. Thus we directly demonstrate that preconditioning leads to mitochondrial respiratory inhibition in the presence of NADH-linked substrates, increased reactive oxygen release, and activation of mitoKATP.
Assuntos
Peróxido de Hidrogênio/metabolismo , Precondicionamento Isquêmico , Mitocôndrias Cardíacas/metabolismo , Miocárdio/metabolismo , Consumo de Oxigênio/fisiologia , Potássio/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Transporte Biológico Ativo/fisiologia , Membrana Celular/fisiologia , Técnicas In Vitro , Masculino , Potenciais da Membrana/fisiologia , Dilatação Mitocondrial/fisiologia , NADP/metabolismo , Ratos , Ratos Sprague-Dawley , Espécies Reativas de Oxigênio/metabolismoRESUMO
Mitochondrial ATP-sensitive K(+) channel (mitoK(ATP)) opening was shown previously to slightly increase respiration and decrease the membrane potential by stimulating K(+) cycling across the inner membrane. Here we show that mitoK(ATP) opening reduces reactive oxygen species generation in heart, liver and brain mitochondria. Decreased H(2)O(2) release is observed when mitoK(ATP) is active both with respiration stimulated by oxidative phosphorylation and when ATP synthesis is inhibited. In addition, decreased H(2)O(2) release is observed when mitochondrial Delta pH is enhanced, an effect expected to occur when mitoK(ATP) is open. We conclude that mitoK(ATP) is an effective pathway to trigger mild uncoupling, preventing reactive oxygen species release.