Heinen André, Aldakkak Mohammed, Stowe David F, Rhodes Samhita S, Riess Matthias L, Varadarajan Srinivasan G, Camara Amadou K S
Anesthesiology Research Laboratories, Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
Am J Physiol Heart Circ Physiol. 2007 Sep;293(3):H1400-7. doi: 10.1152/ajpheart.00198.2007. Epub 2007 May 18.
Mitochondria generate reactive oxygen species (ROS) dependent on substrate conditions, O(2) concentration, redox state, and activity of the mitochondrial complexes. It is well known that the FADH(2)-linked substrate succinate induces reverse electron flow to complex I of the electron transport chain and that this process generates superoxide (O(2)(*-)); these effects are blocked by the complex I blocker rotenone. We demonstrated recently that succinate + rotenone-dependent H(2)O(2) production in isolated mitochondria increased mildly on activation of the putative big mitochondrial Ca(2+)-sensitive K(+) channel (mtBK(Ca)) by low concentrations of 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619). In the present study we examined effects of NS-1619 on mitochondrial O(2) consumption, membrane potential (DeltaPsi(m)), H(2)O(2) release rates, and redox state in isolated guinea pig heart mitochondria respiring on succinate but without rotenone. NS-1619 (30 microM) increased state 2 and state 4 respiration by 26 +/- 4% and 14 +/- 4%, respectively; this increase was abolished by the BK(Ca) channel blocker paxilline (5 microM). Paxilline alone had no effect on respiration. NS-1619 did not alter DeltaPsi(m) or redox state but decreased H(2)O(2) production by 73% vs. control; this effect was incompletely inhibited by paxilline. We conclude that under substrate conditions that allow reverse electron flow, matrix K(+) influx through mtBK(Ca) channels reduces mitochondrial H(2)O(2) production by accelerating forward electron flow. Our prior study showed that NS-1619 induced an increase in H(2)O(2) production with blocked reverse electron flow. The present results suggest that NS-1619-induced matrix K(+) influx increases forward electron flow despite the high reverse electron flow, and emphasize the importance of substrate conditions on interpretation of effects on mitochondrial bioenergetics.
线粒体根据底物条件、氧气浓度、氧化还原状态以及线粒体复合物的活性产生活性氧（ROS）。众所周知，与黄素腺嘌呤二核苷酸（FADH₂）相关的底物琥珀酸会诱导电子逆向流动至电子传递链的复合物I，且该过程会产生超氧化物（O₂⁻）；这些效应会被复合物I阻滞剂鱼藤酮所阻断。我们最近证明，在低浓度的1,3 - 二氢 - 1 - [2 - 羟基 - 5 -（三氟甲基）苯基] - 5 -（三氟甲基）- 2H - 苯并咪唑 - 2 - 酮（NS - 1619）激活假定的大线粒体钙敏感钾通道（mtBKCa）时，分离的线粒体中琥珀酸 + 鱼藤酮依赖性的过氧化氢（H₂O₂）生成会轻度增加。在本研究中，我们检测了NS - 1619对分离的豚鼠心脏线粒体在以琥珀酸为呼吸底物但无鱼藤酮情况下的线粒体氧气消耗、膜电位（ΔΨm）、H₂O₂释放速率以及氧化还原状态的影响。NS - 1619（30 μM）分别使状态2和状态4呼吸增加了26±4%和14±4%；这种增加被BKCa通道阻滞剂紫杉醇（5 μM）消除。单独使用紫杉醇对呼吸没有影响。NS - 1619没有改变ΔΨm或氧化还原状态，但与对照相比使H₂O₂生成减少了73%；这种效应被紫杉醇不完全抑制。我们得出结论，在允许电子逆向流动的底物条件下，通过mtBKCa通道的基质钾离子内流通过加速正向电子流动来减少线粒体H₂O₂的生成。我们之前的研究表明，在电子逆向流动受阻时，NS - 1619会诱导H₂O₂生成增加。目前的结果表明，尽管存在高电子逆向流动，NS - 1619诱导的基质钾离子内流仍会增加正向电子流动，并强调了底物条件在解释对线粒体生物能量学影响方面的重要性。
