Department of Physiology, Juntendo University Faculty of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.
J Physiol Sci. 2012 Jul;62(4):325-32. doi: 10.1007/s12576-012-0206-y. Epub 2012 Apr 19.
The mitochondrial calcium-activated potassium channel (mitoK(Ca)) and the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) are both involved in cardiac preconditioning. Here, we examined whether these two channels are also involved in ischemic or pharmacological postconditioning. Using Langendorff perfusion, rat hearts were made hypoxic for 45 min and then reoxygenated for 30 min. Ischemic postconditioning (IPT) was achieved through application of 3 cycles of 10 s of reperfusion and 10 s of ischemia before reoxygenation, with and without paxilline (Pax; a mitoK(Ca) blocker) or 5-hydroxydecanoate (5-HD; a mitoK(ATP) blocker). Pharmacological postconditioning was carried out for 5 min at the onset of reoxygenation using NS1619 (a mitoK(Ca) opener) or diazoxide (Dia; a mitoK(ATP) opener). Pax and 5-HD abolished IPT-induced cardioprotection from reoxygenation injury, whereas administration of NS1619 or Dia significantly improved cardiac contractile activity and reduced aspartate aminotransferase (an index of myocyte injury) release following reoxygenation. In addition, isolated rat myocytes were loaded with tetramethylrhodamine methyl ester (TMRE; fluorescent mitochondrial membrane potential indicator) and 2',7'-dichlorofluorescein [DCFH; fluorescent reactive oxygen species (ROS) indicator] or Fluo-4-acetoxymethyl ester (Fluo-4-AM; fluorescent calcium indicator). When TMRE-loaded myocytes were laser illuminated, the DCFH and Fluo-4 fluorescence increased, and TMRE fluorescence decreased. These effects were significantly inhibited by NS1619 and Dia. We therefore conclude that IPT may protect the heart through activation of mitoK(ATP) and mitoK(Ca) channels, and that opening of these channels at the onset of reoxygenation protects the heart from reoxygenation injury, most likely by reducing excess generation of ROS and the resultant Ca(2+) overload.
线粒体钙激活钾通道（mitoK(Ca))和线粒体三磷酸腺苷敏感性钾通道（mitoK(ATP))都参与了心脏的预处理。在这里，我们研究了这两种通道是否也参与了缺血或药物后处理。使用 Langendorff 灌注，将大鼠心脏缺氧 45 分钟，然后再复氧 30 分钟。缺血后处理（IPT)是通过在复氧前应用 3 个循环的 10 秒再灌注和 10 秒缺血来实现的，其中包括和不包括 paxilline（Pax; mitoK(Ca) 阻断剂）或 5-羟癸酸（5-HD; mitoK(ATP) 阻断剂）。药物后处理在复氧开始时进行 5 分钟，使用 NS1619（mitoK(Ca) 开放剂）或 diazoxide（Dia; mitoK(ATP) 开放剂）。Pax 和 5-HD 消除了 IPT 诱导的再灌注损伤的心脏保护作用，而 NS1619 或 Dia 的给药显著改善了心脏收缩活动，并减少了再灌注后天冬氨酸氨基转移酶（肌细胞损伤的指标）的释放。此外，分离的大鼠心肌细胞用四甲基罗丹明甲酯（TMRE; 荧光线粒体膜电位指示剂）和 2',7'-二氯荧光素 [DCFH; 荧光活性氧（ROS)指示剂] 或 Fluo-4-乙氧基甲酯（Fluo-4-AM; 荧光钙指示剂）负载。当 TMRE 负载的心肌细胞被激光照射时，DCFH 和 Fluo-4 荧光增加，TMRE 荧光减少。这些作用被 NS1619 和 Dia 显著抑制。因此，我们得出结论，IPT 可能通过激活 mitoK(ATP) 和 mitoK(Ca) 通道来保护心脏，并且在再灌注开始时开放这些通道可以保护心脏免受再灌注损伤，这很可能是通过减少过量的 ROS 生成和由此产生的 Ca(2+) 超载来实现的。
