Chang Huai-Ren, Lien Chih-Feng, Jeng Jing-Ren, Hsieh Jen-Che, Chang Chen-Wei, Lin Jian-Hong, Yang Kun-Ta
Division of Cardiology, Department of Internal Medicine, Buddhist Tzu Chi General Hospital, Hualien, Taiwan.
School of Medicine, Tzu Chi University, Hualien, Taiwan.
Cell Physiol Biochem. 2018;46(3):1252-1262. doi: 10.1159/000489076. Epub 2018 Apr 16.
BACKGROUND/AIMS: Intermittent hypoxia (IH) has been shown to exert preconditioning-like cardioprotective effects. It also has been reported that IH preserves intracellular pH (pHi) during ischemia and protects cardiomyocytes against ischemic reperfusion injury. However, the exact mechanism is still unclear.
In this study, we used proton indicator BCECF-AM to analyze the rate of pHi recovery from acidosis in the IH model of rat neonatal cardiomyocytes. Neonatal cardiomyocytes were first treated with repetitive hypoxia-normoxia cycles for 1-4 days. Cells were then acid loaded with NH4Cl, and the rate of pHi recovery from acidosis was measured.
We found that the pHi recovery rate from acidosis was much slower in the IH group than in the room air (RA) group. When we treated cardiomyocytes with Na+-H+ exchange (NHE) inhibitors (Amiloride and HOE642) or Na+-free Tyrode solution during the recovery, there was no difference between RA and IH groups. We also found intracellular Na+ concentration ([Na+]i) significantly increased after IH exposure for 4 days. However, the phenomenon could be abolished by pretreatment with ROS inhibitors (SOD and phenanathroline), intracellular calcium chelator or Na+-Ca2+ exchange (NCX) inhibitor. Furthermore, the pHi recovery rate from acidosis became faster in the IH group than in the RA group when inhibition of NCX activity.
These results suggest that IH would induce the elevation of ROS production. ROS then activates Ca2+-efflux mode of NCX and results in intracellular Na+ accumulation. The rise of [Na+]i further inhibits the activity of NHE-mediated acid extrusion and retards the rate of pHi recovery from acidosis during IH.
背景/目的：间歇性低氧（IH）已被证明具有类似预处理的心脏保护作用。也有报道称，IH在缺血期间可维持细胞内pH值（pHi），并保护心肌细胞免受缺血再灌注损伤。然而，确切机制仍不清楚。
在本研究中，我们使用质子指示剂BCECF-AM分析大鼠新生心肌细胞IH模型中pHi从酸中毒恢复的速率。新生心肌细胞首先用重复的缺氧-复氧循环处理1-4天。然后用氯化铵使细胞酸负荷，并测量pHi从酸中毒恢复的速率。
我们发现，IH组中pHi从酸中毒恢复的速率比常氧（RA）组慢得多。当我们在恢复过程中用钠-氢交换（NHE）抑制剂（氨氯吡咪和HOE642）或无钠的台氏液处理心肌细胞时，RA组和IH组之间没有差异。我们还发现，暴露于IH 4天后，细胞内钠浓度（[Na+]i）显著增加。然而，用活性氧抑制剂（超氧化物歧化酶和菲咯啉）、细胞内钙螯合剂或钠-钙交换（NCX）抑制剂预处理可消除该现象。此外，抑制NCX活性后，IH组中pHi从酸中毒恢复的速率比RA组更快。
这些结果表明，IH会诱导活性氧产生增加。活性氧随后激活NCX的钙外流模式，导致细胞内钠积累。[Na+]i的升高进一步抑制NHE介导的酸外排活性，并延缓IH期间pHi从酸中毒恢复的速率。
