Power Amelia, Pearson Nicholas, Pham Toan, Cheung Carlos, Phillips Anthony, Hickey Anthony
School of Biological Sciences, Faculty of Science, University of Auckland, Auckland, New Zealand Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
School of Biological Sciences, Faculty of Science, University of Auckland, Auckland, New Zealand.
Physiol Rep. 2014 Sep 28;2(9). doi: 10.14814/phy2.12138. Print 2014 Sep 1.
Heart failure is a common cause of death with hyperthermia, and the exact cause of hyperthermic heart failure appears elusive. We hypothesize that the energy supply (ATP) of the heart may become impaired due to increased inner-mitochondrial membrane permeability and inefficient oxidative phosphorylation (OXPHOS). Therefore, we assessed isolated working heart and mitochondrial function. Ex vivo working rat hearts were perfused between 37 and 43.5°C and showed break points in all functional parameters at ~40.5°C. Mitochondrial high-resolution respirometry coupled to fluorometry was employed to determine the effects of hyperthermia on OXPHOS and mitochondrial membrane potential (ΔΨ) in vitro using a comprehensive metabolic substrate complement with isolated mitochondria. Relative to 37 and 40°C, 43°C elevated Leak O2 flux and depressed OXPHOS O2 flux and ∆Ψ. Measurement of steady-state ATP production from mitochondria revealed decreased ATP synthesis capacity, and a negative steady-state P:O ratio at 43°C. This approach offers a more powerful analysis of the effects of temperature on OXPHOS that cannot be measured using simple measures such as the traditional respiratory control ratio (RCR) or P:O ratio, which, respectively, can only approach 1 or 0 with inner-membrane failure. At 40°C there was only a slight enhancement of the Leak O2 flux and this did not significantly affect ATP production rate. Therefore, during mild hyperthermia (40°C) there is no enhancement of ATP supply by mitochondria, to accompany increasing cardiac energy demands, while between this and critical hyperthermia (43°C), mitochondria become net consumers of ATP. This consumption may contribute to cardiac failure or permanent damage during severe hyperthermia.
心力衰竭是导致体温过高死亡的常见原因，而体温过高导致心力衰竭的确切原因似乎难以捉摸。我们推测，由于线粒体内膜通透性增加和氧化磷酸化（OXPHOS）效率低下，心脏的能量供应（ATP）可能会受损。因此，我们评估了离体工作心脏和线粒体的功能。将离体工作的大鼠心脏在37至43.5°C之间进行灌注，结果显示在约40.5°C时所有功能参数都出现了转折点。采用与荧光测定法相结合的线粒体高分辨率呼吸测定法，使用包含分离线粒体的综合代谢底物补充剂，在体外确定体温过高对OXPHOS和线粒体膜电位（ΔΨ）的影响。相对于37°C和40°C，43°C时增加了基础氧通量，降低了OXPHOS氧通量和ΔΨ。对线粒体稳态ATP生成的测量显示，ATP合成能力下降，在43°C时稳态P:O比值为负。这种方法能够更有力地分析温度对OXPHOS的影响，而这是使用传统呼吸控制率（RCR）或P:O比值等简单测量方法无法实现的，因为随着内膜功能衰竭，这两个指标分别只能接近1或0。在40°C时，基础氧通量仅略有增加，且这并未显著影响ATP生成速率。因此，在轻度体温过高（40°C）期间，线粒体不会增加ATP供应以满足不断增加的心脏能量需求，而在这一温度与临界体温过高（43°C）之间，线粒体成为ATP的净消耗者。这种消耗可能导致严重体温过高期间的心力衰竭或永久性损伤。
