The heart requires continuous ATP availability that is generated in the mitochondria. Although studies using the cell culture and perfused organ models have been carried out to investigate the biochemistry in the mitochondria in response to a change in substrate supply, mitochondrial bioenergetics of heart under normal feed or fasting conditions has not been studied at the tissue level with a sub-millimeter spatial resolution either in vivo or ex vivo. Oxidation of many food-derived metabolites to generate ATP in the mitochondria is realized through the NADH/NAD+ couple acting as a central electron carrier. We employed the Chance redox scanner — the low-temperature fluorescence scanner to image the three-dimensional (3D) spatial distribution of the mitochondrial redox states in heart tissues of rats under normal feeding or an overnight starvation for 14.5 h. Multiple consecutive sections of each heart were imaged to map three redox indices, i.e., NADH, oxidized flavoproteins (Fp, including flavin adenine dinucleotide (FAD)) and the redox ratio NADH/Fp. The imaging results revealed the micro-heterogeneity and the spatial distribution of these redox indices. The quantitative analysis showed that in the fasted hearts the standard deviation of both NADH and Fp, i.e., SD_NADH and SD_Fp, significantly decreased with a p value of 0.032 and 0.045, respectively, indicating that the hearts become relatively more homogeneous after fasting. The fasted hearts contained 28.6% less NADH (p = 0.038). No significant change in Fp was found (p = 0.4). The NADH/Fp ratio decreased with a marginal p value (0.076). The decreased NADH in the fasted hearts is consistent with the cardiac cells' reliance of fatty acids consumption for energy metabolism when glucose becomes scarce. The experimental observation of NADH decrease induced by dietary restriction in the heart at tissue level has not been reported to our best knowledge. The Chance redox scanner demonstrated the feasibility of 3D imaging of the mitochondrial redox state in the heart and provides a useful tool to study heart metabolism and function under normal, dietary-change and pathological conditions at tissue level.

中文翻译：

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正常和禁食条件下大鼠心脏线粒体氧化还原状态的 3D 成像


心脏需要线粒体中产生的持续可用的 ATP。尽管已经进行了使用细胞培养和灌注器官模型的研究来研究线粒体中的生物化学响应底物供应的变化，但正常进食或禁食条件下心脏的线粒体生物能学尚未在组织水平上进行研究体内或离体亚毫米空间分辨率。许多食物来源的代谢物在线粒体中氧化生成 ATP 是通过 NADH/NAD+ 对作为中心电子载体来实现的。我们使用 Chance 氧化还原扫描仪（低温荧光扫描仪）对正常喂养或过夜饥饿 14.5 小时的大鼠心脏组织中线粒体氧化还原状态的三维 (3D) 空间分布进行成像。对每个心脏的多个连续切片进行成像以绘制三个氧化还原指数，即NADH、氧化黄素蛋白（Fp，包括黄素腺嘌呤二核苷酸（FAD））和氧化还原比NADH/Fp。成像结果揭示了这些氧化还原指数的微观异质性和空间分布。定量分析显示，在禁食的心脏中，NADH和Fp的标准差，即SD_NADH和SD_Fp均显着下降，p值分别为0.032和0.045，表明禁食后心脏变得相对更加均匀。禁食的心脏中 NADH 含量减少了 28.6% (p = 0.038)。 Fp 没有发现显着变化 (p = 0.4)。 NADH/Fp 比率随边际 p 值 (0.076) 下降。禁食心脏中 NADH 的减少与当葡萄糖变得稀缺时心肌细胞依赖脂肪酸消耗进行能量代谢是一致的。 据我们所知，尚未有关于心脏组织水平上饮食限制引起的 NADH 减少的实验观察报道。 Chance 氧化还原扫描仪证明了心脏线粒体氧化还原状态 3D 成像的可行性，并为在组织水平上研究正常、饮食变化和病理条件下的心脏代谢和功能提供了有用的工具。