Limited transfer of cytosolic NADH into mitochondria at high cardiac workload
Limited transfer of cytosolic NADH into mitochondria at high cardiac workload
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DOI：
10.1152/ajpheart.01113.2003
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发表时间：
2004-06-01
影响因子：
4.8
通讯作者：
Lewandowski, ED
中科院分区：
文献类型：
--
作者：
O'Donnell, JM;Kudej, RK;Lewandowski, ED
糖酵解在高心脏工作负荷下补充能量合成，不仅产生ATP，而且产生胞质NADH和丙酮酸盐用于氧化ATP合成。尽管有足够的Po-2，但推测并非所有的胞质NADH都被线粒体氧化，导致乳酸产生。在这项研究中，我们阐明了有限的胞质NADH氧化和增加乳酸生产在高负荷，尽管足够的心肌血流量和氧合的机制。糖酵解的还原当量通过线粒体α-酮戊二酸（α-KG）交换为胞质苹果酸进入线粒体。通过比较α-KG氧化产物（琥珀酸盐）和α-KG从线粒体流出产物（谷氨酸盐）之间的C-13富集，在基线和高工作负荷下监测这种交换。在全身麻醉下，对14只狗进行左胸廓切开术，并将[2-C-13]醋酸盐注入左前降支动脉40分钟。基线（n = 7）和多巴酚丁胺时的心率-血压乘积分别为9，035 +/-1，972和21，659 +/-5，266 mmHg.beats.min-1（n = 7）。基线时C-13对琥珀酸的富集为57 +/- 10%，在工作量增加时为45 +/- 13%（不显着），证实了[2-C-13]醋酸盐的氧化。然而，细胞溶质谷氨酸富集，细胞溶质NADH转移到线粒体的标志物，在高心脏工作负荷（11 +/- 1%）与基线（50 +/-14%，P < 0.05）相比显着减少。在高功下C-13从α-KG到胞质谷氨酸的这种减少的交换表明胞质还原当量到线粒体中的穿梭减少。心肌组织乳酸增加78%，抵消了这种减少的细胞质NADH氧化。这些发现阐明了在没有心肌缺血的情况下糖酵解超过葡萄糖氧化的一种机制。
Glycolysis supplements energy synthesis at high cardiac workloads, producing not only ATP but also cytosolic NADH and pyruvate for oxidative ATP synthesis. Despite adequate Po-2, speculation exists that not all cytosolic NADH is oxidized by the mitochondria, leading to lactate production. In this study, we elucidate the mechanism for limited cytosolic NADH oxidation and increased lactate production at high workload despite adequate myocardial blood flow and oxygenation. Reducing equivalents from glycolysis enter mitochondria via exchange of mitochondrial alpha-ketoglutarate (alpha-KG) for cytosolic malate. This exchange was monitored at baseline and at high workloads by comparing C-13 enrichment between the products of alpha-KG oxidation (succinate) and alpha-KG efflux from mitochondria (glutamate). Under general anesthesia, a left thoracotomy was performed on 14 dogs and [2-C-13]acetate was infused into the left anterior descending artery for 40 min. The rate-pressure product was 9,035 +/- 1,972 and 21,659 +/- 5,266 mmHg.beats.min-1 (n = 7) at baseline (n = 7) and with dobutamine, respectively. C-13 enrichment of succinate was 57 +/- 10% at baseline and 45 +/- 13% at elevated workload (not significant), confirming oxidation of [2-C-13]acetate. However, cytosolic glutamate enrichment, a marker of cytosolic NADH transfer to mitochondria, was dramatically reduced at high cardiac workload (11 +/- 1%) vs. baseline (50 +/- 14%, P < 0.05). This reduced exchange of C-13 from alpha-KG to cytosolic glutamate at high work indicates reduced shuttling of cytosolic reducing equivalents into the mitochondria. Myocardial tissue lactate increased 78%, countering this reduced oxidation of cytosolic NADH. The findings elucidate a contributing mechanism to glycolysis outpacing glucose oxidation in the absence of myocardial ischemia.