Sumegi B, Podanyi B, Forgo P, Kover K E
University Medical School, Department of Biochemistry, Pecs, Hungary.
Biochem J. 1995 Nov 15;312 ( Pt 1)(Pt 1):75-81. doi: 10.1042/bj3120075.
The oxidation of [3-13C]pyruvate and [3-13C]propionate was studied in vivo in infused rats. The infused [3-13C]pyruvate was quickly converted to [3-13C]lactate in the blood, and the [3-13C]lactate formed was well metabolized in both normoxic and ischaemic hearts. Large differences (200-600%) in the 13C enrichment of alanine (C-3) and acetyl-CoA (C-2) compared with lactate (C-3) were found in both normoxic and ischaemic hearts, suggesting that the extracellular [3-13C]lactate preferentially entered a region of the cytoplasm which specifically transfers the labelled pyruvate (formed from [3-13C]lactate) to the mitochondria. The highly enriched mitochondrial pyruvate gave high enrichment in alanine and acetyl-CoA, which was detected by 1H- and 13C-NMR spectroscopy. Ischaemia increased 13C incorporation into the main cytoplasmic lactate pool and decreased 13C incorporation into citric acid cycle intermediates, mainly decreasing the pyruvate anaplerosis. Isoprenaline-induced ischaemia of the heart caused only a slight decrease in pyruvate oxidation. In contrast to the decreased anaplerosis of pyruvate, the anaplerosis of propionate (and propionyl-carnitine) increased significantly in ischaemic hearts, which may contribute to the protective effect of propionyl-carnitine seen in ischaemia. In addition, we found that [3-13C]propionate preferentially labelled aspartate C-3 in rat heart, suggesting incomplete randomization of label in the succinyl-CoA-malate span of the citric acid cycle. These data show that proton observed 13C edited spectroscopic methods, i.e. heteronuclear spin-echo and the one-dimensional heteronuclear multiple quantum coherence sequence, can be successfully used to study heart metabolism in vivo.
在输注大鼠体内研究了[3-13C]丙酮酸和[3-13C]丙酸的氧化。输注的[3-13C]丙酮酸在血液中迅速转化为[3-13C]乳酸，并且生成的[3-13C]乳酸在常氧和缺血心脏中均得到良好代谢。在常氧和缺血心脏中均发现，与乳酸（C-3）相比，丙氨酸（C-3）和乙酰辅酶A（C-2）的13C丰度存在很大差异（200-600%），这表明细胞外[3-13C]乳酸优先进入细胞质的一个区域，该区域特异性地将标记的丙酮酸（由[3-13C]乳酸形成）转运至线粒体。高度富集的线粒体丙酮酸使丙氨酸和乙酰辅酶A具有高丰度，这通过1H和13C核磁共振波谱检测到。缺血增加了13C掺入主要的细胞质乳酸池，减少了13C掺入柠檬酸循环中间体，主要是减少了丙酮酸的回补反应。异丙肾上腺素诱导的心脏缺血仅使丙酮酸氧化略有降低。与丙酮酸回补反应减少相反，丙酸（和丙酰肉碱）的回补反应在缺血心脏中显著增加，这可能有助于解释丙酰肉碱在缺血中的保护作用。此外，我们发现[3-13C]丙酸优先标记大鼠心脏中的天冬氨酸C-3，这表明在柠檬酸循环的琥珀酰辅酶A-苹果酸段中标记没有完全随机化。这些数据表明，质子观测的13C编辑光谱方法，即异核自旋回波和一维异核多量子相干序列，可成功用于体内研究心脏代谢。
