Abdel-aleem S, Nada M A, Sayed-Ahmed M, Hendrickson S C, St Louis J, Walthall H P, Lowe J E
Duke University Medical Center, Department of Surgery, Pathology and Pediatrics, Durham, North Carolina 27710, USA.
J Mol Cell Cardiol. 1996 May;28(5):825-33. doi: 10.1006/jmcc.1996.0077.
The regulation of fatty acid oxidation in isolated myocytes was examined by manipulating mitochondrial acetyl-CoA levels produced by carbohydrate and fatty acid oxidation. L-carnitine had no effect on the oxidation of [U-14C]glucose, but stimulated oxidation of [1-14C]palmitate in a concentration-dependent manner. L-carnitine (5 mM) increased palmitate oxidation by 37%. The phosphodiesterase inhibitor, enoximone (250 microM), also increased palmitate oxidation by 51%. Addition of L-carnitine to enoximone resulted in a two-fold increase of palmitate oxidation. Whereas, dichloroacetate (DCA, 1 mM), which stimulates PDH activity, decreased palmitate oxidation by 25%. Furthermore, the addition of DCA to myocytes preincubated with either L-carnitine or enoximone, had no effect on the carnitine-induced stimulation of palmitate, and reduced that of enoximone by 50%. Varied concentrations of DCA decreased the oxidation of palmitate and octanoate; but increased glucose oxidation in myocytes. The rate of efflux of acetylcarnitine was highest when pyruvate was present in the medium compared to efflux rates in presence of palmitate or palmitate plus glucose. Although the addition of L-carnitine plus enoximone resulted in a two-fold increase in palmitate oxidation, acetylcarnitine efflux was minimal under these conditions. Acetylcarnitine efflux was highest when pyruvate was present in the medium. These rates were dramatically decreased when myocytes were preincubated with enoximone, despite the stimulation of palmitate oxidation by this compound. These data suggest that: (1) fatty acid oxidation is influenced by acetyl-CoA produced from pyruvate metabolism; (2) L-carnitine may be specific for mitochondrial acetyl-CoA derived from pyruvate oxidation; and (3) it is probable that acetyl-CoA from beta-oxidation of fatty acids is directly channeled into the citric acid cycle.
通过调控由碳水化合物和脂肪酸氧化产生的线粒体乙酰辅酶A水平，研究了分离的心肌细胞中脂肪酸氧化的调节机制。左旋肉碱对[U-14C]葡萄糖的氧化没有影响，但以浓度依赖的方式刺激了[1-14C]棕榈酸酯的氧化。左旋肉碱（5 mM）使棕榈酸酯氧化增加了37%。磷酸二酯酶抑制剂依诺昔酮（250 microM）也使棕榈酸酯氧化增加了51%。将左旋肉碱添加到依诺昔酮中，可使棕榈酸酯氧化增加两倍。而刺激丙酮酸脱氢酶（PDH）活性的二氯乙酸（DCA，1 mM）使棕榈酸酯氧化减少了25%。此外，将DCA添加到预先用左旋肉碱或依诺昔酮孵育的心肌细胞中，对肉碱诱导的棕榈酸酯刺激没有影响，但使依诺昔酮的刺激作用降低了50%。不同浓度的DCA降低了棕榈酸酯和辛酸的氧化；但增加了心肌细胞中葡萄糖的氧化。与存在棕榈酸酯或棕榈酸酯加葡萄糖时相比，当培养基中存在丙酮酸时，乙酰肉碱的流出率最高。尽管添加左旋肉碱加依诺昔酮使棕榈酸酯氧化增加了两倍，但在这些条件下乙酰肉碱的流出量最小。当培养基中存在丙酮酸时，乙酰肉碱的流出率最高。当心肌细胞预先用依诺昔酮孵育时，尽管该化合物刺激了棕榈酸酯氧化，但这些速率显著降低。这些数据表明：（1）脂肪酸氧化受丙酮酸代谢产生的乙酰辅酶A影响；（2）左旋肉碱可能对源自丙酮酸氧化的线粒体乙酰辅酶A具有特异性；（3）脂肪酸β氧化产生的乙酰辅酶A很可能直接进入柠檬酸循环。
