Weiss R G, Chacko V P, Gerstenblith G
Department of Medicine, Johns Hopkins Hospital, Baltimore, Md. 21205.
J Mol Cell Cardiol. 1989 May;21(5):469-78. doi: 10.1016/0022-2828(89)90787-6.
Although the myocardium is capable of utilizing both glucose and fatty acid substrates, glucose metabolism is inhibited in the presence of fatty acid during normal perfusion conditions. Fatty acid regulation of glucose utilization in intact beating rat hearts was studied with 13C-enriched substrates and 13C and 31P NMR spectroscopy at 8.5 T. During [1-13C]glucose and insulin perfusion, the 13C appeared in alanine, lactate and the glutamate isotopomers, indicating glycolytic flux through pyruvate and glucose-supported tricarboxylic acid (TCA) cycle oxidation, respectively. Following the addition of hexanoic acid, 1 mM, [1-13C]glucose metabolism proceeded through the hexokinase and phosphofructokinase reactions, as evidenced by continued production of [3-13C]alanine and [3-13C]lactate, but was completely inhibited at the pyruvate dehydrogenase (PDH) reaction as evidenced by a lack of appearance of the 13C label in the glutamate isotopomers. This inhibition of PDH was associated with increased PCr/ATP levels and was readily reversed by removal of hexanoic acid. Addition of dichloroacetate, 5 mM, which increases the active form of PDH, to fatty acid and glucose containing perfusate reinstituted carbon flux through the PDH reaction, indicating that the mechanism of fatty acid cessation of PDH flux is by reversible inactivation of the PDH enzyme complex. Thus the point of inhibition and mechanism of action of fatty acid modulation of glucose metabolism can be continuously and non-destructively studied in the intact beating heart with 13C and 31P NMR and is primarily attributable, in this model, to reversible PDH enzyme inactivation.
虽然心肌能够利用葡萄糖和脂肪酸两种底物，但在正常灌注条件下，脂肪酸存在时葡萄糖代谢会受到抑制。利用富含13C的底物以及在8.5T场强下的13C和31P核磁共振波谱技术，研究了完整跳动大鼠心脏中脂肪酸对葡萄糖利用的调节作用。在[1-13C]葡萄糖和胰岛素灌注期间，13C出现在丙氨酸、乳酸和谷氨酸异构体中，分别表明通过丙酮酸的糖酵解通量以及葡萄糖支持的三羧酸（TCA）循环氧化。加入1mM己酸后，[1-13C]葡萄糖代谢通过己糖激酶和磷酸果糖激酶反应进行，这可通过[3-13C]丙氨酸和[3-13C]乳酸的持续产生得到证明，但在丙酮酸脱氢酶（PDH）反应中完全受到抑制，这可通过谷氨酸异构体中缺乏13C标记得到证明。PDH的这种抑制与PCr/ATP水平升高相关，并且通过去除己酸可轻易逆转。向含有脂肪酸和葡萄糖的灌注液中加入5mM二氯乙酸，可增加PDH的活性形式，重新建立通过PDH反应的碳通量，表明脂肪酸使PDH通量停止的机制是通过PDH酶复合物的可逆失活。因此，利用13C和31P核磁共振技术，可以在完整跳动的心脏中连续且无损地研究脂肪酸调节葡萄糖代谢的抑制点和作用机制，在该模型中，这主要归因于PDH酶的可逆失活。
