Stephens Francis B, Constantin-Teodosiu Dumitru, Greenhaff Paul L
Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK.
J Physiol. 2007 Jun 1;581(Pt 2):431-44. doi: 10.1113/jphysiol.2006.125799. Epub 2007 Mar 1.
In skeletal muscle, carnitine plays an essential role in the translocation of long-chain fatty-acids into the mitochondrial matrix for subsequent beta-oxidation, and in the regulation of the mitochondrial acetyl-CoA/CoASH ratio. Interest in these vital metabolic roles of carnitine in skeletal muscle appears to have waned over the past 25 years. However, recent research has shed new light on the importance of carnitine as a regulator of muscle fuel selection. It has been established that muscle free carnitine availability may be limiting to fat oxidation during high intensity submaximal exercise. Furthermore, increasing muscle total carnitine content in resting healthy humans (via insulin-mediated stimulation of muscle carnitine transport) reduces muscle glycolysis, increases glycogen storage and is accompanied by an apparent increase in fat oxidation. By increasing muscle pyruvate dehydrogenase complex (PDC) activity and acetylcarnitine content at rest, it has also been established that PDC flux and acetyl group availability limits aerobic ATP re-synthesis at the onset of exercise (the acetyl group deficit). Thus, carnitine plays a vital role in the regulation of muscle fuel metabolism. The demonstration that its availability can be readily manipulated in humans, and impacts on physiological function, will result in renewed business and scientific interest in this compound.
在骨骼肌中，肉碱在长链脂肪酸转运至线粒体基质以进行后续的β氧化过程中发挥着重要作用，同时也参与线粒体乙酰辅酶A/辅酶A比率的调节。在过去25年里，人们对肉碱在骨骼肌中的这些重要代谢作用的关注似乎有所减少。然而，最近的研究为肉碱作为肌肉燃料选择调节剂的重要性提供了新的线索。已经证实，在高强度次最大运动期间，肌肉中游离肉碱的可利用性可能会限制脂肪氧化。此外，在静息健康人群中增加肌肉总肉碱含量（通过胰岛素介导刺激肌肉肉碱转运）可减少肌肉糖酵解、增加糖原储存，并伴随着脂肪氧化的明显增加。通过增加静息状态下肌肉丙酮酸脱氢酶复合体（PDC）的活性和乙酰肉碱含量，还证实了PDC通量和乙酰基可利用性在运动开始时限制有氧ATP再合成（乙酰基缺乏）。因此，肉碱在肌肉燃料代谢调节中起着至关重要的作用。其可利用性在人体中能够轻易被调控且对生理功能有影响，这一发现将引发对该化合物新的商业和科学兴趣。
