Schrauwen-Hinderling Vera B, Hesselink Matthijs K C, Schrauwen Patrick, Kooi Marianne Eline
Department of Radiology, University Hospital Maastricht, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands.
Obesity (Silver Spring). 2006 Mar;14(3):357-67. doi: 10.1038/oby.2006.47.
Fat can be stored not only in adipose tissue but also in other tissues such as skeletal muscle. Fat droplets accumulated in skeletal muscle [intramyocellular lipids (IMCLs)] can be quantified by different methods, all with advantages and drawbacks. Here, we briefly review IMCL quantification methods that use biopsy specimens (biochemical quantification, electron microscopy, and histochemistry) and non-invasive alternatives (magnetic resonance spectroscopy, magnetic resonance imaging, and computed tomography). Regarding the physiological role, it has been suggested that IMCL serves as an intracellular source of energy during exercise. Indeed, IMCL content decreases during prolonged submaximal exercise, and analogously to glycogen, IMCL content is increased in the trained state. In addition, IMCL content is highest in oxidative, type 1 muscle fibers. Together, this, indeed, suggests that the IMCL content is increased in the trained state to optimally match fat oxidative capacity and that it serves as readily available fuel. However, elevation of plasma fatty acid levels or dietary fat content also increases IMCL content, suggesting that skeletal muscle also stores fat simply if the availability of fatty acids is high. Under these conditions, the uptake into skeletal muscle may have negative consequences on insulin sensitivity. Besides the evaluation of the various methods to quantify IMCLs, this perspective describes IMCLs as valuable energy stores during prolonged exercise, which, however, in the absence of regular physical activity and with overconsumption of fat, can have detrimental effects on muscular insulin sensitivity.
脂肪不仅可以储存在脂肪组织中，还可以储存在其他组织中，如骨骼肌。骨骼肌中积累的脂肪滴[肌内脂质（IMCLs）]可以通过不同的方法进行量化，所有这些方法都各有利弊。在这里，我们简要回顾一下使用活检标本的IMCL量化方法（生化量化、电子显微镜和组织化学）以及非侵入性替代方法（磁共振波谱、磁共振成像和计算机断层扫描）。关于其生理作用，有人提出IMCL在运动过程中作为细胞内的能量来源。事实上，在长时间的次最大运动过程中，IMCL含量会降低，并且与糖原类似，在训练状态下IMCL含量会增加。此外，IMCL含量在氧化型1型肌纤维中最高。总之，这确实表明在训练状态下IMCL含量增加，以最佳地匹配脂肪氧化能力，并且它作为随时可用的燃料。然而，血浆脂肪酸水平或饮食脂肪含量的升高也会增加IMCL含量，这表明如果脂肪酸的可利用性高，骨骼肌也会简单地储存脂肪。在这些情况下，脂肪酸进入骨骼肌可能会对胰岛素敏感性产生负面影响。除了评估量化IMCLs的各种方法外，本文还描述了IMCLs在长时间运动期间作为有价值的能量储存，但在缺乏规律体育活动和脂肪摄入过量的情况下，可能会对肌肉胰岛素敏感性产生有害影响。
