Role of carnitine transporter in skeletal bioenergetics during muscle contraction

在骨骼肌中，肉碱是将长链脂肪酸转移到线粒体基质中进行随后的β氧化所必需的。基于增加肉碱的可获得性有利于骨骼肌代谢过程的概念，大量研究致力于研究补充肉碱对运动能力的影响。然而，关于肉碱对骨骼肌能量代谢的贡献以及补充肉碱是否能改善健康受试者的体能表现，一直存在争议。为了解决这些关键问题，本研究重点研究了肉碱在骨骼肌质膜上的转运机制。由于肌细胞缺乏肉碱的内源性合成，骨骼肌需要从血液中输入肉碱分子，提示肌肉对肉碱的摄取很可能是肌肉肉碱可利用性的限制因素。特定的肉碱转运蛋白OCTN2在骨骼肌中表达，并被认为是将肉碱转运到肌细胞。本研究获得了一些科学证据，表明在肌肉收缩过程中，通过OCTN2的肉碱摄取能力是通过OCTN2从胞浆向质膜转移的机制而上调的。

In skeletal muscle, carnitine is essential for the translocation of long-chain fatty-acids into the mitochondrial matrix for subsequent β-oxidation Based on the concept that increased carnitine availability is beneficial to skeletal muscle metabolic process, a large amount of research was directed towards investigating the effects of carnitine supplementation on exercise performance. However, it has been debated about contribution of carnitine for energy metabolism in skeletal muscle and whether carnitine supplementation can improve physical performance in healthy subjects. In order to resolve the key issues, the present study focused on the carnitine transport mechanism across the skeletal muscle plasma membrane. Due to lack of endogenous synthesis of carnitine in myocytes, skeletal muscles need to import this molecule from blood, suggesting that muscle carnitine uptake is most likely the limiting factor to muscle carnitine availability. The specific carnitine transporter, OCTN2, is expressed in skeletal muscles and is assumed to transport carnitine into myocytes. The present study obtained several scientific evidences that carnitine uptake capacity via the OCTN2 is up-regulated during muscle contraction through the mechanisms of OCTN2 translocation from cytosol toward plasma membrane.