Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada.
J Exp Biol. 2011 Jan 15;214(Pt 2):286-94. doi: 10.1242/jeb.047050.
Animals must regulate the fluxes of multiple fuels to support changing metabolic rates that result from variation in physiological circumstances. The aim of fuel selection strategies is to exploit the advantages of individual substrates while minimizing the impact of disadvantages. All exercising mammals share a general pattern of fuel selection: at the same %V(O(2,max)) they oxidize the same ratio of lipids to carbohydrates. However, highly aerobic species rely more on intramuscular fuels because energy supply from the circulation is constrained by trans-sarcolemmal transfer. Fuel selection is performed by recruiting different muscles, different fibers within the same muscles or different pathways within the same fibers. Electromyographic analyses show that shivering humans can modulate carbohydrate oxidation either through the selective recruitment of type II fibers within the same muscles or by regulating pathway recruitment within type I fibers. The selection patterns of shivering and exercise are different: at the same %V(O(2,max)), a muscle producing only heat (shivering) or significant movement (exercise) strikes a different balance between lipid and carbohydrate oxidation. Long-distance migrants provide an excellent model to characterize how to increase maximal substrate fluxes. High lipid fluxes are achieved through the coordinated upregulation of mobilization, transport and oxidation by activating enzymes, lipid-solubilizing proteins and membrane transporters. These endurance athletes support record lipolytic rates in adipocytes, use lipoprotein shuttles to accelerate transport and show increased capacity for lipid oxidation in muscle mitochondria. Some migrant birds use dietary omega-3 fatty acids as performance-enhancing agents to boost their ability to process lipids. These dietary fatty acids become incorporated in membrane phospholipids and bind to peroxisome proliferator-activated receptors to activate membrane proteins and modify gene expression.
动物必须调节多种燃料的通量，以支持由于生理环境变化而导致的代谢率变化。燃料选择策略的目的是利用个体底物的优势，同时将劣势的影响降到最低。所有运动的哺乳动物都有一个共同的燃料选择模式：在相同的 %V(O(2,max)) 下，它们氧化相同比例的脂肪和碳水化合物。然而，高需氧物种更依赖于肌肉内燃料，因为来自循环的能量供应受到跨肌膜转移的限制。燃料选择是通过募集不同的肌肉、同一肌肉内的不同纤维或同一纤维内的不同途径来实现的。肌电图分析表明，颤抖的人类可以通过选择性募集同一肌肉内的 II 型纤维或调节 I 型纤维内的途径募集来调节碳水化合物的氧化。颤抖和运动的选择模式是不同的：在相同的 %V(O(2,max)) 下，只产生热量（颤抖）或产生显著运动（运动）的肌肉在脂肪和碳水化合物氧化之间达到不同的平衡。长途迁徙者为我们提供了一个很好的模型来描述如何增加最大底物通量。通过激活酶、脂质溶解蛋白和膜转运体，协调上调动员、运输和氧化，实现高脂质通量。这些耐力运动员在脂肪细胞中支持创纪录的脂肪分解率，利用脂蛋白穿梭来加速运输，并显示出肌肉线粒体中脂质氧化能力的增加。一些候鸟使用膳食中的 omega-3 脂肪酸作为增强剂，以提高它们处理脂肪的能力。这些膳食脂肪酸被纳入膜磷脂中，并与过氧化物酶体增殖物激活受体结合，激活膜蛋白并改变基因表达。
