Graham T E, Gibala M J
Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada.
Adv Exp Med Biol. 1998;441:271-86. doi: 10.1007/978-1-4899-1928-1_25.
In comparison to cardiac tissue, relatively few data are available regarding the concentrations of tricarboxylic acid cycle intermediates (TCAI) and the potential influence of TCAI pool size on the regulation of cycle flux in mammalian skeletal muscle. However, recent human exercise studies have confirmed the fundamental observation made in electrically-stimulated rodent muscle that moderate to intense contraction results in a net accumulation of TCAI. The increase in TCAI pool size, termed "anaplerosis," appears exponentially related to work intensity, although the relative changes in the individual cycle intermediates differ markedly. While a number of mechanisms could potentially contribute to the increase in TCAI, the reaction catalyzed by alanine aminotransferase appears primarily responsible for anaplerosis at the onset of exercise in humans. The expansion of the TCAI pool has been suggested to be important for aerobic energy provision, and various theories have been proposed which link the total concentration of TCAI with the capacity for TCA cycle flux during exercise. However, despite the recent advances which have been made with regard to the magnitude and potential source of TCAI expansion in humans, our understanding of the physiological significance of anaplerosis is limited. Indeed, it remains speculative whether the increase in TCAI pool size represents an important regulatory signal or is simply a consequence of the huge increase in metabolic flux which occurs during exercise.
与心脏组织相比，关于三羧酸循环中间体（TCAI）的浓度以及TCAI库大小对哺乳动物骨骼肌中循环通量调节的潜在影响的数据相对较少。然而，最近的人体运动研究证实了在电刺激的啮齿动物肌肉中所做的基本观察结果，即中度至剧烈收缩会导致TCAI的净积累。TCAI库大小的增加，称为“回补反应”，似乎与工作强度呈指数关系，尽管各个循环中间体的相对变化差异显著。虽然有多种机制可能导致TCAI增加，但丙氨酸转氨酶催化的反应似乎是人类运动开始时回补反应的主要原因。有人认为TCAI库的扩大对有氧能量供应很重要，并且已经提出了各种理论，将TCAI的总浓度与运动期间TCA循环通量的能力联系起来。然而，尽管最近在人类TCAI扩张的程度和潜在来源方面取得了进展，但我们对回补反应的生理意义的理解仍然有限。事实上，TCAI库大小的增加是代表一个重要的调节信号，还是仅仅是运动期间发生的代谢通量大幅增加的结果，仍然存在推测性。
