Hochachka P W, McClelland G B
Department of Zoology, University of British Columbia, Vancouver, Canada.
J Exp Biol. 1997 Jan;200(Pt 2):381-6. doi: 10.1242/jeb.200.2.381.
The term homeostasis traditionally refers to the maintenance of a relatively constant internal milieu in the face of changing environmental conditions or changing physiological function. Tissues such as skeletal and cardiac muscles must sustain very large-scale changes in ATP turnover rate during equally large changes in work. In many skeletal muscles, these changes can exceed 100-fold. In unique biological circumstances (for example, during periods of oxygen limitation, vasoconstriction and hypometabolism), tissues such as skeletal muscles may be obliged to sustain further decreases in ATP turnover rates and operate for varying periods at seriously suppressed ATP turnover rates. Examination of a number of cellular and whole-organism systems identifies ATP concentration as a key parameter of the interior milieu that is nearly universally "homeostatic'; it is common to observe no change in ATP concentration even while the change in its turnover rate can increase or decrease by two orders of magnitude. A large number of other intermediates of cellular metabolism are also regulated within narrow concentration ranges, but none seemingly as precisely as is [ATP]. In fact, the only other metabolite in aerobic energy metabolism that is seemingly as "homeostatic' is oxygen-at least in working muscles. The central regulatory question is how such homeostasis of key intermediates in pathways of energy supply and energy demand is achieved.
传统上，内稳态一词指的是在环境条件变化或生理功能改变时，维持相对恒定的内部环境。诸如骨骼肌和心肌等组织在工作量发生同样大的变化时，必须承受ATP周转率的大规模变化。在许多骨骼肌中，这些变化可能超过100倍。在独特的生物学情况下（例如，在氧气受限、血管收缩和代谢减退期间），诸如骨骼肌等组织可能不得不承受ATP周转率的进一步降低，并在严重抑制的ATP周转率下运行不同的时间段。对许多细胞和整个生物体系统的研究表明，ATP浓度是内部环境的一个关键参数，几乎普遍处于“稳态”；即使其周转率的变化可以增加或减少两个数量级，通常也观察到ATP浓度没有变化。细胞代谢的大量其他中间产物也在狭窄的浓度范围内受到调节，但似乎没有一种像[ATP]那样精确。事实上，有氧能量代谢中唯一似乎同样“稳态”的其他代谢物是氧气——至少在工作的肌肉中是这样。核心调控问题是，能量供应和能量需求途径中的关键中间产物是如何实现这种稳态的。
