Essig A, Caplan S R
Proc Natl Acad Sci U S A. 1981 Mar;78(3):1647-51. doi: 10.1073/pnas.78.3.1647.
The impressive linearity of force-flow relationships in epithelial active-transport systems suggests the utility of a linear, nonequilibrium-thermodynamic analysis. We here present a plausibility argument for the appropriateness of such a treatment. Conventional phenomenological equations of nonequilibrium thermodynamics constitute an incomplete description of the processes under study, because a given thermodynamic force may be induced in an infinite number of ways. In general, therefore, flows are nonlinear functions of the forces, and the Onsager reciprocal relations are obeyed only very near equilibrium. If, however, the forces of two coupled processes can be constrained to "proper" pathways, each flow is a linear function of each force, and the phenomenological cross-coefficients are equal far from equilibrium. The nature of such proper pathways is investigated in terms of a simple model of a sodium-active transport system. Where the treatment is appropriate (i.e., for sufficiently small perturbations about a steady state far from equilibrium) it permits a complete thermodynamic characterization of a system, even when only one of the two forces can be controlled experimentally while the other remains constant.
上皮主动运输系统中力 - 流关系令人印象深刻的线性表明了线性非平衡热力学分析的实用性。我们在此提出一个合理性论证，以说明这种处理方法的恰当性。传统的非平衡热力学唯象方程对所研究的过程构成了不完整的描述，因为给定的热力学力可能以无数种方式产生。因此，一般来说，流是力的非线性函数，并且昂萨格互易关系仅在非常接近平衡时才成立。然而，如果两个耦合过程的力可以被限制在“恰当”的路径上，那么每个流都是每个力的线性函数，并且唯象交叉系数在远离平衡时相等。通过一个钠主动运输系统的简单模型来研究这种恰当路径的性质。在这种处理方法适用的地方（即对于远离平衡的稳态附近足够小的扰动），即使在实验中只能控制两个力中的一个而另一个保持不变，它也能对系统进行完整的热力学表征。
