Elmoazzen Heidi Y, Elliott Janet A W, McGann Locksley E
Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Canada.
Biophys J. 2009 Apr 8;96(7):2559-71. doi: 10.1016/j.bpj.2008.12.3929.
The fundamental physical mechanisms of water and solute transport across cell membranes have long been studied in the field of cell membrane biophysics. Cryobiology is a discipline that requires an understanding of osmotic transport across cell membranes under nondilute solution conditions, yet many of the currently-used transport formalisms make limiting dilute solution assumptions. While dilute solution assumptions are often appropriate under physiological conditions, they are rarely appropriate in cryobiology. The first objective of this article is to review commonly-used transport equations, and the explicit and implicit assumptions made when using the two-parameter and the Kedem-Katchalsky formalisms. The second objective of this article is to describe a set of transport equations that do not make the previous dilute solution or near-equilibrium assumptions. Specifically, a new nondilute solute transport equation is presented. Such nondilute equations are applicable to many fields including cryobiology where dilute solution conditions are not often met. An illustrative example is provided. Utilizing suitable transport equations that fit for two permeability coefficients, fits were as good as with the previous three-parameter model (which includes the reflection coefficient, sigma). There is less unexpected concentration dependence with the nondilute transport equations, suggesting that some of the unexpected concentration dependence of permeability is due to the use of inappropriate transport equations.
细胞膜生物物理学领域长期以来一直在研究水和溶质跨细胞膜运输的基本物理机制。低温生物学是一门需要了解在非稀释溶液条件下溶质跨细胞膜渗透运输的学科，然而，目前许多常用的运输形式都采用了极限稀释溶液假设。虽然稀释溶液假设在生理条件下通常是合适的，但在低温生物学中却很少适用。本文的第一个目标是回顾常用的运输方程，以及使用双参数形式和凯德姆 - 卡察尔斯基形式时所做的显式和隐式假设。本文的第二个目标是描述一组不做先前稀释溶液或近平衡假设的运输方程。具体而言，提出了一个新的非稀释溶质运输方程。这种非稀释方程适用于包括低温生物学在内的许多领域，在这些领域中通常不满足稀释溶液条件。文中给出了一个示例。利用适合两个渗透系数的合适运输方程，拟合效果与之前的三参数模型（包括反射系数σ）一样好。非稀释运输方程中浓度依赖性的意外情况较少，这表明渗透率的一些意外浓度依赖性是由于使用了不合适的运输方程。
