Weinstein A M
J Gen Physiol. 1987 Mar;89(3):501-18. doi: 10.1085/jgp.89.3.501.
An electrolyte model of an epithelium (a cell and a tight junction in parallel, both in series with a lateral interspace basement membrane) is analyzed using the formalism of nonequilibrium thermodynamics. It is shown that if the parallel structures are heteroporous (i.e., reflection coefficients for two ion species differ between the components), then a cross-term will appear in the overall transport equations of the epithelium. Formally, this cross-term represents an ion-ion interaction. With respect to the rat proximal tubule, data indicating epithelial ionic reflection coefficients less than unity, together with the assumption of no transcellular solvent drag, imply the presence of convective paracellular solute flux. This means that a model applicable to a heteroporous structure must be used to represent the tubule, and, in particular, the cross-terms for ion-ion interaction must also be evaluated in permeability determinations. A series of calculations is presented that permits the estimation of the Na-Cl interaction for rat proximal tubule from available experimental data. One consequence of tubule heteroporosity is that an electrical potential may be substantially less effective than an equivalent concentration gradient in driving reabsorptive ion fluxes.
利用非平衡热力学形式分析上皮组织（一个细胞和紧密连接并联，二者均与外侧间隙基底膜串联）的电解质模型。结果表明，如果并联结构是异质多孔的（即两种离子的反射系数在各组分之间不同），那么上皮组织的整体传输方程中将会出现一个交叉项。从形式上看，这个交叉项代表离子-离子相互作用。对于大鼠近端小管而言，表明上皮离子反射系数小于1的数据，再加上不存在跨细胞溶剂拖曳的假设，意味着存在对流性细胞旁溶质通量。这意味着必须使用适用于异质多孔结构的模型来表示小管，特别是在渗透率测定中也必须评估离子-离子相互作用的交叉项。给出了一系列计算，可根据现有实验数据估算大鼠近端小管中钠-氯的相互作用。小管异质性的一个结果是，在驱动重吸收性离子通量方面，电势的有效性可能远低于等效浓度梯度。
