Patlak C S, Rapoport S I
J Gen Physiol. 1971 Feb;57(2):113-24. doi: 10.1085/jgp.57.2.113.
When osmotic pressure across an artificial membrane, produced by a permeable electrically neutral solute on one side of it, is balanced by an external pressure difference so that there is no net volume flow across the membrane, it has been found that there will be a net flux of a second electrically neutral tracer solute, present at equal concentrations on either side of the membrane, in the direction that the "osmotic" solute diffuses. This has been ascribed to solute-solute interaction or drag between the tracer and the osmotic solutes. An alternative model, presented here, considers the membrane to have pores of different sizes. Under general assumptions, this "heteroporous" model will account for both the direction of net tracer flux and the observed linear dependence of unidirectional tracer fluxes on the concentration of the osmotic solute. The expressions for the fluxes of solutes and solvent are mathematically identical under the two models. An inequality is derived which must be valid if the solute interaction model and/or the heteroporous model can account for the data. If the inequality does not hold, then the heteroporous model alone cannot explain the data. It was found that the inequality holds for most published observations except when dextran is the osmotic solute.
当人工膜一侧由可渗透的电中性溶质产生的渗透压被外部压力差平衡，从而没有净体积流穿过该膜时，已发现膜两侧浓度相等的第二种电中性示踪溶质会沿“渗透”溶质扩散的方向产生净通量。这归因于示踪剂与渗透溶质之间的溶质 - 溶质相互作用或曳引。这里提出的另一种模型认为膜具有不同大小的孔。在一般假设下，这种“异孔”模型将既能解释净示踪剂通量的方向，又能解释观察到的单向示踪剂通量对渗透溶质浓度的线性依赖性。在这两种模型下，溶质和溶剂通量的表达式在数学上是相同的。推导出一个不等式，如果溶质相互作用模型和/或异孔模型能够解释数据，那么这个不等式必然成立。如果该不等式不成立，那么仅异孔模型无法解释数据。结果发现，除了以右旋糖酐作为渗透溶质的情况外，该不等式对大多数已发表的观测结果都成立。
