Deen W M, Satvat B, Jamieson J M
Am J Physiol. 1980 Feb;238(2):F126-39. doi: 10.1152/ajprenal.1980.238.2.F126.
Previous experimental studies have revealed that for a given molecular size, the glomerular capillary wall restricts the passage of polyanions more than that of neutral macromolecules, and restricts transport of the latter more than that of polycations. We have developed a theoretical model of this charge-selectivity based on the following principal assumptions: a) all ions (tracer macromolecule and univalent cations and anions) obey a modified Nernst-Planck flux expression, including terms for convection and size-selective retardation; b) the capillary wall has a homogeneous distribution of fixed negative charges; and c) Donnan equilibria exist at the surfaces of this "membrane." To allow specific application of the model we measured electrophoretic mobilities of narrow fractions of dextran sulfate (DS) and diethylaminoethyl dextran (DEAE), and used these to estimate effective molecular charge as a function of molecular size. Based on these measurements and fractional clearance data for DS and DEAE reported previously for the normal Munich-Wistar rat, the capillary wall has an apparent fixed charge concentration of 120--170 meq/liter. The effects of this membrane charge on the filtration of water and on the transcapillary electrical potential difference are also discussed.
以往的实验研究表明，对于给定的分子大小，肾小球毛细血管壁对多阴离子的通透限制比对中性大分子的限制更大，对后者的转运限制比对多阳离子的限制更大。我们基于以下主要假设建立了这种电荷选择性的理论模型：a）所有离子（示踪大分子以及单价阳离子和阴离子）均遵循修正的能斯特 - 普朗克通量表达式，包括对流和大小选择性阻滞项；b）毛细血管壁具有固定负电荷的均匀分布；c）在这个“膜”的表面存在唐南平衡。为了使该模型能够具体应用，我们测量了硫酸葡聚糖（DS）和二乙氨基乙基葡聚糖（DEAE）窄级分的电泳迁移率，并利用这些数据来估计有效分子电荷随分子大小的变化。基于这些测量结果以及先前报道的正常慕尼黑 - 威斯塔大鼠的DS和DEAE的分数清除率数据，毛细血管壁的表观固定电荷浓度为120 - 170 毫当量/升。还讨论了这种膜电荷对水过滤和跨毛细血管电位差的影响。
