Edwards A, Daniels B S, Deen W M
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge 02139, USA.
Biophys J. 1997 Jan;72(1):214-22. doi: 10.1016/S0006-3495(97)78660-0.
The filtration rates for water and a polydisperse mixture of Ficoll across films of isolated glomerular basement membrane (GBM) were measured to characterize convective transport across this part of the glomerular capillary wall. Glomeruli were isolated from rat kidneys and the cells were removed by detergent lysis, leaving a preparation containing almost pure GBM that could be consolidated into a layer at the base of a small ultrafiltration cell. A Ficoll mixture with Stokes-Einstein radii ranging from about 2.0 to 7.0 nm was labeled with fluorescein, providing a set of rigid, spherical test macromolecules with little molecular charge. Filtration experiments were performed at two physiologically relevant hydraulic pressure differences (delta P), 35 and 60 mmHg. The sieving coefficient (filtrate-to-retentate concentration ratio) for a given size of Ficoll tended to be larger at 35 than at 60 mmHg, the changes being greater for the smaller molecules. The Darcy permeability also varied inversely with pressure, averaging 1.48 +/- 0.10 nm2 at 35 mmHg and 0.82 +/- 0.07 nm2 at 60 mmHg. Both effects could be explained most simply by postulating that the intrinsic permeability properties of the GBM change in response to compression. The sieving data were consistent with linear declines in the hindrance factors for convection and diffusion with increasing pressure, and correlations were derived to relate those hindrance factors to molecular size and delta P. Comparisons with previous Ficoll sieving data for rats in vivo suggest that the GBM is less size-restrictive than the cell layers, but that its contribution to the overall size selectivity of the barrier is not negligible. Theoretical predictions of the Darcy permeability based on a model in which the GBM is a random fibrous network consisting of two populations of fibers were in excellent agreement with the present data and with ultrastructural observations in the literature.
测量了水和聚蔗糖多分散混合物通过分离的肾小球基底膜（GBM）膜的过滤速率，以表征通过肾小球毛细血管壁这一部分的对流运输。从大鼠肾脏中分离出肾小球，并用去污剂裂解去除细胞，留下几乎纯的GBM制剂，该制剂可在小型超滤池底部固结为一层。用荧光素标记了一组斯托克斯-爱因斯坦半径约为2.0至7.0nm的聚蔗糖混合物，提供了一组几乎没有分子电荷的刚性球形测试大分子。在两个生理相关的液压差（ΔP），即35和60mmHg下进行过滤实验。对于给定大小的聚蔗糖，筛分系数（滤液与截留物浓度比）在35mmHg时往往比在60mmHg时更大，小分子的变化更大。达西渗透率也与压力成反比，在35mmHg时平均为1.48±0.10nm²，在60mmHg时平均为0.82±0.07nm²。最简单的解释是，假设GBM的固有渗透特性会随着压缩而变化，就能解释这两种效应。筛分数据与对流和扩散的阻碍因子随压力增加呈线性下降一致，并推导了相关性以将这些阻碍因子与分子大小和ΔP相关联。与先前大鼠体内聚蔗糖筛分数据的比较表明，GBM的大小限制比细胞层小，但其对屏障整体大小选择性的贡献不可忽略。基于GBM是由两种纤维组成的随机纤维网络模型对达西渗透率的理论预测与当前数据以及文献中的超微结构观察结果非常吻合。
