Booth J W, Lumsden C J
Membrane Biology Group, Department of Medicine, University of Toronto, Canada.
Biophys J. 1993 Jun;64(6):1727-34. doi: 10.1016/S0006-3495(93)81544-3.
The extracellular space of the glomerular capillary wall is occupied by a complex meshwork of fibrous molecules. Little is understood about how the size, shape, and charge recognition properties of glomerular ultrafiltration arise from this space-filling fiber matrix. We studied the problem of size recognition by visualizing the void volume accessible to hard spheres in computer-generated three-dimensional homogeneous random fiber matrices. The spatial organization of the void volume followed a complex "blob-and-throat" pattern in which circumscribed cavities of free space within the matrix ("blobs") were joined to adjacent cavities by narrower throats of void space. For sufficiently small solutes, chains of blobs and throats traversed the matrix, providing pathways for trans-matrix permeation. The matrices showed threshold or gating properties with respect to permeation: solutes whose radius exceeded a critical value, at which a throat on the last connected trans-matrix pathway pinched off, could not cross, whereas smaller solutes had nonzero permeability. The thresholds may give the glomerular fiber matrix porelike response properties and explain why pore models have been such a useful means of treating permselectivity.
肾小球毛细血管壁的细胞外空间被纤维分子构成的复杂网络占据。对于肾小球超滤的大小、形状和电荷识别特性如何源自这种充满空间的纤维基质，人们了解甚少。我们通过在计算机生成的三维均匀随机纤维基质中可视化硬球可及的空隙体积，研究了大小识别问题。空隙体积的空间组织遵循复杂的“液滴与通道”模式，其中基质内自由空间的限定腔室（“液滴”）通过更窄的空隙通道与相邻腔室相连。对于足够小的溶质，液滴和通道链贯穿基质，为跨基质渗透提供途径。这些基质在渗透方面表现出阈值或门控特性：半径超过临界值的溶质无法通过，此时最后连接的跨基质途径上的通道会收缩关闭，而较小的溶质具有非零渗透率。这些阈值可能赋予肾小球纤维基质类似孔隙的响应特性，并解释了为何孔隙模型一直是处理通透选择性的有用方法。
