Hindered transport of macromolecules through a single row of cylinders: application to glomerular filtration

摘要

The slit diaphragms of renal glomerular capillaries form an ultrafiltration barrier which may be approximated as a row of cylindrical fibers of macromolecular dimensions. To describe the hindered transport of plasma proteins and othermacromolecules through this barrier, we developed an approximate hydrodynamic model for spherical, Brownian particles passing through a row of infinitely long cylinders. The selectivity of the slit diaphragm was assessed by computing concentrationprofiles for a wide range of molecular sizes for Pe≤1, where Pe is a Peclet number based on the cylinder radius. The sieving coefficient for the slit diaphragm was computed asθ{sub}SD = C{sub}B/C{sub}0, where C{sup}0 was the average concentration at aspecified distance upstream from the cylinders (corresponding to the location of the basement membrane), and C{sup}B was the concentration far downstream (corresponding to Bowman's space). The results of previous experimental sieving studies using ratscould be accounted for approximately by postulating a wide distribution of spacings between the fibers of the slit diaphragm. Comparing the results forθ{sub}SD with calculations for a model of the glomerular basement membrane suggests that the slitdiaphragm is by far the more size-restrictive part of the overall barrier.