Selectivity of the glomerular filtration barrier in healthy and nephrotic humans.

The glomerular capillary wall imposes a remarkably efficient barrier to the passage of proteins the size of albumin and larger. The development of heavy proteinuria signifies impairment in the function of this barrier. Because endogenous proteins of graded size are heterogeneous with respect to their molecular charge, and undergo extensive tubular reabsorption, they are not useful for quantifying the extent of barrier dysfunction. An alternative approach is to determine the fractional clearance of uncharged and nonreabsorbable polymers of graded size. When combined with a hydrodynamic theory of solute transport through a heteroporous membrane, the intrinsic properties of healthy and diseased glomerular capillary walls can be inferred. This approach reveals the nephrotic range proteinuria that attends membranous nephropathy to be associated with impairment of both the size- and charge-selective properties of glomerular capillary walls.