SELECTIVITY OF THE GLOMERULAR-FILTRATION BARRIER IN HEALTHY AND NEPHROTIC HUMANS

The glomerular capillary wall imposes a remarkably efficient barrier t o the passage of proteins the size of albumin and larger. The developm ent 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 barrie r dysfunction. An alternative approach is to determine the fractional clearance of uncharged and nonreabsorbable polymers of graded size. Wh en combined with a hydrodynamic theory of solute transport through a h eteroporous 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 prop erties of glomerular capillary walls.