GLOMERULAR DYSFUNCTION IN NEPHROTIC HUMANS WITH MINIMAL CHANGES OR FOCAL GLOMERULOSCLEROSIS

Fractional clearances (theta) of uncharged dextrans (radii 28-60 angstrom) were used to characterize glomerular dysfunction in 34 nephrotic humans with either minimal-change nephropathy (MCN) or focal, segmental glomerulosclerosis (FSGS). A theoretical analysis of theta of dextran with a heteroporous membrane model revealed a similar alteration, more marked in FSGS than MCN. The number of restrictive pores perforating the major membrane component was reduced in parallel with the prevailing glomerular filtration rate (GFR). Parallel shuntlike pores in the remaining membrane component were more prominent, pointing to impaired size selectivity. However, the theta of large (60 angstrom) dextrans attributable to these shunts exceeded control in FSGS only, suggesting that coexistent impairment of charge selectivity contributed importantly to the proteinuria in MCN. Membrane properties returned toward normal when MCN remitted. Glomerular morphometry revealed the frequency of epithelial filtration slits to vary with the extent of membrane dysfunction. Despite offsetting hypertrophy of remnant glomeruli in FSGS, a loss of filtration surface due to sclerosis likely contributed to the more marked reductions in pore number and GFR observed in this disorder than in MCN.