Removal of sulfated (heparan sulfate) or nonsulfated (hyaluronic acid) glycosaminoglycans results in increased permeability of the glomerular basement membrane to ¹²⁵I-bovine serum albumin

The role of glycosaminoglycans (GAGs) in establishing the permeability properties of the glomerular basement membrane to ¹²⁵I-bovine serum albumin was studied in glomeruli subjected to digestion with specific GAG-degrading enzymes. Kidneys were perfused and incubated for 30 minutes with heparinase (which digests most GAGs, including heparan sulfate), Streptomyces hyalouronidase (which digests only hyaluronic acid), or chondroitinase-ABC (which digests chondroitin 4- and 6-sulfates, hyaluronic acid, and dermatan sulfate but not heparan sulfate). They were subsequently perfused with ¹²⁵I-bovine serum albumin in Krebs-Ringers bicarbonate containing 7.5 per cent ovalbumin, pH 7.4, and fixed in situ. Control kidneys were perfused and incubated with their specific buffers alone. Light and electron microscopic autoradiograms were prepared from both enzyme-treated and control groups of glomeruli. The number of autoradiographic grains over the capillary lumina and urinary spaces was counted in light microscopic autoradiograms, and the grain density (total grains per total area) was determined for these compartments. A ratio of the grain density of the capillary lumina relative to the urinary spaces (mean grain density ratio) was then computed. Alterations in the leakage of ¹²⁵I-bovine serum albumin across the glomerular basement membrane after the removal of specific species of GAGs was determined by comparing the mean grain density ratios of enzyme-treated glomeruli relative to their buffer controls. The mean grain density ratios for glomeruli from heparinase-, Streptomyces hyaluronidase-, and chondroitinase-ABC-treated kidneys (1.11 ± 0.19, 2.34 ± 0.95, and 2.78 ± 0.36, respectively) were significantly different from their buffer controls (5.21 ± 1.44, 4.36 ± 1.28, and 5.98 ± 0.97, respectively). The results demonstrate that removal of (1) heparan sulfate along with the other GAGs (hyaluronic acid and chondroitin sulfates) or (2) hyaluronic acid alone or in combination with chondroitin sulfates all lead to significant increases in ¹²⁵I-bovine serum albumin leakage relative to their buffer controls. It is concluded that both heparan sulfate and hyaluronic acid, and most likely, chondroitin sulfates play a role in determining the permeability characteristics of the glomerular basement membrane to albumin, suggesting that these GAGs are involved in establishing the charge-selective and/or size-selective properties of the glomerular basement membrane.