Albumin interaction with the glomerular capillary wall in vitro

Abstract

The binding of albumin to the glomerular capillary wall was studied using albumin-gold in perfused kidneys, the interaction of [3H]albumin with isolated glomeruli at 37°C and 4°C and the interaction at [3H]albumin with purified basement membrane. The albumin-gold was found to bind predominantly to the basement membrane and this interaction could be dissociated with high concentrations of albumin. There was binding of albumin to isolated rat glomeruli which exhibited temperature dependence. Glomeruli exhibited a binding site at both 37°C and 4°C with an association constant in the range of 1 to 3 x 104 M-1 that bound 7 x 1013 molecules/glomerulus. At 37°C, however, there was anomalous Scatchard binding behaviour at relatively higher concentrations of albumin (30 to 50 mg/ml) which could be due to either glomerular cell uptake or the appearance of multiple binding sites or both. The binding of albumin to isolated glomeruli and the glomerular albumin levels in isolated kidney perfusion could largely be accounted for by the binding of albumin to the glomerular basement membrane. The albumin binding to glomeruli at 37°C was enhanced by Pronase digestion and heparinase digestion, but remained unchanged following trypsin treatment or neuraminidase treatment. Similarly, albumin was shown to bind to purified basement membrane preparations. This binding was also enhanced (~80 times) by heparinase digestion but remained unchanged after digestion with chondroitinase ABC or hyaluronidase. The studies suggest that there is binding of albumin to the extracellular matrix components of the glomerular capillary wall and that a significant number of binding sites can be revealed on exposure to Pronase or heparinase. This work confirms the suggestion of Kanwar and Rosenzweig (J Cell Biol 93:489-494, 1982) that heparan sulfate may act as an anticlogging agent to the glomerular capillary wall.