Poly-L-lysine-gold probe for the detection of anionic sites in normal glomeruli and in idiopathic and experimentally-induced nephrosis. A comparative ultrastructural study.

Anionic sites play a key role in the charge selectivity of glomerular filtration as well as in the maintenance of the structural integrity of the visceral epithelium and podocytes. Alterations in these sites are believed to be a major factor underlying human idiopathic nephrosis and puromycin-nephrosis in the rat. The poly-L-lysine-gold complex was used for the ultrastructural detection of anionic sites in renal glomeruli of patients with idiopathic nephrosis as well as of rats with puromycin-induced nephrosis, allowing for study of the changes occurring in the anionic sites during nephrosis and for the comparison between human disease and this experimental model. In both normal human and rat controls, the probe was detected on epithelial and endothelial cell surfaces and on the glomerular basement membrane, mainly in both laminae rarae. In proteinuric rats, a decrease in labeling intensity was noted on podocyte membranes and in the lamina rara externa, with a corresponding increase in the more central areas of the glomerular basement membrane. These changes were not as evident in proteinuric humans. Furthermore, a reduction in labeling density was noted in the glomerular basement membrane of proteinuric animals, although this could not be substantiated in human tissues. Poly-L-lysine-gold is a useful probe for anionic sites in fixed tissues, and allows for comparison between human disease and its experimental counterpart.