Loss of anionic sites from the glomerular basement membrane in aminonucleoside nephrosis
Caulfield, J.P.; Farquhar, M.G.
Laboratory Investigation; a Journal of Technical Methods and Pathology 39(5): 505-512
1978
ISSN/ISBN: 0023-6837 PMID: 732274 Document Number: 128242
Lysozyme, a cationic protein, was used to study the distribution of anionic sites in glomeruli of nephrotic rats. Nephrosis was induced by daily injection of the aminonucleoside of puromycin. After 6-11 days, a solution of 1-3% lysozyme was perfused into the left kidney at varying rates, and the kidney was fixed in situ and processed for EM. Lysozyme was visualized as electron-dense deposits that bound to anionic sites. In normal animals lysozyme bound to all components of the glomerular capillary wall-epithelium, endothelium and all the layers of the basement membrane (GBM). There was some binding to the lamina densa of the GBM, but much more striking binding to the lamina rara interna and externa which appeared denser than the lamina densa. The binding sites in the laminae rarae showed a periodicity in normal sections and a discrete reticular pattern in grazing sections. In nephrotic rats lysozyme binding varied with the stage of the disease. There is a progressive loss of fixed negative charges from the glomerulus during aminonucleoside neprhosis to the extent that the lysozyme will no longer bind in most animals. In addition to the well-known loss of anionic sites from the epithelial (and endothelial) cell coat, there is also a loss of anionic sites from the GBM in this disease. There is a partial loss of the charge barrier in nephrosis and previous morphologic studies using electron-opaque tracers indicate that the GBM represents both the charge and the size barrier in the glomerulus.