Structural organization of heterogeneous basal laminas in human glomeruli

Differential response to 5 M guanidine, pH 7.0, shows at least two classes of glomerular basal laminas: epithelial and endothelial-mesangial. The former is the predominant element, folding into capillary tufts and loops but never completely encircle the entire circumference of glomerular capillaries. It remains as a single, continuous sheet within each glomerulus. The mesangial basal lamina partitions the vascular space into individual capillary lumen. The endothelial basal lamina, which extends from mesangium to encircle capillary lumens, is poorly developed, and undetectable in most capillaries. The organization of these two classes of basal laminas provides a structural framework for understanding glomerular permeability, especially the spatial relationship between capillary lumens and the mesangium. Interruption of the juxtaglomerular epithelial basal lamina, with sprouting of a new endothelial-mesangial bud, and formation of a new glomerular capillary tuft are noted in a group of patients with diabetic glomerulosclerosis and chronic renal failure. Wrinkling and resorption of the juxtamesangial epithelial basal lamina with formation of a new epithelial basal lamina are also observed. These findings indicate that the mesangium and the juxtamesangial epithelial basal lamina may be the active site of glomerular basal lamina resorption, turnover, and neoangiogenesis.