[The basal membrane of the kidney].

The glomerular basement membrane consists of the lamina densa and two laminae rarae. The glomerular basement membrane (GBM) functions as both the size and the charge barrier to filtration of macromolecules. Several substances have been localized in the GBM: collagen type IV, V, laminin, entactin, fibronectin, amyloid P and proteoglycans. Anionic sites are present on the epithelial and endothelial cell surface (the cell coat or glycocalyx) due to the presence of sialic acid. The negative charges in the GBM concentrate in the lamina rara interna and lamina rara externa. This anionic charge is in large part caused by heparansulphate. Congenital abnormalities of the biochemical composition are expected in the congenital nephrotic syndrome, in minimal change nephropathy, in Alport's syndrome, in Laurence-Moon-Biedl syndrome and in nail-patella syndrome. The main function of the tubular basement membrane (TBM) is to provide support to the epithelium. The chemical composition of TBM differs from the composition of GBM. Some forms of polycystic disease can perhaps be explained by an abnormal chemical composition of TBM.