Glomerular Basement Membrane

Abstract

The glomerular basement membrane shown in panel A differs from basement membranes in other locations in that it is faced by a cell layer on either side, namely the endothelia and the podocytes and that it is thicker, because it is the product of fusion of the basement membrane of endothelial cells and podocytes. It is composed of three layers: a central electron dense lamina densa and a layer of lower electron density on either side, the lamina rara interna toward the endothelia and the lamina rara interna toward the podocytes. The lamina densa is composed of a compact meshwork of 3 nm filaments. The lamina rara interna contains 10 nm fibrils and both laminae rarae are crossed by filamentous material, which reaches the plasma membrane of endothelia and podocytes. The glomerular basement membrane is extensively cross-linked by disulfide bonds and collagen-type bonds. It is made up of various components also found in other basement membranes: type IV collagen, heparan sulfate and chondroitin sulfate proteoglycans, laminin, nidogen and BM-40/ osteonectin/SPARC.