High resolution three-dimensional meshwork structure of the glomerular basement membrane.

To investigate the ultrastructure of the glomerular basement membrane (GBM), rat GBM was treated with sodium dodecyl sulfate and 2-mercaptoethanol and observed under an electron microscope employing ultrathin sectioning and rotary shadowing methods. Further, thick sections of the treated GBM were examined by high voltage transmission electron microscopy. A fine three-dimensional meshwork structure was clearly observed through the entire thickness of the GBM treated with sodium dodecyl sulfate and 2-mercaptoethanol by conventional transmission electron microscopy and high voltage transmission electron microscopy. The diameter of the fibrils forming the meshwork structure was about 3 nm and the dimensions of the pores present in the meshwork were 3 to 4 nm. The rotary shadowing technique revealed fine fibrils disentangled from the GBM that were bound together, and corresponded morphologically type IV collagen molecules. The present findings suggested that the GBM has a fine three-dimensional meshwork structure through its entire thickness which is composed mainly of type IV collagen and may function as a size barrier in the renal glomerulus.