Three-dimensional ultrastructure of rat acellular glomerulus by scanning electron microscopy

Rats were intravenously injected with polyethyleneimine (PEI), one of the cationic probes. Glomerular basement membranes (GBMs) isolated by detergents were confirmed to be intact by the presence of PEI both in the lamina rara interna and externa. Three-dimensional architecture of rat GBM was studied by scanning electron microscopy (SEM). Three different methods were employed for the preparation of acellular glomeruli and similar results were obtained: acellular glomeruli were obtained from isolated glomeruli by treating them with detergents and from acellular kidney cortex which was prepared either by immersion or by perfusion with detergents. By transmission electron microscope (TEM) all these three preparations showed remarkable structural preservation and all components of the extracellular matrix such as GBM, Bowman's capsule basement membrane, and mesangial matrix were left intact. By SEM, the convoluted spherical shape of glomerular configuration was observed from the epithelial side. In higher magnification GBM had crater-like holes 10 to 25 nm in diameter. In the cryofractured specimen, the GBM was observed from both the epithelial and endothelial side, and the mesangial matrix exhibited the fenestrated plates that separated and supported peripheral glomerular channels. The GBM seems to play an important role both in glomerular permselectivity and in preserving glomerular shape.