Three-dimensional architecture of the mesangial matrix--comparison of the intact and acellular glomerulus

The three-dimensional ultrastructure of the rat mesangial matrix was studied in acellular rat renal cortex in comparison with intact cortex by scanning electron microscopy (SEM). The mesangial region was covered with fenestrated endothelial cells and was not identified in untreated specimens by SEM. Acellular renal cortex was obtained by perfusion with 4 mM EDTA, 3% Triton X-100, 0.0025% deoxyribonuclease in 1 M NaCl and 4% sodium deoxycholate. Transmission electron microscopy revealed that the glomerular basement membrane (GBM) and mesangial matrix maintained their respective shape and did not collapse even after removal of the cellular components. By SEM, the mesangial matrix appeared as fenestrated septa with oval or round stomata between the glomerular capillaries. The diameter of the stomata was 601 +/- 290 nm. The diameter of the fibrils forming the stomata was 177 +/- 80 nm. These fenestrated structures of the mesangial matrix appear to be useful in supporting glomerular tufts, in stretching and retracting mesangial cells and in passing macromolecules from the capillary lumen into the mesangium.