Ultrastructural study of glomerular basement membrane in diabetic rats by quick-freezing and deep-etching method.

The three-dimensional ultrastructure of glomerular basement membrane (GBM) in streptozotocin (STZ)-induced diabetic rats was examined by quick-freezing and deep-etching method. In three layers of the GBM of control rats, the outer and inner layers were formed by files of perpendicular fibrils, which connected the epithelial or endothelial cell surfaces with meshwork structures of the middle layer. In the diabetic rats, the inner layer was diffusely enlarged and the meshwork structure of the middle layer became markedly irregular due to the rupture of fine fibrils and thickening of material adherent to the fibrils. These ultrastructural changes correspond to those of subendothelial oedema, lamellation of lamina densa and fluffy material in the GBM, as revealed on conventional ultra-thin sections. It is suggested that the initial morphological change of STZ-induced diabetic nephropathy is disruption of matrix fibrils in the GBM, seemingly indicating a disturbance of size and/or charge barriers.