To clarify the ultrastructural changes of the glomerular basement membrane (GBM) in diabetic nephropathy, the renal tissues of the patients with diabetic nephropathy were examined by electron microscopy using our newly devised "tissue negative staining method." A fine meshwork structure consisting of fibrils forming the small pores are observed in the normal human GBM. The diameter of these pores was slightly smaller than that of human albumin molecules. The GBM in patients with diabetic nephropathy showed irregular thickening. At higher magnification, cavities and tunnel structures, which were not seen in normal controls, were observed in the thickened GBM. As the diameters of the cavities and tunnels were far larger than the dimensions of albumin molecules, these enlarged structures are considered to allow serum protein molecules to pass through the GBM from the capillary lumen to the urinary space. The present results suggest that the cause of massive proteinuria in diabetic nephropathy is the disruption of the size barrier of the GBM.
Basement Membrane Biopsy