[Biophysicochemical structures of the glomerular filter].

The ultrastructural and the biophysical and biochemical qualities of glomerular permeability to protein molecules are reviewed. With regard to differently located immune deposition in human glomerulonephritis, description and discussion are addressed in a fixed order of layers: 1. endothelial-subendothelial, i.e. the endothelial cells with fenestrate and the lamina rara interna of the basement membrane (bm), 2. membranous, i.e. the lamina densa of the bm, 3. subepithelial-epithelial, i.e. the lamina rara externa of the bm and the podocytes with food processes and slit diaphragms. It is emphasized that the 3 layers act as gradually (coarse to fine) filter barriers. On the basis of well known structural peculiarities, in the last 10 years experimental studies revealed that the meshwork of type IV collagen and the negatively charged heparan sulfate-proteoglycans - "the glomerular polyanion" - are integrated in sieving of protein molecules. These components are differently located in the stratified cellular and extracellular layers of the glomerular filter and their combined action is the basis of a size, charge and configuration depended filtration of macromolecules. In this way the passage of the mostly negative charge blood proteins, especially albumin, is prevented under normal conditions.