Aims: 

To present our current understanding of one of Nature's intricate mysteries – the properties of the glomerular membrane. In recent years, there has been a debate regarding the properties of the glomerular barrier. Most researchers have found data consistent with the classical view of a negatively charged barrier reducing the albumin concentration across the filter by four orders of magnitude . However, an alternative view has been proposed, the albumin retrieval hypothesis, according to which the glomerular capillary has similar properties at that of skeletal muscle. Proteinuria would then be a consequence of tubular, not glomerular, disorder. Today, this debate has been settled. Thus, evidence based on molecular biology, physiological measurements, theoretical modeling, as well as intravital microscopy clearly show that the barrier is highly permselective. Our knowledge of the podocyte has increased tremendously, but the glomerular basement (GBM) is also important for the properties of the barrier. The endothelium has been neglected until recently, but is know attracting substantial interest. In particular, the endothelial surface layer (ESL, or 'glycocalyx') probably plays an important role in restricting large molecules, such as albumin, from entering the GBM. More molecular and physiological details of the ESL and the glomerular barrier will be discussed during the talk.

Conclusion: 

The normal glomerular barrier requires intact endothelium, basement membrane and podocytes and defects in any of these layer result in proteinuria. The normal barrier restricts solutes dependent on their size, charge and shape in qualitative agreement with the classical view.