Figure 3. A) Schematic representation of the glomerular filter. Foot processes of podocytes are interconnected by the so-called slit diaphragm, a modified adherens junction whose composition by Ig-like and cadherin proteins is similar to that of neuron-neuron synaptic adhesions. The basal membrane of foot processes is connected to the glomerular basement membrane (GBM) by molecules that are found in the neuromuscular junction, such as integrins and dystroglycans. Furthermore, to increase the similarity, the GBM contains agrin and the so-called synaptic laminin, i.e., the laminin beta 2 chain. On the basis of our results, we hypothesize that stimuli coming from blood or from the glomerular microenvironment, produce neurotransmitter release from synaptic-like vesicles contained in podocyte processes, and the neurotransmitter can act on neurotransmitter receptors located on podocytes and other glomerular cells, triggering further signals. B) Transmission electron microscopy of a normal mouse glomerulus. Several vesicular structures can be observed in both primary processes and foot processes of podocytes. Scale Bar = 200 nm. C) Scanning EM of a normal mouse glomerulus. By scanning EM, it is possible to appreciate the complex ramification and interdigitation occurring between podocyte processes. The technique also allows observation of small rounded protrusions periodically bulging from the web of processes. These small structures, which during disease are subject to profound remodeling, are morphologically highly reminiscent of dendritic spines. Scale bar = 1.0 µm