[Neuronal porosome in the rat and cat brain]

It is well established that during cell secretion, membrane-bound secretory vesicles dock and fuse at the base of supramolecular cup-shaped structures at the cell plasma membrane called "porosomes", to expel intra-vesicular contents to the outside. In neurons, it has been demonstrated that 12-17 nm cup-shaped lipoprotein structure possessing a central plug are present at the presynaptic membrane, where 50 nm in diameter synaptic vesicles transiently dock and fuse to release neurotransmitter. In the past decade, the neuronal porosome has been isolated and its major chemical composition determined. Additionally, the porosome has been both structurally and functionally reconstituted into artificial lipid membrane, establishing its role as the secretory portal in neurons. Studies utilizing atomic force and electron microscopy, combined with electron density and 3D contour mapping, provide at the nanoscale, the structure and assembly of proteins within the neuronal porosome. In the current study, ultrahigh resolution imaging of the presynaptic membrane of isolated brains from both rats and cats, demonstrate for the first time, the presence of neuronal porosomes in cat brain, and further confirms the presence of porosomes at the presynaptic membrane in rat brain synaptosomes. Results from the present study further confirm the cup-shaped morphology of porosomes in the rat brain, and demonstrates their similar shape and size in the cat nerve terminal. The study also demonstrates for the first time, the universal presence of similar porosomes in different species of mammals.