Three-dimensional characterization of interior structures of exocytotic apertures of nerve cells using atomic force microscopy

We examined the interior structure of exocytotic apertures in synaptic vesicles of neuroblastoma × glioma hybrid cells using atomic force microscopy. The atomic force microscopy detected apertures of 50–100 nm in diameter at various depths within the varicosities of these cells. We were also able to image a regular radial pattern on the wall and lump-like structures at the bottom of these apertures. In contrast, scanning electron microscopy could only detect the apertures but not the fine details of their interior. The cells examined here exhibited the same electrophysiological properties and expression of synaptophysin and syntaxin 1 as presynaptic terminals, as studied by various electrophysiological and imaging techniques. Our results indicate that atomic force microscopy allows three-dimensional viewing of the fine structures located inside exocytotic apertures in nerve cells.