Credit: © 2008 ACS

It is known that water-soluble single-walled carbon nanotubes can cause neurons to have fewer but longer cell extensions known as neurites. This elongation is thought to be due to the way cell membranes are recycled (that is, how they pinch in to form vesicles during the uptake of materials in a process called endocytosis, and how vesicles from inside the cells rejoin with the membrane during expulsion in a process called exocytosis). Now, researchers at the University of Alabama and University of California, Riverside have shown that single-walled nanotubes can block stimulated neurons, but not unstimulated ones, from internalizing materials.

Vladimir Parpura, Robert Haddon and colleagues1 treated unstimulated and stimulated neurons with water-soluble nanotubes and monitored the recycling of the cell membranes with a fluorescent dye, which will only enter and exit the cells by endocytosis and exocytosis, respectively. The nanotubes did not affect unstimulated cells but reduced the uptake of the dye in stimulated cells. It was suggested that cells exposed to nanotubes have longer neurites because more cell membrane can be inserted at the elongating front through exocytosis than can be retrieved by the reverse process of endocytosis, which is impaired by the nanotubes, presumably because of their length.

Although it has been shown that nanotubes can enter cells, it remains unclear how this happens.