Metal catalysts in carbon nanotubes block critical signalling pathway in neurons

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Washington, August 28 (ANI): In what may prove very useful in improving treatments for human neurological disorders, Brown University scientists have found out why carbon nanotubes tend to block a critical signalling pathway in neurons.

Writing about their findings in the journal Biomaterials, the researchers have revealed that it is not the tubes, but the metal catalysts used to form them, that are to blame.

They say that minute amounts of a metal called 'yttrium' may impede neuronal activity.

They add that the findings mean that carbon nanotubes without metal catalysts may be able to treat human neurological disorders, although other possible biological effects still need to be studied.

"It's a problem we can fix. We can purify the nanotubes by removing the metals, so it's a problem we can fix," said Lorin Jakubek, a Ph.D. candidate in biomedical engineering and lead author of the paper.

Taking single-walled carbon nanotubes to the laboratory of Brown neuroscientist Diane Lipscombe, the research team zeroed in on ion channels located at the end of neurons' axons.

These channels are gateways of sorts, driven by changes in the voltage across neurons' membranes. When an electrical signal, known as an action potential, is triggered in neurons, these ion channels "open", each designed to take in a certain ion.

One such ion channel passes only calcium, a protein that is critical for transmitter release and thus for neurons to communicate with each other.

In experiments using cloned calcium ion channels in embryonic kidney cells, the researchers found that nickel and yttrium, two metal catalysts used to form the single-walled carbon nanotubes, were interfering with the ion channel's ability to absorb the calcium.

Lipscombe, who specializes in neuronal ion channels and is a corresponding author on the paper, pointed out that yttrium's ionic radius is nearly identical to calcium's, which is why it "gets stuck and prevents calcium from entering and passing through. It's an ion pore blocker."

The experiments showed that yttrium in trace amounts - less than 1 microgram per milliliter of water - may disrupt normal calcium signalling in neurons and other electrically active cells, an amount far lower than what had been thought to be safe levels.

With nickel, the amount needed to impede calcium signalling was 300 times higher.

"Yttrium is so potent that ... a very low nanotube dose" would be needed to affect neuronal activity, said Robert Hurt, professor of engineering and a corresponding author on the paper.

Jakubek said she was surprised that the metals turned out to be the cause.

"Based on the literature, I thought it would be the nanotubes themselves," she said. (ANI)

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