Stroke patients could gain from turtle studies

April 7, 1995

Treatment for strokes may be revolutionised by a drug that exploits the ability of turtles to survive without oxygen for several hours without brain damage, the Biochemical Society heard this week, writes Aisling Irwin.

Brain damage from strokes is caused when a blood clot stops blood carrying vital oxygen getting to the brain. This triggers a massive influx of calcium and sodium ions into the cells - which poisons them.

Turtles have a mechanism which they switch on when they go under water - that blocks the sodium channels in cell walls which allow these ions in. This method is being developed into a drug that could be available in a few years' time, said Michael Spedding, a neuroscientist at Servier Research Institute in Paris.

Initial studies show that, by blocking calcium channels as well, the area of damage to the brain could be reduced by half if the drug is given within a few hours of the stroke, he told the society's annual meeting in Leicester. Some 100,000 people suffer from strokes in the United Kingdom every year.

The drug is an example of the rapid progress in understanding the flows of the ubiquitous calcium ion in and around brain cells, which forms the basis of how cells communicate with each other, the meeting was told.

"Calcium is a crucial messenger," says Stephan Nahorski, head of the department of cell physiology and pharmacology at Leicester University. "It opens up an enormous amount of neuroscience. It can also be neurotoxic, causing cell death. It is therefore now a target for many pharmaceutical companies."

Professor Nahorski said that scientists can now track ions as they move in, out and within single cells, by tagging them with fluorescent dyes and using the latest in microscopy, such as confocal imaging in which they can look at several planes through the cell.

As a result they have discovered that calcium conveys messages not just by rushing in and out of cells but by surging in waves from one side of a cell to the other. The meaning of the messages is held in the frequency of the surges of ions.

Calcium also sits in different concentrations in the various organelles within cells, which can release it when stimulated.

The result is that complicated and hugely varied messages can be transmitted to cells. The conference also heard that calcium's central role in producing memories is "becoming clearer and clearer", paving the way for drug treatments for pre-senile dementia and cognition and memory improvers.

UK scientists have been studying calcium's role in enabling synapses in the brain to remember information. When nerve cells are stimulated in a certain pattern they remember that pattern and show an enhanced signal the next time that particular stimulation occurs.

Flows of calcium are important in laying down the pattern. Mechanisms involved in forming the pattern are complicated but elucidating them could help understand diseases associated with memory loss.

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