How a cell controls the levels of chloride ions inside it affects its ability to inhibit brain activity. This is because of the way chloride ions interact with GABA, the main inhibitory neurotransmitter in the brain. Changes in inhibition can result in epilepsy, and drugs that improve inhibition are amongst the most effective treatments for epilepsy.

Researchers from the Pitié-Salpêtrière Hospital in Paris, looked at samples of brain tissue from people with epilepsy caused by hippocampal sclerosis, a condition which causes thickening and hardening of brain tissue in the hippocampus. The cells in these slices of brain tissue are electrically active, producing a pattern of activity like that seen in between seizures in a person with epilepsy.

Dr Gilles Huberfeld and his colleagues were interested in whether chloride ion levels and GABA use were disturbed in these cells. Using electrodes to detect the electrical activity of cells, they found that a number of cells in one part of the hippocampus fired in a way that indicated altered levels of chloride ions. Further tests showed that 30% of these cells lacked a protein that aids transport of chloride ions in the cell. The cells without the transporter protein did not behave normally electrically and therefore didn't inhibit properly.

The researchers tried adding a drug to the cells which interfered with chloride transporter proteins, and found that this stopped the electrical activity in the brain slices. They discovered in this way that chloride transporter proteins are important in epilepsy, and that drugs which affect how they work may be useful anti-epileptic drugs. This study was published in the Journal of Neuroscience in September 2007.

GABA, inhibition and communication
Brain cells which produce GABA slow down the rate of transmission of messages in the brain. GABA stands for gamma-aminohydroxybutyric acid.

In an inhibitory neurone, when a molecule of GABA binds to one of its dedicated receptors, this opens a pore in the wall of the cell. This allows particles called ions to flow into or out of the cell. Ions are particles which carry an electric charge. When GABA binds to its receptors, this lets chloride ions (which carry a negative charge) flow out of out the cell, or potassium ions (which carry a positive charge) flow in. Both these flows change the overall electrical charge of the cell. In this way, the flow of GABA controls the electrical properties of the cell. Since nerve cells communicate by sending electrical signals, GABA controls how these cells send messages.

Read more about how nerve cells communicate electrically and
how neurotransmitters work