If the sodium level drops, an accompanying drop in the leak current will maintain the signal, whereas if the sodium drops but the leak current doesn't, signal transmission may fail. Conversely, if the sodium level is too high and the leak current doesn't increase, a patient may experience twitching. The "safe" zone lies between the two limits.

"Trying to influence the balance between the two ion channels is a completely new approach, and drugs that target leak currents could be as important as those targeting the sodium current," adds Sejnowski. "I think we have a good chance at some point to help MS patients. The first step is to understand what's going on."

"Our model offers a novel explanation for many of the peculiar and intermittent symptoms that MS patients experience," says first author Jay S. Coggan, who had studied leak channels in previous work. "The injured axon is continually struggling to maintain order within a functional range. There is danger to the right and left. A variety of perturbations can nudge the axon one way or the other. It makes sense that leak channels might participate in these changes."

In some instances, for example, their symptoms worsen if they are too warm, but improve if they are cooled off-a phenomenon that correlates to the fact that these channels are temperature-dependent. "If a patient is near one of the boundaries and only marginally 'safe,' heating up could cause him or her to cross into the failure zone," Coggan adds. Temperature, therefore, hints at which boundary the patient is approaching.

Beyond MS and demyelinating diseases, insights into the sodium/leak current have applications to intractable pain-a field that Sejnowski's group will be investigating next.

SOURCE Salk Institute for Biological Studies