02/01/94
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STANFORD -- Stanford University chemists have demonstrated that external electric fields can have a disruptive effect on a simple model of a biological membrane.
Writing in the Feb. 4 issue of the journal Science, chemistry Professor Harden M. McConnell and postdoctoral fellows Ka Yee C. Lee and Jurgen F. Klinger report that weak but non-uniform electric fields can cause significant disruptions in such a membrane under conditions that may be present in living cells.
"This does not prove that external electric fields have a deleterious effect on cell membranes, but it suggests that they might have such effects," says McConnell.
There is considerable interest in determining how electromagnetic fields affect living cells. Population studies have shown statistical links between some types of cancer and the very weak electrical fields to which people are commonly exposed from sources such as household appliances and power lines. But, recognizing the limitations of such statistical associations, the scientific community has demanded that a mechanism by which weak electric or magnetic fields can cause harm be established before accepting such links as real.
One proposed mechanism for such effects is that electric fields might affect cell membranes in ways that could trigger cells to function inappropriately.
An example of inappropriate triggering caused by a different type of stimulus is asbestosis: Immune system killer cells react to asbestos fibers as if they are invading bacteria and produce toxins that have no effect on the fibers but cause this serious lung disease by killing the cells in the fibers' vicinity.
To test whether electric fields have the power to disrupt membranes, McConnell and his colleagues devised a conceptually simple experiment. In a small covered dish with a glass pipette mounted vertically at its center, they created a Langmuir film, a simple membrane made of lipid molecules floating on a water surface. (Langmuir films have been used for many years to study membrane properties.)
By running a wire through the vertical tube and connecting it to a power source, the researchers were able to expose the membrane to an electric field that varied with distance from the wire.
Next, the scientists varied the pressure in the dish. Changing the pressure caused an important factor called the critical temperature to change as well. The critical temperature is the temperature at which the membrane undergoes a process called phase separation. In essence, the membrane breaks down into its constituent ingredients, much as salad dressing separates into oil and vinegar.
Finally, they used a technique called fluorescent microscopy to monitor the condition of the membrane.
"Basically, our experiment shows that as the critical temperature approaches the ambient temperature, the weaker the electric field required to disrupt it," McConnell says.
That is significant because previous experiments suggest that cell membranes adjust their chemical make-up so that they remain very close to the critical temperature, the scientist reports. This gives the membranes the plasticity they need to hold in place the array of proteins that are attached to them.
As a consequence, even weak electrical fields have the capacity to cause large changes in the lipid organization of membranes. If the fields can disrupt the lipids, then they also should be able to disrupt the protein receptors on the membrane surface and so trigger an inappropriate cellular response, the scientist argues.
McConnell and his colleagues are following up on this study with additional research to look at the effects that electromagnetic fields produced by alternating currents have on living cell membranes.
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