Because each different chemical moves at a characteristic speed, the various compounds arrive at a detecting station at different times. The detecting station watches for the lights to pass, a brighter glow indicating a larger amount of one chemical, a dimmer light meaning a smaller quantity. In this way, Lillard and Chiu measure the relative amounts of the various chemicals.
The chemists then identify each chemical compound in collaboration with researchers led by two former postdoctoral researchers from Zare's lab: Owe Orwar, a chemist at Chalmers University in Göteborg, Sweden, and Evan R. Williams, a chemistry professor at the University of California-Berkeley. The researchers can thereby read the cellular mail.
Using this technique, the researchers have found that individual vesicles have varying contents, even though the vesicles came from the same gland. "One vesicle would have one component but it would be completely absent from another vesicle," Lillard says. "We knew that in a population, both components were present, but when we got down to the level of a single vesicle, there were clear differences."
But what does this variability mean for the sea slug? "I can summarize that in three words," says Zare. "I don't know. Not yet. Is it the difference between mature and immature vesicles? Is it the difference of some control? I don't know."
It's one thing to read individual words in cellular mail; it's another problem altogether to translate the language. But simply reading the chemical codes that the vesicles contain is an important step toward understanding cellular communication, the researchers maintain.
Eventually, Zare
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Contact: David F. Salisbury
salisbury@stanford.edu
650-725-1944
Stanford University
28-May-1998