At the University of Tokyo, Vosshall's colleague Kazushige Touhara and his lab members puffed molecules onto cells engineered to make insect olfactory receptors. They then measured how long it took for the ion channel to open and recorded their electrical movement as they surged inside the cell via the channel. The rush of electrical activity occurred too fast for a series of steps to be involved, says Vosshall. In addition, poisoning several proteins involved in the G-protein pathway didn't affect the ions or the ion channel, suggesting that G-protein signaling isn't primarily involved in insect smell.
Experiment after experiment, "the most consistent interpretation is that these are ion channels directly gated by odors," says Vosshall. "But the dominant thinking in the field may have reflected an experimental bias that aimed at proving a more elaborate scheme."
The ion channels don't resemble any known ion channel on Earth, says Vosshall. They are composed of two proteins that work in tandem with one another: an olfactory receptor and its coreceptor, Or83b. While the coreceptor is common to every ion channel, the olfactory receptor is unique. Together, they form the olfactory receptor complex. Vosshall and Touhara specifically show that this complex forms nonselective cation channels, meaning that they allow any ion to pass through the gate as long as it has a positive charge.
Touhara and Vosshall developed their ion channel hypothesis in parallel with Vosshall's work on DEET, a widely used chemical in bug spray that jams the receptor complex. This research, which was published in Science last month, also showed that DEET jams other proteins that have nothing to do with smell, including several different types of ion channels that play importan
|Contact: Thania Benios|