Tuesday, February 27, 2007

How Do We Detect Temperature?

We know how light sensation or sound sensation take place, how we smell, how we taste, but till a recent research we did not understand how we feel temperature. "For a long time, we didn’t know how temperature sensing was being carried out in animals," said Jie Zheng, assistant professor in the Department of Physiology and Membrane Biology at the UC Davis School of Medicine.

“Huge progress was made in the last decade, when scientists discovered four ion channels sensitive to heat and two cold-sensitive ones. But, it was still unclear how only six temperature-sensor channels could cover wide ranges of temperature and still discriminate subtle



differences," Zheng said.

Zheng's team employed a new technique to deal with the problem, revealing that the subunits of one channel can come together with subunits from another channel or co-assemble in laboratory cell cultures to make new functioning channels. “Assuming this process also happens in normal cells, it suggests a likely mechanism for the thermosensitivity seen in all animal cells. We found that, by reassembling subunits we potentially have a lot more than six channel types responsible for the sensing of temperature," he said.

Ion channels are tubular proteins from the cell membrane that can open and close, controlling the ions flow and the electrical charge difference between the inside and outside of the living cells. The team investigated the transient receptor potential (TRP) channels, 6 out of 20 being the channels involved in sensing temperature. “Previous studies concluded that different thermosensitive TRP channel subunits did not coassemble”, Zheng said.

The team employed a 2006 technology named spectra FRET (spectroscopy-based fluorescence resonance energy transfer) to observe interactions between different channel subunits under a microscope. "This technique allows us to look at the channel subunit composition in real-time in live cells," Zheng said. "Using spectra FRET, we were able to focus on just the signal from the plasma membrane," Zheng explained.

"What we found was that the subunits of one kind of heat-sensitive channel coassembled with subunits of other heat-sensitive channels to form new channels. This means that instead of four heat-sensitive channels we have a potential of 256 heat-sensitive channels with potentially different temperature sensitivity ranges. Using these single-molecule recordings, we see many different channel types. The next question we are trying to address is whether they really have different temperature sensitivity. We believe the answer is ‘yes,’ but we have to show that." said Zheng. “The cold- and heat-sensing subunits, however, do not seem to coassemble,” he said.

As the thermosensitive cells also detect pain, the research of these channels could prove useful for novel pain remedies. “We have to re-examine everything from how people acclimate to hot climates to how they respond to spicy food based on the understanding that there are many more kinds of channels involved," Zheng said.
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