Washington: The winter sun feels welcome, but not so a summer sunburn. Have you ever wondered how the human body senses a range of hot temperatures?
Well, scientists claim to have found that a few proteins on surface of nerve cells, known as ion channels, distinguish dozens of discrete temperatures, from mildly warm to very hot, the `Journal of Biological Chemistry` reported.
A team at California University has showed that the building blocks, or subunits, of heat-sensitive ion channels can assemble in many different combinations, yielding new channels, each capable of detecting a different temperature.
The discovery, in cell cultures, demonstrates for the first time that only four genes, each encoding one subunit type, can generate dozens of different heat-sensitive channels, say the scientists.
"Researchers in the past have assumed that because there are only four genes, there are only four heat-sensitive channels, but now we have shown that there are many more," said Jie Zheng, who led the team.
Ion channels are pores in cell membranes. Their ability to open and close controls the flow of charged ions, which turns neuron signalling on or off -- in this case to inform the body of the temperature the neuron senses.
The team found that when different subunits combine, the resultant hybrid, or heteromeric, channel can detect temperatures about midway between what the "parent" channels detect.
One of the channels they studied, called TRPV1, reacts to hot temperatures -- about 100 degrees Fahrenheit. It is also responsible for the ability to sense spicy foods, such as chili peppers.
A second channel, TRPV3, responds to temperatures of about 85 degrees. It also senses many food flavors such as those found in rosemary, oregano, vanilla and cinnamon that elicit a warm sensation, according to the scientists.
When the TRPV1 and TRPV3 subunits recombine, the heteromeric channel is tuned to about 92 degrees. Their study, surprisingly, showed the hybrid channel has an even higher chemical sensitivity than the channels that made it up.
The scientists also showed that channels made up of TRPV1 and TRPV3 subunits react to heat at a rate about midway between that of the two constituent channel subunits.