Too hot to handle! Scientists identify heat sensing...( Neuroscientists at Johns Hopkins are...)

Neuroscientists at Johns Hopkins are a step closer to understanding pain sensitivity - specifically why its variable instead of constant - having identified a gene that regulates a heat-activated molecular sensor.

Their description of the function of a membrane protein called Pirt appears in the May 2 issue of Cell.

Pain sensitivity increases during inflammation or injury and we want to know what molecules are involved in pain sensation when sensitivity is elevated, says Xinzhong Dong, Ph.D., an assistant professor of neuroscience at Hopkins.

The ability to sense temperature heat and spice is controlled by the TRPV1 protein channel found on the surface of certain nerve cells. In an inactive state, TRPV1 channels remain closed-there is no pain sensation. However, when noxious heat-temperatures above 108 degrees Fahrenheit-or capsaicin-the main ingredient in hot peppers-activates a TRPV1 channel, ions flow through, depolarizing the nerve to create an electrical current that sends pain signals to the brain.

The interesting thing about this channel is its not always constant, says Dong, whose team set out to find proteins that modulate TRPV1s action. They found the Pirt protein,phosphoinositide interacting regulator of TRP, and named it for its ability to regulate the TRPV1 channel.

To better understand how Pirt works, the researchers made mice that lacked Pirt and tested their ability to respond to heat. The mice were placed on a hot surface and monitored for how long it took them to scurry off. Mice lacking Pirt responded significantly slower than normal mice.

The team then exposed one hind paw to capsaicin and found that mice lacking Pirt did not lick their paws as long as normal mice, suggesting that without Pirt, they were compromised in their ability to sense the spice of capsaicin. The researchers also tried mustard oil on the hind paw and found mice lacking Pirt licked for about the same amount o
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