On the surface of these axons are ion channel (pore-forming) proteins, which span the axon's membrane, connecting the inside with the outside. Some of these ion channels act like temperature receptors or "molecular thermometers" by opening and closing according to the temperature. At a particular temperature, the receptors open. This allows an influx of ions into the neuronal processes, and this electrical signal is relayed through the neuron to the brain.
The existence of specialized hot- and cold-neurons had been known for years, but the molecules that actually sense the temperatures and signal back to the neuron through the axon were a mystery. That changed in 1997 when a group cloned TRPV1, which is a type of transient receptor potential (TRP) channel. TRPV1, an ion channel, opens when it senses hot temperaturesabove 42 C (108 F).
That discovery opened the floodgates for identifying other temperature-detecting proteins. Within a few years, several laboratoriesincluding Patapoutian'shad identified additional temperature-detecting proteins and confirmed that mammals used them to detect temperature.
But how the proteins achieved their temperature-sensing ability remained a mystery. While scientists in the field knew in much detail how ion channels were activated by chemicals or voltage signals, the molecular structures required for temperature activation remained unknown.
Two competing theories were advanced to explain the activation of ion channels in response to temperature. Drawing on the proteins' similarity to voltage-gated potassium channels, the first theory posited that TRP channels are generating temperature sensitivity because the energies required for voltage activation are very finely tuned. In contrast, the second theory proposed that these channels have a modular structure and therefore possess a specific domain that enables them to be activated by tempe
|Contact: Keith McKeown|
Scripps Research Institute