It is no linguistic coincidence that high temperature and spiciness share the same word in the English dictionary: they induce the same burning sensation. The biological basis for this commonality was discovered in 1997 by David Julius’s group at UCSF1.
Like all the best discoveries in biology, this work epitomizes hard work and creativity. To find the molecular target of capsaicin, the main spicy ingredient in most common peppers, Julius’s group screened through 2,400,000 pieces of mouse DNA fragments to find one that is activated by this molecule. They soon realized that this piece of DNA codes for a new channel, VR1, later named TrpV1 (pronounced “Trip-Vee-One”). This channel is specifically expressed in sensory neurons and opens when binding to capsaicin, thus activating the sensory neurons and giving us the burning sensation we experience when our skin touches pepper seeds.
The most amazing part of this paper comes when Julius’s group increased the temperature surrounding this channel without adding capsaicin, and found that high temperature (48 °C, or 118.4 °F) activates this channel just as well as the pepper molecule. Therefore, the reason why pepper seeds and high temperature feel similar is that they activate the same TrpV1 channel that enables the burning sensation.
Lastly, it turned out that the Trp channel family is extremely large and used ubiquitously across the animal kingdom for sensory purposes. Another channel that causes a familiar sensation is TrpM8, which is activated by both cold temperature and menthol2. Nature played her trick again.
- Caterina, M. J. et al. The capsaicin receptor: a heat-activated ion channel in the pain pathway. Nature389, 816–24 (1997).
- Bautista, D. M. et al. The menthol receptor TRPM8 is the principal detector of environmental cold. Nature448, 204–8 (2007).