Capsaicin receptor and its homologue in nociception

Capsaicin, the main ingredient in 'hot' chilli peppers, elicits burning pain by activating specific (vanilloid) receptors on sensory nerve endings. The cloned capsaicin receptor (VR1) is a nonselective cation channel with six transmembrane domains. When expressed heterologously in HEK293 cells or Xenopus oocytes, VR1 is activated not only by capsaicin but also by heat in the noxious range (>43 degreesC) or by protons. A VR1 homologue, VRL-1 is not activated by vanilloids or protons, but can be activated by higher heat (>52 degreesC). VR1 function as a detector of multiple pain-producing stimuli was verified by a behavioural study in mice lacking VR1. Thus, VR1 and VRL-1 form a novel ion channel family and play an important role in nociception.