Resiniferatoxin

Resiniferatoxin (RTX) is a naturally occurring, ultrapotent capsaicin analog that activates the vanilloid receptor in a subpopulation of primary afferent sensory neurons involved in nociception (the transmission of physiological pain). RTX causes an ion channel in the plasma membrane of sensory neurons — the transient receptor potential vanilloid 1 — to become permeable to cations, most particularly the calcium cation; this evokes a powerful irritant effect followed by desensitization and analgesia. Resiniferatoxin has a rating of 16,000,000,000 on the Scoville Scale, the measurement of the piquancy (spicy heat) of chili peppers, making it one of the highest rated substances known.