Pain Receptors And Chili Peppers, Garlic, Wasabi And Menthol Mints

We had an interesting lecture this week titled "Molecular basis of nociception." Hot chili peppers (specifically the chemical capsaicin) induce pain by binding to transient receptor potential vanilloid-1 (TRPV1), an ion channel of non-selective cation permeability that transduces specific noxious stimuli (in this case capsaicin) into electrical impulses. What's interesting is that the TRPV1 channel is also activated by temperatures higher than 43 degrees Celsius and acidic extracellular pH. My notes explain, "Because capsaicin activates TRPV1 as effectively or more effectively than noxious heat, it evokes a similar hot and burning sensation like hot temperature does."

My notes continue, "TRPA1 is an ion channel frequently co-expressed with TRPV1 in heat sensitive sensory neurons. TRPA1 is activated by pungent chemicals, including allicin from garlics and mustard oil from Japanese Wasabi roots." TRPA1 is also activated by THC (the active ingredient in Marijuana) and some pungent anesthetics like isoflurane, desflurane and propofol. Interestingly, "because TRPA1 positive neurons usually contain TRPV1, allicin and mustard oil evokes hot burning pain similar to how chili peppers do."

Finally, another channel in the TRP family, TRPM8, is "considered to be the molecular cold sensor for thermal sensation." It is activated by temperatures lower than 30 degrees Celsius. It is also activated by menthol, which explains the cool sensation associated with menthol mints.