Camphor is a naturally occurring compound used as the main active ingredient in balms and liniments supplied as topical analgesics.
Despite its long history of common medical use, the underlying molecular mechanism of camphor’s action is not understood.
Capsaicin and menthol, two other topical agents widely used for similar purposes, are known to excite and desensitize sensory nerves by acting on two members of the transient receptor potential (TRP) channel superfamily: the sensory-sensitive TRP. subtype 1 heat (TRPV1) and cold. -sensitive TRP channel M8, respectively.
Camphor has recently been shown to activate TRPV3, and there is one study1 showing that camphor also activates heterologously expressed TRPV1, requiring higher concentrations than capsaicin. Activation was enhanced by stimulation of the phospholipase C-coupled receptor mimicking inflamed conditions. Also, in the same study1, camphor was found to inhibit several other related TRP channels, including the TRP ankyrin repeat 1 (TRPA1). Camphor-induced TRPV1 desensitization and TRPA1 blockade may underlie the analgesic effects of camphor.
Notes:
1 Camphor Activates and Strongly Desensitizes the Transient Receptor Potential Vanilloid Subtype 1 Channel in a Vanilloid-Independent Mechanism. Haoxing Xu, Nathaniel T. Blair, and David E. Clapham. J Neurosci. 2005 Sep 28; 25(39): 8924–8937. doi: 10.1523/JNEUROSCI.2574-05.2005. PMCID: PMC6725586 PMID: 16192383