Hydroxy‐α‐sanshool activates TRPV1 and TRPA1 in sensory neurons

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Abstract
Sanshools are major active ingredients of Zanthoxylum piperitum and are used as food additives in East Asia. Sanshools cause irritant, tingling and sometimes paresthetic sensations on the tongue. However, the molecular mechanism underlying the pungent or tingling sensation induced by sanshools is not known. Because many transient receptor potential (TRP) channels are responsible for the sensations induced by various spices and food additives, we expressed 17 TRP channels in human embryonic kidney (HEK) cells and investigated their activation by hydroxy‐α‐sanshool (HαSS) or hydroxy‐β‐sanshool (HβSS) isolated from Zanthoxylum piperitum. It was found that HαSS, but not HβSS, depolarized sensory neurons with concomitant firing of action potentials and evoked inward currents. Among 17 TRP channels expressed in HEK cells, HαSS caused Ca2+ influx in cells transfected with TRPV1 or TRPA1, and evoked robust inward currents in cells transfected with TRPV1 or TRPA1. In primary cultured sensory neurons, HαSS induced inward currents and Ca2+ influx in a capsazepine‐dependent manner. Moreover, HαSS‐induced currents and Ca2+ influx were greatly diminished in TRPV1–/– mice. HαSS evoked licking behavior when injected into a single hind paw of wild‐type mice, but this was much reduced in TRPV1‐deficient mice. These results indicate that TRPV1 and TRPA1 are molecular targets of HαSS in sensory neurons. We conclude that the activations of TRPV1 and TRPA1 by HαSS explain its unique pungent, tingling sensation.