Regulation of 5-hydroxytryptamine secretion mediated by quercetin-modulated TRPA1 activity in RIN-14B cells

Quercetin, a dietary flavonoid, contributes to bowel regulation and anti-inflammatory effects. Enterochromaffin (EC) cells express transient receptor potential ankyrin1 (TRPA1) and significantly contribute to gastrointestinal motility and secretion via 5-hydroxytryptamine (5-HT) release. A recent study reported that flavonoids, including quercetin, activate heterogeneously expressed TRPA1. We here evaluated the effects of quercetin and its analogs (kaempferol and galangin) on TRPA1 channels using RIN-14B, an EC model cell line. To elucidate the function of these flavonoids, intracellular Ca2+ concentration ([Ca2+]i) was measured, and 5-HT release from RIN-14B cells was analyzed. Quercetin- and kaempferol-induced [Ca2+]i increases, which were abolished by extracellular Ca2+ removal. The [Ca2+]i responses to quercetin and kaempferol were partially suppressed by TRPA1 antagonists and nearly completely abolished by L-type voltage-dependent Ca2+ (Cav) channel inhibitors. Reverse transcription-polymerase chain reaction analysis confirmed the expression of both TRPA1 and L-type Cav channels in RIN-14B cells. Quercetin- and kaempferol-induced 5-HT release from RIN-14B cells was inhibited by TRPA1 antagonists and L-type Cav channel inhibitors. Along with the activation effects, flavonoids inhibited the [Ca2+]i responses to TRPA1 agonists, with the inhibitory potency ranking as follows: quercetin, kaempferol, and galangin. Moreover, these flavonoids demonstrated inhibitory effects on heterogeneously expressed TRPA1. Furthermore, flavonoids inhibited TRPA1 agonist-induced 5-HT release from RIN-14B cells. These results suggest that flavonoids can regulate 5-HT secretion through TRPA1 and L-type Cav channels. Dietary flavonoids may hold therapeutic potential for gastrointestinal functions and disorders.