Hange-Shashin-to Suppresses Serotonin-Induced Neurogenic Intestinal Contraction via Inhibition of 5-HT3A Receptor Signaling.

BACKGROUND/AIMS: Hange-shashin-to (HST) is a standardized multi-component herbal formulation widely used for the treatment of irritable bowel syndrome (IBS), a functional gastrointestinal disorder characterized by dysregulated serotonergic signaling and abnormal intestinal motility. Despite its clinical application, the cellular mechanisms underlying its therapeutic effects remain unclear. This study investigated the effects of HST on serotonin (5-HT)-induced neuronal responses and the underlying role of 5-HT3A receptor signaling. MATERIALS: Differentiated PC12 cells were used as a neuron-like model to evaluate 5-HT-induced cell shrinkage, membrane depolarization, intracellular Ca²⁺ elevation, and acetylcholine release. Whole-cell patch-clamp recordings were performed in HEK293T cells expressing 5-HT3A receptors to examine receptor-mediated cation currents. The effects of HST on 5-HT-induced colonic contractions were further evaluated using ex vivo rat colonic tissue. RESULTS: HST attenuated 5-HT-induced cell shrinkage in a concentration-dependent manner and suppressed membrane depolarization, intracellular Ca²⁺ elevation, and acetylcholine release in PC12 cells. Patch-clamp analysis demonstrated that HST directly inhibited 5-HT3A receptor-mediated cation currents without altering voltage dependence or reversal potential. Furthermore, HST significantly reduced 5-HT-induced colonic contractions, with efficacy comparable to that of the selective 5-HT3 receptor antagonist ramosetron. CONCLUSION: HST suppresses 5-HT-induced neuronal excitation through inhibition of 5-HT3A receptor-mediated ion channel activity, resulting in reduced downstream intestinal motor responses. These findings identify the 5-HT3A receptor as a molecular target of HST and provide mechanistic insight into its pharmacological actions on 5-HT-mediated intestinal dysfunction.