Effects of triterpenoids from Poria cocos Wolf on the serotonin type 3A receptor-mediated ion current in Xenopus oocytes

Abstract

Poria cocos Wolf ( P. cocos Wolf) is used to treat chronic gastritis, edema, nephrosis, gastric atony, acute gastroenteric catarrh, dizziness, emesis and vomiting. Triterpenoids are a class of natural compounds produced by P. cocos Wolf that contain acyclic 30-carbon precursors. In this study, we investigated the effect of triterpenoids (PA, Pachymic acid; DA, dehydroeburicoic acid; HA, 3β-hydroxylanosta-7,9(11),24-trien-21-oic acid) on human 5-hydroxytryptamine 3A (5-HT 3A) receptor channel activity, which is one of the ligand-gated ion channel families. The two-electrode voltage-clamp technique was used to examine the 5-HT3A mediated current. The inhibitory effect of triterpenoids on 5HT-induced inward current ( I 5-HT) occurred in a concentration dependent and reversible manner. Furthermore, the half-inhibitory concentrations (IC 50) of PA, DA and HA were 3.2 ± 0.2, 5.5 ± 0.6 and 1.4 ± 0.2 µM, respectively. This corresponded to an order of potency for the inhibition of I 5-HT in oocytes expressing human 5-HT 3A receptor of HA > PA > DA. Finally, inhibition of I 5HT by triterpenoids occurred in a non-competitive manner, while inhibition by HA and PA showed more voltage-dependency. Taken together, these results indicate that triterpenoids may regulate the expressed 5-HT 3A receptors in Xenopus oocytes. Furthermore, this regulation of the ligand-gated ion channel activity by triterpenoids may be one of the pharmacological actions of P. cocos Wolf.