The regulatory effect of Alisma Rhizomes and their triterpenoids on α3β4 nicotinic acetylcholine receptor activity

Abstract

Alisma Rhizomes is used as a diuretic, hypolipidemic, anti-diabetic and anti-inflammatory agent in traditional East-Asian medicine. In this study, we tested the effect of Alisma Rhizomes on the α3β4 nicotinic acetylcholine (nACh) receptor channel current in Xenopus oocytes. The acetylcholine-induced inward peak current (IACh) was measured with the two-electrode voltage-clamp technique. This experiment shows that the α3β4 nACh receptor cRNA injected into oocytes followed by co-application with Alisma Rhizomes inhibited IACh in a noncompetitive or voltage insensitive condition. The half maximal inhibitory concentration (IC50) of Alisma Rhizomes was 12.5 ± 3.4 μg/ml and the Vmax was 55.4 ± 4.7. Protostane-type triterpenoids are the main active ingredient of Alisma Rhizomes (Alisol A, Alisol B, Alisol B 23-acetate, Alisol C 23-acetate). The respective IC50 values of Alisol A, Alisol B, Alisol B 23-acetate, and Alisol C 23-acetate were 1.7 ± 0.1, 2.8 ± 0.5, 2.6 ± 0.7 and 3.5 ± 0.3 μM in the α3β4 nACh receptor expressed in Xenopus oocytes. Altogether, our research shows that protostane-type triterpenoids may modulate the α3β4 nACh receptors expressed in oocytes in a reversible, concentration dependent and non-competitive manner. Furthermore, this modulation of the nACh receptor activity by protostane-type triterpenoids could underlie the pharmaceutics actions of Alisma rhizome.