Ardipusilloside-I stimulates gastrointestinal motility and phosphorylation of smooth muscle myosin by myosin light chain kinase

Ardipusilloside-I is a natural triterpenoid saponin, which was isolated from Ardisia pusilla A. DC. The aim of the study was to evaluate the stimulation of ardipusilloside-I on gastrointestinal motility in vitro and in vivo. The experiment of smooth muscle contraction directly monitored the contractions of the isolated jejunal segment (IJS) in different contractile states, and the effects of ardipusilloside-I on myosin were measured in the presence of $Ca^{2+}$-calmodulin using the activities of 20 kDa myosin light chain ($MLC_{20}$) phosphorylation and myosin $Mg^{2+}$-ATPase. The effects of ardipusilloside-I on gastro emptying and intestinal transit in constipation-predominant rats were observed, and the MLCK expression in jejuna of constipated rats was determined by western blot. The results showed that, ardipusilloside-I increased the contractility of IJS in a dose-dependent manner and reversed the low contractile state (LCS) of IJS induced by low $Ca^{2+}$, adrenaline, and atropine respectively. There were synergistic effects on contractivity of IJS between ardipusilloside-I and ACh, high $Ca^{2+}$, and histamine, respectively. Ardipusilloside-I could stimulate the phosphorylation of $MLC_{20}$ and $Mg^{2+}$-ATPase activities of $Ca^{2+}$- dependent phosphorylated myosin. Ardipusilloside-I also stimulated the gastric emptying and intestinal transit in normal and constipated rats in vivo, respectively, and increased the MLCK expression in the jejuna of constipation-predominant rats. Briefly, the findings demonstrated that ardipusilloside-I could effectively excite gastrointestinal motility in vitro and in vivo.