Effect Of Cyclovirobuxine D On The Contractility Of Gastrointestinal Smooth Muscle

Research background and objective: Cyclovirobuxine D, which belongs to non-glucoside cardioctonic agents, inhibits the activity of Na~+-K~+-ATPase. Up to nowadays, the characterization of cyclovirobuxine D's effect on gastrointestinal smooth muscle is still not clear. In this study, we tried to characterize the effect of cyclovirobuxine D on gastrointestinal smooth muscle contractility, to partially reveal the possible mechanism, and to provide information for further corresponding investigation.Methods The contractility of ex vivo gastric and intestinal smooth muscle of rat, and in vitro phosphorylation of myosin light chain were chosen as the indexes. Deslanoside was used as the positive control in the study. Low and high contractile states of gastric and intestinal smooth muscle were established by changing ionic concentration of Krebs'solution or modification of Krebs'solution using other agents. Myosin and MLCK used in the assay were purified from chicken gizzard smooth muscle. 10% GLY-PAGE was used to detect the effect of cyclovirobuxine D and deslanoside on myosin light chain phosphorylation which was interacted by MLCK in a Ca2+-CaM dependant manner. The comparison and concurrent use of the cyclovirobuxine D and deslanoside on gastrointestinal smooth muscle were performed in both of low and high contractile states of gastric and intestinal smooth muscle. The effects of cyclovirobuxine D and deslanoside on myosin light chain phophorylation were studied.Results (1) Cyclovirobuxine D stimulated the contraction of ex vivo gastric smooth muscle; in contrast, deslanoside was inhibited the contraction of ex vivo gastric smooth muscle. Concurrent use of cyclovirobuxine D and deslanoside enhanced the contraction of vivo gastric smooth muscle in low contractile states and inhibited the contraction in high contractile states; it is a bidirectional regulation. (2) Both of cyclovirobuxine D and deslanoside produced bidirectional regulation on ex vivo intestinal smooth muscle in aforementioned assay conditions. (3) Concurrent use of cyclovirobuxine D and deslanoside inhibited the phosphorylation of myosin light chain in fully phosphorylated extent but could not enhance the phosphorylation exent of partially phosphorylated of myosin.Conclusion The bidirectional regulation of cyclovirobuxine D on intestinal smooth muscle contraction and the bidirectional regulation obtained from concurrent use of cyclovirobuxine D and deslanoside on gastric smooth muscle contraction may decrease the adverse drug reaction and provide information for the preclinical investigation of drugs for relieving the functional disorder of gastrointestinal smooth muscle.