Objective: To study the effects of gypenoside (Gyp) on the activity of microsomal Na(+), K(+)-ATPase in rat's heart and brain in vitro.
Methods: The microsomal Na(+), K(+)-ATPase was prepared from rat's heart and brain by differential centrifugation. The activity of microsomal Na(+), K(+)-ATPase was assayed by colorimetric technique. Enzyme kinetic analysis method was used to analyze the effect of Gyp on the microsomal Na(+), K(+)-ATPase of rats.
Results: Gyp reversibly inhibited the brain and heart's microsomal Na(+), K(+)-ATPase in a concentration-dependent manner, and showed a more potent effect on enzyme in the brain. The IC(50) of Gyp for the heart and brain were 58.79+/-8.05 mg/L and 52.07+/-6.25 mg/L, respectively. The inhibition was enhanced by lowering the Na(+), or K(+) concentrations or increasing the ATP concentration. Enzyme kinetic studies indicated that the inhibitory effect of Gyp on the enzyme is like that of competitive antagonist of Na(+), the counter-competitive inhibitor for the substrate ATP, and the mixed-type inhibitor for K(+).
Conclusion: Gyp displays its cardiotonic and central inhibitory effects by way of inhibiting heart and brain's microsomal Na(+), K(+)-ATPase activities in rats.