Objective: Astragaloside Ⅳ (As(Ⅳ)) is the major effective component extracted from the Chinese herb Astragalus membranaceus,which has been widely used to treat cardiovascular disease.Recent studies have shown that As(Ⅳ)can potentially protect the heart from myocardial ischemic injury,but the mechanisms of action are unknown.ATP-sensitive potassium (KATP) channels are activated during ischemia and exert a compensatory protective effect on cardiomyocytes.We therefore examined the effects of As(Ⅳ) on KATP channel currents and channel expression in isolated rat ventricular cardiomyocytes after ischemia-reperfusion injury.Methods: Forty Wistar rats were divided into five groups: control group,ischemia-reperfusion (IP) group,IP +glibenclamide group,IP + pinacidil group and IP + AsIV group.The ischemia-reperfusion injury model was established in enzymatically isolated ventricular cardiomyocytes by perfusion with calcium-free Tyrode solution for 10 min,arrest for 30 min,and reperfusion for 45 min.The different drugs were applied for 10-15 min,and the KATP channel current (IKATP) was recorded with voltage-clamp mode by whole-cell patch-clamp technique.Protein and mRNA expression of the KATP channel subunits Kir6.1,Kir6.2,SUR2A and SUR2B was quantified using west blotting and real-time PCR.Results: The KATP current in IP group was significantly greater than that in control group (211.45+33.67 vs 83.51+23.67 pA; P＜0.01).Glibenclamide (10 μmol/L) blocked KATP currents,whereas both AsIV (1 mg/L) and the known channel opener pinacidil (50 μmol/L) significantly increased IKATP (P＜0.05).Consistent with this,As(IV)significantly up-regulated protein and mRNA expression of Kir6.1,Kir6.2,SUR2A,SUR2B (P＜0.01 vs IP group).Conclusion: The protective effects of As(IV) in ischemia-reperfusion injury may be related to the up-regulation of several KATP channel subunits and facilitation of KATP currents.