Abstract: Objective To study the changes of the transient outward K+ current (Ito), delayed rectifier K+ current(IkDR) and the inward rectifier K+ current(Ik1) of the rat bone mesenchymal stem cells (MSCs) induced by 5-azacytidine（5-Aza） during proliferating and differentiating process in vitro. Methods The MSCs were cultured according to related articles for two weeks and then some of the cells were induced by 5-azacytidine .The experiment was divined into uninduced（cultured for 6w） and induced(1、2、3、4w) cell groups. Each week had twenty cells random tested by the whole-cell patch clamp technology and the K+ currents were identified by corresponding ionic blockers. Results The detection rate of the same type of K+ current among test weeks had no significant deviation; The three types of K+ current intensity were gradually augmented after being inducing cultured for 1﹑2﹑3﹑4weeks(p<0.05).When compared to the uninduced cells, the same type of K+ current intensity of 1w-induced cells had no significant deviation, however, the current intensity was augmented begin at 2w-induced cells（p<0.05）and significant augmented at 4w-induced cells（p<0.01）.Conclusion 5-Aza induction had the early stage augmented effects to the MSCs induced by 5-Aza during proliferating and differentiating process in vitro.

Key words: mesenchymal stem cells, 5-azacytidine, whole-cell patch clamp, K+ current