Abstract: Objective The purpose of this study was to investigate the change of AQP4 and Kir4.1's expression to explore the mechanism of brain edema after CIR. Methods A total of 136 healthy SD rats were randomly divided into two groups , CIR group and control group.CIR models were established by occluding unilateral middle cerebral artery of the rats with suture method.The sutures were removed after two hours to allow reperfusion.The brains of the rats were taken out at 6h、12h、24h、48h、72h and 7d after reperfusion.The change of brain water content(BWC) was measured by the wet and dry weight .AQP4 and Kir4．l were detected by immunofluorescence．The contents of AQP4 and Kir4．1 mRNA were detected by RT-PCR．And calculated the ratios of AQP4 mRNA and Kir4．1 mRNA Results The BWC of ischemic brain tissue increased form CIR 6h ,and reached its peak during the CIR 48-72h. The permeability of BBB increased after CIR,the increasing permeability had two peaks,at CIR12h and CIR 48h respectively。AQP4 and Kir4．1 were co-expressed at cerebral pia mater、choroid plexes and ependyma 。The expression of AQP4 and Kir4.1mRNA increased after CIR.The ratio of AQP4 and Kir4．1 mRNA began to increased at 12 h after CIR．Conclusions In the early stage after CIR,The increased capillary vessel permeability induced the brain edema;In the later stage．The redistribution of AQP4 and Kir4．1 played an important role in the pathological course of CIR brain edema.

Key words: Cerebral ischemia reperfusion, Aquaporin, Potassium, Brain edema