Abstract: Objective This paper discusses the effects of two weeks exhaustive treadmill running on rapidly activating IKr channel of rat sinoatrial node. Methods SD rats were equally assigned into 5 groups，including 1 control groups（C group）, 2 groups undergoing single exhaustive treadmill running（O group）, and 2 groups undergoing two weeks repeated treadmill running（R group）,10 rats each group. After two weeks normal feeding，single exhaustive treadmill running was carried out for the O group. Exhaustive treadmill running was carried out for the R groups 6 days per week for total of two weeks. The samples were drawn from rats at 0 and 24 hours after exercise. The rats of O group were named O-0h、O-24h, respectively, the rats of R group were named R-0h、R-24h, respectively. The mRNA and protein expression of IKr channel subunit in sinoatrial node were analyzed by real-time fluorescent quantitative PCR and Western Blot，the current density of IKr channel were analyzed by whole-cell patch clamp analysis. Results 1) The ERG1b mRNA and protein expression of the repeated treadmill running R-0h and R-24h group were significantly lower than that of C and O-0h group（P<0.01）. 2) The current density of IKr of the repeated treadmill running R-0h and R-24h group were 0.89±0.03pA/pF、1.02±0.01pA/pF respectively, significantly lower than that of C and O-0h group（P<0.01, P<0.01）. Conclusion Exhaustive exercise downregulated the sinoatrial node ERG1b gene subunit expression, along with the corresponding current IKr, and may be one of the most important mechanism of exercise-induced sinoatrial node dysfunction and arrhythmia.

Key words: treadmill running, sinoatrial node, rapidly activating IKr channel, the pore-forming subunite ERG1b