Abstract Oxidative stress could be a possible mechanism and a therapeutic target of atrial fibrillation (AF). However, the effects of the xanthine oxidase (XO) inhibition for AF remain to be fully elucidated. We investigated the effects of a novel XO inhibitor febuxostat on AF compared to allopurinol in hypertension rat model. Five-week-old Dahl salt-sensitive rats were fed to either low-salt (LS) (0.3% NaCl) or high-salt (HS) (8% NaCl) diet. After 4 weeks of diet, HS diet rats were divided into 3 groups: orally administered to vehicle (HS-C), febuxostat (5mg/kg/day) (HS-F), or allopurinol (50mg/kg/day) (HS-A). After 4 weeks of treatment, systolic blood pressure was significantly higher in HS-C than LS, and it was slightly but significantly decreased by treatment with each XO inhibitor. AF duration was significantly prolonged in HS-C compared with LS, and significantly suppressed in both HS-F and HS-A (LS; 5.8±3.5 sec, HS-C; 33.9±23.7 sec, HS-F; 15.0±14.1 sec, HS-A; 20.1±11.9 sec: P<0.05). Ca2+ spark frequency was obviously increased in HS-C rats and reduced in the XO inhibitor-treated rats, especially in HS-F group. Western blotting revealed that the atrial expression levels of methionine 281/282-oxidized Ca2+/Calmodulin-dependent kinase II and serine 2814-phosphorylated ryanodine receptor 2 were significantly increased in HS-C, and those were suppressed in HS-F and HS-A. Decreased expression of gap junction protein connexin 40 in HS-C was partially restored by treatment with each XO inhibitor. In conclusion, XO inhibitor febuxostat, as well as allopurinol, could reduce hypertension-related increase in AF perpetuation by restoring Ca2+ handling and gap junction.

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