1. Supplemental figure 1 (S1) Levels of circulating AngII. There is a significant higher amount of circulating AngII in both AngII (+) / OA- NO 2 (+) (n=9) and AngII (+) / OA-NO 2 (-) (n=11) animals when compared with to AngII(-) / OA-NO 2 (-) mice (n=11). AngII levels were measured in heparinized mouse plasma by using an AngII Elisa (USCN Business Co., Ltd, Texas, USA) following the standard protocol. Supplement AngII OA-NO 2 +- - - + + 1.5 1 0.5 Ang II concentration (ng/mL) * *

2. Supplemental figure 2 (S2) A B C D E Influence of OA-NO 2 on action potential of isolated cardiomyocytes, assessed by patch clamp technique. There are no significant differences between OA-NO 2 and vehicle treated cells concerning to the membrane potential and the action potential overshoot (A, B). Also regarding to the action potential duration no change could observed when the cells were treated with OA- NO 2 (n=5) (C). Connexin43/N-Cadherin co-staining of murine atrial sections shows no changes in Cx43 expression and distribution in atrial tissue of the different treatment groups (n=6/4/4) (D, E). Scale bar indicates 40 µm. Cx43 positive areas AU

3. Supplemental figure 3 (S3) α-SMA (42 kDa) β-Actin (45 kDa) Influence of OA-NO 2 on α-SMA expression in native cardiac fibroblasts. An 8 hour incubation of isolated murine fibroblasts with OA-NO 2 (n=4) led to a significant reduction of α-SMA expression as compared to control (n=5). For isolation of native cardiac fibroblasts, hearts of wild-type C57BL/6J mice underwent a digestion by using a cocktail of collagenase I and II (Liberase TM Research Grade, Sigma Aldrich, Missouri, USA) following a standard protocol. The isolated cells were cultivated on a petri dish coated with 1% gelatine. After an 8 h incubation with OA-NO 2 (500 nM) or control, proteins were isolated and a Western blot analysis by using a primary antibody against α-SMA was performed. Protein expression (OD ratio)