Figure 4a shows a significantly smaller increase in cytosolic cAMP levels upon ISO stimulation in AF myocytes compared to Ctl myocytes (p < 0.0001). Interestingly, this deregulation on cAMP levels is differentially regulated in the different cellular compartments. Contrary to the reaction in the cytosol, the increase of cAMP levels upon ISO stimulation was similar between Ctl and AF myocytes in the sarcolemma and the RyR2 compartments (Figure 4a). This evidence concerns the gene RYR2 and atrial fibrillation.