When MEK1/2 inhibitors (PD98059, U0129) were added with AF, ERK1/2 phosphorylation was inhibited significantly in the cortical neurons (PD98059, 0.54 ± 0.08; UO126, 0.24 ± 0.04, n = 4) (Fig. 1b). Here, MAP2K1 is linked to atrial fibrillation.