(A) Inhibitory effect of LNA–miR-mimic on induction (left) and maintenance in inducible animals (right) of AF induced in mice also treated with LNA–anti–miR-26a. MM LNA–miR-mimic, mismatched miR-mimic (negative control). Number inducible/total used is indicated by n/N values within brackets. *P < 0.05, ***P < 0.001 vs. WT; ^ϕϕP < 0.01, ^ϕϕϕP < 0.001 vs. LNA–anti–miR-26a alone; ^§P < 0.05 vs. LNA–anti–miR-26a + LNA–miR-mimic. (B) Western blot verifying ability of miR-mimic to knock down Kir2.1. **P < 0.01 vs. WT; ^ϕϕP < 0.01 vs. LNA–anti–miR-26a alone; ^§§P < 0.01 vs. LNA–anti–miR-26a + LNA–miR-mimic; n = 6 for each group. (C) LNA–miR-mask abolishes the protective effect of adv–miR-26a against AF induction (left) and maintenance (right). +LNA–miR-mask,mice injected with LNA–miR-mask (5 mg/kg/d daily for 3 days before injection of adv–miR-26a); LNA–miR-mask, mice injected with LNA–miR-mask alone; MM miR-mask, mismatched miR-mask (negative control). *P < 0.05 vs. WT; ^ϕP < 0.05, ^ϕϕP < 0.01 vs. adv–miR-26a alone; ^§§P < 0.01 vs. adv–miR-26a + LNA–miR-mask. (D) Western blot verifying ability of miR-mask to protect against Kir2.1 knockdown by adv–miR-26a. ***P < 0.001 vs. WT; ^ϕϕϕP < 0.001 vs. adv–miR-26a alone; ^§§§P < 0.001 vs. adv–miR-26a + LNA–miR-mask; n = 6/group. Values are mean ± SEM. Group definitions as in Figure 3. Note: the experiments shown in Figure 3A and Figure 4, A and C, were done contemporaneously. Thus, the same WT group data serve as controls in each case, and the same LNA–anti–miR-26a and adv–miR-26a data are shown in Figure 3 and Figure 4. Related data sets for AF incidence and AF duration are shown separately for clarity in display. However, statistical comparisons were performed between all animals with interventions simultaneously (see Supplemental Figure 6).