TNFRSF11B and atrial fibrillation: The mRNA expression levels of RANKL and OPG by NP cells were significantly higher than those by AF cells (relative expression in the NP (vs. AF): RANKL 2.77 ± 0.76; OPG 4.92 ± 0.74, p < 0.05, respectively) (Fig. 2b, c).