TNFRSF11B and atrial fibrillation: However, there were no significant differences in the expression levels of RANK and OPG among the three types of cells (relative expression in the NP (vs. the AF): RANK 2.26 ± 0.91, RANKL 1.01 ± 0.37, OPG 1.34 ± 0.21; expression in the CEP (vs. the AF): RANK 4.27 ± 1.88, RANKL 2.54 ± 0.58, OPG 1.11 ± 0.39).