MMP13 and atrial fibrillation: Treatment with RANKL in the absence of rhIL-1β did not produce a significant effect on the mRNA expression of IL-1β, MMP-3 and MMP-13 by AF cells (relative expression: RANKL 100 ng/mL (vs. RANKL 0 ng/mL), IL-1β 0.89, p = 0.91; MMP-3 1.45, p = 0.98; MMP-13 2.92, p = 0.98) (Fig. 5a–c).