TNF and atrial fibrillation: This stretch protocol promoted significant upregulation of NGF gene expression in both NP and AF cells (2.33- ± 0.93-fold and 1.99- ± 0.65-fold, respectively; P = 0.0099 and P = 0.032, respectively), as well as significant upregulation of TNF expression in AF cells (3.02- ± 1.41-fold; P = 0.027), compared to static controls (Figure 3B).