Abstract 1525: Atrial Rhythm Acutely Modulates Connexin43 Expression and Phosphorylation State in Human Atrial Fibrillation
Background: Adjacent areas of heterogenous conduction in the atria form a substrate for atrial fibrillation (AF). Connexin proteins (Cx) underlie conduction between myocytes; conduction is modulated by connexin expression and phosphorylation. Here we tested the hypothesis that left atrial (LA) expression and/or phosphorylation of Cx43 is distinctly regulated by atrial rhythm.
Methods: Cx43 expression and phosphorylation was evaluated in LA tissue homogenates from 3 groups:
cardiac surgery patients with history of AF presenting for surgery in AF (AFAF, n=8);
history of AF but in sinus rhythm (AFSR, n=8);
patients with no history of AF (CTL, n=8). Groups were matched for age, LA size, EF (>50%), CAD, valve disease, and hypertension.
Results: Western blot analysis revealed increased total Cx43 expression (t-Cx43) in AFAF (2.03±0.38) compared to AFSR (0.85±0.15, p=0.01) and SR (0.98±0.16, p=0.02) groups. Blots re-probed with an antibody detecting non-phosphorylated Cx43 at S368 (Np-Cx43) revealed a significant decrease in the Np-Cx43/t-Cx43 ratio, indicating increased S368 phosphorylation in the AFAF group (by 23% in AFAF vs. AFSR, p=0.046; by 12% in AFAF vs. CTL, p=0.051). Subcellular compartmentation of t-Cx43 was assessed in 3 samples per group using tissue fractionation and immunoblotting. Cytoskeletal t-Cx43 levels were increased in AFAF vs. AFSR and vs. CTL, ANOVA, p=0.016); t-Cx43 expression was not different between groups in membrane, cytoplasmic or nuclear fractions. Confocal microscopy revealed greater Cx43 lateralization in both AF groups compared to CTL.
Conclusion: Our results (increased Cx43 expression and phosphorylation) suggest that AF rhythm at the time of surgery, more than the history of AF, has a distinct impact on LA Cx43 remodeling. Further the dynamic increase restricted to the cytoskeletal compartment suggests that cytoskeletal changes in AF may modulate connexin trafficking to the cell surface. This may affect the anisotropic properties of atrial conduction. Additional electrophysiological studies are needed to determine the functional contribution of lateralized Cx. Our study provides the first evidence linking acute rhythm status with regulation of Cx43 expression and phosphorylation in human atria.