Abstract
In cardiomyocytes, β-adrenergic receptor (β-AR) stimulation activates protein kinase A (PKA), which increases electrical conduction velocity. Connexin-43 (Cx43) form gap junction (GJ) channels at the intercalated discs of cardiomyocytes and ensure electrical impulse propagation. This is essential for coordinated cardiac contractions. In myocardial infarction (MI), Cx43 is altered that affects GJ communication, electrical conduction leading to fatal arrhythmias. Regardless the cause, the β-AR system is activated after a MI. Considering the key role of Cx43, we investigated the functional regulation of GJ by PKA-anchored through A-Kinase Anchoring Protein (AKAP) in cardiac physiology and pathophysiology (MI). Neonatal rat ventricular cardiomyocytes were cultured with peptides that inhibit PKA or displace PKA anchoring from AKAP in basal condition or after β-AR stimulation. Cx43 phosphorylation level and GJ communication were assessed by immunoblot and GAP-Fluorescence Loss In Photobleaching experiments. A Cx43-PKA-AKAP signaling complex in cardiomyocytes and heart was investigated by immunofluorescence, immunoblot or immunoprecipitation. Proximity ligation assays were performed in cells and tissue in physiological conditions and after MI. Our experiments point to a PKA-scaffold protein required for PKA-mediated regulation of Cx43 phosphorylation and GJ communication. We show that the AKAP named ezrin forms a molecular complex with PKA and Cx43 in rat heart at the cellular and tissue levels. While PKA and ezrin expression levels remain constant, Cx43 showed a significant reduction after a MI. Interestingly, we noticed a decreased in Cx43 vicinity with ezrin at the ID of ventricular cardiomyocytes. These data suggest for a role of PKA-ezrin-Cx43 complex in the regulation of GJ communication in cardiac physiology. A deregulation of this complex could explain partly the altered electrical propagation observed after a MI.
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