Abstract 20459: Calcium/Calmodulin-Dependent Protein Kinase II Regulates KCNQ1 to Reduce the Slow Component of the Delayed Rectifier Potassium Current, I Ks

Introduction: Sustained β-adrenergic receptor (β-AR) activation during heart failure has pathologic consequences including enhanced calcium/calmodulin-dependent protein kinase II (CaMKII) activity, which is arrhythmogenic. We previously identified phosphorylated threonine (T) and serine (S) residues (T482, S484, S457) that are in close proximity to the calmodulin-binding domain on the carboxy-terminus of KCNQ1, the pore-forming subunit responsible for I Ks . The objective of this study was to assess the functional impact of phosphorylation at these sites and to investigate the potential for CaMKII to regulate I Ks via phosphorylation of these sites. Methods & Results: Dephosphorylated (alanine; A) and phosphorylated (aspartic acid; D) mimics were introduced on KCNQ1 at T482, S484 and S457. Whole-cell, voltage-clamp experiments were performed in HEK293 cells co-expressing wild-type (WT) or mutant hKCNQ1 and the auxiliary subunit hKCNE1. Sustained β-AR stimulation with isoproterenol (ISO; 100 nM) exposure for 12-24 hours reduced peak I Ks (ISO: 21.5 ± 15.1 pA/pF [mean ± SD], n=14 vs. control: 45.7 ± 35.3, n=20; p Ks versus KN-92 control (n=14; p Ks relative to their dephosphorylated (A) mimics. Lentiviral-mediated CaMKII overexpression reduced I Ks similar to ISO in both WT (n=15; p 0.05). KCNQ1 peptide fragments were synthesized to identify CaMKII phosphorylation sites. The S484 peptide fragment was the strongest phospho-acceptor site for CaMKII whereas the S457 peptide fragment was not phosphorylated by CaMKII. Conclusion: CaMKII phosphorylates S484 on KCNQ1 during sustained β-AR stimulation to reduce I Ks . Phosphorylation at S457 reduces I Ks function but is not regulated via sustained β-AR stimulation or CaMKII. Functional deficits in I Ks during sustained β-AR stimulation may be mediated through enhanced CaMKII signaling.