Abstract 13658: Identification of Two Native Nav1.5 Phosphorylation Sites as Potential Determinants of the Increased Late Na+ Current in Heart Failure

Voltage-gated Na+ (Nav) channels are key determinants of myocardial excitability and defects in Nav channel functioning or regulation, associated with inherited and acquired cardiac disease, increase the risk of life-threatening arrhythmias. In heart failure, the inactivation properties of Nav1.5 channels are altered, resulting in decreased channel availability and increased late Na+ current. Although previous studies have suggested roles for CaMKII and CaMKII-dependent Nav1.5 phosphorylation, the global native phosphorylation pattern of Nav1.5 channels associated with these alterations is unknown. Phosphoproteomic analyses were undertaken to identify and quantify in situ the native phosphorylation sites on the Nav1.5 proteins purified from wild-type and CaMKIIdc-overexpressing (CaMKIIdc-Tg) mouse ventricles. A total of 18 phosphosites were identified, 8 of which are novel compared with our previous MS analyses. Of these 18 phosphosites, the C-terminal phosphoserines pS1937/pS1938 are present in the CaMKIIdc-Tg IPs (n=3/4) and absent in the WT IPs (n=0/4). In addition, pS1989 is 9-fold more represented (p