Abstract 16120: PDZ Domain-Binding Motif of the Cardiac Sodium Channel Nav1.5 Regulates Functional Channel Expression at the Cell Membrane
Background: Regulation of cardiac ion channels through their interaction with proteins is an essential aspect of cardiac ion channel function. Previous evidence has implicated PDZ domain-binding motifs in the correct targeting, localization, and anchoring of ion channels in the heart. Using a knock-out dystrophin mouse strain, we showed that disruption of the dystrophin-syntrophin macromolecular complex that associates with this motif, contributes to impaired cardiac excitability and impulse propagation.
Aim: Goal of this study was to investigate the significance of the PDZ-domain binding motif in the expression and function of the cardiac sodium channel, Nav1.5, using a new knock-in mouse strain.
Methods and Results: In vivo studies were performed using a homozygous knock-in mouse line lacking the last three amino acids of the Nav1.5 channel, Ser-Ile-Val (ΔSIV), which constitute the PDZ domain-binding motif. Immunostainings of ventricular sections showed loss of Nav1.5 channels at the lateral membranes of ΔSIV cardiomyocytes, where dystrophin and syntrophin are specifically localized. At the intercalated discs, Nav1.5 expression was not significantly altered. Western blots of SIV hearts revealed a decrease of 22% in the protein levels of Nav1.5 while levels of syntrophin and dystrophin were unchanged. These observations were consistent with patch-clamp studies showing a decrease of sodium current by 36.5±4.9% in ΔSIV cardiomyocytes when compared to wild-type cells. This was also reflected in a slowing of 35.4±3.2% of maximal upstroke velocity of the cardiac action potential. Finally, surface ECGs of ΔSIV mice displayed a pronounced QRS-interval prolongation of 25.3% compared to wild-type mice, which reflects an impeded ventricular conduction as a consequence of the loss of functional Nav1.5 channels.
Conclusions: These results suggest that the PDZ-domain binding motif of Nav1.5 is necessary for the correct expression of Nav1.5 channels, particularly at the lateral membrane of cardiomyocytes, which could be attributed to its interaction with stabilizing PDZ domain-containing proteins such as syntrophin.
- © 2011 by American Heart Association, Inc.