Dystrophin deficiency in mdx(5cv) mice caused a 50% decrease in Na(v)1.5 protein levels, a 29% decrease in sodium current, and an 18% increase in QRS duration compared with controls.
The dystrophin protein complex is required for proper expression and function of the cardiac sodium channel Na(v)1.5, providing a mechanistic explanation for conduction abnormalities in dystrophinopathies.
The cardiac sodium channel Na(v)1.5 plays a key role in cardiac excitability and conduction. The purpose of this study was to elucidate the role of the PDZ domain-binding motif formed by the last three residues (Ser-Ile-Val) of the Na(v)1.5 C-terminus. Pull-down experiments were performed using Na(v)1.5 C-terminus fusion proteins and human or mouse heart protein extracts, combined with mass spectrometry analysis. These experiments revealed that the C-terminus associates with dystrophin, and that this interaction was mediated by alpha- and beta-syntrophin proteins. Truncation of the PDZ domain-binding motif abolished the interaction. We used dystrophin-deficient mdx(5cv) mice to study the role of this protein complex in Na(v)1.5 function. Western blot experiments revealed a 50% decrease in the Na(v)1.5 protein levels in mdx(5cv) hearts, whereas Na(v)1.5 mRNA levels were unchanged. Patch-clamp experiments showed a 29% decrease of sodium current in isolated mdx(5cv) cardiomyocytes. Finally, ECG measurements of the mdx(5cv) mice exhibited a 19% reduction in the P wave amplitude, and an 18% increase of the QRS complex duration, compared with controls. These results indicate that the dystrophin protein complex is required for the proper expression and function of Na(v)1.5. In the absence of dystrophin, decreased sodium current may explain the alterations in cardiac conduction observed in patients with dystrophinopathies.
Gavillet et al. (2006) studied Dystrophin deficiency. Dystrophin deficiency vs. Controls was evaluated on Na(v)1.5 protein levels and sodium current. Dystrophin deficiency in mdx(5cv) mice caused a 50% decrease in Na(v)1.5 protein levels, a 29% decrease in sodium current, and an 18% increase in QRS duration compared with controls.