SAP97 and Dystrophin Macromolecular Complexes Determine Two Pools of Cardiac Sodium Channels Na v 1.5 in Cardiomyocytes
Copyright policy )SAP97 and Dystrophin Macromolecular Complexes Determine Two Pools of Cardiac Sodium Channels Na v 1.5 in Cardiomyocytes
Rationale: The cardiac sodium channel Na v 1.5 plays a key role in excitability and conduction. The 3 last residues of Na v 1.5 (Ser-Ile-Val) constitute a PDZ-domain binding motif that interacts with the syntrophin–dystrophin complex. As dystrophin is absent at the intercalated discs, Na v 1.5 could potentially interact with other, yet unknown, proteins at this site. Objective: The aim of this study was to determine whether Na v 1.5 is part of distinct regulatory complexes at lateral membranes and intercalated discs. Methods and Results: Immunostaining experiments demonstrated that Na v 1.5 localizes at lateral membranes of cardiomyocytes with dystrophin and syntrophin. Optical measurements on isolated dystrophin-deficient mdx hearts revealed significantly reduced conduction velocity, accompanied by strong reduction of Na v 1.5 at lateral membranes of mdx cardiomyocytes. Pull-down experiments revealed that the MAGUK protein SAP97 also interacts with the SIV motif of Na v 1.5, an interaction specific for SAP97 as no pull-down could be detected with other cardiac MAGUK proteins (PSD95 or ZO-1). Furthermore, immunostainings showed that Na v 1.5 and SAP97 are both localized at intercalated discs. Silencing of SAP97 expression in HEK293 and rat cardiomyocytes resulted in reduced sodium current ( I Na ) measured by patch-clamp. The I Na generated by Na v 1.5 channels lacking the SIV motif was also reduced. Finally, surface expression of Na v 1.5 was decreased in silenced cells, as well as in cells transfected with SIV-truncated channels. Conclusions: These data support a model with at least 2 coexisting pools of Na v 1.5 channels in cardiomyocytes: one targeted at lateral membranes by the syntrophin-dystrophin complex, and one at intercalated discs by SAP97.
- Cornell University United States
- University of Bern Switzerland
- University of Paris France
- Sorbonne Paris Cité France
- Universitätsmedizin Göttingen Germany
Cell Membrane, Membrane Proteins, Muscle Proteins, NAV1.5 Voltage-Gated Sodium Channel, Discs Large Homolog 1 Protein, Dystrophin, Mice, Inbred C57BL, Mice, HEK293 Cells, Connexin 43, Dystrophin-Associated Proteins, Models, Animal, Mice, Inbred mdx, Animals, Humans, Myocytes, Cardiac, Gene Silencing, Guanylate Kinases, Cells, Cultured, Adaptor Proteins, Signal Transducing
Cell Membrane, Membrane Proteins, Muscle Proteins, NAV1.5 Voltage-Gated Sodium Channel, Discs Large Homolog 1 Protein, Dystrophin, Mice, Inbred C57BL, Mice, HEK293 Cells, Connexin 43, Dystrophin-Associated Proteins, Models, Animal, Mice, Inbred mdx, Animals, Humans, Myocytes, Cardiac, Gene Silencing, Guanylate Kinases, Cells, Cultured, Adaptor Proteins, Signal Transducing
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