title: SAP97 and dystrophin macromolecular complexes determine two pools of cardiac sodium channels Nav1.5 in cardiomyocytes.
abstract: BACKGROUND
  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.
  
  
  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.
authors.affiliation: University of Bern, Department of Clinical Research, Murtenstrasse, 35, 3010 Bern, Switzerland.
authors.forename: Séverine
authors.initials: S
authors.lastname: Petitprez
authors.forename: Anne-Flore
authors.initials: AF
authors.lastname: Zmoos
authors.forename: Jakob
authors.initials: J
authors.lastname: Ogrodnik
authors.forename: Elise
authors.initials: E
authors.lastname: Balse
authors.forename: Nour
authors.initials: N
authors.lastname: Raad
authors.forename: Said
authors.initials: S
authors.lastname: El-Haou
authors.forename: Maxime
authors.initials: M
authors.lastname: Albesa
authors.forename: Philip
authors.initials: P
authors.lastname: Bittihn
authors.forename: Stefan
authors.initials: S
authors.lastname: Luther
authors.forename: Stephan E
authors.initials: SE
authors.lastname: Lehnart
authors.forename: Stéphane N
authors.initials: SN
authors.lastname: Hatem
authors.forename: Alain
authors.initials: A
authors.lastname: Coulombe
authors.forename: Hugues
authors.initials: H
authors.lastname: Abriel
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism; D000074288:Discs Large Homolog 1 Protein; D016189:Dystrophin / Q000235:genetics / Q000378:metabolism*; D049029:Dystrophin-Associated Proteins / Q000378:metabolism; D020868:Gene Silencing; D051528:Guanylate Kinases; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018101:Mice, Inbred mdx; D023421:Models, Animal; D009124:Muscle Proteins / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000378:metabolism*; D014162:Transfection
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018031:Connexin 43; C513314:DLG1 protein, human; D000074288:Discs Large Homolog 1 Protein; C000614189:Dlg1 protein, mouse; C501119:Dlg1 protein, rat; D016189:Dystrophin; D049029:Dystrophin-Associated Proteins; D008565:Membrane Proteins; D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; C568321:Scn5a protein, mouse; C568322:Scn5a protein, rat; D015222:Sodium Channels; C091824:syntrophin; D051528:Guanylate Kinases