title: Contribution of neuronal sodium channels to the cardiac fast sodium current INa is greater in dog heart Purkinje fibers than in ventricles.
abstract: OBJECTIVE
  To determine the presence and the potential contribution of neuronal sodium channels to dog cardiac function.
  
  
  METHODS
  We used a combination of electrophysiological (patch clamp), RT-PCR, biochemical and immunohistochemical techniques to identify and localize neuronal Na(+) channels in dog heart and determine their potential contribution to the fast sodium current.
  
  
  RESULTS
  In all cardiac tissues investigated, Na(v)1.1, Na(v)1.2 and Na(v)1.3 transcripts were detected. In immunoblots, we found Na(v)1.1 and Na(v)1.2 proteins in the ventricle (V) and in Purkinje fibers (PF). Na(v)1.3 immunoblots suggested strong proteolytic activity against this isoform in the heart. Na(v)1.6 was not found in any of the tissues tested. Confocal immunofluorescence on cardiac myocytes showed that Na(v)1.1 was predominantly localized at the intercalated disks in V and PF and around the nucleus (V). Na(v)1.2 was only present at the Z lines (V). Consistent with the immunoblot data, an intense but diffuse intracellular staining was observed for Na(v)1.3. Na(v)1.6 fluorescence staining was faint and diffuse. Surprisingly, immunoblots indicated the presence of two Na(v)beta 2 variants: a 42-kDa protein that co-localized with Na(v)1.2 at the Z lines in V and a 34-kDa protein that co-localized with Na(v)1.1 at the intercalated disks in PF. In agreement with the biochemical data, electrophysiological results suggest that neuronal sodium channels generate 10+/-5% and 22+/-5% of the peak sodium current in dog ventricle and Purkinje fibers, respectively.
  
  
  CONCLUSIONS
  Our results suggest that neuronal NaChs are more abundant in Purkinje fibers than in ventricles, and this suggests a role for them in cardiac conduction.
authors.affiliation: Friedrich Schiller University Jena, Institute of Physiology II, Teichgraben 8, 07740 Jena, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Haufe
authors.forename: J M
authors.initials: JM
authors.lastname: Cordeiro
authors.forename: T
authors.initials: T
authors.lastname: Zimmer
authors.forename: Y S
authors.initials: YS
authors.lastname: Wu
authors.forename: S
authors.initials: S
authors.lastname: Schiccitano
authors.forename: K
authors.initials: K
authors.lastname: Benndorf
authors.forename: R
authors.initials: R
authors.lastname: Dumaine
mesh_terms: D000818:Animals; D004285:Dogs; D006352:Heart Ventricles; D015151:Immunoblotting; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000737:chemistry / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011690:Purkinje Fibers / Q000737:chemistry / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015222:Sodium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D015222:Sodium Channels; D000254:Sodium-Potassium-Exchanging ATPase