title: Characterization of a novel SCN5A mutation associated with Brugada syndrome reveals involvement of DIIIS4-S5 linker in slow inactivation.
abstract: OBJECTIVE
  Mutations in SCN5A, the gene encoding the alpha-subunit of the cardiac sodium channel (Na(v)1.5), have been associated with various inherited arrhythmia syndromes, including Brugada syndrome (BrS). Here, we report the functional consequences of a novel missense SCN5A mutation, G1319V, identified in a BrS patient. The G1319V mutation is located in the loop connecting transmembrane segments 4 and 5 in domain III (DIIIS4-S5), a region so far considered to be exclusively involved in fast inactivation.
  
  
  METHODS
  Whole-cell mutant (G1319V) and wild-type (WT) sodium currents (I(Na)) were studied in the Human Embryonic Kidney cell line (HEK-293) transfected with Na(v)1.5 alpha-subunit cDNA (WT or mutant) together with h beta(1)-subunit cDNA, using the patch-clamp technique.
  
  
  RESULTS
  Maximal peak I(Na) and persistent sodium current were similar in WT and channel G1319V channels. The G1319V mutation shifted the potential of half-maximal (V(1/2)) activation towards more positive potentials (+3.7 mV), thereby increasing the degree of depolarization required for activation. The V(1/2) of inactivation of G1319V channels was shifted by -6.0 mV compared to WT, resulting in a reduced channel availability. The change in the steady-state inactivation was completely due to a negative shift (-6.8 mV) of the voltage-dependence of slow inactivation, while the voltage-dependence of fast inactivation was unaffected. The fast component of recovery from inactivation of G1319V channels was slowed down. Finally, the G1319V mutation caused a two-fold increase in the propensity of the channels to enter the slow inactivated state. Reduction in I(Na) peak amplitude on repetitive depolarizations at short interpulse intervals (40 ms) was significantly more pronounced in G1319V compared to WT. Accordingly, carriers of the G1319V mutation showed marked QRS widening upon increases in heart rate during exercise testing, pointing to enhancement of slow inactivation.
  
  
  CONCLUSIONS
  We identified the DIIIS4-S5 linker as a new region involved in slow inactivation of Na(v)1.5. The biophysical alterations of the G1319V mutation all contribute to a reduction in I(Na), in line with the proposed mechanism underlying BrS.
authors.affiliation: Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Simona
authors.initials: S
authors.lastname: Casini
authors.forename: Hanno L
authors.initials: HL
authors.lastname: Tan
authors.forename: Zahurul A
authors.initials: ZA
authors.lastname: Bhuiyan
authors.forename: Connie R
authors.initials: CR
authors.lastname: Bezzina
authors.forename: Phil
authors.initials: P
authors.lastname: Barnett
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Cerbai
authors.forename: Alessandro
authors.initials: A
authors.lastname: Mugelli
authors.forename: Arthur A M
authors.initials: AA
authors.lastname: Wilde
authors.forename: Marieke W
authors.initials: MW
authors.lastname: Veldkamp
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D053840:Brugada Syndrome / Q000235:genetics* / Q000503:physiopathology; D002460:Cell Line; D004562:Electrocardiography; D055724:Electrophysiological Phenomena; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics*; D020125:Mutation, Missense / Q000235:genetics*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D018408:Patch-Clamp Techniques; D010641:Phenotype; D017434:Protein Structure, Tertiary / Q000235:genetics*; D015222:Sodium Channels / Q000032:analysis / Q000737:chemistry / Q000235:genetics*
chemical_list: D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; D015222:Sodium Channels