title: Functional characterization of a novel frameshift mutation in the C-terminus of the Nav1.5 channel underlying a Brugada syndrome with variable expression in a Spanish family.
abstract: BACKGROUND
  We functionally analyzed a frameshift mutation in the SCN5A gene encoding cardiac Na(+) channels (Nav1.5) found in a proband with repeated episodes of ventricular fibrillation who presented bradycardia and paroxysmal atrial fibrillation. Seven relatives also carry the mutation and showed a Brugada syndrome with an incomplete and variable expression. The mutation (p.D1816VfsX7) resulted in a severe truncation (201 residues) of the Nav1.5 C-terminus.
  
  
  RESULTS
  Wild-type (WT) and mutated Nav1.5 channels together with hNavβ1 were expressed in CHO cells and currents were recorded at room temperature using the whole-cell patch-clamp. Expression of p.D1816VfsX7 alone resulted in a marked reduction (≈90%) in peak Na(+) current density compared with WT channels. Peak current density generated by p.D1816VfsX7+WT was ≈50% of that generated by WT channels. p.D1816VfsX7 positively shifted activation and inactivation curves, leading to a significant reduction of the window current. The mutation accelerated current activation and reactivation kinetics and increased the fraction of channels developing slow inactivation with prolonged depolarizations. However, late INa was not modified by the mutation. p.D1816VfsX7 produced a marked reduction of channel trafficking toward the membrane that was not restored by decreasing incubation temperature during cell culture or by incubation with 300 μM mexiletine and 5 mM 4-phenylbutirate.
  
  
  CONCLUSIONS
  Despite a severe truncation of the C-terminus, the resulting mutated channels generate currents, albeit with reduced amplitude and altered biophysical properties, confirming the key role of the C-terminal domain in the expression and function of the cardiac Na(+) channel.
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Gregorio Marañón, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Dolz-Gaitón
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Gregorio Marañón, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Núñez
authors.affiliation: Complejo Hospitalario Universitario de A Coruña and Instituto de Ciencias de la Salud, Universidad de A Coruña, A Coruña, Spain.
authors.forename: Lucía
authors.initials: L
authors.lastname: Núñez
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Hospital Clínico San Carlos, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Adriana
authors.initials: A
authors.lastname: Barana
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Gregorio Marañón, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Amorós
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Gregorio Marañón, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Marcos
authors.initials: M
authors.lastname: Matamoros
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Hospital Clínico San Carlos, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Pérez-Hernández
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Hospital Clínico San Carlos, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: González de la Fuente
authors.affiliation: Arrhytmias Unit, Cardiology Department, Hospital Universitario Virgen de las Nieves, Granada, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Alvarez-López
authors.affiliation: Arrhytmias Unit, Cardiology Department, Hospital Universitario Virgen de las Nieves, Granada, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: Macías-Ruiz
authors.affiliation: Arrhytmias Unit, Cardiology Department, Hospital Universitario Virgen de las Nieves, Granada, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Tercedor-Sánchez
authors.affiliation: Arrhytmias Unit, Cardiology Department, Hospital Universitario Virgen de las Nieves, Granada, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Jiménez-Jáimez
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Gregorio Marañón, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Delpón
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Gregorio Marañón, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Caballero
authors.affiliation: Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain ; Instituto de Investigación Sanitaria Hospital Clínico San Carlos, School of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Tamargo
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D053840:Brugada Syndrome / Q000235:genetics*; D005260:Female; D016368:Frameshift Mutation / Q000235:genetics*; D006801:Humans; D008801:Mexiletine / Q000494:pharmacology; D008875:Middle Aged; D062554:NAV1.5 Voltage-Gated Sodium Channel / Q000235:genetics* / Q000378:metabolism*; D010654:Phenylbutyrates / Q000494:pharmacology
chemical_list: D062554:NAV1.5 Voltage-Gated Sodium Channel; D010654:Phenylbutyrates; D008801:Mexiletine; C075773:4-phenylbutyric acid