title: NCX is an important determinant for premature ventricular activity in a drug-induced model of Andersen-Tawil syndrome.
abstract: OBJECTIVE
  Andersen-Tawil syndrome (ATS1)-associated ventricular arrhythmias are initiated by premature ventricular activity (PVA) resulting from diastolic Ca(2+) (Ca(D)) accumulation. We hypothesized that relatively high Na(+)-Ca(2+) exchanger (NCX) expression coupled with slower Ca(2+) uptake may constitute an arrhythmogenic substrate during drug-induced ATS1 (DI-ATS1).
  
  
  RESULTS
  DI-ATS1 was induced with 10 µmol/L BaCl(2) and 2 mmol/L [K(+)](o). Ca(2+) transients and action potentials were optically mapped from Langendorff-perfused guinea pig ventricles. Intracellular Ca(2+) handling was modulated by either direct NCX inhibition with 5 µmol/L KB-R7943 or by sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) inhibition with cyclopiazonic acid (CPA). During DI-ATS1, PVA was more frequent in left ventricular (LV)-base (LVB) vs. LV-apex (LVA) (2.2 ± 0.8 vs. 0.6 ± 0.3 PVA/10 min), consistent with greater Ca(D) (1.65 ± 0.13 vs. 1.42 ± 0.09 normalized-Ca(D) units) and western blot-assessed NCX protein expression (81.2 ± 30.9%) in LVB relative to LVA. Further, regions of high NCX (LVB) evidenced a shorter PVA coupling interval relative to regions of low NCX expression (LVA, 67.7 ± 3.5 vs. 78.5 ± 3.6%). Inhibiting NCX during DI-ATS1 lowered the incidence of ventricular tachycardias (VTs, 0 vs. 25%) and PVA (1.5 ± 0.4 vs. 4.3 ± 1.4 PVA/10 min), but it did not affect PVA coupling intervals in LVB nor LVA (70.8 ± 4.3 vs. 73.8 ± 2.5%). Conversely, inhibition of SERCA2a with CPA, thereby increasing the role of NCX in Ca(2+) handling, significantly increased the incidence of VTs and PVA relative to DI-ATS1 alone, while decreasing the PVA coupling interval in all regions.
  
  
  CONCLUSIONS
  PVA preferentially occurs in regions of enhanced NCX expression with relatively slower Ca(2+) uptake and during perfusion of CPA which further reduces sarcoplasmic reticular Ca(2+) uptake.
authors.affiliation: Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112-5000, USA.
authors.forename: Przemysław B
authors.initials: PB
authors.lastname: Radwański
authors.forename: Steven
authors.initials: S
authors.lastname: Poelzing
mesh_terms: D000200:Action Potentials; D050030:Andersen Syndrome / Q000139:chemically induced / Q000503:physiopathology*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology*; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004562:Electrocardiography; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000503:physiopathology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D019831:Sodium-Calcium Exchanger; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium