© 2004 by European Society of Cardiology
Copyright © 2004, European Society of Cardiology
Prolonged repolarization and triggered activity induced by adenoviral expression of HERG N629D in cardiomyocytes derived from stem cells*
aDepartment of Medicine, University of Calgary, Calgary, Alberta, Canada
bDepartment of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, Canada
cDepartment of Paediatrics, University of Alberta, Edmonton, Alberta, Canada
dDepartment of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
* Corresponding author. Department of Medicine, University of Calgary, 3330 Hospital Drive, N.W., Calgary, Alberta, Canada, T2N 4N1. Tel.: +1-403-220-6841; fax: +1-403-270-0313. hduff{at}ucalgary.ca
Objective: The long QT syndrome, N629D HERG mutation, alters the pore selectivity signature sequence, GFGN to GFGD. Heterologous co-expression of N629D and the wildtype HERG resulted in a relative loss of the selectivity of K+ over Na+, but its physiologic relevance has not been assessed in cardiac myocytes. Methods and results: Accordingly, N629D was overexpressed, via adenoviral gene transfer, in cardiomyocytes derived from mouse stem cells. Three IKr phenotypes were observed: (1) the wildtype-like IKr showed inward rectification and a positive tail current; (2) the N629D-like IKr showed outward rectification and an inward tail current; and (3) intermediate IKr showed a small outward tail current. Action potentials (AP) were paired with the IKr measurements in each cell. Resting membrane potential (RMP) was critically dependent on the IKr phenotype. The resting membrane potential of the cells was –61±5 mV (n = 40) in wildtype, –63±3 mV (n = 18) in wildtype-like IKr phenotype, –30±2 mV (n = 12) in N629D-like and –47±2 mV (n = 24) in intermediate phenotype (p<0.00001). Triggered action potential durations (APD) were: 62±12 ms (n = 6) in wildtype, 65±11 ms (n = 6) in wildtype-like IKr phenotypes and 106±10 ms (n = 6) (p<0.01) in intermediate IKr phenotypes. Lowering [K+]o hyperpolarized wildtype cells and cells with a wildtype-like IKr phenotype, but depolarized those with intermediate phenotype (from –45±1 to –35±0.5 mV (n = 12), p<0.01). In 6 of 12 cells, with intermediate phenotype, the hypokalemia-induced depolarization resulted in triggered activity. TTX suppressed this triggered activity. Conclusion: Overexpression of N629D in cardiomyocytes derived from stem cells results in phenotypic variability in IKr, which was the critical determinant of the resting membrane potential, action potential duration and arrhythmogenic response to low [K+]o.
KEYWORDS Long QT syndrome; Arrhythmia (mechanisms); Ion channels; K+-channel; Stem cells
Time for primary review 27 days
* This study was supported by the Alberta Heart and Stroke Foundation, the Andrew Family Professorship in Cardiovascular Science and the Canadian Institutes of Health Research.
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