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This Article Full Text Full Text (PDF) Supplemental Data All Versions of this Article: 570/2/237    most recent jphysiol.2005.096578v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Berecki, G. Articles by van Ginneken, A. C. G. Search for Related Content PubMed PubMed Citation Articles by Berecki, G. Articles by van Ginneken, A. C. G. Related Collections Cellular

¹ Experimental and Molecular Cardiology Group and the Departments of
² Physiology
³ Clinical Genetics, Academic Medical Center, University of Amsterdam, the Netherlands

Long-QT3 syndrome (LQT3) is linked to cardiac sodium channel gene (SCN5A) mutations. In this study, we used the ‘dynamic action potential clamp’ (dAPC) technique to effectively replace the native sodium current (I_Na) of the Priebe–Beuckelmann human ventricular cell model with wild-type (WT) or mutant I_Na generated in a human embryonic kidney (HEK)-293 cell that is voltage clamped by the free-running action potential of the ventricular cell. We recorded I_Na from HEK cells expressing either WT or LQT3-associated Y1795C or A1330P SCN5A at 35°C, and let this current generate and shape the action potential (AP) of subepicardial, mid-myocardial and subendocardial model cells. The HEK cell's endogenous background current was completely removed by a real-time digital subtraction procedure. With WT I_Na, AP duration (APD) was longer than with the original Priebe–Beuckelmann model I_Na, due to a late I_Na component of 30 pA that could not be revealed with conventional voltage-clamp protocols. With mutant I_Na, this late component was larger (100 pA), producing a marked increase in APD (70–80 ms at 1 Hz for the subepicardial model cell). The late I_Na magnitude showed reverse frequency dependence, resulting in a significantly steeper APD–frequency relation in the mutant case. AP prolongation was more pronounced for the mid-myocardial cell type, resulting in increased APD dispersion for each of the mutants. For both mutants, a 2 s pause following rapid (2 Hz) pacing resulted in distorted AP morphology and beat-to-beat fluctuations of I_Na. Our dAPC data directly demonstrate the arrhythmogenic nature of LQT3-associated SCN5A mutations.

(Received 12 August 2005; accepted after revision 27 October 2005; first published online 27 October 2005)
Corresponding author G. Berecki: Department of Experimental Cardiology, Academic Medical Center, University of Amsterdam, Room M01-217, Meibergdreef 9, 1105 AZ Amsterdam, PO Box 22700, 1100 DE Amsterdam, The Netherlands. Email: g.berecki{at}amc.uva.nl

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