Scn3b knockout mice exhibit abnormal ventricular electrophysiological properties

Parvez Hakim,Iman S Gurung,Thomas H Pedersen,Rosemary Thresher,Nicola Brice,Jason Lawrence,Andrew A Grace,Christopher L.-H Huang

doi:10.1016/j.pbiomolbio.2009.01.005

Parvez Hakim, Iman S Gurung + Show 6 more

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https://doi.org/10.1016/j.pbiomolbio.2009.01.005

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Abstract

We report for the first time abnormalities in cardiac ventricular electrophysiology in a genetically modified murine model lacking the Scn3b gene (Scn3b−/−). Scn3b−/− mice were created by homologous recombination in embryonic stem (ES) cells. RT-PCR analysis confirmed that Scn3b mRNA was expressed in the ventricles of wild-type (WT) hearts but was absent in the Scn3b−/− hearts. These hearts also showed increased expression levels of Scn1b mRNA in both ventricles and Scn5a mRNA in the right ventricles compared to findings in WT hearts. Scn1b and Scn5a mRNA was expressed at higher levels in the left than in the right ventricles of both Scn3b−/− and WT hearts. Bipolar electrogram and monophasic action potential recordings from the ventricles of Langendorff-perfused Scn3b−/− hearts demonstrated significantly shorter ventricular effective refractory periods (VERPs), larger ratios of electrogram duration obtained at the shortest and longest S1–S2 intervals, and ventricular tachycardias (VTs) induced by programmed electrical stimulation. Such arrhythmogenesis took the form of either monomorphic or polymorphic VT. Despite shorter action potential durations (APDs) in both the endocardium and epicardium, Scn3b−/− hearts showed ΔAPD90 values that remained similar to those shown in WT hearts. The whole-cell patch-clamp technique applied to ventricular myocytes isolated from Scn3b−/− hearts demonstrated reduced peak Na+ current densities and inactivation curves that were shifted in the negative direction, relative to those shown in WT myocytes. Together, these findings associate the lack of the Scn3b gene with arrhythmic tendencies in intact perfused hearts and electrophysiological features similar to those in Scn5a+/− hearts.

Highlights

Voltage-gated sodium (Na+) channels, critical for the excitation of cardiac muscle (Keating and Sanguinetti, 2001), are formed of pore-forming α-subunits and one or more β-subunits (Isom, 2001)
The arms were cloned into the plasmid pTK5IBLMNL (Paradigm Therapeutics Ltd, Cambridge, U.K.) using the restriction sites incorporated in the arm primers, such that the 5′ and 3′ arms flank an IRES-fronted LacZ reporter gene followed by a loxP-flanked PGKNeopA selectable marker
Targeted 129 SvEv embryonic stem (ES) cells, containing the Scn3b knockout (KO) allele were injected into host blastocysts as previously described (Bradley et al, 1984), generating male chimeras which were subsequently mated with 129 SvEv females

Summary

Introduction

Voltage-gated sodium (Na+) channels, critical for the excitation of cardiac muscle (Keating and Sanguinetti, 2001), are formed of pore-forming α-subunits and one or more β-subunits (Isom, 2001). Six β-subunits have been identified and are encoded by 4 different genes; SCN1B, SCN2B, SCN3B and SCN4B (Isom et al, 1992, 1995a; Kazen-Gillespie et al, 2000; Morgan et al, 2000; Qin et al, 2003; Yu et al, 2003). These genes, which encode for β1, β2, β3 and β4 subunits respectively, are expressed in human tissues including the brain, skeletal muscle and the heart (Candenas et al, 2006; Stevens et al, 2001). The β1 and β3 subunits have been demonstrated in the transverse tubules, and β2 and β4 subunits in the intercalated disks of murine ventricular myocytes (Maier et al, 2004)

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