Functional modulation of atrio-ventricular conduction by enhanced late sodium current and calcium-dependent mechanisms in Scn5a1798insD/+ mice
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Rivaud, Mathilde R
Marchal, Gerard A
Wolswinkel, Rianne
Jansen, John A
van der Made, Ingeborg
Beekman, Leander
Ruiz-Villalba, Adrián
Baartscheer, Antonius
Rajamani, Sridharan
Belardinelli, Luiz
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Oxford University Press
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Aims: SCN5A mutations are associated with arrhythmia syndromes, including Brugada syndrome, long QT syndrome type 3 (LQT3), and cardiac conduction disease. Long QT syndrome type 3 patients display atrio-ventricular (AV) conduction slowing which may contribute to arrhythmogenesis.
Methods/Results: We assessed electrophysiological and molecular alterations underlying AV-conduction abnormalities in mice carrying the Scn5a1798insD/+ mutation (mutants). Langendorff-perfused mutants hearts showed prolonged AV-conduction compared to wild type (WT) without changes in atrial and His-ventricular (HV) conduction. The late sodium current (INa,L) inhibitor ranolazine (RAN) normalized AV-conduction in mutants mice, likely by preventing the mutation-induced increase in intracellular sodium ([Na+]i) and calcium ([Ca2+]i) concentrations. Indeed, further enhancement of [Na+]i and [Ca2+]i by the Na+/K+-ATPase inhibitor ouabain caused excessive increase in AV-conduction time in mutants hearts. Mutants mice from the 129P2 strain displayed more severe AV-conduction abnormalities than FVB/N-mutants mice, in line with their larger mutation-induced INa,L. Transverse aortic constriction (TAC) caused excessive prolongation of AV-conduction in FVB/N-Scn5a1798insD/+ mice (while HV-intervals remained unchanged), which was prevented by chronic RAN treatment. Mutants-TAC hearts showed decreased mRNA levels of conduction genes in the AV-nodal region, but no structural changes in the AV-node or His bundle. In mutants-TAC mice deficient for the transcription factor Nfatc2 (effector of the calcium-calcineurin pathway), AV-conduction and conduction gene expression were restored to WT levels.
Conclusions: Our findings indicate a detrimental role for enhanced INa,L and consequent calcium dysregulation on AV-conduction in Scn5a1798insD/+ mice, providing evidence for a functional mechanism underlying AV-conduction disturbances secondary to gain-of-function SCN5A mutations.