Dataset Information

Contrasting Nav1.8 Activity in Scn10a-/- Ventricular Myocytes and the Intact Heart.

ABSTRACT:

Background

Genome-wide association studies have implicated variants in SCN10A, which encodes Nav1.8, as modulators of cardiac conduction. Follow-up work has indicated the SCN10A sequence includes an intronic enhancer for SCN5A. Yet the role of the Nav1.8 protein in the myocardium itself is still unclear. To investigate this, we use homozygous knockout mice (Scn10a^-/-) generated by disruption of exons 4 and 5, leaving the Scn5a enhancer intact.

Methods and results

We previously reported that pharmacologic blockade of Nav1.8 in wild-type animals blunts action potential prolongation by ATX-II at slow drive rates (?1 Hz). Here we present evidence of the same blunting in Scn10a^-/- compared to wild-type ventricular myocytes, supporting the conclusion that Nav1.8 contributes to late sodium current at slow rates. In contrast to earlier studies, we found no differences in electrocardiographic parameters between genotypes. Low-dose ATX-II exposure in lightly anesthetized animals and Langendorff-perfused hearts prolonged QTc and generated arrhythmias to the same extent in wild-type and Scn10a^-/-. RNA sequencing failed to identify full-length Scn10a transcripts in wild-type or knockout isolated ventricular myocytes. However, loss of late current in Scn10a^-/- myocytes was replicated independently in a blinded set of experiments.

Conclusions

While Scn10a transcripts are not detectible in ventricular cardiomyocytes, gene deletion results in reproducible loss of late sodium current under extreme experimental conditions. However, there are no identifiable consequences of this Scn10a deletion in the intact mouse heart at usual rates. These findings argue that common variants in SCN10A that affect ventricular conduction do so by modulating SCN5A.

SUBMITTER: Stroud DM

PROVIDER: S-EPMC5210363 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

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Publications

Contrasting Nav1.8 Activity in Scn10a-/- Ventricular Myocytes and the Intact Heart.

Stroud Dina Myers DM Yang Tao T Bersell Kevin K Kryshtal Dymtro O DO Nagao Satomi S Shaffer Christian C Short Laura L Hall Lynn L Atack Thomas C TC Zhang Wei W Knollmann Bjorn C BC Baudenbacher Franz F Roden Dan M DM

Journal of the American Heart Association 20161102 11

<h4>Background</h4>Genome-wide association studies have implicated variants in SCN10A, which encodes Nav1.8, as modulators of cardiac conduction. Follow-up work has indicated the SCN10A sequence includes an intronic enhancer for SCN5A. Yet the role of the Nav1.8 protein in the myocardium itself is still unclear. To investigate this, we use homozygous knockout mice (Scn10a<sup>-/-</sup>) generated by disruption of exons 4 and 5, leaving the Scn5a enhancer intact.<h4>Methods and results</h4>We pre ...[more]

PMID: 27806966

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Project description:AimsRecent studies have demonstrated electrotonic coupling between scar tissue and the surrounding myocardium in cryoinjured hearts. However, the electrical dynamics occurring at the myocyte-nonmyocyte interface in the fibrotic heart remain undefined. Here, we sought to develop an assay to interrogate the nonmyocyte cell type contributing to heterocellular coupling and to characterize, on a cellular scale, its voltage response in the infarct border zone of living hearts.Methods and resultsWe used two-photon laser scanning microscopy in conjunction with a voltage-sensitive dye to record transmembrane voltage changes simultaneously from cardiomyocytes and adjoined nonmyocytes in Langendorff-perfused mouse hearts with healing myocardial infarction. Transgenic mice with cardiomyocyte-restricted expression of a green fluorescent reporter protein underwent permanent coronary artery ligation and their hearts were subjected to voltage imaging 7-10 days later. Reporter-negative cells, i.e. nonmyocytes, in the infarct border zone exhibited depolarizing transients at a 1:1 coupling ratio with action potentials recorded simultaneously from adjacent, reporter-positive ventricular myocytes. The electrotonic responses in the nonmyocytes exhibited slower rates of de- and repolarization compared to the action potential waveform of juxtaposed myocytes. Voltage imaging in infarcted hearts expressing a fluorescent reporter specifically in myofibroblasts revealed that the latter were electrically coupled to border zone myocytes. Their voltage transient properties were indistinguishable from those of nonmyocytes in hearts with cardiomyocyte-restricted reporter expression. The density of connexin43 expression at myofibroblast-cardiomyocyte junctions was ∼5% of that in the intercalated disc regions of paired ventricular myocytes in the remote, uninjured myocardium, whereas the ratio of connexin45 to connexin43 expression levels at heterocellular contacts was ∼1%.ConclusionMyofibroblasts contribute to the population of electrically coupled nonmyocytes in the infarct border zone. The slower kinetics of myofibroblast voltage responses may reflect low electrical conductivity across heterocellular junctions, in accordance with the paucity of connexin expression at myofibroblast-cardiomyocyte contacts.

Dataset Information

Contrasting Nav1.8 Activity in Scn10a-/- Ventricular Myocytes and the Intact Heart.

Background

Methods and results

Conclusions

Publications

Contrasting Nav1.8 Activity in Scn10a-/- Ventricular Myocytes and the Intact Heart.

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