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Complex restitution behavior and reentry in a cardiac tissue model for neonatal mice.

ABSTRACT: Spatiotemporal dynamics in cardiac tissue emerging from the coupling of individual cardiomyocytes underlie the heart's normal rhythm as well as undesired and possibly life-threatening arrhythmias. While single cells and their transmembrane currents have been studied extensively, systematically investigating spatiotemporal dynamics is complicated by the nontrivial relationship between single-cell and emergent tissue properties. Mathematical models have been employed to bridge this gap and contribute to a deepened understanding of the onset, development, and termination of arrhythmias. However, no such tissue-level model currently exists for neonatal mice. Here, we build on a recent single-cell model of neonatal mouse cardiomyocytes by Wang and Sobie (Am. J. Physiol. Heart Circ. Physiol 294:H2565) to predict properties that are commonly used to gauge arrhythmogenicity of cardiac substrates. We modify the model to yield well-defined behavior for common experimental protocols and construct a spatially extended version to study emergent tissue dynamics. We find a complex action potential duration (APD) restitution behavior characterized by a nonmonotonic dependence on pacing frequency. Electrotonic coupling in tissue leads not only to changes in action potential morphology but can also induce spatially concordant and discordant alternans not observed in the single-cell model. In two-dimensional tissue, our results show that the model supports stable functional reentry, whose frequency is in good agreement with that observed in adult mice. Our results can be used to further constrain and validate the mathematical model of neonatal mouse cardiomyocytes with future experiments.

SUBMITTER: Mayer A

PROVIDER: S-EPMC5641936 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Dysregulated cardiac function after sepsis is common in intensive care unit (ICU) and known to predict poor long-term outcome and increase mortality. Effective therapeutic strategies are largely lacking. Moreover, the pathological feature and the molecular mechanism underlying cardiac dysfunction induced by sepsis remain unclear. Here, by performing echocardiograms on rodents after induction of polymicrobial sepsis with cecum ligation and puncture (CLP), we assessed the temporal dynamics of left ventricular ejection fraction (LVEF) and a serial of hemodynamics parameters on animals at different time point after CLP. Intriguingly, the mean LVEF is comparable in mice induced by CLP and sham, whereas survivors post CLP had stable LVEF and non-survivors had markedly fluctuated LVEF at early phase of CLP induction, suggesting LVEF away from normal range is highly associated with mortality. Consistent with clinical observations of depressed, preserved or hyperdynamic LVEF in septic patients from data compiled using our ICU cohort and from other studies, CLP-induced mice fall into three groups based on LVEF measured at 24 hours after surgery: high LVEF (HEF, LVEF>=90%), low LVEF (LEF, LVEF<65%), and normal LVEF (NEF, 65%=<LVEF<90%). We performed genome-wide transcriptomic and proteomic profiling on left ventricle samples collected from three CLP groups and sham mice. By implementing pathway analysis, gene set enrichment and coexpression network analysis, we identified jointly and distinctively changed genes, proteins and biologically-essential processes and pathways in three CLP groups with different LVEF. Notably, transmission electron microscopy examination shows remarkable mitochondrial and sarcomere defects in three CLP groups with different phenotypes associated with LVEF variances. Together, this study systematically characterizes the molecular, morphological, and functional alterations in CLP-induced cardiac injury, serving as a framework for future research into pathology and molecular mechanism of sepsis-induced cardiomyopathy.

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Complex restitution behavior and reentry in a cardiac tissue model for neonatal mice.

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