The overall goal of this proposal is to investigate new mechanisms that underlie SCD through the application of innovative technology, computer modeling and the use of new genetic models of long QT syndrome type 1and type 2 (LQT1 and LQT2). This multi-pronged approach includes the investigation of orchiectomized male LQT2 rabbits and LQT1 rabbits that underwent ablation of the AV node (LQT1-AVB). Studies at the cellular levels with myocytes derived from these rabbits will be used to investigate the role of sex hormones in modulation of the function of key proteins that regulate calcium dynamics in cardiomyocytes. Since the calcium (Ca) transients and action potential dynamics are bi-directionally coupled through Ca-induced-Ca-release and the feedback of the Ca transient on Ca-sensitive membrane current (ICa,L, INCX, and IKs), assessing the relative contributions of unstable Ca cycling and altered repolarization to triggered activity is in general difficult. Here e propose to investigate the subcellular Ca cycling dynamics first without Vm influence to characterize RyR sensitivity, and then with a clamped action potential waveform to investigate the uni-directional effect of Vm on Ca cycling dynamics (i.e. without feedback of Cai on Vm), thereby identify conditions leading to arrhythmogenic whole cell Cai oscillations, Vm dynamics without CaT influence to study EADs facilitated by reopening of ICa,L in the presence of altered repolarization, and finally bi-directionally coupled free Cai and free Vm dynamics to investigate synergistic effects of Cai oscillations and reopening of ICa,. Iteration will consist of functional electrophysiological measurements of the specific currents and their biophysical properties, and biochemical and electrophysiological studies (as well as measured subcellular Ca dynamical properties-spark frequency and Ca wave threshold), to calibrate relevant ranges of computational model parameters to be used in the exploration of arrhythmogenic state (unsafe zone) and safe zone (no spontaneous arrhythmias or SCD). Studies at the tissue and organ levels will examine the role synchronization of the triggered activity combined with bi-stable wave conduction (bi- excitability) and tissue heterogeneities mediate the R-on-T phenomenon as well as test whether short-long-short sequence increases EAD formations and tissue heterogeneities, thus self propels until the onset of TdP and weather TdP and PVT are maintained by Ica-mediated wavefronts and chaos synchronization.
The characterization of transgenic rabbit models for cardiac arrhythmias, the effects of myocardial dysfunction, and the identification of the relationship between mutant LQTS genes that encode for dysfunctional ion channels and life-threatening ventricular tachyarrhythmias should provide more complete knowledge into the genetic and electrophysiologic factors involved in repolarization disorders. These studies into altered ventricular repolarization should contribute important new insights into sudden cardiac death mechanisms associated with acquired cardiac disorders that accompany ischemic and nonischemic cardiomyopathy and QT- prolonging drugs. This enhanced knowledge should lead to more effective strategies for prevention of sudden death in a broad spectrum of genetic and acquired cardiac disorders with meaningful public health benefits.
|Petry, Clive J; Sanz Marcos, Nuria; Pimentel, Gracielle et al. (2016) Associations Between Fetal Imprinted Genes and Maternal Blood Pressure in Pregnancy. Hypertension 68:1459-1466|
|Sadick, Jessica S; Boutin, Molly E; Hoffman-Kim, Diane et al. (2016) Protein characterization of intracellular target-sorted, formalin-fixed cell subpopulations. Sci Rep 6:33999|
|Song, Zhen; Karma, Alain; Weiss, James N et al. (2016) Long-Lasting Sparks: Multi-Metastability and Release Competition in the Calcium Release Unit Network. PLoS Comput Biol 12:e1004671|
|Boutin, Molly E; Hoffman-Kim, Diane (2015) Application and assessment of optical clearing methods for imaging of tissue-engineered neural stem cell spheres. Tissue Eng Part C Methods 21:292-302|
|Kim, Tae Yun; Kunitomo, Yukiko; Pfeiffer, Zachary et al. (2015) Complex excitation dynamics underlie polymorphic ventricular tachycardia in a transgenic rabbit model of long QT syndrome type 1. Heart Rhythm 12:220-8|
|Liu, Michael B; de Lange, Enno; Garfinkel, Alan et al. (2015) Delayed afterdepolarizations generate both triggers and a vulnerable substrate promoting reentry in cardiac tissue. Heart Rhythm 12:2115-24|
|Song, Zhen; Ko, Christopher Y; Nivala, Michael et al. (2015) Calcium-voltage coupling in the genesis of early and delayed afterdepolarizations in cardiac myocytes. Biophys J 108:1908-21|
|Dingle, Yu-Ting L; Boutin, Molly E; Chirila, Anda M et al. (2015) Three-Dimensional Neural Spheroid Culture: An In Vitro Model for Cortical Studies. Tissue Eng Part C Methods 21:1274-83|
|Qu, Zhilin; Hu, Gang; Garfinkel, Alan et al. (2014) Nonlinear and Stochastic Dynamics in the Heart. Phys Rep 543:61-162|
|Odening, Katja E; Koren, Gideon (2014) How do sex hormones modify arrhythmogenesis in long QT syndrome? Sex hormone effects on arrhythmogenic substrate and triggered activity. Heart Rhythm 11:2107-15|
Showing the most recent 10 out of 14 publications