The broad and long term goal of this research project is to explore the roles of small conductance Ca2+- activated K (SK) channels in the mechanisms of ventricular arrhythmogenesis. We hypothesize that the SK current upregulation is an endogenous compensatory mechanism to protect the heart from arrhythmias related to reduced repolarization reserve, but under some conditions can result in excess repolarization reserve and proarrhythmic effects. The SK channel became a focus of our research after we discovered that the apamin- sensitive potassium current (IKAS, or SK current) is increased in both the rabbit and human ventricles with heart failure (HF). We also discovered that SK current is acutely increased in normal ventricles with hypokalemia, in a manner that depends on the ventricular activation sequence. These findings raise the intriguing possibility that SK current is a rescue current that compensates for the electrophysiological effects of increased intracellular Ca2+ load. While maintaining repolarization reserve in HF may be antiarrhythmic, we also found that excessive or heterogeneous shortening of the APD by SK current may be proarrhythmic. Our recent preliminary results indicate that IKAS is activated by isoproterenol, and that female rabbit ventricles express more SK current during early phase 2 than male ventricles. CyPPA activation of SK2 and SK3 causes ECG J point elevation, heterogeneous APD distribution, phase 2 reentry and spontaneous VF in normal rabbit ventricles. The latter finding suggests that SK current may also contribute to proarrhythmia in certain clinical conditions by creating excess repolarization reserve, such as in the J-wave syndromes. The incorporation of IKAS in computer models will generate important new insights into the dynamical effects of IKAS in ventricular repolarization. A combined mapping and computer simulation approach will be needed to fully understand the importance of IKAS in cardiac arrhythmogenesis, including both the proarrhythmic and antiarrhythmic potentials. We propose the following specific aims:
Aim 1 : Antiarrhythmic and proarrhythmic mechanisms of SK current in rabbit ventricles.
The Aim 1 A is designed to study the Purkinje cells (PCs) in both normal and failing rabbit ventricles to test the hypothesis that the SK current is increased in PCs and that blocking the SK current decreases the Ca2+-membrane potential coupling gain and promotes Ca2+ induced arrhythmias.
The Aim 1 B is designed to study SK current and J-wave syndrome. We hypothesize that (a) SK current is in part responsible for J-wave elevation and VF during hypothermia, and apamin reverses these proarrhythmic effects and (b) heterogeneous SK current activation can cause J wave elevation and spontaneous VF through heterogeneous shortening of APD and phase 2 reentry.
Aim 2 : Antiarrhythmic and proarrhythmic mechanisms of SK current in computer simulation.
Aim 2 A will systematically investigate the mechanisms of SK currents as a rescue mechanism preventing arrhythmias under QT prolongation and as a proarrhythmic mechanism under early repolarization.
Aim 2 B will extend and validate the hypotheses tested in the rabbits to human models.

Public Health Relevance

Ventricular arrhythmia and sudden cardiac death is a major public health problem. Our study is focused on the mechanisms of ventricular arrhythmogenesis and will provide new insights into the mechanisms of sudden death. Therefore, this study is clinically relevant.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL139829-03
Application #
9838804
Study Section
Electrical Signaling, Ion Transport, and Arrhythmias Study Section (ESTA)
Program Officer
Balijepalli, Ravi C
Project Start
2017-12-15
Project End
2021-11-30
Budget Start
2019-12-01
Budget End
2020-11-30
Support Year
3
Fiscal Year
2020
Total Cost
Indirect Cost
Name
Indiana University-Purdue University at Indianapolis
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
603007902
City
Indianapolis
State
IN
Country
United States
Zip Code
46202
Landaw, Julian; Qu, Zhilin (2018) Memory-induced nonlinear dynamics of excitation in cardiac diseases. Phys Rev E 97:042414
Chen, Mu; Xu, Dongzhu; Wu, Adonis Z et al. (2018) Phospholamban regulates nuclear Ca2+ stores and inositol 1,4,5-trisphosphate mediated nuclear Ca2+ cycling in cardiomyocytes. J Mol Cell Cardiol 123:185-197
Jiang, Zhaolei; Zhao, Ye; Tsai, Wei-Chung et al. (2018) Effects of Vagal Nerve Stimulation on Ganglionated Plexi Nerve Activity and Ventricular Rate in Ambulatory Dogs With Persistent Atrial Fibrillation. JACC Clin Electrophysiol 4:1106-1114
Yin, Dechun; Chen, Mu; Yang, Na et al. (2018) Role of apamin-sensitive small conductance calcium-activated potassium currents in long-term cardiac memory in rabbits. Heart Rhythm 15:761-769
Chen, Mu; Xu, Dong-Zhu; Wu, Adonis Z et al. (2018) Concomitant SK current activation and sodium current inhibition cause J wave syndrome. JCI Insight 3:
Landaw, Julian; Qu, Zhilin (2018) Control of voltage-driven instabilities in cardiac myocytes with memory. Chaos 28:113122
Shelton, Richard S; Ogawa, Masahiro; Lin, Hongbo et al. (2018) Effects of Stellate Ganglion Cryoablation on Subcutaneous Nerve Activity and Atrial Tachyarrhythmias in a Canine Model of Pacing-Induced Heart Failure. JACC Clin Electrophysiol 4:686-695
Zhao, Ye; Yuan, Yuan; Tsai, Wei-Chung et al. (2018) Antiarrhythmic effects of stimulating the left dorsal branch of the thoracic nerve in a canine model of paroxysmal atrial tachyarrhythmias. Heart Rhythm 15:1242-1251
Everett 4th, Thomas H; Doytchinova, Anisiia; Cha, Yong-Mei et al. (2017) Recording sympathetic nerve activity from the skin. Trends Cardiovasc Med 27:463-472