Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, C016

Oral Communications

Optogenetic hyperpolarization of cardiomyocytes to terminate ventricular arrhythmia

M. Funken1, P. Sasse1, T. Bruegmann1

1. Institute of Physiology I, University of Bonn, Bonn, Germany.

Introduction: Defibrillation to terminate lethal ventricular arrhythmia is currently performed by applying high energy electrical shocks which induce simultaneously depolarization as well as hyperpolarization in different areas in the ventricles. The importance of hyperpolarization for the success of defibrillation has been suggested by in silico modeling but could yet not be determined experimentally. Here we report selective optogenetic hyperpolarization in cardiomyocytes of transgenic hearts expressing the light-activated proton pump Archaerhodopsin-T (ArchT) to terminate episodes of ventricular tachycardia and fibrillation (VT/VF). Methods: Transgenic mice with cardiac expression of ArchT were generated by crossbreeding αMHC-Cre mice with a mouse line expressing ArchT-eGFP from the CAG promoter after Cre-mediated excision of a floxed stop cassette. Histological analysis was performed to detect transgene expression in slices and after dissociation. Hearts were explanted, perfused in Langendorff configuration and stimulated electrically with silver electrodes on the right ventricle while ECG recording. Action potentials were recorded by sharp electrode impalement during pharmacological contraction inhibition (10 µM Blebbistatin). Perfusion with low K+ (2 mM) and the KATP-channel activator Pinazidil (100 µM) allowed induction of sustained VT/VF by electrical burst stimulation to explore optogenetic arrhythmia termination. Precisely timed light pulses (525 nm) were applied with a high power LED coupled to a macroscope (1x objective, 0.25 NA). Results: Membrane-bound eGFP signals confirmed ArchT expression in >90% of ventricular cardiomyocytes. Action potential measurements proved light-induced (525 nm) hyperpolarization resulting in faster upstroke and shorter duration of action potentials as well as faster conduction velocities. Illumination (6.5 mW/mm2) focused on the epicardial surface of the anterior ventricular wall (24 mm2) was able to terminate VT/VF episodes with an average success rate of 53.3±7.1% in ArchT expressing hearts (n=11) which was significantly higher (p=0.0007, Kruskal Wallis test) than spontaneous termination rate within the same time period in illuminated control hearts (25±4.5%, n=14) or ArchT expressing hearts without illumination (14±6.3%, n=5). Conclusions: We herein provide the first evidence that hyperpolarization is able to terminate ventricular arrhythmia and could play an important role for the success of defibrillation by electrical shocks. Therefore this study confirms the value of optogenetic approaches to understand electrical defibrillation and to potentially improve current defibrillation strategies. All data displayed as mean±standard error of the mean.

Where applicable, experiments conform with Society ethical requirements