Abstract 19856: Optogenetic Modulation of Pacemaking, Arrhythmia Generation, and Inhibition with Sustained (Non-pulsed) Light
The induction of automaticity by persistent depolarizing current in non-pacemaking cardiac cells was demonstrated experimentally over 40 years ago, when Sperelakis, Katzung, and others transformed single ventricular myocytes into pacemakers with tunable frequencies by the injection of non-pulsed, constant current. The full dynamic response (bifurcations) to such depolarizing current, including arrhythmia generation and inhibition, has been corroborated in silico. Here we report an optogenetic reincarnation of the method applicable in the cardiac tissue setting. Quiescent syncytia of neonatal rat ventricular myocytes, expressing the light-sensitive ion channel channelrhodopsin-2 (ChR2), were exposed to continuous very low-intensity light (470 nm) while optically mapped. In silico, ChR2-expressing human ventricular cardiomyocytes were subjected to a range of irradiances (0.08-0.3 mW/mm2) to map their dynamic response. Both in vitro and in silico delivery of sustained depolarizing current via optical ChR2 actuation produced stable pacemaking. As irradiance varied, the full dynamic response to constant light revealed regions of: 1) robust pacemaking with tunable frequency (1-3 Hz, in silico), 2) arrhythmia generation, and 3) complete inhibition of activity. In vitro tests in cardiac syncytia confirmed a pacemaking region with tunable frequency - 1.83±0.29 times increase in rate as irradiance varied 3-9 μW/mm2 (n=4). Suppression of the inward rectifier current (0.5 mM barium, n=4) widened the effective range of the tunable pacemaker, in addition to reducing the onset threshold for pacemaking by 73±14% experimentally. In sum, we present a new optogenetic method for contactless, spatially-resolved generation of pacemaking, induction and suppression of instabilities in heart tissue with implications for rate-adaptive, biological alternatives to electronic pacemaking and for simple comprehensive testing of electrical stability by low light.
Author Disclosures: C.M. Ambrosi: None. J.C. Williams: None. E. Entcheva: None.
- © 2014 by American Heart Association, Inc.