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Front Physiol. 2018 Dec 17;9:1806. doi: 10.3389/fphys.2018.01806. eCollection 2018.

Cardiac Electrophysiological Effects of Light-Activated Chloride Channels.

Author information

1
Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg-Bad Krozingen Medical Center-University of Freiburg, Freiburg, Germany.
2
Faculty of Medicine University of Freiburg, Freiburg, Germany.
3
Faculty of Biology University of Freiburg, Freiburg, Germany.
4
Department of Physiology and Biophysics, Dalhousie University Halifax, NS, Canada.
5
Department of Pediatrics, Dalhousie University Halifax, NS, Canada.
6
Department of Medical Neuroscience, Dalhousie University Halifax, NS, Canada.
7
School of Biomedical Engineering, Dalhousie University Halifax, NS, Canada.

Abstract

During the last decade, optogenetics has emerged as a paradigm-shifting technique to monitor and steer the behavior of specific cell types in excitable tissues, including the heart. Activation of cation-conducting channelrhodopsins (ChR) leads to membrane depolarization, allowing one to effectively trigger action potentials (AP) in cardiomyocytes. In contrast, the quest for optogenetic tools for hyperpolarization-induced inhibition of AP generation has remained challenging. The green-light activated ChR from Guillardia theta (GtACR1) mediates Cl--driven photocurrents that have been shown to silence AP generation in different types of neurons. It has been suggested, therefore, to be a suitable tool for inhibition of cardiomyocyte activity. Using single-cell electrophysiological recordings and contraction tracking, as well as intracellular microelectrode recordings and in vivo optical recordings of whole hearts, we find that GtACR1 activation by prolonged illumination arrests cardiac cells in a depolarized state, thus inhibiting re-excitation. In line with this, GtACR1 activation by transient light pulses elicits AP in rabbit isolated cardiomyocytes and in spontaneously beating intact hearts of zebrafish. Our results show that GtACR1 inhibition of AP generation is caused by cell depolarization. While this does not address the need for optogenetic silencing through physiological means (i.e., hyperpolarization), GtACR1 is a potentially attractive tool for activating cardiomyocytes by transient light-induced depolarization.

KEYWORDS:

GtACR1; action potential; heart; natural anion channelrhodopsin; optogenetics; zebrafish

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