Optogenetic manipulation of cardiac repolarization gradients using sub-threshold illumination

Gerard A Marchal; Valentina Biasci; Leslie M Loew; Annibale Biggeri; Marina Campione; Leonardo Sacconi

doi:10.3389/fphys.2023.1167524

Optogenetic manipulation of cardiac repolarization gradients using sub-threshold illumination

Front Physiol. 2023 May 5:14:1167524. doi: 10.3389/fphys.2023.1167524. eCollection 2023.

Authors

Gerard A Marchal^{1

2

3}, Valentina Biasci^{1

4}, Leslie M Loew⁵, Annibale Biggeri⁶, Marina Campione⁷, Leonardo Sacconi^{3

8}

Affiliations

¹ European Laboratory for Non-Linear Spectroscopy-LENS, Florence, Italy.
² National Institute of Optics (INO-CNR), Florence, Italy.
³ Institute of Clinical Physiology (IFC-CNR), Pisa, Italy.
⁴ Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy.
⁵ Center for Cell Analysis and Modeling, University of Connecticut, Farmington, CT, United States.
⁶ Department of Cardiac, Thoracic, Vascular Sciences and Public Health, University of Padua, Padua, Italy.
⁷ Institute of Neuroscience (IN-CNR) and Department of Biomedical Science University of Padua, Padua, Italy.
⁸ Institute for Experimental Cardiovascular Medicine, University Heart Center and Medical Faculty, University of Freiburg, Freiburg, Germany.

Abstract

Introduction: Mechanisms underlying cardiac arrhythmias are typically driven by abnormalities in cardiac conduction and/or heterogeneities in repolarization time (RT) across the heart. While conduction slowing can be caused by either electrophysiological defects or physical blockade in cardiac tissue, RT heterogeneities are mainly related to action potential (AP) prolongation or abbreviation in specific areas of the heart. Importantly, the size of the area with altered RT and the difference between the short RT and long RT (RT gradient) have been identified as critical determinators of arrhythmogenicity. However, current experimental methods for manipulating RT gradient rely on the use of ion channel inhibitors, which lack spatial and temporal specificity and are commonly only partially reversible. Therefore, the conditions facilitating sustained arrhythmia upon the presence of RT heterogeneities and/or defects in cardiac conduction remain to be elucidated. Methods: We here employ an approach based on optogenetic stimulation in a low-intensity fashion (sub-threshold illumination), to selectively manipulate cardiac electrical activity in defined areas of the heart. Results: As previously described, subthreshold illumination is a robust tool able to prolong action potentials (AP), decrease upstroke velocity as well as slow cardiac conduction, in a fully reversible manner. By applying a patterned sub-threshold illumination in intact mouse hearts constitutively expressing the light-gated ion channel channelrhodopsin-2 (ChR2), we optically manipulate RT gradients and cardiac conduction across the heart in a spatially selective manner. Moreover, in a proof-of-concept assessment we found that in the presence of patterned sub-threshold illumination, mouse hearts were more susceptible to arrhythmias. Hence, this optogenetic-based approach may be able to mimic conduction slowing and RT heterogeneities present in pathophysiological conditions.

Keywords: electrophysiological modulation; optical mapping; optogenetics; repolarization gradients; sub-threshold illumination.

Grants and funding

This study was funded by Fondazione CR Firenze, SALUS project. Additional funding was provided by the European Union’s HORIZON programme through a MSCA postdoctoral fellowship awarded to GM (No. 101110977, OPTOCARD). LS is member of the German Research Foundation Collaborative Research Centre SFB1425 (DFG #422681845). We acknowledge support by the Open Access Publication Fund of the University of Freiburg.