Recent advances and current limitations of available technology to optically manipulate and observe cardiac electrophysiology

Abstract

Optogenetics, utilising light-reactive proteins to manipulate tissue activity, are a relatively novel approach in the field of cardiac electrophysiology. We here provide an overview of light-activated transmembrane channels (optogenetic actuators) currently applied in strategies to modulate cardiac activity, as well as newly developed variants yet to be implemented in the heart. In addition, we touch upon genetically encoded indicators (optogenetic sensors) and fluorescent dyes to monitor tissue activity, including cardiac transmembrane potential and ion homeostasis. The combination of the two allows for all-optical approaches to monitor and manipulate the heart without any physical contact. However, spectral congestion poses a major obstacle, arising due to the overlap of excitation/activation and emission spectra of various optogenetic proteins and/or fluorescent dyes, resulting in optical crosstalk. Therefore, optogenetic proteins and fluorescent dyes should be carefully selected to avoid optical crosstalk and consequent disruptions in readouts and/or cellular activity. We here present a novel approach to simultaneously monitor transmembrane potential and cytosolic calcium, while also performing optogenetic manipulation. For this, we used the novel voltage-sensitive dye ElectroFluor 730p and the cytosolic calcium indicator X-Rhod-1 in mouse hearts expressing channelrhodopsin-2 (ChR2). By exploiting the isosbestic point of ElectroFluor 730p and avoiding the ChR2 activation spectrum, we here introduce a novel optical imaging and manipulation approach with minimal crosstalk. Future developments in both optogenetic proteins and fluorescent dyes will allow for additional and more optimised strategies, promising a bright future for all-optical approaches in the field of cardiac electrophysiology.

A cross species thermoelectric and spatiotemporal analysis of alternans in live explanted hearts using dual voltage-calcium fluorescence optical mapping

“…Optical mapping techniques have prompted the quantitative study of local activation and repolarization timings, as well as calcium handling, with high spatiotemporal resolution in different Langendorff-perfused heart species (Herron et al 2012, Crocini et al 2014, Hernández-Romero et al 2019, Marchal et al 2023. Output signals, however, can be highly noisy, especially concerning calcium traces.…”

Optogenetics meets physiology

“…Recently, Marchal et al presented a perspective on the latest technological breakthroughs facilitating optical control and observation of cardiac electrophysiology [ 22 ]. A significant challenge in all-optical methods arises from crosstalk, caused by the overlap of the excitation and emission spectra of commonly used optogenetic proteins and/or fluorescent dyes.…”

“…A significant challenge in all-optical methods arises from crosstalk, caused by the overlap of the excitation and emission spectra of commonly used optogenetic proteins and/or fluorescent dyes. To tackle this issue, the authors propose an innovative approach that enables the optogenetic manipulation of cardiac electrophysiology with simultaneous monitoring of transmembrane voltage and intracellular calcium levels, establishing the basis for a multimodal investigation of whole-heart activity [ 22 ].…”