Optogenetic current in myofibroblasts acutely alters electrophysiology and conduction of co-cultured cardiomyocytes

Geran M Kostecki,Leslie Tung,Daniel H Reich,Yu Shi,Emilia Entcheva,Christopher S Chen

doi:10.1038/s41598-021-83398-4

Geran M Kostecki, Leslie Tung + Show 4 more

Open Access

https://doi.org/10.1038/s41598-021-83398-4

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Abstract

Interactions between cardiac myofibroblasts and myocytes may slow conduction and generate spontaneous beating in fibrosis, increasing the chance of life-threatening arrhythmia. While co-culture studies have shown that myofibroblasts can affect cardiomyocyte electrophysiology in vitro, the extent of myofibroblast-myocyte electrical conductance in a syncytium is unknown. In this neonatal rat study, cardiac myofibroblasts were transduced with Channelrhodopsin-2, which allowed acute and selective increase of myofibroblast current, and plated on top of cardiomyocytes. Optical mapping revealed significantly decreased conduction velocity (− 27 ± 6%, p < 10–3), upstroke rate (− 13 ± 4%, p = 0.002), and action potential duration (− 14 ± 7%, p = 0.004) in co-cultures when 0.017 mW/mm2 light was applied, as well as focal spontaneous beating in 6/7 samples and a decreased cycle length (− 36 ± 18%, p = 0.002) at 0.057 mW/mm2 light. In silico modeling of the experiments reproduced the experimental findings and suggested the light levels used in experiments produced excess current similar in magnitude to endogenous myofibroblast current. Fitting the model to experimental data predicted a tissue-level electrical conductance across the 3-D interface between myofibroblasts and cardiomyocytes of ~ 5 nS/cardiomyocyte, and showed how increased myofibroblast-myocyte conductance, increased myofibroblast/myocyte capacitance ratio, and increased myofibroblast current, which occur in fibrosis, can work in tandem to produce pro-arrhythmic increases in conduction and spontaneous beating.

Highlights

Interactions between cardiac myofibroblasts and myocytes may slow conduction and generate spontaneous beating in fibrosis, increasing the chance of life-threatening arrhythmia
To assess whether inward current in MFBs can alter CM electrophysiology at a tissue level, neonatal rat cardiac fibroblasts were transduced with ChR2 and differentiated into MFBs by treatment with transforming growth factor-β1 (TGF-β1), plated on top of neonatal rat ventricular CM monolayers
In ChR2MFB co-cultures with CMs, electrically paced at 500 ms cycle length (CL, Fig. 2Ai), application of continuous blue light to open ChR2 channels could induce diastolic depolarization and spontaneous beating at a rate faster than the 500 ms paced CL (Fig. 2Aii), whereas this did not occur in MFB co-cultures with CMs

Summary

Introduction

Interactions between cardiac myofibroblasts and myocytes may slow conduction and generate spontaneous beating in fibrosis, increasing the chance of life-threatening arrhythmia. It is believed that such effects are due to electrical coupling between CMs and less electrically polarized MFBs which causes current to flow into CMs at rest, thereby raising CM resting or maximum diastolic potential (MDP), which can inactivate sodium channels or generate spontaneous a ctivity[6,7] These events can contribute to the o ccurrence[10] and complexity[11] of spiral waves that have been observed with an increasing fraction of MFBs in co-culture. MFBs were plated on top of CMs, so that their interactions with CMs occurred over a large area in 3-D, and were transduced with Channelrhodopsin-2 (ChR2), a relatively non-selective cation channel that opens in response to light[15], to acutely depolarize them This MFB-specific perturbation enabled the study of acute effects of MFB depolarizing current on the macroscopic electrophysiological properties of syncytia containing co-cultured MFBs and CMs, and was used in tandem with computational modeling to estimate MFB-CM electrical conductance. These results have been reported in large part in a preprint of this w ork[16]

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