The in vivo study of cardiac mechano-electric and mechano-mechanical coupling during heart development in zebrafish

Abstract

In the adult heart, acute adaptation of electrical and mechanical activity to changes in mechanical load occurs via feedback processes known as “mechano-electric coupling” and “mechano-mechanical coupling.” Whether this occurs during cardiac development is ill-defined, as acutely altering the heart’s mechanical load while measuring functional responses in traditional experimental models is difficult, as embryogenesis occurs in utero, making the heart inaccessible. These limitations can be overcome with zebrafish, as larvae develop in a dish and are nearly transparent, allowing for in vivo manipulation and measurement of cardiac structure and function. Here we present a novel approach for the in vivo study of mechano-electric and mechano-mechanical coupling in the developing zebrafish heart. This innovative methodology involves acute in vivo atrial dilation (i.e., increased atrial preload) in larval zebrafish by injection of a controlled volume into the venous circulation immediately upstream of the heart, combined with optical measurement of the acute electrical (change in heart rate) and mechanical (change in stroke area) response. In proof-of-concept experiments, we applied our new method to 48 h post-fertilisation zebrafish, which revealed differences between the electrical and mechanical response to atrial dilation. In response to an acute increase in atrial preload there is a large increase in atrial stroke area but no change in heart rate, demonstrating that in contrast to the fully developed heart, during early cardiac development mechano-mechanical coupling alone drives the adaptive increase in atrial output. Overall, in this methodological paper we present our new experimental approach for the study of mechano-electric and mechano-mechanical coupling during cardiac development and demonstrate its potential for understanding the essential adaptation of heart function to acute changes in mechanical load.

ERG potassium channels and T‐type calcium channels contribute to the pacemaker and atrioventricular conduction in zebrafish larvae

“…It was recently shown that acute atrial dilation in 2 dpf zebrafish by injection of a given volume into the venous circulation upstream of the heart increased the atrial stroke area, suggesting that mechano-mechanical coupling drives the adaptive increase in atrial output during development. 30 These and the present results highlight the advantage of the zebrafish model to investigate cardiac performance in vivo.…”

“…26 As in mammals, Ca 2+ is central in excitation-contraction coupling and largely determines force generation. 27 We have recently imaged Ca 2+ and contraction simultaneously in beating hearts of zebrafish expressing ratiometric gene-encoded Ca 2+ biosensors, 28,29 preserving the mechano-electric and mechano-mechanical coupling 30 and normal heart development. In the present study, we show the involvement of TTCCs in the conduction system of zebrafish larvae and characterize AV conduction defects induced by block of TTCCs and ERG channels.…”

POPDC1 Variants Cause Atrioventricular Node Dysfunction and Arrhythmogenic Changes in Cardiac Electrophysiology and Intracellular Calcium Handling in Zebrafish

“…Zebrafish were then transferred to an imaging dish lined with black Sylgard (DC 170, Dow Corning, Midland, TX, USA) under a layer of 3% methylcellulose (M0387, Sigma-Aldrich, St. Louis, MO, USA) and positioned in a left-lateral-side-up orientation for an optimal view of both heart chambers. The observation dish was filled with an E3 solution containing 0.35 mM tricaine (MS-222; E10521, Sigma-Aldrich, which provides adequate anesthesia, while causing no effects on HR or cardiac mechanical function [ 40 ]) and temperature-controlled at 28 °C (TC-344C, Warner Instruments) with a warmed platform (WP-16, Warner Instruments, Hamden, CT, USA) for the duration of the experiment. Larvae were left to acclimatise for 5 min, followed by a 10 s recording of membrane voltage (V m ) or intracellular Ca 2+ dynamics.…”

Suppression of Contraction Raises Calcium Ion Levels in the Heart of Zebrafish Larvae

“…Another approach is to use inhibitors of actin-myosin interaction like blebbistatin or its analogs [3,4]. Although these methods have allowed the investigation of electrical excitation and Ca 2+ dynamics in zebrafish [5,6], the mechano-electric and mechano-mechanic coupling mech-anisms [7], which adjust the heart rate and stroke volume to the changing physiological needs, are abrogated.…”