Optical Electrophysiology in the Developing Heart

Abstract

The heart is the first organ system to form in the embryo. Over the course of development, cardiomyocytes with differing morphogenetic, molecular, and physiological characteristics are specified and differentiate and integrate with one another to assemble a coordinated electromechanical pumping system that can function independently of any external stimulus. As congenital malformation of the heart presents the leading class of birth defects seen in humans, the molecular genetics of heart development have garnered much attention over the last half century. However, understanding how genetic perturbations manifest at the level of the individual cell function remains challenging to investigate. Some of the barriers that have limited our capacity to construct high-resolution, comprehensive models of cardiac physiological maturation are rapidly being removed by advancements in the reagents and instrumentation available for high-speed live imaging. In this review, we briefly introduce the history of imaging approaches for assessing cardiac development, describe some of the reagents and tools required to perform live imaging in the developing heart, and discuss how the combination of modern imaging modalities and physiological probes can be used to scale from subcellular to whole-organ analysis. Through these types of imaging approaches, critical insights into the processes of cardiac physiological development can be directly examined in real-time. Moving forward, the synthesis of modern molecular biology and imaging approaches will open novel avenues to investigate the mechanisms of cardiomyocyte maturation, providing insight into the etiology of congenital heart defects, as well as serving to direct approaches for designing stem-cell or regenerative medicine protocols for clinical application.

Development and evolution of the metazoan heart

“…During lateralization, pacemaker activity will become both left-and right-sided phenomena, eventually restricted to the right side to become the definitive sinus node. 180 The pacemaker has connections to the atrial cardiomyocytes, 181 probably in the form of preferential internodal pathways, [182][183][184][185] as confirmed with electrophysiology, 186 connecting the sinus node to the AV node (Figure 8).…”

The Anatomy, Development, and Evolution of the Atrioventricular Conduction Axis

“…This is again comparable with the bundle of His of mammals and birds [ 12 ]. Consistent with the presence of a specialised pathway in the alligator, the crest of the ventricular septum shows the earliest activation [ 12 , 50 ]. Early electrical activation also occurs deep in the ventricles in crocodilians, as in mammals and birds.…”

“…In the initial stages, as the ventricles begin their maturation [ 47 , 48 , 49 ], activation is initially detected near the forming septum. In the fetal stages, the first epicardial activation is deep at the ventricular apexes, presumably at some terminal parts of the left and right bundle branches [ 47 , 48 , 49 , 50 ]. The ventricular septum nonetheless remains the earliest activated part of the ventricles [ 51 , 52 , 53 ].…”

Sex Differences in Mouse Cardiac Electrophysiology Revealed by Simultaneous Imaging of Excitation-Contraction Coupling

“…Fluorescent dyes were used to detect action potential and Ca 2+ flux [49,50]. Fluo-volt (ThermoFisher cat# F10488) was used to detect action potentials, as used previously in mice, and induced pluripotent stem cell-derived cardiomyocytes [51,52].…”