Optical stimulation enables paced electrophysiological studies in embryonic hearts

Abstract

Cardiac electrophysiology plays a critical role in the development and function of the heart. Studies of early embryonic electrical activity have lacked a viable point stimulation technique to pace in vitro samples. Here, optical pacing by high-precision infrared stimulation is used to pace excised embryonic hearts, allowing electrophysiological parameters to be quantified during pacing at varying rates with optical mapping. Combined optical pacing and optical mapping enables electrophysiological studies in embryos under more physiological conditions and at varying heart rates, allowing detection of abnormal conduction and comparisons between normal and pathological electrical activity during development in various models. 440-447 (1978). 12. K. Kamino, "Optical approaches to ontogeny of electrical activity and related functional organization during early heart development," Physiol. Rev. 71(1), 53-91 (1991 Macrae, and D. S. Rosenbaum, "The zebrafish as a novel animal model to study the molecular mechanisms of mechano-electrical feedback in the heart," Prog. Biophys. Mol. Biol. 110(2-3), 154-165 (2012). 18. M. Bressan, G. Liu, and T. Mikawa, "Early mesodermal cues assign avian cardiac pacemaker fate potential in a tertiary heart field," Science 340 (

Volumetric optical mapping in early embryonic hearts using light-sheet microscopy

“…The total conduction time of the sample shown in Fig. 4 is approximately 200 ms, which is also very consistent with our previous reports of similar stage embryos imaged with conventional OM [13,26].…”

“…Unfortunately, pacing produces an artifact at the pacing site. The artifact is caused by thermal lensing, as described previously [26]. While this does not affect the visualization and analysis of the rest of the heart tube, we believe that the size of the artifact region may be further reduced by optimizing the delivery of light to decrease the pacing threshold.…”

“…2). At early looping stages, avian embryonic hearts present a unidirectional conduction pattern, with slower conduction at the atrioventricular junction and the outflow region, and faster conduction at the ventricle region [2,13,26,[31][32][33]. Furthermore, within the ventricle the outer curvature conducts faster than the inner curvature [2,13,26,[31][32][33].…”

“…The optical pacing setup includes a 1465 nm laser diode coupled into a single-mode fiber (QPhotonics, Ann Arbor, MI) and a laser diode controller (Newport Corporation, Irvine, CA) [26]. During imaging, hearts were paced at 1Hz with 20 ms pulses (3.75 mJ/pulse).…”

“…Unfortunately, electrical artifacts from point stimulation electrodes obscure signals in small-sized samples. Optical pacing overcomes the limitations of electrical pacing allowing point stimulation in early-stage embryos [25][26][27].…”