Abstract 15940: Optogenetic Voltage Sensor VSFP2.3 as a Novel Tool in Cardiac Electriophysiology
Fluorescent dyes and optical imaging are commonly applied to study the electrical activities of the cardiac functional syncytium, but are limited by dye toxicity, suboptimal stability, and inhomogeneous loading. Stable optogenetic labeling with a voltage sensitive fluorescent protein (VSFP2.3) may alleviate some of these shortcomings. We hypothesized that VSFP2.3 can be stably expressed in mouse hearts to specifically label sarcolemmal membranes and monitor electrical properties of the heart from cellular to organ level.
Methods: Transgenic mice expressing VSFP2.3 under the control of cardiac specific alpha myosin heavy chain promoter (αMHC) were generated. Echocardiography was performed to assess myocardial structure and cardiac function. Transgene localization was confirmed on isolated adult cardiomyocytes by confocal microscopy. Voltage dependence of fluorescent changes was assessed by synchronized whole-cell patch clamping and FRET imaging. Action potentials (APs) were assessed in both cellular and whole heart levels, using photomultipliers and optical mapping, respectively.
Results: Epifluorescent images of intact hearts showed homogeneous patterns of CFP and YFP expression throughout the ventricles with variable transgene levels in four established mouse lines. Echocardiography (n=8/line) showed no significant differences in cardiac function and morphology between transgenic and wildtype mice, suggesting lack of transgene toxicity. Prominent sarcolemmal targeting was confirmed on a single cell basis. Voltage dependence of fluorescent changes (YFP/CFP ratio) fitted in Boltzmann function with a V1/2 of -41±5 mV (n=6). Cellular optical APs could be detected under field stimulation and responded appropriately (1:1) to changes in stimulation frequencies. Optical APs recordings from whole hearts were feasible under sinus rhythm (8 Hz), electrical stimulation (10 Hz), and stimulated arrhythmias.
Conclusion: We have established the first mouse model with a genetically encoded optical voltage sensor. We anticipate that in particular longitudinal in vitro and in vivo studies on electrophysiological properties of cells, tissue and organs will greatly benefit from the availability of stable optical cardiograms.
- © 2011 by American Heart Association, Inc.