Optical recording of single cardiomyocyte transmembrane potential in Langendorff-perfused mouse hearts

Spatial heterogeneity of action potential properties has been related to cardiac arrhythmogenesis. In this study we used laser scanning confocal microscopy in conjunction with the fast potentiometric dye ANNINE-6 to monitor changes in cardiomyocyte transmembrane potentials in Langendorff-perfused mouse hearts on a subcellular scale. Line-scan images from up to three neighboring cardiomyocytes were obtained during continuous electrical stimulation at 3 Hz. Fluorescence changes for each cardiomyocyte along the scan line were resolved from the corresponding line-scan image. Peak changes in fluorescence intensity during an action potential exceeded 20%. Signal-to-noise ratio of the optical signal was ≫20. Action potential durations were not significantly different between adjacent cardiomyocytes under our conditions. We conclude that this imaging technique can be used to investigate cell-to-cell repolarization heterogeneity in the intact heart.