Optical Action Potential Screening on Adult Ventricular Myocytes as an Alternative QT-screen

BACKGROUND/AIMS: QT-interval screens are increasingly important for cardiac safety on all new medications. So far, investigations rely on animal experiments or cell-based screens solely probing for conductance alterations in heterologously expressed hERG-channels in cell lines allowing for a high degree of automation. Adult cardiomyocytes can not be handled by automated patch-clamp setups. Therefore optical screening of primary isolated ventricular myocytes is regarded as an alternative. Several optical voltage sensors have been reported for ratiometric measurements, but they all influenced the naïve action potential. The aim of the present study was to explore the recording conditions and define settings that allow optical QT-interval screens. METHODS: Based on an improved optical design, individual action potentials could be recorded with an exceptional signal-to-noise-ratio. The sensors were validated using the patch-clamp technique, confocal microscopy and fluorescence lifetime imaging in combination with global unmixing procedures. RESULTS: We show that the small molecule dye di-8-ANEPPS and the novel genetically encoded sensor Mermaid provide quantitative action potential information. When applying such sensors we identified distinctly different pharmacological profiles of action potentials for adult and neonatal rat cardiomyocytes. CONCLUSION: Optical methods can be used for QT-interval investigations based on cellular action potentials using either the small molecule dye di-8-ANEPPS or the genetically encoded sensor Mermaid. Adult cardiomyocytes are superior to neonatal cardiomyocytes for such pharmacological investigations. Optical QT-screens may replace intricate animal experiments.