Measurement of Contractility and Calcium Release in Cardiac Spheroids
There is a need for organotypic in vitro models that resemble the native tissue in functionality and tissue architecture for disease models and drug development. To this end, many 3D culture formats have been developed over time. Among the most often used type is the scaffold-free multicellular aggregate, also called spheroid, that forms by self-assembly. However, working with 3D cultures can be challenging because single cells are not as accessible as in 2D cultures and standard lab procedures must be adapted or replaced altogether. This chapter describes methods to create cardiac spheroids consisting of human iPSC-derived cardiomyocytes and cardiac fibroblasts and how to measure contractility or calcium signals using quantitative video analysis and confocal microscopy. Emphasis is on the particular challenges that 3D cultures pose and on affordable methods that do not require specialized equipment.
Key words3D culture Cardiomyocytes Calcium Contractility Beating Spheroid Microtissue Video Image processing Confocal microscopy
Funding was provided by the Swiss Heart Foundation to C. Z. We acknowledge technical support by Patrick Furer (University of Bern) for help with making the field pacing culture dish. We thank Sarah Longnus (Cardiac Surgery Department, University Hospital Bern) for support and discussions. This study was performed with the support of the Microscopy Imaging Center (MIC).
“Calcium_cycling_CCD_camera.mov” shows video recordings of spontaneously contracting cells and microtissues of different sizes loaded with Calbryte520 and captured at 25 frames per second using a CCD camera on a Nikon Eclipse microscope with a 60×/1.4 oil immersion lens. Panel (a) shows a small aggregate of hiPSC-CMs. Panel (b) shows a loose aggregate of only a few cells showing asynchronous calcium cycling. Panel (c) shows a larger microtissue of hiPSC-CMs and HCF that shows synchronous calcium cycling (MP4 2955 kb)
“Electrical_pacing_spheroids.mov” shows a cardiac spheroid contracting at the spontaneous rate at 37 °C and electrically paced at 2, 3, 4, and 5 Hz (MP4 334 kb)