Figure 3: (A) Morphological characterization of cells retrieved after Percoll gradient centrifugation. Cells collected from newly formed bands 1 and 2 were cultured separately under cardiomyocyte growth conditions. Brightfield images taken after 4 days show a predominantly fibroblast-like morphology in the stromal cell fraction collected from band 1. Cells harvested from band 2 develop a typical rod-shaped cardiomyocyte phenotype and display rhythmic electric activity (corresponding videos can be found in the supplemental material (Suppl. Videos 2, 3)). (B) Purity of cardiomyocytes in culture. Cells were plated in 8-well-chamber slides and immunostaining was performed after 4 days in culture. Simultaneous expression of cardiomyocyte-specific α-actin (red) and ubiquitous marker β-actin (green) in almost all cells reveals a homogenous cardiomyocyte culture. Nuclei were counterstained with DAPI. Scale bar represents 100μm.