2.2. Assessment of cell proliferation by Ki67 staining and CCK8 assay

For Ki67 staining, H9C2 cardiomyoblasts were fixed with cold 4% paraformaldehyde followed by permeabilization with 0.1% Triton X‐100. Fixed cells were incubated with murine anti‐Ki67 monoclonal antibody (1:500, ab155801, Abcam) and goat anti‐rabbit Alexa Fluor 594 secondary antibody, as well as counterstained with DAPI. The cells were examined by fluorescence microscopy. For CCK8 assay, H9C2 cardiomyoblasts growing in 96‐well culture dish were treated with PCS in different concentrations for three days. At the end of the culture, 10 μL of the CCK8 reagent (96992, SIGMA‐ALDRICH) was added to each well. After two hours of incubation at 37°C, the absorbance was determined by spectrophotometer at 450 nm.