Figure 2. Induction of senescent rat chondrocytes by ionization irradiation and dose-dependent killing effect of ABT263 on IR-SC via apoptosis. (A) Morphology and crystal violet staining of senescent rat chondrocytes and normal rat chondrocytes. (B) Quantitative analysis of SA–β–gal staining and crystal violet staining. IR-SC 1 and IR-SC 2 were independently cultured IR-SCs generated from different batches of ionization irradiation under same circumstance. Data were presented as mean ± standard deviation. N = 3 per group. of fold changes from 3 independent experiments. **P < 0.01 and ***P < 0.001 vs. NC by unpaired t-test. (C) Representative images of IR-SC in culture after incubation with increasing concentrations of ABT263 for 72 h. Scale bar: 100 μm. (D) statistical analysis of living cells of three independent experiments is shown. (E) Analysis of cell apoptosis by flow cytometry with increasing concentrations of ABT263 after 48h treatment. (F) Statistical results of apoptotic cells of three replicates are also shown.