Analysis of cell proliferation and alkaline phosphatase expression. (A) The proportion of ³H-thymidine–labeled cells at different stages of cellular differentiation was determined (mean labeling index ± SEM) after a 3-hour pulse of ³H-thymidine to detect proliferating cells. (B) The proportion of cells expressing alkaline phosphatase (AP index) at the same time points analyzed for cellular proliferation was determined by staining cells with Naphthol AS Phosphate substrate containing Fast Blue BB salts and the proportion of blue stained cells was counted (mean index ± SEM). (C) Proportion of cells exhibiting both labeling for [³H]-thymidine and AP staining (mean ± SEM).