Figure 7.

Pretreatment with PT increases the sensitivity of leukaemia cells to 1,25-(OH)₂D₃. HL-60 cells were pretreated with 10 μM PT for 24 h or not pretreated. After washing with DMEM, the cells were incubated with varying concentrations of 1,25-(OH)₂D₃ for 48 h (A), or with 5 nM 1,25-(OH)₂D₃ for 24, 48, 72 and 96 h (B). The cellular differentiation was determined by the NBT reduction assay. The results are represented as the mean±s.e.mean of triplicate determinations. The experiment was repeated twice with similar results.