High concentrations of calcium induce detachment of cytokine- and manganese-dependent CD34⁺ BM HPC adhesion to fibronectin. After preincubation with 5 mmol/L EDTA, CD34⁺ HPC were suspended in HBS, 0.2% BSA with 1 mmol/L MgCl₂, and were incubated at 37°C for 20 minutes in fibronectin-coated wells containing 10 ng/mL each of IL-1β, IL-3, and SCF (•), 10 ng/mL each of IL-1β, IL-3, IL-6, G-CSF, GM-CSF, and SCF (▪), 300 μmol/L of MnCl₂ (▵), or without stimulus (○) to promote attachment of HPC onto Fn-coated surfaces. CaCl₂ was then added at specified concentrations into wells for a further 20-minute incubation at 37°C to induce cell detachment. The percentage of cells remaining attached was measured as described in Materials and Methods. These data represent the mean ± SD of triplicates.