Role of Intracellular Calcium Ion in Human Promyelocytic Leukemia HL-60 Cell Differentiation1

The relationship between calcium ions and the differentiation of human promyelocytic leukemia HL-60 cells was investigated. Proliferation of HL-60 cells incubated in calcium-free medium was inhibited without cell differentiation. On the other hand, incubation with 100 /¿Mverapamil markedly inhibited cell proliferation and caused slight cell differentiation into monocytes. Both calcium-free medium and 100 MM verapamil en hanced HL-60 cell differentiation after treatment with 1 IIM la,2Sdihydroxyvitamin D3, 1 DM /9-alI-frani-retinoic acid, or 0.75% dimethyl sulfoxide. However, no enhancement was obtained by treatment with 1 tiM n-O-tetradecanoylphorbol-O-acetate. The free cytosolic calcium concentration was measured by the intracellularly trappable fluorescent calcium indicator, quin 2. The increase of intracellular calcium induced by 250 IIM ionomycin was completely blocked by 100 «IMverapamil in calcium-free medium, suggesting that the high concentration of verapamil (100 /IM) blocks the intracellular calcium mobilization in HL-60 cells. Therefore, the enhancing effect of calcium deprivation or verapamil of HL-60 cell differentiation seemed to be closely related to the inhibition of intracellular calcium mobilization. This speculation is supported by the finding that 50 UM 8-(yV,Amiethylamino)octyl-3,4,5-triinethoxybenzoate, an intracellular calcium antagonist, also enhanced HL-60 cell differentiation induced by la,25-dihydrox> vitamin Di. ß-M-trans-retinoic acid, or dimethyl sulfoxide.