Mechanism of transient increase in intracellular concentration of free calcium ions in HL-60 cell differentiation induced by vitamin D3 and phorbol ester

A promyelocytic leukemia cell line, HL-60, was induced to differentiate into monocyte-macrophage lineage cells by treatment with active vitamin D3 and phorbol esters, and into granulocyte lineage ones by retinoic acid and dimethylsulfoxide. The changes in intracellular concentration of free calcium ions ([Ca2+]i) were measured and analyzed by calcium-imaging analysis with Fura 2-AM. A significant and transient increase in [Ca2+]i was observed in active vitamin D3 and phorbol ester systems; however, no change was detected with retinoic acid and dimethylsulfoxide. This increase was due to the influx of calcium ions from outside of the cells, and L-type calcium channels were shown to mainly contribute to this influx. Protein kinase C was also shown to be involved in the increase in [Ca2+]i.