Differential effects of 1,25-dihydroxyvitamin D3 on cytosolic calcium in two human cell lines (HL-60 and U-937)

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Abstract
1,25‐Dihydroxyvitamin D3 (1,25‐(OH)2D3) has been shown to induce maturational changes in the human promyelocytic leukemia cell line HL‐60 and in the human monocytic cell line U‐937. Changes in cytosolic calcium have been reported to regulate cellular processes. We used the fluorescent dye Quin 2 to examine the effects of vitamin D metabolites on cytosolic calcium levels in HL‐60 and U‐937 cells. 1,25‐(OH)2D3 (20 nM) increases cytosolic calcium by 24% over a 5‐min period in HL‐60 but not in U‐937 cells. 1,25‐(OH)2D3 (0.2 nM and 4 nM) has no effect on cytosolic calcium levels in either cell type. 24,25‐(OH)2D3 (20 nM) has no effect on cytosolic calcium in HL‐60 cells. Nifedipine (1 m M) has no effect on cytosolic calcium levels over 30 min and likewise does not block the 1,25‐(OH)2D3‐induced increase in cytosolic calcium in HL‐60 cells. However, chelation of extracellular calcium with EGTA (10 m M) blocks the 1,25‐(OH)2D3‐induced increment in cytosolic calcium, but does not block the 1,25‐(OH)2D3‐induced maturational changes in HL‐60 cells. The data suggest that 1,25‐(OH)2D3 but not 24,25‐(OH)2D3 increases cytosolic calcium in HL‐60 cells within 5 min and the increment is due to increased influx of calcium. 1,25‐(OH)2D3 modifies membrane permeability to calcium independent of calcium channels sensitive to nifedipine. Finally, 1,25‐(OH)2D3‐induced maturational changes in HL‐60 cells can take place without an increase in cytosolic calcium.

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