The role of increased calcium influx rate in receptor mediated function of differentiating HL-60 cells

In this study we have investigated the link between increased Ca²⁺ influx rate, acquired upon the differentiation of HL-60 cells, to changes in cytosolic free Ca²⁺ ([Ca²⁺]_i], evoked by the chemotactic peptide-FMLP and the mitogen Con-A. Although differentiating and undifferentiated HL-60 cells exhibited similar steady-state levels of [Ca²⁺]_i, cells induced to differentiate by dibutyryl-cAMP, at 48 h, exhibited enhanced Ca²⁺ influx rate, measured by non-steady state ⁴⁵Ca²⁺ uptake, and augmentation of FMLP-stimulated Ca²⁺ influx. At 120 h the above cells responded to FMLP but not to Con-A, by a marked augmentation of Ca²⁺ influx, and elevated levels of [Ca²⁺]_i. On the other hand HL-60 cells induced to differentiate by retinoic acid responded, as described above, to Con-A but not to FMLP. HL-60 cells grown in the presence of cholera-toxin, were reported to express high levels of FMLP-receptors without expressing cell differentiation. We have demonstrated that, in these cells the Ca²⁺ influx rate was unchanged, moreover, FMLP-stimulated Ca²⁺ influx and [Ca²⁺]_i rise were low. These findings strongly suggest that the presence of receptor is not sufficient for FMLP-mediated changes in [Ca²⁺]_i. A link between increased Ca²⁺ influx rate, acquired upon induction of differentiation, and receptor mediated response in these cells is proposed.