Diverse effects of sphingosine on calcium mobilization and influx in differentiated HL-60 cells

Sphingosine induces a biphasic increase in cytosolic-free Ca²⁺ ([Ca²⁺](i)) with an initial peak followed by a sustained increase in HL-60 cells differentiated into neutrophil-like cells. The initial peak is not affected by the presence of ethylene glycol bis (β-aminoethyl ether) N, N, N', N-tetraacetic acid (EGTA) in the buffer and appears to be dependent on conversion of sphingosine to sphingosine -1-phosphate (S1P) by sphingosine kinase, since it is blocked by the presence of N, N-dimethylsphingosine (DMS), which, like sphingosine, causes a sustained increase itself. The sustained increase that is elicited by sphingosine or DMS is abolished by the presence of EGTA in the buffer. The sustained sphingosine-induced Ca²⁺ influx does not appear due to Ca²⁺ influx through store-operated Ca²⁺ (SOC) channels, since the influx is not inhibited by SKF 96365, nor is it augmented by loperamide. In addition, sphingosine and DMS attenuate the Ca²⁺ influx through SOC channels that occurs after depletion of intracellular stores by ATP or thapsigargin. Both the initial peak and the sustained increase in [Ca²⁺](i) elicited by sphingosine can be blocked by phorbol 12-myristate 13-acetate (PMA)-elicited activation of protein kinase C. Thus, in HL-60 cells sphingosine causes a mobilization of Ca²⁺ from intracellular Ca²⁺ stores, which requires conversion to S1P, while both sphingosine and DMS elicit a Ca²⁺ influx through an undefined Ca²⁺ channel and cause a blockade of SOC channels. (C) Harcourt Publishers Ltd 2000.