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 differ entiated into neutrophil-like cells. The initial peak is not affected by th e presence of ethylene glycol bis (beta-aminoethyl ether) N, N, N', N-tetra acetic acid (EGTA) in the buffer and appears to be dependent on conversion of sphingosine to sphingosine -1-phosphate (S1P) by sphingosine kinase, sin ce it is blocked by the presence of N, N-dimethylsphingosine (DMS), which, like sphingosine, causes a sustained increase itself. The sustained increas e that is elicited by sphingosine or DMS is abolished by the presence of EG TA in the buffer. The sustained sphingosine-induced Ca2+ influx does not ap pear due to Ca2+ influx through store-operated Ca2+ (SOC) channels, since t he influx is not inhibited by SKF 96365, nor is it augmented by loperamide. In addition, sphingosine and DMS attenuate the Ca2+ influx through SOC cha nnels that occurs after depletion of intracellular stores by ATP or thapsig argin. Both the initial peak and the sustained increase in [Ca2+](i) elicit ed by sphingosine can be blocked by phorbol 12-myristate 13-acetate (PMA)-e licited activation of protein kinase C. Thus, in HL-60 cells sphingosine ca uses a mobilization of Ca2+ from intracellular Ca2+ stores, which requires conversion to S1P, while both sphingosine and DMS elicit a Ca2+ influx thro ugh an undefined Ca2+ channel and cause a blockade of SOC channels. (C) Har court Publishers Ltd 2000.