SPHINGOSINE AND SPHINGOSINE 1-PHOSPHATE DIFFERENTIALLY MODULATE PLATELET-DERIVED GROWTH FACTOR-BB-INDUCED CA2+ SIGNALING IN TRANSFORMED OLIGODENDROCYTES

The roles of sphingosine and sphingosine 1-phosphate in Ca2+ signaling following platelet-derived growth factor (PDGF) receptor stimulation were investigated in the oligodendrocyte cell line CEINGE cl3, using s ingle-cell fura-a microfluorimetry and videoimaging. Two different Ca2 + responses were observed, which differed in their delays and kinetics , The first response, which occurred after a shorter delay, exhibited a single Ca2+ peak. often followed by a plateau, while the second type of response was characterized by a longer delay and by Ca2+ spikes wi th different frequencies and amplitudes, The latter phenomenon was nev er observed after stimulation of G protein coupled receptors for ATP, ET-1, and BK, The incubation with the inhibitor of sphingosine kinase, DL-threo-dihydrosphingosine, significantly increased the percentage o f cells responding to PDGF-BB exposure with Ca2+ spikes (87 versus 47% ), while it did not modify the Ca2+ response elicited by exposure to A TP, ET-1, or BK. Exposure to exogenous 10 mu M sphingosine or 1 mu M s phingosine 1-phosphate produced oscillatory and non-oscillatory Ca2+ r esponses, respectively, similar to those elicited by PDGF-BB. A second application of PDGF-BB, 30 min after the first, was normally ineffect ive in producing a Ca2+ response, However, if the second exposure was preceded by the inhibition of sphingosine 1-phosphate formation, an os cillatory Ca2+ response occurred in all cells, We conclude that intrac ellular levels of sphingosine and sphingosine 1-phosphate may differen tially modulate Ca2+ signaling triggered by PDGF receptor stimulation in CEINGE cl3-transformed oligodendrocytes.