Sphingosine and sphingosine 1-phosphate differentially modulate platelet-derived growth factor-BB-indueed 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 c13, using single-cell fura-2 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 with different frequencies and amplitudes. The latter phenomenon was never 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 of cells responding to PDGF-BB exposure with Ca²⁺ spikes (87 versus 47%), while it did not modify the Ca²⁺ response elicited by exposure to ATP, ET-1, or BK. Exposure to exogenous 10 μM sphingosine or 1 μM sphingosine 1-phosphate produced oscillatory and non-oscillatory Ca²⁺ responses, respectively, similar to those elicited by PDGF-BB. A second application of PDGF-BB, 30 min after the first, was normally ineffective in producing a Ca²⁺ response. However, if the second exposure was preceded by the inhibition of sphingosine 1-phosphate formation, an oscillatory Ca²⁺ response occurred in all cells. We conclude that intracellular levels of sphingosine and sphingosine 1-phosphate may differentially modulate Ca²⁺ signaling triggered by PDGF receptor stimulation in CEINGE c13-transformed oligodendrocytes.