Fig. 1. Cell viability after treating with sphingosine-1-phosphate (), sphingosine (•) or N,N-dimethylsphingosine (). After serum starvation, cells were incubated for 24 hours in serum-free media with various concentrations (1-10 µM) of sphingolipids. The viability of the cells was determined by the crystal violet assay. Each determination was made in triplicate and the data represent means ± s.d.