Figure 1. Sphingosine inhibited growth and caused death of RH30 and RH18 cells. A: Sub-confluent RH30 cells were cultured with sphingosine at 0 (○), 1 (●), 2.5 (▿), 5 (▾), 10 (□), and 15 μM (▪) for 1, 3, and 5 days. B: Sub-confluent RH18 cells were cultured with sphingosine at 0 (○), 1 (●), 2.5 (▿), 3.5 (⋄), 5 (▾), and 10 μM (□) for 1, 3, and 5 days. *Means at each time of cells treated with sphingosine at 2.5 to 15 μM differed significantly from the corresponding controls at p<0.001 by two-way ANOVA. C, D: For determination of the half-maximal inhibitory concentration (IC50), RH30 cells (C) and RH18 cells (D) were cultured with sphingosine at different concentrations (1 to 15 μM) for 24 h. *Significantly different at p<0.001 by one-way ANOVA compared to the corresponding control and different sphingosine concentrations. Total nucleic acids were measured as an index of cell number and results are expressed as a percentage of the quantity at zero hour (mean±SEM, n=3, except n=6 for time zero). Where an error bar is not seen, it lies within the dimensions of the symbol.