Phosphatidylserine exposure on myeloid cells induced by ceramide is prevented by cAMP-elevating agents. MC/9 cells growing in IL-3 were treated with vehicle (DMSO; □), C2-ceramide (50 μmol/L; •), C2-ceramide plus forskolin and IBMX (10 μmol/L and 50 μmol/L, respectively; ○), or only forskolin and IBMX (▪). At the times indicated, cells were harvested, washed twice with PBS, and resuspended in buffer containing annexin-V-FITC and PI. Cells stained with annexin-V-FITC but excluding PI were quantitated by flow cytometry. Representative experiment of 3 is shown, with each point being the mean of duplicate determinations, and with error bars representing the range.