U937 cells were exposed to ceramide (10 μm) or sphingosine (10 μm) for 6 hr in the absence or presence of the selective pharmacological p38-RK inhibitor SB-213580 or the inactive analog SKF-105209. The fraction of cells exhibiting cytological evidence of apoptotic DNA damage was then determined by fluorescence microscopy as described in Materials and Methods; all values are expressed as the percentage of apoptotic cells within the total scored for a given treatment.

• ↵5-a Increased vs.vehicle-treated controls (p < 0.01).