Changes in Molt-4 cells after treatment with GW1843. (A) Changes in acidic pH, Mg²⁺-independent sphingomyelinase activity (ASMase), neutral pH, Mg²⁺-dependent sphingomyelinase activity (NSMase), and ceramide. Log-phase Molt-4 cells were treated for the indicated times with 8 nmol/L GW1843 alone (solid lines) or in combination with 50 μmol/L Ac-DEVD-CHO (dashed lines). Cell aliquots were assayed for ASMase activity (▪), NSMase activity (•), or ceramide levels (▴) as described in Materials and Methods. (B) Quantitation of dead cells (both blebbed and dead fractions). Log-phase Molt-4 cells were treated for the indicated times with 8 nmol/L GW1843 alone (▪) or in combination with 50 μmol/L Ac-DEVD-CHO (•). Cells aliquots assayed for the number of blebbed and dead cells after trypan blue staining as described in Materials and Methods. This data is from a representative experiment from three separate determinations.