z-VAD prevents Na-Sal–induced apoptosis of TF-1 cells. (A) Morphological changes. TF-1 cells were left untreated (control) or were treated with 5 mmol/L Na-Sal for 5 hours with or without 1-hour pretreatment with 100 μmol/L Z-VAD. fmk (Calbiochem) as indicated. (B) z-VAD prevents caspase-3 activation. Cells were left untreated (control) or were treated with 5 mmol/L Na-Sal alone or in the presence of 100 μmol/L Z-VAD for 16 hours. Caspase-3 activity was determined as described in Materials and Methods. (C and D) Z-VAD prevents Na-Sal–induced cleavage of gelsolin (C) and PARP (D). Cells were untreated (lane 1), or treated with 5 mmol/L Na-Sal for 5 hours in the absence (lane 2) or presence of 100 μmol/L Z-VAD (lane 3). The assays for PARP and gelsolin cleavage are described in the legend to Fig 3.