Cell Line Specificity – Are there differences in Z-VAD-FMK permeability or metabolism between T cells and HeLa cells?

Yes, significantly.

• Permeability: HeLa cells (epithelial) generally require higher concentrations of Z-VAD-FMK (20-50 μM) due to their robust membrane structure. Primary T cells are much more sensitive and may achieve complete Caspase blockade with Z-VAD-FMK at 5-10 μM.
• Metabolism: Immune cells often have higher metabolic turnover of peptide-based inhibitors like Z-VAD-FMK. You may need to "refresh" the Z-VAD-FMK if your assay exceeds 24–48 hours.