Apoptosis and necrosis are two distinct modes of cell death with respective morphological characteristics. However, apoptosis and some forms of necrosis must share common steps since both modes of cell death can be suppressed by the anti-apoptotic Bcl-2 protein and caspase inhibitors. Intracellular ATP levels have been implicated both in vitro and in vivo as a determinant of the cell's decision to die by apoptosis or necrosis.