Re: Do apoptotic cells consume oxygen?

Cells undergo programmed cell death (apoptosis) in response to many different stimuli ranging from DNA damage to stress to commands from other cells. As such, there are several pathways leading to apoptosis, which have been divided into two broad pathways referred to as extrinsic (from outside) and intrinsic (from inside), each ultimately causing the activation of enzymes called Caspases (Cysteine [aspartyl specific] proteinases) that carry out deactivating and destroying the cell. The key event in the intrinsic pathway is the disruption of the mitochondrial membranes and subsequent release of cytochrome c and other mitochondrial factors into the cytosol. Since the mitochondria are the oxygen-using organelles of the cell, and since mitochondria rely on intact membranes and cytochrome c to function, cells activating the intrinsic apoptotic pathway will stop consuming oxygen even before they become visibly apoptotic. The extrinsic pathway bypasses the mitochondria and goes straight to caspase activation; however, one of the downstream targets of caspase activation turns out to be cytochrome c oxidase, part of the mitochondrial machinery required for using oxygen. Thus, activating the extrinsic apoptotic pathway will eventually cause cells to stop consuming oxygen, but this will occur simultaneously with other downstream apoptotic markers, such as DNA fragmentation. So, the short answer is, no, apoptotic cells do not consume oxygen. In fact, oxygen consumption has been proposed as an accurate measure of cell viability.