Flow cytometry based assays for the measurement of apoptosis-associated mitochondrial membrane depolarisation and cytochrome c release

Mitochondria play a pivotal role in life and death of the cell because they produce the majority of energy required for survival and also regulate the intrinsic pathway to apoptosis. The involvement of mitochondria in cell death is generally measured by following mitochondrial membrane depolarisation or mitochondrial outer membrane permeabilisation (MOMP). These events can be assayed using cationic dyes that are attracted to the negative charge across the inner membrane of healthy mitochondria or by following translocation of cytochrome c from the mitochondria to the cytoplasm respectively. These events progress rapidly in individual cells but are observed as bi-phasic peaks in flow cytometry assays because cell death generally occurs asynchronously in a population. This allows researchers to use flow cytometry to easily distinguish healthy cells with intact mitochondria healthy from dying cells with permeabilised mitochondria. This article will therefore review methods using flow cytometry to follow mitochondrial membrane depolarisation and cytochrome c release during apoptosis, and will highlight some studies that resulted in development of these assays.