Volume regulation and ion transport during apoptosis

The loss of cell volume is a defining characteristic of programmed cell death, which separates apoptosis from necrosis. Assessment of cell volume during apoptosis can easily be accomplished by flow cytometry, by examining changes in the light-scattering properties of living cells that are directly proportional to cell size and density. Flow cytometry quantitates only relative changes in cell size; however, when used in conjunction with Coulter (Hialeah, FL) counter analysis, more precise cell volume data can be obtained. Flow cytometric analysis of multiple characteristics during apoptosis, such as changes in intracellular ion concentrations, membrane integrity, and DNA content, along with changes in cell size, permits sorting of various subpopulations of apoptotic cells. Below, we describe methods for rapid examination of cell volume and ion changes during apoptosis.