CHARACTERIZATION OF CELL-VOLUME LOSS IN CEM-C7A CELLS DURING DEXAMETHASONE-INDUCED APOPTOSIS

A reduction in cell volume is a fundamental feature of apoptosis. We h ave characterized changes in cell volume, together with nuclear change s, occurring in dexamethasone-induced apoptosis in CEM-C7A lymphoblast oid cells. Cell volume was measured by electronic cell sizing and flow cytometry, and two distinct phases of volume loss were observed. The first phase began 12 h after addition of dexamethasone (5 mu M) and pr ogressed until 36 h when chromatin condensation was detected in intact cells. Removal of dexamethasone before 36 h (the precommitment period ) resulted in reversal of the volume decrease and prevented the appear ance of nuclear changes. Cell shrinkage in the first 24 h of dexametha sone exposure was associated with a net loss of potassium but no chang e in cellular buoyant density. There were no significant differences i n the rates of volume recovery after either hypertonic or hypotonic st imuli. These observations favor a mechanism of cell shrinkage involvin g loss of the entire cytoplasmic contents, possibly following proteoly sis, rather than loss of only osmolytes and water. The second phase of volume loss was coincident with chromatin condensation and was associ ated with cellular fragmentation and a reduction in cellular density. We conclude that volume loss in this model of apoptosis is mediated by multiple mechanisms that are both dependent and independent of cellul ar fragmentation.