Normotonic cell shrinkage induces apoptosis under extracellular low Cl conditions in human lymphoid and epithelial cells.
OBJECTIVE
Sustained cell shrinkage is associated with apoptosis. Apoptotic volume decrease, which is known to be induced by release of osmolytes including Cl- ions, may be an essential event for apoptosis induction. Provided any anion channels and/or anion transporters are basally functioning, there is a possibility that imposition of a driving force for Cl- efflux per se results in sustained cell shrinkage and thereby induces apoptotic death. Here, this possibility was tested by reducing the extracellular Cl- concentration.


METHODS
Human lymphoid U937 and epithelial HeLa cells were provided for experiments after exposing to isotonic electrolyte solution which contains 146 or 1 mM Cl-. Measurements of mean cell volume, caspase-3 activity and cell viability were performed by a Coulter-type cell size analyzer, a fluorometric assay and a colorimetric assay, respectively.


RESULTS
After exposure to low Cl- solution in which most chloride was replaced with aspartate, gluconate, phosphate or methanesulphonate, both U937 and HeLa cells exhibited, for up to 60 min, shrinkage to a level (90-80%) significantly lower than that in control high Cl- solution. Reduction in cell viability started within 2 h and reached below 20% within 8 h after exposure to low Cl- solution. The cell death was found to be associated with caspase-3 activation and DNA fragmentation.


CONCLUSIONS
Exposure to isotonic low Cl- solution induced sustained shrinkage and thereafter apoptotic death in U937 and HeLa cells. Thus, it is suggested that sustained cell shrinkage per se provides a sufficient condition for apoptosis induction.
Maeno
E
E
Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
Shimizu
T
T
Okada
Y
Y
D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D048429:Cell Size; D018118:Chloride Channels / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D053938:DNA Fragmentation; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000378:metabolism* / Q000473:pathology; D045604:Extracellular Fluid / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007552:Isotonic Solutions; D008221:Lymphoid Tissue / Q000378:metabolism* / Q000473:pathology; D013997:Time Factors; D020298:U937 Cells
D018118:Chloride Channels; D002712:Chlorides; D007552:Isotonic Solutions; D053148:Caspase 3