The absence of volume regulatory mechanisms contributes to the
rapid activation of apoptosis in thymocytes.
Bortner, Carl D., and John A. Cidlowski.
The Laboratory of Integrative Biology, National Institute of
Environmental Health Sciences, Research Triangle Park, NC 27709 USA,
Phone (919) 541-1564, Fax (919) 541-1367
APStracts 3:0088C, 1996.
A common event that occurs during apoptosis is a loss of cell volume,
but little information is available on its role in the cell death
process. Lymphocytes undergo apoptosis in response to glucocorticoids
and exhibit cell shrinkage, nuclear condensation, internucleosomal
DNA fragmentation, and apoptotic body formation. Interestingly, only
cells which exhibit a loss in cell volume degrade their DNA. To
determine if physical shrinkage was sufficient to initiate apoptosis,
S49 Neo lymphocytes were cultured in hypertonic medium. The normal
osmolality (approximately 300 mOsm) of tissue culture medium was
increased to either 550 or 800 mOsm using impermeant sugars such as
mannitol and sucrose, or NaCl. These hypertonic conditions led to a
rapid killing of S49 Neo cells. Evaluation of the mode of cell death
revealed that these hypertonic conditions resulted in apoptosis.
Unlike glucocorticoid-induced cell death, hypertonically-induced
apoptosis did not require protein synthesis. When S49 Neo cells were
cultured under hypotonic conditions, the cells swelled but apoptosis
did not occur. Analysis of several cell types revealed that all
lymphoid cells examined (S49 Neo, CEM-C7, primary thymocytes) undergo
apoptosis in response to hypertonic conditions, whereas several other
cell types (L-cells, COS, HeLa, GH3) did not. Although these non
-lymphoid cells showed a similar initial reduction in cell volume in
response to hypertonic conditions, they subsequently maintained
volume or regulated back to a near normal cell volume. These data
indicate that thymic lymphoid cells have the machinery in place for
rapid induction of apoptosis in response to physical shrinkage
whereas other cell types resist shrinkage-induced apoptosis by the
activation of cell volume regulatory mechanisms.
Received 16 January 1996; accepted in final form 4 March 1996.
APS Manuscript Number C21-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96