Uncoupling Cell Shrinkage from Apoptosis Reveals That Na+ Influx Is Required for Volume Loss during Programmed Cell Death

Abstract

Cell shrinkage, or the loss of cell volume, is a ubiquitous characteristic of programmed cell death that is observed in all examples of apoptosis, independent of the death stimulus. This decrease in cell volume occurs in synchrony with other classical features of apoptosis. The molecular basis for cell shrinkage during apoptosis involves fluxes of intracellular ions including K+, Na+, and Cl-. Here we show for the first time that these ion fluxes, but not cell shrinkage, are necessary for apoptosis. Using sodium-substituted medium during anti-Fas treatment of Jurkat cells, we observed cellular swelling, a property normally associated with necrosis, in contrast to the typical cell shrinkage. Surprisingly, these swollen cells displayed all of the other classical features of apoptosis, including chromatin condensation, externalization of phosphatidylserine, caspase activity, poly(ADP)-ribose polymerase cleavage, and internucleosomal DNA degradation. These swollen cells had a marked decrease in intracellular potassium, and subsequent inhibition of this potassium loss completely blocked apoptosis. Reintroduction of sodium ions in cell cultures reversed this cellular swelling, resulting in a dramatic loss of cell volume and the characteristic apoptotic morphology. Additionally, inhibition of sodium influx using a sodium channel blocker saxitoxin completely prevented the onset of anti-Fas-induced apoptosis in Jurkat cells. These findings suggest that sodium influx can control not only changes in cell size but also the activation of apoptosis, whereas potassium ion loss controls the progression of the cell death process. Therefore cell shrinkage can be separated from other features of apoptosis. Cell shrinkage, or the loss of cell volume, is a ubiquitous characteristic of programmed cell death that is observed in all examples of apoptosis, independent of the death stimulus. This decrease in cell volume occurs in synchrony with other classical features of apoptosis. The molecular basis for cell shrinkage during apoptosis involves fluxes of intracellular ions including K+, Na+, and Cl-. Here we show for the first time that these ion fluxes, but not cell shrinkage, are necessary for apoptosis. Using sodium-substituted medium during anti-Fas treatment of Jurkat cells, we observed cellular swelling, a property normally associated with necrosis, in contrast to the typical cell shrinkage. Surprisingly, these swollen cells displayed all of the other classical features of apoptosis, including chromatin condensation, externalization of phosphatidylserine, caspase activity, poly(ADP)-ribose polymerase cleavage, and internucleosomal DNA degradation. These swollen cells had a marked decrease in intracellular potassium, and subsequent inhibition of this potassium loss completely blocked apoptosis. Reintroduction of sodium ions in cell cultures reversed this cellular swelling, resulting in a dramatic loss of cell volume and the characteristic apoptotic morphology. Additionally, inhibition of sodium influx using a sodium channel blocker saxitoxin completely prevented the onset of anti-Fas-induced apoptosis in Jurkat cells. These findings suggest that sodium influx can control not only changes in cell size but also the activation of apoptosis, whereas potassium ion loss controls the progression of the cell death process. Therefore cell shrinkage can be separated from other features of apoptosis. Apoptosis is a mode of cell death defined by unique biochemical and morphological components that include cell shrinkage, nuclear condensation, caspase activation, poly(ADP)-ribose polymerase (PARP) 1The abbreviations used are: PARP, poly(ADP)-ribose polymerase; NMDG, N-methyl-d-glucamine; PBFI-AM, potassium-binding benzofuran isophthatate acetyloxymethylester; SBFI-AM, sodium-binding benzofuran isophthatate acetyloxymethylester; PI, propidium iodide; DIC, differential interference contrast; FITC, fluorescein isothiocyanate. cleavage, and DNA fragmentation (1Kerr J.F.R. Wyllie A.H. Currie A.R. Br. J. Cancer. 1972; 26: 239-257Crossref PubMed Scopus (12927) Google Scholar, 2Hengartner M.O. Nature. 2000; 407: 770-776Crossref PubMed Scopus (6296) Google Scholar, 3Saraste A. Pulkki K. Cardiovascular Res. 2000; 45: 528-537Crossref PubMed Scopus (1042) Google Scholar). The shrinkage of cells is a universal feature of apoptosis that is completely conserved among species ranging from Caenorhabditis elegans to man, regardless of the apoptotic stimuli. When apoptotic cells shrink, a significant loss of intracellular potassium, sodium, and chloride occurs (4Jonas D. Walev I. Berger T. Liebetrau M. Palmer M. Bhakdi S. Infect. Immun. 1994; 62: 1304-1312Crossref PubMed Google Scholar, 5Barbiero G. Duranti F. Bonelli G. Amenta J.S. Baccino F.M. Exp. Cell Res. 1995; 217: 410-418Crossref PubMed Scopus (141) Google Scholar, 6Beauvais F. Michel L. Dubertret. L. J. Leukocyte Biol. 1995; 57: 851-855Crossref PubMed Scopus (136) Google Scholar, 7Bortner C.D. Hughes Jr., F.M. Cidlowski J.A. J. Biol. Chem. 1997; 272: 32436-32442Abstract Full Text Full Text PDF PubMed Scopus (509) Google Scholar, 8Hughes Jr., F.M. Bortner C.D. Purdy G.D. Cidlowski J.A. J. Biol. Chem. 1997; 272: 30567-30576Abstract Full Text Full Text PDF PubMed Scopus (428) Google Scholar, 9McCarthy J.V. Cotter T.G. Cell Death Differ. 1997; 4: 756-770Crossref PubMed Scopus (106) Google Scholar, 10Yu S.P. Yeh C.H. Sensi S.L. Gwag B.J. Canzoniero L.M. Farhangrazi Z.S. Ying H.S. Tian M. Dugan L.L. Choi D.W. Science. 1997; 278: 114-117Crossref PubMed Scopus (536) Google Scholar, 11Bilney A.J. Murray A.W. FEBS Lett. 1998; 424: 221-224Crossref PubMed Scopus (29) Google Scholar, 12Dallaporta B. Hirsch T. Susin S.A. Zamzami N. Larochette N. Brenner C. Marzo I. Kroemer G. J. Immunol. 1998; 160: 5605-5615PubMed Google Scholar, 13Nietsch H.H. Roe M.W. Fickers J.F. Moore A.L. Lidofshy S.D. J. Biol. Chem. 2000; 275: 20556-20561Abstract Full Text Full Text PDF PubMed Scopus (104) Google Scholar) that is necessary for maximal caspase activation and optimal apoptotic nuclease activity (7Bortner C.D. Hughes Jr., F.M. Cidlowski J.A. J. Biol. Chem. 1997; 272: 32436-32442Abstract Full Text Full Text PDF PubMed Scopus (509) Google Scholar, 8Hughes Jr., F.M. Bortner C.D. Purdy G.D. Cidlowski J.A. J. Biol. Chem. 1997; 272: 30567-30576Abstract Full Text Full Text PDF PubMed Scopus (428) Google Scholar, 14Yu S.P. Yeh C.H. Gottron F. Wang X. Grabb M.C. Choi D.W. J. Neurochem. 1999; 73: 933-941Crossref PubMed Scopus (131) Google Scholar, 15Yu S.P. Yeh C.H. Strasser M. Tian M. Choi D.W. Science. 1999; 284: 336-339Crossref PubMed Scopus (210) Google Scholar, 16Maeno E. Ishizaki Y. Kanaseki T. Hazama A. Okada Y. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 9487-9492Crossref PubMed Scopus (654) Google Scholar, 17Widlak P. Garrard W.T. Mol. Cell Biochem. 2001; 218: 125-130Crossref PubMed Scopus (45) Google Scholar). Maintenance of the normal physiologic intracellular concentration of these monovalent ions has been shown to inhibit apoptosis and thus can serve as a repressive mechanism during programmed cell death (7Bortner C.D. Hughes Jr., F.M. Cidlowski J.A. J. Biol. Chem. 1997; 272: 32436-32442Abstract Full Text Full Text PDF PubMed Scopus (509) Google Scholar, 18Perez G.I. Maravei D.V. Trbovich A.M. Cidlowski J.A. Tilly J.L. Hughes Jr., F.M. Biol. Reprod. 2000; 63: 1358-1369Crossref PubMed Scopus (59) Google Scholar, 19Cain K. Langlais C. Sun X.M. Brown D.G. Cohen G.M. J. Biol. Chem. 2001; 276: 41985-41990Abstract Full Text Full Text PDF PubMed Scopus (177) Google Scholar, 20Krick S. Platoshyn O. Sweeney M. Kim H. Yuan J.X. Am. J. Physiol. 2001; 280: C970-C979Crossref PubMed Google Scholar, 21Thompson G.J. Langlais C. Cain K. Conley E.C. Cohen G.M. Biochem. J. 2001; 357: 137-145Crossref PubMed Google Scholar, 22Bortner C.D. Cidlowski J.A. Cell Death Different. 2002; 9: 1307-1310Crossref PubMed Scopus (192) Google Scholar). Recently, we showed that a variety of apoptotic stimuli result in an early transient increase in intracellular sodium associated with a marked plasma membrane depolarization that occurs prior to the loss of cell volume and other characteristics of apoptosis (23Bortner C.D. Gomez-Angelats M. Cidlowski J.A. J. Biol. Chem. 2001; 276: 4304-4314Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). Although this increase in intracellular sodium appears to occur in part because of an early inhibition of the Na+/K+-ATPase during anti-Fas induced apoptosis, the precise role for this sodium influx is not completely known. In healthy cells, a balance of intracellular potassium and sodium ions is required not only to maintain a constant cell size but also for the overall viability of the cell. Variations in the cellular ionic composition are normally compensated via inherent volume regulatory mechanisms, suggesting the importance of maintaining this balance in ionic content (24Hoffman E.K. Curr. Top. Membr. Transp. 1987; 30: 125-180Crossref Scopus (86) Google Scholar, 25Al-Habori M. Int. J. Biochem. 1994; 26: 319-334Crossref PubMed Scopus (42) Google Scholar, 26Lang F. Ritter M. Gamper N. Huber S. Fillon S. Tanneur V. Lepple-Wienhues A. Szabo I. Gulbins E. Cell. Physiol. Biochem. 2000; 10: 417-428Crossref PubMed Scopus (211) Google Scholar, 27Bortner C.D. Cidlowski J.A. Cell Death in Reproductive Physiology. Springer-Verlag, New York1997: 230-248Crossref Google Scholar). Changes in the concentration of intracellular potassium and chloride have been a primary focus of studies examining apoptotic cell shrinkage. The high intracellular concentration of potassium in most mammalian cells has made this ion an attractive target in dissecting the consequence of cell shrinkage during apoptosis. However, the exact mechanism that accounts for the loss of intracellular potassium during apoptosis and subsequent cell shrinkage has not been identified, although it has been suggested that inhibition of the Na+/K+-ATPase may be one of the mechanisms contributing to the eventual potassium efflux and loss of cell volume during apoptosis (23Bortner C.D. Gomez-Angelats M. Cidlowski J.A. J. Biol. Chem. 2001; 276: 4304-4314Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar, 28Nobel C.S. Aronson J.K. van den Dobbelsteen D.J. Slater A.F. Apoptosis. 2000; 5: 153-163Crossref PubMed Scopus (80) Google Scholar). In contrast, studies elucidating a role for intracellular sodium during apoptosis have lagged behind its aforementioned intracellular cation counterpart, despite the critical function sodium plays in controlling and maintaining a homeostatic cell volume. To date no evidence, either genetic or biochemical, has been reported separating cell shrinkage from other characteristics of apoptosis. Here we report that ion fluxes, but not cell shrinkage, are necessary for apoptosis. We show that sodium influx is necessary for cell shrinkage but not for the activation of the cell death effectors. In contrast, potassium efflux is critical for death by apoptosis, regardless of changes in cell size. Additionally, complete inhibition of sodium influx results in a delay in the activation of the apoptotic program, suggesting that sodium may have multiple roles during programmed cell death. Cell Culture—Jurkat cells, E6.1 (human lymphoma) were cultured in RPMI 1640 medium containing 10% heat-inactivated fetal calf serum, 4 and of apoptosis in Jurkat cells using The cells were for of or RPMI 1640 medium made chloride or for Additionally, and used in of sodium and sodium In the potassium and sodium were the concentration to normal concentration of RPMI and the chloride or concentration to normal concentration of RPMI and as of the were for maintaining using a used a concentration of and by intracellular sodium and potassium of or were to of cells a concentration of prior to the time of prior to propidium to a concentration of cells were by of the cells containing and and using a and used to differential interference contrast The were using the from the ion as the and the as the The used for for and that used for for cells were a an with a to and from an and with a The that the in of by in the using to and control or cells, in were with of and for to the were in of and using a with cells were and and for and of by activity using the activity for the of and to the control or cells were to the caspase and for prior to to a concentration of cells were using a with an of and and for caspase activity and PI, for by of a and the to The membrane with primary a concentration of and with an the with the DNA by DNA content for by by of cells from control and The cells were by the of to a volume of to with and 4 the cells were in and in of of PI, in for cells were by using a by a to cell and cell The of DNA by the of cells with DNA by the of cells DNA by by cells by in of and The were The cell were and with The were with and with to a concentration of and the DNA by the of of The DNA and in of to The were DNA were by and of DNA were a with cells cultured in sodium-substituted medium were with and of an anti-Fas for 4 this the cells were and either sodium-substituted medium or normal RPMI 1640 the of the of The cells were for an of these cells using prior to the of Cell Jurkat cells the for changes in intracellular sodium using the and only the normally or cells, anti-Fas treatment in the of in of one with a control of intracellular sodium and one with intracellular sodium studies that the cell with intracellular sodium with that had plasma and it is these cells that to the characteristic features of apoptosis (23Bortner C.D. Gomez-Angelats M. Cidlowski J.A. J. Biol. Chem. 2001; 276: 4304-4314Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). these cells cell shrinkage, in part because of an inhibition of the thus cellular (23Bortner C.D. Gomez-Angelats M. Cidlowski J.A. J. Biol. Chem. 2001; 276: 4304-4314Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). However, this inhibition of the Na+/K+-ATPase not for the of sodium in the cells not suggesting that ion to for the increase in intracellular These mechanisms may be to the activation of the programmed cell death process. of Cell the consequence of this early increase in intracellular sodium during apoptosis, we Jurkat cells to sodium-substituted thus the normal concentration or for sodium maintaining RPMI 1640 medium that with complete of sodium from this medium by the fetal calf with the cells were cultured in a of sodium that in normal heat-inactivated fetal calf of intracellular sodium using in Jurkat cells with anti-Fas normal showed a significant increase in the of cells with intracellular sodium In contrast, either or for sodium in the anti-Fas treatment not result in intracellular sodium that the observed increase in intracellular sodium is a consequence of sodium influx the plasma Surprisingly, Jurkat cells with anti-Fas in the of sodium-substituted or sodium-substituted medium showed an in cell size by normal sodium an increase in the of cells that had a to in the of cells with a or cell size typical of apoptosis Google observed in Jurkat cells with anti-Fas However, treatment of cells with anti-Fas in sodium-substituted an increase in of cellular control cells cultured in either sodium-substituted medium had a to in the with the control cells cultured in normal suggesting that the of cells cell volume. of Jurkat cells with anti-Fas for in normal RPMI 1640 medium a with showed cells with cellular characteristic of apoptosis In marked contrast, Jurkat cells with anti-Fas in either sodium-substituted or sodium-substituted medium a swollen associated with However, these swollen cells had chromatin and apoptotic of the apoptotic as observed by Apoptosis Cell these we to other apoptotic characteristics in the swollen Jurkat cells cultured in sodium-substituted of the cell using and of Jurkat cells normal with anti-Fas in of prior to the loss of membrane characteristic of apoptosis Jurkat cells cultured in either sodium-substituted or sodium-substituted medium also externalization to an as observed normal medium suggesting that this feature of apoptosis can occur in the of sodium and cell shrinkage. Additionally, cells cultured in the of normal or sodium-substituted medium were for activation of associated with apoptosis I. H. M. X. Wang X. Biol. 1999; PubMed Scopus Google Scholar, Y. Mol. Cell. 2002; 9: Full Text Full Text PDF PubMed Scopus Google Scholar, C. S. B. J. Immunol. 2002; PubMed Scopus Google Scholar) using for and and in cells. normal medium treatment of Jurkat cells with anti-Fas in an increase in and activity When cells with anti-Fas were cultured in either sodium-substituted or sodium-substituted NMDG, activation of all observed suggesting that sodium influx and cell shrinkage are not required for caspase activation To the of caspase activity, we these cells for the of PARP, a nuclear in DNA and a for of control from normal or sodium-substituted medium showed no of However, in of the observed all These that not only are in the swollen cells, but are and to has been that internucleosomal DNA characteristic of apoptosis, is completely to the apoptotic cells (7Bortner C.D. Hughes Jr., F.M. Cidlowski J.A. J. Biol. Chem. 1997; 272: 32436-32442Abstract Full Text Full Text PDF PubMed Scopus (509) Google Scholar, 8Hughes Jr., F.M. Bortner C.D. Purdy G.D. Cidlowski J.A. J. Biol. Chem. 1997; 272: 30567-30576Abstract Full Text Full Text PDF PubMed Scopus (428) Google Scholar, C.D. Cidlowski J.A. Am. J. Physiol. PubMed Google Scholar). We cells cultured normal or sodium-substituted for changes in DNA by Jurkat cells with anti-Fas normal sodium the of a of the of DNA results were observed in cells cultured in either sodium-substituted or sodium-substituted medium The of this DNA fragmentation by The of internucleosomal DNA cleavage, a characteristic of apoptosis, in Jurkat cells with anti-Fas in either normal or sodium-substituted medium of programmed cell death in the of the normal concentration of sodium that although this ion is critical for cell shrinkage during apoptosis, sodium is not necessary for the of other apoptotic we show for the first time that cell shrinkage can be from the programmed cell death process. of the of the loss of intracellular potassium has been shown to a role in the activation of the apoptosis, and of the normal of this ion has been shown to apoptosis. To changes in intracellular potassium in cells cultured sodium-substituted we used the and of Jurkat cells with anti-Fas normal sodium in a marked decrease in intracellular potassium Jurkat cells were cultured in either sodium-substituted or a decrease in intracellular potassium also observed This that the loss of intracellular potassium is not an increase in intracellular sodium, that independent ionic can and for the of sodium and potassium ions during programmed cell death. the we that this loss of intracellular potassium, in the swollen cells, for the of the apoptotic To this we Jurkat cells with anti-Fas in sodium-substituted or medium the normal concentration of or components and were maintaining These a high potassium sodium-substituted Jurkat cells cultured in either sodium-substituted or high medium were from cells cultured in the normal sodium-substituted medium in to intracellular potassium of Jurkat cells with anti-Fas sodium-substituted high in the inhibition of intracellular potassium loss to made in normal sodium, high medium (7Bortner C.D. Hughes Jr., F.M. Cidlowski J.A. J. Biol. Chem. 1997; 272: 32436-32442Abstract Full Text Full Text PDF PubMed Scopus (509) Google Scholar, 8Hughes Jr., F.M. Bortner C.D. Purdy G.D. Cidlowski J.A. J. Biol. Chem. 1997; 272: 30567-30576Abstract Full Text Full Text PDF PubMed Scopus (428) Google Scholar, 19Cain K. Langlais C. Sun X.M. Brown D.G. Cohen G.M. J. Biol. Chem. 2001; 276: 41985-41990Abstract Full Text Full Text PDF PubMed Scopus (177) Google Scholar, 21Thompson G.J. Langlais C. Cain K. Conley E.C. Cohen G.M. Biochem. J. 2001; 357: 137-145Crossref PubMed Google Scholar). the of high the of other apoptotic including externalization of membrane phosphatidylserine, activity, and DNA in the sodium medium the loss of intracellular potassium plays a role in the of apoptosis, regardless of the or of of Cell and the precise role sodium has in cell shrinkage during apoptosis, sodium in Jurkat cells with anti-Fas in sodium-substituted medium a of time by for changes in cell size. shown an increase in cell size or a swollen observed in Jurkat cells with anti-Fas sodium-substituted in sodium-substituted medium However, of these cells in medium that the normal of sodium, the cells a characteristic of apoptosis These a role for sodium influx in the apoptotic volume decrease or cell shrinkage during apoptosis. also show that changes in cell size are of sodium, whereas other features of the cell death are by the loss of intracellular we to the of sodium channel inhibition the early increase in intracellular sodium during apoptosis using the sodium channel blocker The of saxitoxin had no significant Jurkat cells, because these cells were to control first with When Jurkat cells were with anti-Fas for we observed an increase in intracellular sodium, the loss of intracellular potassium, with a cell by Additionally, these cells had all characteristic of apoptosis the of the sodium channel blocker saxitoxin completely prevented the increase in intracellular sodium during anti-Fas treatment a result of this inhibition of sodium cells not apoptosis as by to intracellular potassium, shrink, or DNA This that sodium influx may also a role in the activation of the apoptotic these that early and apoptotic can be prevented in the of sodium influx and that ionic fluxes can control or programmed cell death. the ions have the apoptotic process. results show for the first time that cell shrinkage can be separated from other characteristics of apoptosis, with sodium controlling cell size and potassium the progression of the apoptotic process. The importance of the early increase in intracellular sodium by studies sodium-substituted medium used to the concentration of this this the cells induced to apoptosis shrink, suggesting that the influx of sodium plays a role in controlling cell size. these swollen cells classical apoptotic including externalization of phosphatidylserine, caspase activation, cleavage, internucleosomal DNA cleavage, and the loss of intracellular of potassium loss using high potassium medium completely prevented apoptosis, suggesting potassium as the intracellular ion that the apoptotic death in although cellular has been a of necrosis, we show that the characteristics associated with apoptosis in to anti-Fas treatment in sodium-substituted despite cellular of sodium the sodium-substituted the of cells to shrink, that sodium controls cell shrinkage during apoptosis. the in intracellular sodium is prevented using the sodium channel blocker a complete inhibition of apoptosis is the in intracellular sodium not only appears to a role in controlling changes in cell size but also appears to have an in the of the apoptotic in cell size has been a characteristic to apoptosis from necrosis, with the of the the apoptotic cells shrink, and cells In the used to a mode of cellular death with features of an J.F.R. J. PubMed Scopus Google Scholar, J.F.R. J. PubMed Scopus Google Scholar). This apoptosis shown to a role in cell in as as during normal and to occur in (1Kerr J.F.R. Wyllie A.H. Currie A.R. Br. J. Cancer. 1972; 26: 239-257Crossref PubMed Scopus (12927) Google Scholar). for the of cells with or no a cell is for a role in maintaining cellular have been in of the importance of associated with apoptosis. membrane depolarization or the of is a necessary feature for apoptosis, apoptosis is by or is and as to internucleosomal DNA fragmentation a required for the activation of the cell death process. However, in all examples of apoptosis, the cells for the first to this from other characteristics of apoptosis that it is not the morphological that is but the of ions that the to this mode of cell death is The increase in intracellular sodium reported that occurs prior to the loss of cell volume during apoptosis is and as the cells a loss of sodium and potassium is with have suggested an early increase in intracellular sodium during apoptosis (4Jonas D. Walev I. Berger T. Liebetrau M. Palmer M. Bhakdi S. Infect. Immun. 1994; 62: 1304-1312Crossref PubMed Google Scholar, C.D. Gomez-Angelats M. Cidlowski J.A. J. Biol. Chem. 2001; 276: 4304-4314Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar, D. I. S. A. E. 1995; PubMed Scopus Google Scholar, E. A. A. Exp. Cell Res. 1999; PubMed Scopus Google Scholar, I. L. A. J. 1999; PubMed Scopus Google Scholar). to the onset of apoptosis using the sodium channel blocker saxitoxin that programmed cell death can be the of the plasma Additionally, this result that an of ions plays an role in the overall programmed death process. in studies using sodium as or show that cell shrinkage is not necessary for the progression of apoptosis. primary the saxitoxin and sodium-substituted studies is the of a of sodium in the sodium-substituted medium from the fetal calf In heat-inactivated fetal calf we this to be with because control cells in the complete of sodium loss membrane and cellular not suggest that the of sodium by the fetal calf serum, although not a significant to cell shrinkage apoptotic is to Additionally, studies show that the of sodium the plasma membrane is not during the cell death because of sodium the cells to and apoptotic morphology. The mechanisms for the cellular in sodium-substituted medium and potassium loss sodium-substituted are not completely although normal inhibition of potassium and activation of potassium efflux to be (23Bortner C.D. Gomez-Angelats M. Cidlowski J.A. J. Biol. Chem. 2001; 276: 4304-4314Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar, 28Nobel C.S. Aronson J.K. van den Dobbelsteen D.J. Slater A.F. Apoptosis. 2000; 5: 153-163Crossref PubMed Scopus (80) Google Scholar). of a for the regulatory volume decrease not the loss of intracellular potassium during apoptosis in sodium-substituted medium not suggesting the of an ionic efflux This result is not because it has been suggested that multiple may for the loss of intracellular potassium during cell death the cell apoptotic C.D. Cidlowski J.A. 2002; PubMed Scopus Google Scholar). In this it is to that Jurkat cells in sodium-substituted medium also have a swollen with the loss of intracellular potassium, D. Bortner and J. A. suggesting that this is not to apoptosis and that a mechanism for the loss of this ion may be these In this for the first time the morphological of cell shrinkage from other apoptotic roles for sodium and potassium ion fluxes during apoptosis. Additionally, that cell volume changes during apoptosis are Although not in of a role for sodium in cell shrinkage during apoptosis. These studies the for to apoptosis in the of ion channel We and for critical the and for in the