Nukui Miho, Shimizu Takahiro, Okada Yasunobu
Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 445-8585 Japan.
J Physiol Sci. 2006 Oct;56(5):335-9. doi: 10.2170/physiolsci.RP009606. Epub 2006 Sep 12.
Apoptosis is a major form of cell death that occurs in response to a variety of signals in both physiological and pathological situations. A hallmark of apoptosis is normotonic cell shrinkage, called apoptotic volume decrease (AVD), the process of which involves fluxes of K(+), Cl(-), and Na(+). Na(+) influx was suggested to be required in Fas-induced apoptosis in human Jurkat T cells, whereas Na(+) efflux was found to be associated with AVD and apoptosis in human HL-60 cells. Here we examined the effects of extracellular Na(+) deprivation on cell volume and viability in human epithelial HeLa cells. The incubation of HeLa cells in normotonic Na(+)-free Ringer solution resulted in persistent cell shrinkage after > or = 30 min and reduction in cell viability after > or = 1 h. After exposure to Na(+)-free solution for 5 h, a marked reduction in cell viability was found to be associated with an activation of caspase-3 without showing significant LDH release, indicating that the cells underwent apoptosis but not necrosis. Na(+) deprivation-induced cell shrinkage and apoptotic cell death were significantly inhibited by a blocker of Na(+)-K(+)-2Cl(-) cotransporter (NKCC) or of the reverse-mode operation of Na(+)/Ca(2+) exchanger (NCX), but not by a blocker of Na(+)/H(+) exchanger (NHE). Therefore it is concluded that Na(+) deprivation causes persistent cell shrinkage resulting from Na(+) efflux mainly via NKCC and NCX and thereafter leads to apoptotic death of HeLa cells. It is also suggested that normotonic cell shrinkage per se, if persistent, provides a sufficient condition for apoptosis induction.
凋亡是细胞死亡的一种主要形式，在生理和病理情况下，细胞会对多种信号作出反应而发生凋亡。凋亡的一个标志是等渗性细胞皱缩，即凋亡性体积减小（AVD），这一过程涉及钾离子（K⁺）、氯离子（Cl⁻）和钠离子（Na⁺）的流动。有研究表明，在人Jurkat T细胞的Fas诱导凋亡过程中需要钠离子内流，而在人HL-60细胞中发现钠离子外流与AVD和凋亡有关。在此，我们研究了细胞外钠离子缺失对人上皮性HeLa细胞体积和活力的影响。将HeLa细胞置于等渗无钠林格液中孵育，≥30分钟后细胞持续皱缩，≥1小时后细胞活力降低。在无钠溶液中暴露5小时后，发现细胞活力显著降低，同时伴有半胱天冬酶-3的激活，但未出现明显的乳酸脱氢酶释放，这表明细胞发生了凋亡而非坏死。钠离子缺失诱导的细胞皱缩和凋亡性细胞死亡可被钠离子-钾离子-2氯离子协同转运体（NKCC）阻滞剂或钠离子/钙离子交换体（NCX）反向模式运行阻滞剂显著抑制，但不能被钠离子/氢离子交换体（NHE）阻滞剂抑制。因此可以得出结论，钠离子缺失导致细胞持续皱缩是由于主要通过NKCC和NCX的钠离子外流所致，进而导致HeLa细胞发生凋亡性死亡。研究还表明，等渗性细胞皱缩本身，如果持续存在，为诱导凋亡提供了充分条件。
