Musgrove E, Seaman M, Hedley D
Ludwig Institute for Cancer Research (Sydney Branch), University of Sydney, New South Wales, Australia.
Exp Cell Res. 1987 Sep;172(1):65-75. doi: 10.1016/0014-4827(87)90093-0.
Flow cytometry was used to measure intracellular pH (pHi) on an individual cell basis during exponential and plateau phases of growth. In all three cell lines examined a range of pHi values was associated with exponential growth. When cells from the extremes of the pHi distribution were sorted using a fluorescence-activated cell sorter and then restained for cellular DNA content, it was found that the higher pHi values were associated with enrichment of the S, G2, and M phases of the cell cycle, with a corresponding increase in the percentage of G1 cells at the lower pH1 range, suggesting cell-cycle dependence of pHi. It has been shown previously (I. W. Taylor and P. Hodson, 1984, J. Cell Physiol. 121, 517) that PMC-22 human melanoma cells are capable of entering a distinct pH-dependent quiescent state in response to the acidification of the growth medium which occurs naturally during growth to plateau phase. Simultaneous measurement of pHi and external pH showed that under these conditions pHi was maintained at control values down to an external pH of approximately 6.5, below which cytoplasmic acidification took place. This fall in pHi coincided with the onset of the transition to quiescence. Individual quiescent cells (defined by failure to incorporate bromodeoxyuridine during a 24-h exposure) could not be identified as such on the basis of a low pHi, suggesting that the probability of cell cycling is reduced by lowering pHi. Those cells which remained in cycle showed a markedly reduced rate of DNA synthesis, but a cell-cycle phase distribution similar to that in exponential growth, indicating that prolongation of all cell-cycle phases is an additional factor influencing overall population growth. The external pH at which both of these effects on cell proliferation kinetics took place in vitro is similar to that which occurs regionally within solid tumors, suggesting that pH effects could play a significant role in determining tumor cell growth in vivo.
采用流式细胞术在细胞生长的指数期和平台期对单个细胞的细胞内pH值（pHi）进行测量。在所检测的三种细胞系中，一系列pHi值与指数生长相关。当使用荧光激活细胞分选仪对pHi分布两端的细胞进行分选，然后重新染色以检测细胞DNA含量时，发现较高的pHi值与细胞周期的S期、G2期和M期富集相关，在较低pH1范围内G1期细胞百分比相应增加，这表明pHi与细胞周期相关。先前已经表明（I. W. 泰勒和P. 霍德森，1984年，《细胞生理学杂志》121卷，517页），PMC - 22人黑色素瘤细胞能够响应生长至平台期时自然发生的生长培养基酸化而进入一种独特的pH依赖性静止状态。pHi和细胞外pH的同步测量表明，在这些条件下，直至细胞外pH约为6.5时pHi都维持在对照值，低于此值则发生细胞质酸化。pHi的这种下降与向静止状态转变的开始相吻合。单个静止细胞（定义为在24小时暴露期间未掺入溴脱氧尿苷）不能基于低pHi来识别，这表明降低pHi会降低细胞周期的概率。那些仍处于细胞周期的细胞显示DNA合成速率明显降低，但细胞周期阶段分布与指数生长时相似，这表明所有细胞周期阶段的延长是影响总体细胞群体生长的另一个因素。在体外发生这两种对细胞增殖动力学影响的细胞外pH与实体瘤局部区域发生的pH相似，这表明pH效应可能在决定体内肿瘤细胞生长方面发挥重要作用。
