Cassel D, Whiteley B, Zhuang Y X, Glaser L
J Cell Physiol. 1985 Feb;122(2):178-86. doi: 10.1002/jcp.1041220203.
Previous studies have documented the activation of Na+/H+ exchange in A431 cells by the addition of epidermal growth factor or serum (Rothenberg et al., 1983b). Here we show that exposure of A4 31 cells to medium of increased osmolarity also leads to activation of Na+/H+ exchange and to an increase in intracellular pH (pHi), which under a variety of conditions displays similar kinetics to that observed upon addition of mitogens to the cells. Measurements of cell volume using the 3-0-methylglucose equilibration technique clearly show that mitogens do not activate Na+/H+ exchange by an osmotic mechanism (i.e., a decrease in cell volume). In fact, mitogens can induce further intracellular alkalinization if added to cells which have been shrunken in hypertonic medium. Activation of the Na+/H+ antiport does not lead to an obligatory change in pHi. Addition of epidermal growth factor of hypertonic solution to A431 cells in bicarbonate buffer activates Na+/H+ exchange without a concomitant increase in pHi. Under these conditions the increased proton efflux via Na+/H+ exchange must therefore be compensated by other mechanisms that control cytoplasmic pH.
以往的研究已证明，在A431细胞中添加表皮生长因子或血清会激活Na⁺/H⁺交换（Rothenberg等人，1983b）。在此我们表明，将A431细胞暴露于渗透压升高的培养基中也会导致Na⁺/H⁺交换激活以及细胞内pH值（pHi）升高，在多种条件下，其动力学与向细胞中添加有丝分裂原时观察到的相似。使用3 - O - 甲基葡萄糖平衡技术测量细胞体积清楚地表明，有丝分裂原并非通过渗透机制（即细胞体积减小）激活Na⁺/H⁺交换。事实上，如果将有丝分裂原添加到在高渗培养基中已发生皱缩的细胞中，它们会诱导进一步的细胞内碱化。Na⁺/H⁺反向转运体的激活并不一定会导致pHi发生必然变化。在碳酸氢盐缓冲液中，向A431细胞添加表皮生长因子或高渗溶液会激活Na⁺/H⁺交换，而pHi不会随之升高。因此，在这些条件下，通过Na⁺/H⁺交换增加的质子外流必须由控制细胞质pH值的其他机制来补偿。
