Department of Biochemistry and Biotechnology, Royal Institute of Technology, S-100 44, Stockholm, Sweden.
Cytotechnology. 1996 Jan;22(1-3):251-4. doi: 10.1007/BF00353945.
Ammonium can be transported into the cell by ion pumps in the cytoplasmic membrane. Ammonia then diffuse out through the cell membrane. A futile cycle is created that results in cytoplasmic acidification and extracellular alkalinisation. Ammonium transport can be quantified by measuring the extracellular pH changes occurring in a cell suspension (in PBS) after addition of ammonium. By using this technique, in combination with specific inhibitors of various ion pumps, it was shown that ammonium ions are transported across the cytoplasmic membrane by the Na(+)K(+)2Cl(-)-cotransporter in both hybridoma and myeloma cells. Further, the Na(+)/H(+) exchanger, which regulates intracellular pH by pumping out protons, was shown to be active during ammonium exposure. The viability of hybridoma cells suspended in PBS and exposed to NH (inf4) (sup+) for only 90 min, was reduced by 11% (50% necrosis and 50% apoptosis). A control cell suspension did not loose viability during this time. Turning off the activity of the Na(+)/H(+) exchanger (by amiloride) during ammonium exposure decreased viability further, while inhibiting transport itself (by bumetanide) restored viability to the same level as for the control experiment with bumetanide alone. These results show that one effect of ammonia/ammonium on cell physiology is specifically related to the inward transport of ammonium ions by membrane bound ion pumps.
铵可以通过细胞质膜中的离子泵进入细胞。然后，氨通过细胞膜扩散出来。这样就形成了一个无效循环，导致细胞质酸化和细胞外碱化。可以通过测量铵加入细胞悬浮液（在 PBS 中）后细胞外 pH 值的变化来定量铵的转运。通过使用这种技术，结合各种离子泵的特异性抑制剂，表明铵离子通过杂交瘤和骨髓瘤细胞中的 Na(+)K(+)2Cl(-)-共转运体穿过细胞质膜进行转运。此外，Na(+)/H(+)交换器在铵暴露期间也被证明是活跃的，它通过泵出质子来调节细胞内 pH 值。在 PBS 中悬浮的杂交瘤细胞在暴露于 NH (inf4) (sup+) 仅 90 分钟后，其活力降低了 11%（50%坏死和 50%凋亡）。在此期间，对照细胞悬浮液没有失去活力。在铵暴露期间关闭 Na(+)/H(+)交换器的活性（通过阿米洛利）进一步降低了活力，而抑制转运本身（通过布美他尼）则使活力恢复到单独使用布美他尼的对照实验水平。这些结果表明，氨/铵对细胞生理学的一种影响与膜结合离子泵向内转运铵离子特别相关。
