Na(+)-H+ and Na(+)-Li+ exchange are mediated by the same membrane transport protein in human red blood cells: an NMR investigation.
Na(+)-H+ and Na(+)-Li+ exchange are mediated by the same membrane transport protein in human red blood cells: an NMR investigation.
复制标题
Na( )-H 和 Na( )-Li 交换由人红细胞中相同的膜转运蛋白介导：核磁共振研究。
DOI：
10.1021/bi960814l
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发表时间：
1996
期刊：
影响因子：
2.9
通讯作者：
MotadeFreitas,D
中科院分区：
文献类型：
--
作者：
Chi,Y;Mo,S;MotadeFreitas,D
Na+-−-H+交换是存在于红细胞内的一种转运系统，在调节细胞内pH、细胞体积和跨膜离子转运方面发挥着重要作用。Na+−Li+交换由于具有较高的重复性，受到了人们的广泛关注，并得到了比其他任何离子传输系统更详细的研究。高血压病患者红细胞Na+−H+和Na+−Li+交换量均高于正常血压者。红细胞Na+−Li+交换可能是Na+−H+交换的一种操作方式。阿米洛利及其类似物5-(N，N-六亚甲基)阿米洛利是已知的Na+−H+交换的抑制剂，而根视黄素则强烈地抑制Na+−Li+交换。在这项研究中，我们用原子吸收法检测了阿米洛利、甲基丙烯酸甲酯和根皮素对完整红细胞Na+-−-Li+交换活性的影响。我们用~7Li核磁共振波谱研究了在无pH梯度和存在pH梯度的情况下，HMA和根皮素抑制对重新密封的H+和Li+负载RBC幽灵的Li+外流的影响。通过~(23)Na和~(7)Li核磁共振弛豫时间的测定，研究了不同pH条件下阿米洛利对红细胞膜上Na~+和Li~+结合的抑制作用。我们发现，在完整的红细胞悬液和再密封的红细胞幽灵的悬浮液中，阿米洛利、HMA和根霉素能抑制Na+−Li+交换活性。当存在pH梯度时，通过重新密封的H+和Li+负载的RBC幽灵的Li+外流速率显著降低，可能是因为Li+和H+之间竞争通过相同的转运蛋白进行运输。阿米洛利对Na+和Li+与红细胞膜结合的抑制常数相似(pH 8.0时为1021±48 M-1比964±40 M-1；pH 7.0时为731±147 M-1比716±27 M-1)。这些结果表明，Na+−H+交换和Na+−Li+交换是由同一红细胞膜转运蛋白介导的。
Na+−H+exchange is a transport system present in erythrocytes which plays an important role in the regulation of intracellular pH, cellular volume, and transmembrane ion transport. Na+−Li+exchange has received much attention and has been investigated in more detail than have any of the other ion transport systems, because of its high reproducibility. Both red blood cell (RBC) Na+−H+and Na+−Li+exchange are elevated in essential hypertensive patients relative to normotensive individuals. RBC Na+−Li+exchange may be a mode of operation of Na+−H+exchange. Amiloride and its analogue, 5-(N,N-hexamethylene)amiloride (HMA), are well-known inhibitors of Na+−H+exchange, whereas phloretin strongly inhibits Na+−Li+exchange. In this study, we tested the effects of amiloride, HMA, and phloretin on Na+−Li+exchange activity in intact RBCs by using atomic absorption. We investigated by using7Li nuclear magnetic resonance (NMR) spectroscopy the effects of HMA and phloretin inhibition on Li+efflux across resealed H+- and Li+-loaded RBC ghosts in the absence and presence of pH gradients. Amiloride inhibitory activities on both Na+and Li+binding to exposed RBC membranes under different pH conditions were also studied by23Na and7Li NMR relaxation time measurements. We found that Na+−Li+exchange activity was inhibited by amiloride, HMA, and phloretin in suspensions of intact RBCs and of resealed RBC ghosts. Li+efflux rates across resealed H+- and Li+-loaded RBC ghosts were significantly lower when a pH gradient was present, presumably because of the competition between Li+and H+for transport by the same transport protein. Amiloride had similar inhibitory constants on both Na+and Li+binding to RBC membranes (1021 ± 48 M-1vs 964 ± 40 M-1at pH 8.0; 731 ± 147 M-1vs 716 ± 27 M-1at pH 7.0). These results suggest that Na+−H+exchange and Na+−Li+exchange are mediated by the same RBC membrane transport protein.