Rivera Alicia, De Franceschi Lucia, Peters Luanne L, Gascard Philippe, Mohandas Narla, Brugnara Carlo
Children's Hospital Boston, Dept. of Laboratory Medicine, Harvard Medical School, Boston, MA 02115, USA.
Am J Physiol Cell Physiol. 2006 Nov;291(5):C880-6. doi: 10.1152/ajpcell.00436.2005. Epub 2006 Jun 14.
Moderate hemolytic anemia, abnormal erythrocyte morphology (spherocytosis), and decreased membrane stability are observed in mice with complete deficiency of all erythroid protein 4.1 protein isoforms (4.1(-/-); Shi TS et al. J Clin Invest 103: 331, 1999). We have examined the effects of erythroid protein 4.1 (4.1R) deficiency on erythrocyte cation transport and volume regulation. 4.1(-/-) mice exhibited erythrocyte dehydration that was associated with reduced cellular K and increased Na content. Increased Na permeability was observed in these mice, mostly mediated by Na/H exchange with normal Na-K pump and Na-K-2Cl cotransport activities. The Na/H exchange of 4.1(-/-) erythrocytes was markedly activated by exposure to hypertonic conditions (18.2 +/- 3.2 in 4.1(-/-) vs. 9.8 +/- 1.3 mmol/10(13) cell x h in control mice), with an abnormal dependence on osmolality (EC(50) = 417 +/- 42 in 4.1(-/-) vs. 460 +/- 35 mosmol/kgH(2)O in control mice), suggestive of an upregulated functional state. While the affinity for internal protons was not altered (K(0.5) = 489.7 +/- 0.7 vs. 537.0 +/- 0.56 nM in control mice), the V(max) of the H-induced Na/H exchange activity was markedly elevated in 4.1(-/-) erythrocytes (V(max) 91.47 +/- 7.2 compared with 46.52 +/- 5.4 mmol/10(13) cell x h in control mice). Na/H exchange activation by okadaic acid was absent in 4.1(-/-) erythrocytes. Altogether, these results suggest that erythroid protein 4.1 plays a major role in volume regulation and physiologically downregulates Na/H exchange in mouse erythrocytes. Upregulation of the Na/H exchange is an important contributor to the elevated cell Na content of 4.1(-/-) erythrocytes.
在所有红系蛋白4.1蛋白异构体完全缺乏的小鼠（4.1(-/-)；Shi TS等人，《临床研究杂志》103: 331, 1999）中观察到中度溶血性贫血、异常红细胞形态（球形红细胞症）和膜稳定性降低。我们研究了红系蛋白4.1（4.1R）缺乏对红细胞阳离子转运和体积调节的影响。4.1(-/-)小鼠表现出红细胞脱水，这与细胞内钾减少和钠含量增加有关。在这些小鼠中观察到钠通透性增加，主要由钠/氢交换介导，钠钾泵和钠钾-2氯协同转运活性正常。4.1(-/-)红细胞的钠/氢交换在暴露于高渗条件下时明显被激活（4.1(-/-)小鼠为18.2±3.2，而对照小鼠为9.8±1.3 mmol/10(13)细胞×小时），对渗透压有异常依赖性（4.1(-/-)小鼠的EC(50)=417±42，对照小鼠为460±35 mosmol/kgH(2)O），提示功能状态上调。虽然对内部质子的亲和力没有改变（对照小鼠的K(0.5)=489.7±0.7与537.0±0.56 nM），但在4.1(-/-)红细胞中，氢诱导的钠/氢交换活性的V(max)明显升高（V(max)为91.47±7.2，而对照小鼠为46.52±5.4 mmol/10(13)细胞×小时）。冈田酸对4.1(-/-)红细胞的钠/氢交换激活作用不存在。总之，这些结果表明红系蛋白4.1在体积调节中起主要作用，并在生理上下调小鼠红细胞中的钠/氢交换。钠/氢交换的上调是4.1(-/-)红细胞细胞内钠含量升高的重要原因。
