Lahajnar Gojmir, Pecar Slavko, Sepe Ana
Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
Bioelectrochemistry. 2007 May;70(2):462-8. doi: 10.1016/j.bioelechem.2006.07.009. Epub 2006 Jul 14.
The passage of water through the aquaporin-1 (AQP1) transmembrane channel protein of the human erythrocyte is known to be inhibited by organic mercurials such as p-chloromercuribenzoate (pCMB), which react with the free SH-group of the critical cysteine (Cys189) located near the constriction of the AQP1 water-specific channel. Sodium nitroprusside (SNP), which is known as a nitric oxide (NO) donor in interactions with SH-containing molecules, is shown here to suppress the diffusional water permeability (P(d)) of the erythrocyte membrane, presumably as a result of reaction with the Cys189 of the human erythrocyte AQP1 water channels. Further, treatment of erythrocytes with HgCl(2) is found to result in a cell volume decrease that can be related to activation of membrane K(+)-selective Gárdos channels and subsequent loss of intracellular K(+) and cell shrinkage. The variations in P(d) and volume of the erythrocyte were deduced from induced variations in the measured proton ((1)H) nuclear magnetic resonance (NMR) transverse (T(2)) relaxation functions of water exchanging between diamagnetic intracellular and paramagnetic extracellular compartments of the 20-25% hematocrit samples. The extracellular solvent contained 10 mM membrane-impermeable paramagnetic Mn(2+) ions. The (1)H-T(2) NMR technique allows determination of the time constant tau(exch) (for exchange of the erythrocyte intracellular water) that is inversely proportional to the permeability coefficient P(d) when the intracellular water volume is left unmodified, as in the case of SNP-treated erythrocytes. However, for HgCl(2)-treated erythrocytes, this technique showed simultaneous variation of both tau(exch) and the volume ratio V(in)/V(out) of intracellular and extracellular water in proportions suggesting that P(d) was left unmodified. The HgCl(2) effect has been found to be partly reversible by the reducing activity of added mercaptoethanol.
已知水通过人红细胞的水通道蛋白-1（AQP1）跨膜通道蛋白的过程会受到有机汞化合物如对氯汞苯甲酸（pCMB）的抑制，pCMB会与位于AQP1水特异性通道缩窄处附近的关键半胱氨酸（Cys189）的游离巯基发生反应。硝普钠（SNP）在与含巯基分子相互作用时是一种一氧化氮（NO）供体，此处显示它会抑制红细胞膜的扩散水渗透性（P(d)），推测这是与人类红细胞AQP1水通道的Cys189发生反应的结果。此外，发现用HgCl₂处理红细胞会导致细胞体积减小，这可能与膜K⁺选择性加尔多斯通道的激活以及随后细胞内K⁺的丢失和细胞收缩有关。红细胞P(d)和体积的变化是根据20 - 百分之二十五血细胞比容样本中抗磁性细胞内和顺磁性细胞外隔室之间水交换的测量质子（¹H）核磁共振（NMR）横向（T₂）弛豫函数的诱导变化推导出来的。细胞外溶剂含有10 mM不能透过膜的顺磁性Mn²⁺离子。¹H - T₂ NMR技术可以确定时间常数tau(exch)（用于红细胞细胞内水的交换），当细胞内水体积不变时，如SNP处理的红细胞情况，该时间常数与渗透系数P(d)成反比。然而，对于HgCl₂处理的红细胞，该技术显示tau(exch)和细胞内与细胞外水的体积比V(in)/V(out)同时变化，其比例表明P(d)未改变。已发现HgCl₂的作用可通过添加的巯基乙醇的还原活性部分逆转。
