Involvement of AQP6 in the mercury-sensitive osmotic lysis of rat parotid secretory granules.
Involvement of AQP6 in the mercury-sensitive osmotic lysis of rat parotid secretory granules.
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AQP6 参与大鼠腮腺分泌颗粒的汞敏感渗透裂解。
DOI：
10.1007/s00232-012-9522-7
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
H. Sugiya
中科院分区：
文献类型：
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作者：
M. Matsuki-Fukushima;J. Fujita-Yoshigaki;M. Murakami;O. Katsunmata-Kato;M. Yokoyama;H. Sugiya
在分泌颗粒和囊泡中，膜转运蛋白可以渗透水分子、离子和/或小溶质，使颗粒膨胀并促进膜融合。我们之前已经证明水通道蛋白-6 (AQP6)，一种渗透阴离子的水通道蛋白，定位于大鼠腮腺分泌颗粒中（Matsuki-Fukushima et al., Cell Tissue Res 332:73 - 80,2008）。由于AQP6在其他器官中的定位仅限于胞质囊泡，因此AQP6在体内的天然功能尚未得到很好的确定。为了表征颗粒膜的通道特性，溶质渗透诱导的纯化分泌颗粒的裂解是一个有用的标记。为了分析AQP6在分泌颗粒膜中的作用，我们使用已知能激活AQP6的Hg2+，研究Hg2+(Hg lysis)诱导大鼠腮腺分泌颗粒溶解时溶质通透性的特点。用分光光度计测定了等渗透氯化钾溶液中渗透分泌颗粒在540 nm处的光密度衰减。0.5 ~ 2.0 μM Hg2+可激活AQP6，显著促进了渗透分泌颗粒的裂解。通过破坏Hg2+结合的β-巯基乙醇或从反应介质中去除氯离子，Hg的裂解被完全阻断。阴离子通道阻滞剂DIDS不影响AQP6，可以区分Hg裂解过程中DIDS不敏感和敏感的组分。这些结果表明，汞裂解是阴离子通过蛋白质转运体渗透所必需的。Hg的溶解依赖于NO3 - > Br - > I - > Cl -的阴离子电导，并受酸性pH的促进。对NO3 -的阴离子选择性和酸性pH敏感性与AQP6的通道性质相似。综上所述，AQP6可能作为Hg2+敏感阴离子通道渗透到大鼠腮腺分泌颗粒中的卤化物基团阴离子中。
In secretory granules and vesicles, membrane transporters have been predicted to permeate water molecules, ions and/or small solutes to swell the granules and promote membrane fusion. We have previously demonstrated that aquaporin-6 (AQP6), a water channel protein, which permeates anions, is localized in rat parotid secretory granules (Matsuki-Fukushima et al., Cell Tissue Res 332:73–80, 2008). Because the localization of AQP6 in other organs is restricted to cytosolic vesicles, the native function or functions of AQP6 in vivo has not been well determined. To characterize the channel property in granule membranes, the solute permeation-induced lysis of purified secretory granules is a useful marker. To analyze the role of AQP6 in secretory granule membranes, we used Hg2+, which is known to activate AQP6, and investigated the characteristics of solute permeability in rat parotid secretory granule lysis induced by Hg2+(Hg lysis). The kinetics of osmotic secretory granule lysis in an iso-osmotic KCl solution was monitored by the decay of optical density at 540 nm using a spectrophotometer. Osmotic secretory granule lysis was markedly facilitated in the presence of 0.5–2.0 μM Hg2+, concentrations that activate AQP6. The Hg lysis was completely blocked by β-mercaptoethanol which disrupts Hg2+-binding, or by removal of chloride ions from the reaction medium. An anion channel blocker, DIDS, which does not affect AQP6, discriminated between DIDS-insensitive and sensitive components in Hg lysis. These results suggest that Hg lysis is required for anion permeability through the protein transporter. Hg lysis depended on anion conductance with a sequence of NO3−> Br−> I−> Cl−and was facilitated by acidic pH. The anion selectivity for NO3−and the acidic pH sensitivity were similar to the channel properties of AQP6. Taken together, it is likely that AQP6 permeates halide group anions as a Hg2+-sensitive anion channel in rat parotid secretory granules.