Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Gastroenterology. 2011 Feb;140(2):560-71. doi: 10.1053/j.gastro.2010.10.042. Epub 2010 Oct 23.
BACKGROUND & AIMS: Oral rehydration solutions reduce diarrhea-associated mortality. Stimulated sodium absorption by these solutions is mediated by the Na(+)/H(+) hydrogen exchanger NHE3 and is increased by Na(+)-glucose co-transport in vitro, but the mechanisms of this up-regulated process are only partially understood.
Intracellular pH was measured in jejunal enterocytes of wild-type mice and mice with disrupted Na+/H+ exchange regulatory co-factor 2 (NHERF2-/- mice) by multiphoton microscopy. Diarrhea was induced by cholera toxin. Caco-2BBe cells that express NHE3 and the sodium/glucose cotransporter 1 (SGLT1) were studied by fluorometry, before and after siRNA-mediated knockdown of NHERF1 or NHERF2. NHE3 distribution was assessed by cell-surface biotinylation and confocal microscopy. Brush-border mobility was determined by fluorescence recovery after photobleaching and confocal microscopy.
The nonmetabolized SGLT1 substrate α-methyl-D-Glu (α-MD-G) activated jejunal NHE3; this process required Akt and NHERF2. α-MD-G normalized NHE3 activity after cholera toxin-induced diarrhea. α-MD-G-stimulated jejunal NHE3 activity was defective in NHERF2-/- mice and cells with NHERF2 knockdown, but occurred normally with NHERF1 knockdown; was associated with increased NHE3 surface expression in Caco-2 cells, which also was NHERF2-dependent; was associated with dissociation of NHE3 from NHERF2 and an increase in the NHE3 mobile fraction from the brush border; and was accompanied by a NHERF2 ezrin-radixin-moesin-binding domain-dependent increase in co-precipitation of ezrin with NHE3.
SGLT1-mediated Na-glucose co-transport stimulates NHE3 activity in vivo by an Akt- and NHERF2-dependent signaling pathway. It is associated with increased brush-border NHE3 and association between ezrin and NHE3. Activation of NHE3 corrects cholera toxin-induced defects in Na absorption and might contribute to the efficacy of oral rehydration solutions.
口服补液溶液可降低腹泻相关死亡率。这些溶液通过钠离子/氢离子交换器 NHE3 刺激钠吸收，并且在体外通过钠-葡萄糖协同转运增加，但是这种上调过程的机制仅部分了解。
通过多光子显微镜测量野生型小鼠和 Na+/H+交换调节因子 2（NHERF2-/- 小鼠）破坏的回肠肠细胞内的 pH 值。用霍乱毒素诱导腹泻。用氟测定法研究表达 NHE3 和钠/葡萄糖协同转运蛋白 1（SGLT1）的 Caco-2BBe 细胞，在 NHERF1 或 NHERF2 的 siRNA 介导敲低前后。通过细胞表面生物素化和共聚焦显微镜评估 NHE3 分布。通过荧光恢复后光漂白和共聚焦显微镜确定刷状缘流动性。
非代谢 SGLT1 底物 α-甲基-D-吡喃葡萄糖（α-MD-G）激活回肠 NHE3；这个过程需要 Akt 和 NHERF2。α-MD-G 可在霍乱毒素诱导的腹泻后使 NHE3 活性正常化。α-MD-G 刺激 NHERF2-/- 小鼠和 NHERF2 敲低细胞的 NHE3 活性缺陷，但 NHERF1 敲低时正常发生；与 Caco-2 细胞中 NHE3 的表面表达增加有关，这也依赖于 NHERF2；与 NHE3 从 NHERF2 解离以及 NHE3 从刷状缘的可移动部分增加有关；并伴随着 NHERF2 埃兹蛋白-根蛋白-膜突蛋白结合域依赖性增加与 NHE3 的共沉淀。
SGLT1 介导的 Na-葡萄糖协同转运通过 Akt 和 NHERF2 依赖性信号通路刺激体内 NHE3 活性。它与增加的刷状缘 NHE3 和埃兹蛋白与 NHE3 之间的关联有关。NHE3 的激活纠正霍乱毒素诱导的 Na 吸收缺陷，可能有助于口服补液溶液的疗效。
