Down-regulated in adenoma mediates apical Cl-/HCO3- exchange in rabbit, rat, and human duodenum
Down-regulated in adenoma mediates apical Cl-/HCO3- exchange in rabbit, rat, and human duodenum
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DOI：
10.1053/gast.2002.31875
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发表时间：
2002-03-01
期刊：
影响因子：
29.4
通讯作者：
Seidler, U
中科院分区：
文献类型：
--
作者：
Jacob, P;Rossmann, H;Seidler, U
背景与目的：十二指肠重碳酸盐的分泌部分是由顶端的Cl-/HCO 3-交换器介导的，其分子性质未知。最近发现的dra（down-regulated in adenoma）基因编码SO 42-、Cl-和HCO 3-的转运蛋白（transport protein，TRIP）。本研究的目的是探讨十二指肠顶端Cl-/HCO 3-交换器是否可能。方法：采用半定量逆转录聚合酶链反应和原位杂交技术（人小肠中的RT-PCR），研究大鼠、家兔和人胃肠道中Cl-、Na+/H+交换器（NHE）亚型3和阴离子交换器亚型（AE）2信使RNA的表达水平。Western分析和免疫组化法测定细胞内PCNA的亚细胞定位。用兔和大鼠十二指肠刷状缘膜囊泡研究了其阴离子交换特性。结果：NHE 3 mRNA在所有种属动物的十二指肠和结肠中表达量较高，而在十二指肠中表达量较低，在结肠中表达量较高。Western分析和免疫组织化学显示，兔和大鼠十二指肠刷状缘膜囊泡显示4，4 '-二异硫氰基芪-2，2'-二磺酸敏感的Cl-/Cl-、HCO 3-/Cl-、SO 42-/Cl-和Cl-/SO 42-交换，有证据表明一个主要的刷状缘膜Cl-/阴离子交换剂，对Cl- > HCO 3-的亲和力，大鼠对SO_（42-）的亲和力明显高于家兔。十二指肠中DRA对NHE 3和NHE 2表达的强烈优势与刷状缘膜囊泡中Cl-/HCO 3-比Na+/H+交换率高得多相平行，这可能解释了十二指肠HCO 3-分泌率高的原因。结论：这些数据表明，在十二指肠和结肠中，HCO 3-是主要的顶端阴离子交换剂，并且可能是十二指肠电中性HCO 3-分泌的转运蛋白。
Background & Aims: Duodenal bicarbonate secretion is in part mediated by an apical Cl-/HCO3- exchanger of unknown molecular nature. The recently discovered dra (down-regulated in adenoma) gene encodes a transport protein (DRA) for SO42-, Cl-, and HCO3-. The aim of this study was to investigate whether DRA may be the duodenal apical Cl-/HCO3- exchanger, Methods: DRA, Na+/H+ exchanger (NHE) isoform 3, and anion exchanger isoform (AE) 2 messenger RNA expression levels were studied in rat, rabbit, and human gastrointestinal tract by semiquantitative reverse-transcription polymerase chain reaction and in situ hybridization (DRA in human intestine). The subcellular localization of DRA was determined by Western analysis and immunohistochemistry. Using rabbit and rat duodenal brush border membrane vesicles, anion exchange characteristics were investigated. Results: DRA expression was high in duodenum and colon of all species, whereas NHE3 messenger RNA expression was low in duodenum and high in colon. Western analysis and immunohistochemistry showed an apical localization for DRA, Rabbit and rat duodenal brush border membrane vesicles showed 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive Cl-/Cl-, HCO3-/Cl-, SO42-/Cl-, and Cl-/SO42- exchange, with evidence for one major brush border membrane Cl-/anion exchanger, an affinity for Cl- > HCO3-, and a much higher affinity for SO42- in rat than rabbit. The strong predominance of DRA over NHE3 and NHE2 expression in duodenum was paralleled by much higher Cl-/HCO3- than Na+/H+ exchange rates in brush border membrane vesicles and likely explains the high duodenal HCO3- secretory rates. Conclusions: These data suggest that DRA is the major apical anion exchanger in the duodenum as well as the colon and the likely transport protein for duodenal electroneutral HCO3- secretion.