Kulaksiz H, Bektas H, Cetin Y
Department of Molecular Cell Biology, Institute of Anatomy and Cell Biology, Philipps University, Robert-Koch-Strasse 6, 35033 Marburg, Germany.
Cell Tissue Res. 2001 Mar;303(3):337-43. doi: 10.1007/s004410000329.
Na+/H+ exchangers (NHEs) are vital transmembrane transport proteins mediating the electroneutral exchange of Na+ and H+ ions in mammalian cells. In the epithelium of the lower intestine, the isoform NHE-3 is apparently involved in Na+ absorption; however, its presence and cellular localization in the duodenum and particularly in the stomach remain largely unclear. Therefore, we studied the human and guinea pig stomach and duodenum for the expression, regional and mucosal distribution pattern, and membrane-specific localization of NHE-3. Reverse transcription/polymerase chain reaction analyses revealed strong expression of NHE-3 in the stomach and duodenum, where it was identified as a 85-kDa immunoreactive protein by Western blotting experiments. Whereas NHE-3 was localized to the basolateral membrane of surface mucous cells of the stomach, it was exclusively confined to the brush border membrane of epithelial cells in the duodenum. We conclude that the basolateral NHE-3 in the stomach protects the mucosa by secreting protons that diffuse into the mucous cells. In the duodenum, the localization of NHE-3 to the apical membrane of enterocytes suggests a resorptive function by directional Na+ transport. These findings indicate that NHE-3 may be involved in various segment-specific functions in the upper gastrointestinal tract.
钠氢交换体（NHEs）是重要的跨膜转运蛋白，介导哺乳动物细胞中钠离子和氢离子的电中性交换。在下段小肠上皮中，NHE-3亚型显然参与了钠离子的吸收；然而，其在十二指肠尤其是胃中的存在情况和细胞定位仍不清楚。因此，我们研究了人及豚鼠胃和十二指肠中NHE-3的表达、区域和黏膜分布模式以及膜特异性定位。逆转录/聚合酶链反应分析显示，NHE-3在胃和十二指肠中表达强烈，通过蛋白质印迹实验将其鉴定为一种85 kDa的免疫反应性蛋白。NHE-3定位于胃表面黏液细胞的基底外侧膜，而在十二指肠中则仅局限于上皮细胞的刷状缘膜。我们得出结论，胃中基底外侧的NHE-3通过分泌扩散到黏液细胞中的质子来保护黏膜。在十二指肠中，NHE-3定位于肠上皮细胞的顶端膜，提示其具有通过定向钠离子转运进行重吸收的功能。这些发现表明，NHE-3可能参与上消化道的各种节段特异性功能。
