Dudeja P K, Rao D D, Syed I, Joshi V, Dahdal R Y, Gardner C, Risk M C, Schmidt L, Bavishi D, Kim K E, Harig J M, Goldstein J L, Layden T J, Ramaswamy K
Department of Medicine, University of Illinois at Chicago, USA.
Am J Physiol. 1996 Sep;271(3 Pt 1):G483-93. doi: 10.1152/ajpgi.1996.271.3.G483.
The identity of Na+/H+ exchanger (NHE) isoforms in the human small intestine and colon and their role in vectorial Na+ absorption are not known. The present studies were undertaken to examine the regional and vertical axis distribution of NHE-1, NHE-2, and NHE-3 mRNA in the human intestine. Ribonuclease protection assays were used to quantitate the levels of mRNA of these isoforms in various regions of the human intestine. In situ hybridization technique was used to localize NHE-2 and NHE-3 mRNA in the colon. The NHE-1 isoform message was present uniformly throughout the length of the human intestine. In contrast, mRNA levels for human NHE-2 and NHE-3 isoforms demonstrated significant regional differences. The NHE-3 abundance was found in decreasing order: ileum > jejunum > proximal colon = distal colon. The NHE-2 message level in the distal colon was significantly higher than in the proximal colon but was evenly distributed in the small intestine. In addition, NHE-2 mRNA was present in surface epithelial cells as well as in cells of the crypt region, suggesting the presence of NHE-2 message throughout the vertical axis of the colonic crypts. In contrast, NHE-3 mRNA was localized to surface colonocytes in the proximal colon. On the basis of this tissue-specific localization of NHE-2 and NHE-3 mRNA, it can be speculated that the relative contribution of NHE-2 and NHE-3 isoforms in Na+ absorption in the human intestine may be region specific, and these putative apical isoforms may be differentially regulated.
人类小肠和结肠中钠氢交换体（NHE）亚型的身份及其在向量性钠吸收中的作用尚不清楚。本研究旨在检测人肠道中NHE-1、NHE-2和NHE-3 mRNA的区域和垂直轴分布。采用核糖核酸酶保护分析法对人肠道不同区域这些亚型的mRNA水平进行定量。原位杂交技术用于在结肠中定位NHE-2和NHE-3 mRNA。NHE-1亚型的信息在人肠道全长中均匀存在。相比之下，人NHE-2和NHE-3亚型的mRNA水平显示出显著的区域差异。发现NHE-3的丰度顺序为：回肠＞空肠＞近端结肠 = 远端结肠。远端结肠中的NHE-2信息水平显著高于近端结肠，但在小肠中分布均匀。此外，NHE-2 mRNA存在于表面上皮细胞以及隐窝区域的细胞中，表明在结肠隐窝的垂直轴上均存在NHE-2信息。相比之下，NHE-3 mRNA定位于近端结肠的表面结肠细胞。基于NHE-2和NHE-3 mRNA的这种组织特异性定位，可以推测NHE-2和NHE-3亚型在人肠道钠吸收中的相对贡献可能具有区域特异性，并且这些假定的顶端亚型可能受到不同的调节。
