Marino C R, Jeanes V, Boron W F, Schmitt B M
Veterans Affairs Medical Center, University of Tennessee, Memphis, Tennessee 68163, USA.
Am J Physiol. 1999 Aug;277(2):G487-94. doi: 10.1152/ajpgi.1999.277.2.G487.
The cellular mechanisms of HCO(-)(3) secretion in the human pancreas are unclear. Expression of a Na(+)-HCO(-)(3) cotransporter (NBC) mRNA has been observed recently, but the distribution and physiological role of the NBC protein are not known. Here we examined the expression and localization of NBC in human pancreas by Northern blot, immunoblot, and immunofluorescence microscopy. Rat kidney NBC probes detected a single 9.5-kb band by Northern blot. On immunoblots, two polyclonal antisera directed against different epitopes of rat kidney NBC identified a single approximately 130-kDa protein. In cryosections of normal human pancreas, both antisera labeled basolateral membranes of large, morphologically identifiable ducts and produced a distinct labeling pattern in the remainder of the parenchyma. In double-labeling experiments, NBC immunoreactivity in the parenchyma colocalized with the Na(+)-K(+) pump, a basolateral marker. In contrast, NBC and cystic fibrosis transmembrane conductance regulator, an apical membrane marker, were detected within the same histological structures but at different subcellular localizations. The NBC antisera did not label acinar or islet cells. Our observations suggest that secretion of HCO(-)(3) by human pancreatic duct cells involves the basolateral uptake of Na(+) and HCO(-)(3) via NBC, an electrogenic Na(+)-HCO(-)(3) cotransporter.
人类胰腺中HCO(-)(3)分泌的细胞机制尚不清楚。最近观察到钠-碳酸氢根共转运体（NBC）mRNA的表达，但NBC蛋白的分布和生理作用尚不清楚。在此，我们通过Northern印迹、免疫印迹和免疫荧光显微镜检查了NBC在人类胰腺中的表达和定位。大鼠肾脏NBC探针通过Northern印迹检测到一条单一的9.5-kb条带。在免疫印迹上，两种针对大鼠肾脏NBC不同表位的多克隆抗血清识别出一条单一的约130-kDa蛋白。在正常人胰腺的冷冻切片中，两种抗血清均标记了形态可识别的大导管的基底外侧膜，并在实质的其余部分产生了独特的标记模式。在双重标记实验中，实质中的NBC免疫反应性与基底外侧标记物钠钾泵共定位。相比之下，NBC和顶端膜标记物囊性纤维化跨膜传导调节因子在相同的组织结构中被检测到，但在不同的亚细胞定位。NBC抗血清未标记腺泡或胰岛细胞。我们的观察结果表明，人类胰腺导管细胞分泌HCO(-)(3)涉及通过NBC（一种电中性钠-碳酸氢根共转运体）从基底外侧摄取Na(+)和HCO(-)(3)。
