Parkkila S, Parkkila A K, Juvonen T, Waheed A, Sly W S, Saarnio J, Kaunisto K, Kellokumpu S, Rajaniemi H
Department of Anatomy, University of Oulu, Finland.
Hepatology. 1996 Nov;24(5):1104-8. doi: 10.1002/hep.510240521.
Alkaline hepatic bile is acidified in the gallbladder to prevent calcium precipitation and gallstone formation. Because membrane-bound carbonic anhydrase (CA) isoenzyme IV participates with cytoplasmic CA II in the acidification of urine in the kidney, we studied its expression in different regions of the human biliary tract using immunohistochemical techniques. The enzyme was expressed in the apical plasma membrane of the gallbladder epithelial cells and in the endothelium of the subepithelial capillaries. In the liver, some epithelial cells of the large bile ducts showed positive staining. Its presence in the gallbladder epithelium could be confirmed by Western blotting, which showed a single 35-kd polypeptide band, corresponding in molecular weight to the intact enzyme. The majority of the enzyme was phased to Triton X-114 detergent phase. A small amount of 35-kd polypeptide was also seen in the water phase. Smaller proteolytic fragments of the enzyme were not seen, suggesting that the tissue sample was well preserved. The results show that CA IV is expressed in abundance in the human gallbladder epithelium, where it may participate together with cytoplasmic CA II and ion transporters in acidification of the gallbladder bile via bicarbonate reabsorption.
碱性肝胆汁在胆囊中被酸化以防止钙沉淀和胆结石形成。由于膜结合碳酸酐酶（CA）同工酶IV与细胞质CA II共同参与肾脏尿液的酸化过程，我们使用免疫组织化学技术研究了其在人胆道不同区域的表达。该酶在胆囊上皮细胞的顶端质膜和上皮下毛细血管的内皮中表达。在肝脏中，大胆管的一些上皮细胞显示出阳性染色。通过蛋白质印迹法可证实其在胆囊上皮中的存在，该方法显示出一条单一的35-kd多肽带，其分子量与完整酶相对应。大部分酶进入了Triton X-114去污剂相。在水相中也可见少量35-kd多肽。未见到该酶较小的蛋白水解片段，表明组织样本保存良好。结果表明，CA IV在人胆囊上皮中大量表达，在那里它可能与细胞质CA II和离子转运体一起通过重吸收碳酸氢盐参与胆囊胆汁的酸化过程。
