Parkkila Seppo, Kivelä Antti J, Kaunisto Kari, Parkkila Anna-Kaisa, Hakkola Jukka, Rajaniemi Hannu, Waheed Abdul, Sly William S
Department of Clinical Chemistry, 90014 University of Oulu, Finland.
BMC Gastroenterol. 2002 May 21;2:13. doi: 10.1186/1471-230x-2-13.
Biochemical and histochemical studies have both previously indicated plasma membrane-associated carbonic anhydrase (CA) activity in hepatocytes which has been assumed to be CA IV. However, immunohistochemical data did not support this assignment. Recent northern blotting results indicated the presence of mRNA for the most recently discovered membrane-bound CA isozyme, CA XIV, in the liver. The present study was designed to examine whether CA XIV could contribute to the CA activity described in the hepatocytes.
Tissue samples from mouse liver were subjected to immunohistochemical staining using the antibodies raised against recombinant mouse CA XIV and CA IV. RT-PCR and western blotting were also performed for CA XIV.
A strong immunofluorescent signal was observed in the plasma membrane of mouse hepatocytes. Although CA XIV was expressed on both the apical and basolateral surfaces, the staining was more prominent at the apical (canalicular) membrane domain. The expression of CA XIV in the liver was confirmed by RT-PCR and western blotting.
The presence of CA XIV in the hepatocyte plasma membrane places this novel enzyme at a strategic site to control pH regulation and ion transport between the hepatocytes, sinusoids and bile canaliculi.
生化和组织化学研究先前均表明肝细胞中存在与质膜相关的碳酸酐酶（CA）活性，该活性一直被认为是CA IV。然而，免疫组化数据并不支持这一归属。最近的Northern印迹结果表明，肝脏中存在最新发现的膜结合CA同工酶CA XIV的mRNA。本研究旨在检验CA XIV是否对肝细胞中描述的CA活性有贡献。
使用针对重组小鼠CA XIV和CA IV产生的抗体，对小鼠肝脏组织样本进行免疫组化染色。还对CA XIV进行了逆转录聚合酶链反应（RT-PCR）和蛋白质印迹分析。
在小鼠肝细胞的质膜中观察到强烈的免疫荧光信号。尽管CA XIV在顶端和基底外侧表面均有表达，但在顶端（胆小管）膜区域的染色更为明显。通过RT-PCR和蛋白质印迹分析证实了肝脏中CA XIV的表达。
CA XIV存在于肝细胞质膜中，这使得这种新型酶处于控制肝细胞、血窦和胆小管之间pH调节和离子转运的关键位置。
