Evidence for a membrane carbonic anhydrase?IV anchored by its C-terminal peptide in normal human pancreatic ductal cells

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• 作者：Marjorie Fanjul ; Laetitia Alvarez ; Christel Salvador ; Valéry Gmyr ; Julie Kerr-Conte ; Fran?ois Pattou ; Nicholas Carter and Etienne Hollande
• 关键词：Human pancreas ; Ductal cells ; Carbonic anhydrase IV ; HCO3 – secretion
• 刊名：Histochemistry and Cell Biology
• 出版年：2004
• 出版时间：February 2004
• 年：2004
• 卷：121
• 期：2
• 页码：91-99
• 全文大小：464 KB
• 刊物类别：Medicine
• 刊物主题：Medicine & Public Health
  Anatomy
  Medicine/Public Health, general
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-119X

文摘

The high concentration of HCO₃ – ions (150 mM) in the human pancreatic ducts raises the question of the membrane proteins responsible for their secretion in addition to the Cl–/HCO₃ – exchanger. In this study, we investigated the expression of carbonic anhydrase IV (CA IV), a possible candidate. Experiments were carried out on specimens of normal human pancreas obtained from brain-dead donors (n=9) as well as on isolated human ductal cells. Two antibodies were generated: CA IV NH₂ antibody directed against the NH₂ terminal of human glycosyl phosphatidylinositol (GPI)-anchored CA IV and CA IV COOH antibody directed against the COOH terminal of the same protein before its association with a GPI in the rough endoplasmic reticulum. A 35-kDa CA IV was detected in the homogenates of human pancreas. Immunocytochemistry demonstrated the expression of CA IV in centroacinar cells and in intercalated, intralobular, and interlobular ductal cells. The immunoreactivity observed with the CA IV COOH antibody was mainly localized on luminal membranes of ductal cells. Treatment of purified plasma membranes with phosphatidylinositol-phospholipase C indicated that the CA IV expressed in pancreatic ducts was not GPI-anchored. Its detection in the same extracts by the CA IV COOH antibody indicated that it was anchored by a hydrophobic segment at the carboxy terminal. Taken together, these results suggest that normal human pancreatic ductal cells express a 35-kDa CA IV anchored in their luminal plasma membrane by a hydrophobic segment of the COOH terminus. In view of its localization and its mode of anchorage in luminal plasma membranes, this CA IV may participate in the maintenance of luminal pH.