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The plasma membrane carbonic anhydrase in murine hepatocytes identified as isozyme XIV
Seppo Parkkila1, Antti J Kivelä, Kari Kaunisto
1Department of Clinical Chemistry, 90014 University of Oulu, Finland. seppo.parkkila@uta.fi
Background:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
Insights
Carbonic anhydrase XIV (CA XIV) is present in mouse liver cell membranes, not CA IV as previously assumed. This finding positions CA XIV to regulate pH and ion transport in hepatocytes.
Area of Science:
- Hepatocyte biology
- Enzymology
- Membrane protein research
Background:
- Previous studies suggested plasma membrane carbonic anhydrase (CA) activity in hepatocytes was CA IV.
- Immunohistochemical data contradicted the CA IV assignment.
- Recent findings indicated liver expression of CA XIV mRNA.
Purpose of the Study:
- To investigate if CA XIV contributes to hepatocyte plasma membrane CA activity.
- To determine the localization of CA XIV in hepatocytes.
Main Methods:
- Immunohistochemical staining of mouse liver tissue using antibodies against CA XIV and CA IV.
- Reverse transcription-polymerase chain reaction (RT-PCR) for CA XIV.
- Western blotting for CA XIV.
Main Results:
- Strong immunofluorescent signal for CA XIV detected on the plasma membrane of mouse hepatocytes.
- CA XIV expression observed on both apical and basolateral surfaces, predominantly apical (canalicular).
- RT-PCR and western blotting confirmed CA XIV expression in the liver.
Conclusions:
- Carbonic anhydrase XIV is localized to the hepatocyte plasma membrane.
- CA XIV is strategically positioned to influence pH regulation and ion transport.
- This study clarifies the identity of membrane-bound CA in hepatocytes.