Acid-base effects on electrolyte transport in CA II-deficient mouse colon
D S Goldfarb1, W S Sly, A Waheed
1Nephrology Section, Veterans Affairs Medical Center and New York University School of Medicine, New York, New York 10010, USA.
Summary
Carbonic anhydrase I (CA I) is essential for colonic electrolyte absorption and pH sensitivity in mice. Deficiency in carbonic anhydrase II (CA II) did not affect these processes.
Area of Science:
- Physiology
- Biochemistry
- Molecular Biology
Background:
- Carbonic anhydrase (CA) enzymes are crucial for regulating pH and ion transport.
- The specific roles of different CA isoforms in colonic electrolyte transport remain incompletely understood.
Purpose of the Study:
- To investigate the role of carbonic anhydrase (CA) in colonic electrolyte transport using a mouse model deficient in cytosolic CA II.
- To elucidate the contribution of CA isoforms to basal and pH-stimulated ion absorption in the colon.
Main Methods:
- Utilized Car-2(0) mice, lacking cytosolic CA II, to assess colonic function.
- Measured ion fluxes under short-circuit conditions in an Ussing chamber.
- Analyzed CA activity via enzyme assays and Western blots.
Main Results:
- Car-2(0) mice showed an 80% reduction in total CA activity, with no compensatory increase in CA I or CA IV.
- Normal mouse distal colon demonstrated pH-sensitive Na(+) and Cl(-) absorption, which was inhibited by a membrane-permeant CA inhibitor.
- Car-2(0) mice exhibited similar basal transport and pH responses, indicating CA II is not essential for these functions.
Conclusions:
- Basal and pH-stimulated colonic electrolyte absorption in mice critically requires carbonic anhydrase I (CA I).
- Carbonic anhydrase II (CA II) and carbonic anhydrase IV (CA IV) may play accessory roles in colonic function.
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