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First published online May 15, 2009
Journal of Experimental Biology 212, 1647-1661 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.029181
Review Article |
Carbonic anhydrase and acid–base regulation in fish
Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, ON, Canada
* Author for correspondence (e-mail: kgilmour{at}uottawa.ca)
Accepted 23 March 2009
Carbonic anhydrase (CA) is the zinc metalloenzyme that catalyses the reversible reactions of CO2 with water. CA plays a crucial role in systemic acid–base regulation in fish by providing acid–base equivalents for exchange with the environment. Unlike air-breathing vertebrates, which frequently utilize alterations of breathing (respiratory compensation) to regulate acid–base status, acid–base balance in fish relies almost entirely upon the direct exchange of acid–base equivalents with the environment (metabolic compensation). The gill is the critical site of metabolic compensation, with the kidney playing a supporting role. At the gill, cytosolic CA catalyses the hydration of CO2 to H+ and HCO3– for export to the water. In the kidney, cytosolic and membrane-bound CA isoforms have been implicated in HCO3– reabsorption and urine acidification. In this review, the CA isoforms that have been identified to date in fish will be discussed together with their tissue localizations and roles in systemic acid–base regulation.
Key words: carbonic anhydrase, acid–base regulation, fish, gill, kidney, gut, V-type H+-ATPase, Na+/H+ exchanger, Cl–/HCO3– exchanger, Na+/HCO3– cotransporter, CA isoforms
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