Review Article
Ammonia excretion in aquatic and terrestrial crabs
Dirk Weihrauch1,*, Steve Morris2 and David W. Towle3
1 Department of Biology, Division of Animal Physiology, University of Osnabrück, D-49076 Osnabrück, Germany
2 Morlab, School of Biological Sciences, University of Bristol, BS8 1UG, UK
3 Mount Desert Island Biological Laboratory, Salsbury Cove, ME 04672, USA
* Author for correspondence at present address: Department of Biology, Division of Animal Physiology, Universität Osnabrück, D-49076 Osnabrück, Germany (e-mail: Weihrauchblues@gmx.net
)
Summary
The excretory transport of toxic ammonia across epithelia is not fully understood. This review presents data combined with models of ammonia excretion derived from studies on decapod crabs, with a view to providing new impetus to investigation of this essential issue. The majority of crabs preserve ammonotely regardless of their habitat, which varies from extreme hypersaline to freshwater aquatic environments, and ranges from transient air exposure to obligate air breathing. Important components in the excretory process are the Na+/K+(NH4+)-ATPase and other membrane-bound transport proteins identified in many species, an exocytotic ammonia excretion mechanism thought to function in gills of aquatic crabs such as Carcinus maenas, and gaseous ammonia release found in terrestrial crabs, such as Geograpsus grayi and Ocypode quadrata. In addition, this review presents evidence for a crustacean Rhesus-like protein that shows high homology to the human Rhesus-like ammonia transporter both in its amino acid sequence and in its predicted secondary structure.
Key words: ammonia excretion, ammonia transporter, crab, exocytosis, Rhesus-like protein, Na+/K+-ATPase
Journal of Experimental Biology 207, 4491-4504 (2004). Published by The Company of Biologists 2004.
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