Transport‐related ATPases as probes of tissue function in three terrestrial crabs of Palau

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Abstract
Distribution and properties of Na+ + K+‐dependent ATPase and Cl−/HCO‐activated ATPase were used as probes of tissue function in relation to salt and water regulation in three terrestrial crabs, Cardisoma carnifex, Gecarcoidea lalandii, and Birgus latro. Of the three predominant tissues in the branchial chamber, gill consistently exhibited highest specific activity of both enzymes, indicating that terrestrial crabs may use ion regulation by the gills as an important mechanism of salt and water balance. Branchial epithelium lining the cavity does not appear to be important in regulation of monovalent ions, although it is highly specialized in B. latro as a respiratory organ. Pericardial sac also lacks the biochemical machinery for active salt and water uptake. Antennal gland of all three species showed high activity of Na+ + K+‐ATPase, perhaps facilitating water retention by that organ. Na+ + K+‐ATPase activity of intestine showed wide species‐related variation, and was enhanced in B. latro exposed to freshwater. The gill of B. latro maintained constant high activity of the Na+ + K+‐ATPase, irrespective of environmental conditions.