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First published online December 3, 2004
Journal of Experimental Biology 207, 4623-4631 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01333

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Ion-motive ATPases and active, transbranchial NaCl uptake in the red freshwater crab, Dilocarcinus pagei (Decapoda, Trichodactylidae)

Dirk Weihrauch^1,*, John Campbell McNamara², David W. Towle³ and Horst Onken⁴

¹ Department of Animal Physiology, University of Osnabrueck, 49076 Osnabrueck, Germany
² Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto 14040-901, São Paulo, Brasil
³ Mount Desert Island Biological Laboratory, Salsbury Cove, ME 04672, USA
⁴ School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA

^* Author for correspondence (e-mail: weihrauch{at}biologie.uni-osnabrueck.de)

Accepted 5 October 2004

The present investigation examined the microanatomy and mRNA expression and activity of ion-motive ATPases, in anterior and posterior gills of a South American, true freshwater crab, Dilocarcinus pagei. Like diadromous crabs, the anterior gills of this hololimnetic trichodactylid exhibit a highly attenuated (2–5 µm), symmetrical epithelium on both lamellar surfaces. In sharp contrast, the posterior gill lamellar epithelia are markedly asymmetrical. Their proximal side consists of thick (18–20 µm) cells, displaying features typical of a transporting epithelium, while the distal epithelium is thin (3–10 µm) and formed entirely by apical pillar cell flanges. Both anterior and posterior gills express Na⁺/K⁺- and V-ATPases. Phylogenetic analysis of partial cDNA sequences for the Na⁺/K⁺-ATPase -subunit and V-ATPase B-subunit among various crab species confirmed the previous classification and grouping of D. pagei based on morphological criteria. Semi-quantitative RT-PCR clearly showed that mRNA for both ion pump subunits is more intensely expressed in posterior gills. Na⁺/K⁺-ATPase activity in the posterior gills was nearly fourfold that of anterior gills, while V-ATPase and F-ATPase activities did not differ. A negative short-circuit current (I_sc) was measured using the distal side of split, posterior gill lamellae, mounted in a modified Ussing chamber and perfused symmetrically with identical hemolymph-like salines. Although hemolymph-side ouabain did not affect this current, concanamycin significantly reduced I_sc without altering preparation conductance, suggesting V-ATPase-driven Cl^– absorption on the distal side of the posterior gill lamellae, as known to occur in diadromous crabs adapted to freshwater. These findings suggest that active Na⁺ uptake predominates across the thick proximal epithelium, and Cl^– uptake across the thin, distal epithelium of the posterior gill lamellae.

Key words: osmoregulation, crab, Dilocarcinus pagei, gill epithelia, phylogenetic analysis, NaCl uptake, Na⁺/K⁺-ATPase, V-type H⁺-ATPase, transepithelial voltage, short-circuit current, ouabain, concanamycin

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