WEIHRAUCH, Dirk; MCNAMARA, John/C; TOWLE, David/W; ONKEN, Horst; Univ. of Osnabrueck, Germany; Univ. de S�o Paulo, S�o Paulo, Brasil; MDIBL, Salsbury Cove, USA, ; Washington State Univ., Pullman, USA : The gills of the red freshwater crab Dilocarcinus pagei: microanatomy, ion-motive ATPases and NaCl absorption

The present investigation examines the gills of a true freshwater crab, D. pagei. The anterior gills of this hololimnetic trichodactylid exhibit a thin epithelium on both sides of their lamellae, while those of the posterior gills show marked intralamellar asymmetry. The proximal face consists of a thick epithelium with features typical of a transporting tissue. The distal epithelium, however, is thin and formed almost entirely by pillar cell flanges. Both anterior and posterior gills express Na+/K+- and V-ATPases. However, semi-quantitative RT-PCR reveals that the mRNAs for both ion pump subunits are clearly more intensely expressed in the posterior gills. Na+/K+-ATPase activity in the posterior gills is nearly four-fold that of the anterior gills, while V-ATPase activity tends to be greater (not significant) in the posterior gills. On mounting split posterior gill lamellae in Ussing-type chambers, the distal half-lamellae produced negative, Cl–dependent, short-circuit currents, inhibited by concanamycin. In contrast, the proximal half-lamellae generated positive, Na+-dependent currents, inhibited by ouabain. These data reveal that the red freshwater crab, like diadromous species, exhibits marked microanatomical and functional differences between the anterior and posterior gills. However, the anatomical and functional asymmetries seen in the posterior gill lamellae, indicative of V-ATPase-driven Cl- absorption across the distal epithelium, and Na+/K+-ATPase-driven Na+ absorption across the proximal epithelium, constitute a novel arrangement, which may reflect a specific adaptation of the trichodactylid, freshwater crabs.