Structural and biochemical correlates of Na+,K+-ATPase driven ion uptake across the posterior gill epithelium of the true freshwater crab, Dilocarcinus pagei (Brachyura, Trichodactylidae)

• Published in: Journal of experimental zoology. Part A, Ecological genetics and physiology Vol. 313A; no. 8; pp. 508 - 523
• Main Authors: Furriel, Rosa Prazeres Melo, Firmino, Kelly Cristina Silva, Masui, Douglas Chodi, Faleiros, Rogério Oliveira, Torres, Antonio Hernandes, McNamara, John Campbell
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-10-2010
• Subjects: Adaptations; Animals; Blotting, Western; Brachyura; Brachyura - enzymology; Brachyura - metabolism; Brachyura - ultrastructure; Cell size; Cytoplasm; Decapoda; Dilocarcinus pagei; Ecological genetics; Enzyme Inhibitors - pharmacology; Enzymes; Epithelium; Epithelium - enzymology; Epithelium - metabolism; Epithelium - ultrastructure; Fresh Water; Freshwater; Freshwater environments; Gills - enzymology; Gills - metabolism; Gills - ultrastructure; Hemolymph; Houses; Invaginations; Ion Transport; Isoenzymes; Kinetics; Lamellae; Marine; Microscopy, Electron, Transmission; Mitochondria; Mitochondria - enzymology; Mitochondria - metabolism; Mitochondria - ultrastructure; Mushroom gills; Na super(+)/K super(+)-exchanging ATPase; Ouabain; Ouabain - pharmacology; Potassium; Salinity effects; Sodium-Potassium-Exchanging ATPase - antagonists & inhibitors; Sodium-Potassium-Exchanging ATPase - metabolism; Trichodactylidae; Western blotting
• ISSN: 1932-5223; 1932-5231; 1932-5231
• DOI: 10.1002/jez.622

To better comprehend the structural and biochemical underpinnings of ion uptake across the gills of true freshwater crabs, we performed an ultrastructural, ultracytochemical and morphometric investigation, and kinetically characterized the Na+,K+‐ATPase, in posterior gill lamellae of Dilocarcinus pagei. Ultrastructurally, the lamellar epithelia are markedly asymmetrical: the thick, mushroom‐shaped, proximal ionocytes contain elongate mitochondria (41% cell volume) associated with numerous (≈14 µm2 membrane per µm3 cytoplasm), deep invaginations that house the Na+,K+‐ATPase, revealed ultracytochemically. Their apical surface is amplified (7.5 µm2 µm−2) by stubby evaginations whose bases adjoin mitochondria below the subcuticular space. The apical membrane of the thin, distal ionocytes shows few evaginations (1.6 µm2 µm−2), each surrounding a mitochondrion, abundant in the cytoplasm below the subcuticular space; basolateral invaginations and mitochondria are few. Fine basal cytoplasmic bridges project across the hemolymph space, penetrating into the thick ionocytes, suggesting ion movement between the epithelia. Microsomal Na+,K+‐ATPase specific activity resembles marine crabs but is ≈5‐fold less than in species from fluctuating salinities, and freshwater shrimps, suggesting ion loss compensation by strategies other than Na+ uptake. Enzyme apparent K+ affinity attains 14‐fold that of marine crabs, emphasizing the relevance of elevated K+ affinity to the conquest of fresh water. Western blotting and biphasic ouabain inhibition disclose two α‐subunit isoforms comprising distinct functional isoenzymes. While enzyme activity is not synergistically stimulated by NH 4+ and K+, each increases affinity for the other, possibly assuring appropriate intracellular K+ concentrations. These findings reveal specific structural and biochemical adaptations that may have allowed the establishment of the Brachyura in fresh water. J. Exp. Zool. 313A:508–523, 2010. © 2010 Wiley‐Liss, Inc.