| Autor(es): |
Melo Furriel, Rosa Prazeres
[1]
;
Silva Firmino, Kelly Cristina
[1]
;
Masui, Douglas Chodi
[1]
;
Faleiros, Rogerio Oliveira
[2]
;
Torres, Antonio Hernandes
[2]
;
McNamara, John Campbell
[2]
Número total de Autores: 6
|
| Afiliação do(s) autor(es): | [1] Univ Sao Paulo, Dept Quim, Fac Filosofia Ciencias & Letras Ribeirao Preto, BR-14040901 Sao Paulo - Brazil
[2] Univ Sao Paulo, Dept Biol, Fac Filosofia Ciencias & Letras Ribeirao Preto, BR-14040901 Sao Paulo - Brazil
Número total de Afiliações: 2
|
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 (approximate to 14 mu m(2) membrane per mu m(3) cytoplasm), deep invaginations that house the Na(+), K(+)-ATPase, revealed ultracytochemically. Their apical surface is amplified (7.5 mu m(2) mu m(-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 mu m(2) mu m(-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 approximate to 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 alpha-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. (C) 2010 Wiley-Liss, Inc. (AU) |