Na+/K+-ATPase activity and gill ultrastructure in the hyper-hyporegulating crab Chasmagnathus granulatus acclimated to dilute, normal, and concentrated seawater.

GENOVESE, G.; LUCHETTI, C. G.; LUQUET, C. M.

Marine Biology

Springer

Lugar: Berlin; Año: 2004 vol. 144 p. 111 - 118

0025-3162

We studied Na+/K+?ATPase activity andultrastructure in gills of the hyper-hypo-regulating crabChasmagnathus granulatus Dana, 1851 acclimated todifferent salinities: 10, 30 and 45&, known to be hypo-,iso-, and hyper-osmotic to the hemolymph, respectively.After centrifugation of homogenates at 11,000 g, Na+/K+?ATPase activity was almost entirely found in thepellets from the posterior (6?8) and anterior (3?5) gills,whereas very little was detected in the supernatant liquid.Specific activity of gill 6 was 41.3, 30.2, and28.2 lmol Pi h?1 mg prot?1 for crabs acclimated to 10,30, and 45&, respectively, the result for 10& beingsignificantly higher than those at 30 and 45&. Althoughthe concentration of sodium at which the reaction rate ishalf-maximal (KM) was similar in the three acclimationsalinities, only the enzyme from crabs acclimated to 10&was inhibited by high sodium concentration. Specificactivity of gill 5 increased with the increment in externalsalinity (10.1, 15, and 18.1 lmol Pi h?1 mg prot?1 for 10,30, and 45&, respectively), the only significant differencebeing that between the extreme salinities. The epitheliumthickness of the dorsal portion of gill 6 showed a variationamong salinities: 21.7, 15.8 and 17.2 lm for 10, 30and 45&, respectively. There were significant differencesin epithelium thickness between the 10& and the othersalinities. In all three salinities, the ultrastructure of gill 6epithelium showed a high density of mitochondria,estimated by their volume fraction (Vvm=0.307?0.355).These mitochondria were packed between extensive basolateralmembrane interdigitations in ionocytes andpillar cells. Gill 5 showed three cell types: pillars whichpossess mitochondria packed between membrane foldsonly in their interdigitations with neighbouring cells;type-I cells 8.0 lm thick with low density of mitochondria(Vvm=0.088), and type-II cells, 9.9 lm thick andrich in mitochondria (Vvm=0.423), but lacking basolateralinterdigitations. Vvm of type-I cells of gill 5 wassignificantly lower than those of type-II cells of the samegill and the ionocytes of gill 6. No significant differencein Vvm was detected between the latter cell types.