Journal of Experimental Marine Biology and Ecology 256 2001 215–227
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Gill Na ,K -ATPase and osmoregulation in the estuarine crab, Chasmagnathus granulata Dana, 1851 Decapoda,
Grapsidae
Pedro Carvalho Castilho, Isabel Amaral Martins, Adalto Bianchini
˜ ´
ˆ ´
Laboratorio de Zoofisiologia , Departamento de Ciencias Fisiologicas, Fundac¸ao Universidade Federal do
Rio Grande , Caixa Postal 474, CEP 96.201-900 Rio Grande, RS, Brazil
Received 5 June 2000; received in revised form 7 September 2000; accepted 26 October 2000
Abstract
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Some kinetic properties of gill Na ,K -ATPase of the estuarine crab, Chasmagnathus granulata, and its involvement in osmotic adaptation were analyzed. Results suggest the presence
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of different Na ,K -ATPase isoforms in anterior and posterior gills. They have different affinities
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for Na , but similar affinity values for K , Mg , ATP and similar enzymatic profiles as a
function of temperature of the incubation medium. Ouabain concentrations which inhibit 50 of
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enzyme activity were also similar in the two types of gills. Enzyme activity and affinity for Na
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are higher in posterior gills than in anterior ones. Furthermore, affinities of Na ,K -ATPase of
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posterior gills for Na and K
were similar to or higher than those of gills or other structures involved in the osmoregulation in several euryaline decapod crustaceans. Acclimation to low
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salinity was related to a significant increase in the maximum Na , K -ATPase activity, mainly in posterior gills. On the other hand, crab acclimation to high salinity induced a significant decrease
in maximum enzyme activity, both in anterior and posterior gills. These results are in accordance to the osmoregulatory performance showed by C
. granulata in diluted media, and point out the major role of posterior gills in the osmoregulation of this species.
2001 Elsevier Science B.V.
All rights reserved.
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Keywords : Chasmagnathus granulata; Crustacea; Gill; Hypoosmotic regulation; Na ,K -ATPase
1. Introduction
The estuarine crab, Chasmagnathus granulata, inhabits salt marshes distributed along
Corresponding author. Tel.: 1 55-53-233-8655; fax: 1 55-53-233-8680. E-mail address
: dcfadaltsuper.furg.br A. Bianchini. 0022-0981 01 – see front matter
2001 Elsevier Science B.V. All rights reserved.
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.C. Castilho et al. J. Exp. Mar. Biol. Ecol. 256 2001 215 –227
the coast of Southern Brazil, Uruguay and Argentina Boschi, 1964. In this habitat, it is usually exposed to a broad range of environmental salinities Castello, 1985. Therefore,
ability to cope with salinity changes is essential for the establishment of a population in this habitat. Nery and Santos 1993, studying the ability of C
. granulata to regulate carbohydrate metabolism during osmotic stress, reported that this crab tolerates long-
term exposure to freshwater and hypersaline medium 40‰. In spite of a seasonal difference in osmoregulatory ability, C
. granulata is a good hyper- and hypo-
smoregulator, with an isosmotic point in external media of 30‰ salinity Bromberg, 1992; Miranda, 1994. Also, it was demonstrated that hemolymph osmolality tends to be
maintained at the same level after the hyposmotic stress, both in winter and summer Bromberg et al., 1995.
Sodium and chloride are the major osmotic effectors in the hemolymph of C
.granulata and their concentrations are maintained out of electrochemical equilibrium, both in concentrated and diluted media Bromberg et al., 1995, as do many other
´ osmoregulating crabs Mantel and Farmer, 1983; Pequeux, 1995. In C
.granulata, gills
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are presumed to be the sites of active transport of Na and Cl , in both concentrated
and diluted media. However, the mechanisms of hyper- and hypoosmotic regulation are not well understood.
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The presence of Na ,K -ATPase activity in the gills of estuarine and freshwater decapod crustaceans has been widely reported. Many studies have pointed out a central
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role of this enzyme in active Na uptake. Studies of the biochemical basis of ion uptake
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have shown that Na ,K -ATPase is present at high specific activities in gills and antennal gland of hyperosmotically regulating species. A larger enzyme activity in
salt-transporting gills posterior pairs than in respiratory ones anterior pairs, as well as changes of this activity as a function of the acclimation salinity, have also been reported
´ Pequeux, 1995.
The present study was undertaken to determine the major kinetic characteristics of the
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Na ,K -ATPase present in anterior and posterior gills of C . granulata, and to verify a
possible correlation between enzyme activity and hemolymph osmolality, during acclimation to diluted sea water or sea water.
2. Materials and methods
