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12 species of osmoconforming and osmoregulating Crustacea. During evolution, hyperos- moregulating Crustacea have achieved internal osmolyte gradients generated by Na,K-ATPase and
lowering the gill surface permeability. However these adaptive characteristics are not present in marine osmoconforming Crustacea, restraining them to migrate in the brackish water habitats.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Isosmotic haemolymph; Na; K-ATPase activity; Trichobranchiate gills; Epipodite; Voltage clamp
1. Introduction
In spite of the fact that representatives of the superfamily Palinuroidea Latreille 1802 has great economic value on the market, there is a dearth of publications on their
physiology and biochemistry Dall, 1974. No substantial progress, except in the field of the nervous system and its physiology Schmidt and Ache, 1994, has been attained up
to this point. The Western rock lobster Panulirus longipes is an isosmotic crustacean tolerating seawater salinity in the range 25–40 ppt Dall, 1974. The osmotic adjustment
of principal monovalent ions is made by the gills and Ca and Mg regulation by the gut Dall, 1974; 1977.
Marine osmoconforming Crustacea have haemolymph in osmotic equilibrium with seawater and all show very limited ionic regulation. Differences between plasma and
seawater in these species are mostly due to the indiffusibility of haemolymph proteins and formation of complexes between proteins and inorganic osmolytes. In isolated
perfused gills of the osmoconforming decapod Maja squinado, transepithelial potential was close to 0 mV and no net sodium fluxes were found over the concentration range
20–100 seawater King and Schoffeniels, 1969. In these osmoconforming species which allow their blood osmolarity to parallel their environment over a narrow salinity
range, intracellular volume regulation occurs controlling organic osmolyte content in the cells Gilles, 1987.
In the hyperosmoregulating Crustacea, gill Na,K-ATPase activity increases pro- portionally with the increase in the number of chloride cells Neufeld et al., 1980 and as
a key enzyme for Na K exchange indirectly regulates activities of the Na H exchanger Shetlar and Towle, 1989; Towle et al., 1997 and Na K 2Cl cotransporter Riestenpatt
et al., 1996 on the apical membrane side, and the Na Ca exchanger on the basolateral membrane side Flik et al., 1994. In the marine osmoconforming Crustacea Calappa
hepatica Spencer et al., 1979, Cancer and Nephrops Harris and Bayliss, 1988, haemolymph is isosmotic with surrounding seawater and Na,K-ATPase specific ac-
tivities were reported to be at the detection limits. Accordingly, specific activity of the gill Na,K-ATPase in marine Crustacea is lower than in the brackish water and freshwater
Crustacea and sodium gradients between haemolymph and medium are in positive correlation with Na,K-ATPase activity Harris and Bayliss, 1988.
In the spiny lobster Palinurus elephas the role of the Na,K-ATPase in gills and epipodites and short-circuit current and conductance in epipodites were studied in
relation to this species’ limited osmoregulatory ability in dilute seawater. In addition,
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. Lucu et al. J. Exp. Mar. Biol. Ecol. 246 2000 163 –178 165
Na,K-ATPase specific activity of the marine osmoconformers Maja crispata and Dromia personata were examined to find out any adaptive distinction between the Na,K-ATPase
activities of stenohaline-osmoconforming and euryhaline-hyperosmoregulating Crus- tacea.
2. Materials and methods
