A. Pequeux

A morphological study on gills of a crab acclimated to fresh water.

The gills of the fully euryhaline Chinese crab Eriocheir sinensis were studied by light and electron microscopy. In these Phyllobranchiates, the gills consist of a double row of lamellae extending laterally from a central shaft. Haemolymph flow pattern inside the gill is described and the existence of a complex secondary vascularization inside the platelets is reported. It is shown that important differences exist between the ultrastructure of the three anterior and the three posterior pairs of large gills. The epithelium of the posterior gills is much thicker and possesses an extensive elaboration of the plasma membranes in the form of infoldings, crypts and interdigitations, along which are packed numerous mitochondria. The presence of such a complex membrane system opening to the extracellular space and closely associated with mitochondria is common to all salt-transporting tissues. This study corroborates the idea that the posterior pairs of gills of Eriocheir sinensis are the only ones implicated in active Na+ uptake when the crab lives in dilute aquatic environment. The epithelium of anterior gills is much thinner and the cells poor in intracellular organelles. It seems to be involved essentially in respiration. Thus this work clearly corroborates the existence already suggested by physiological approach of a functional difference between the different pairs of E. sinensis branchiae with respect to their participation in the respiration and in the regulation of the blood ions content. Common to both types of gills is the presence of a lamellar septum separating the haemolymph space into two compartments. The part played by that structure in determining the pattern of haemolymph flow, together with periodic bridges forming pillars across the haemolymph space, is emphasized.

The transepithelial potential difference of isolated perfused gills of the Chinese crab Eriocheir sinensis acclimated to fresh water

Abstract 1. 1. The so-called anterior and posterior gills of the euryhaline Chinese crab Eriocheir sinensis acclimated to fresh water show polarities of opposite signs when bathed with the same saline on both sides. 2. 2. The transepithelial potential difference (PD) in the anterior gills can be accounted for by several diffusive components for Na+, K+ and Cl−. At the serosal side of the epithelium, one has to consider diffusion potentials for K+ and Cl− short-circuited by a Na+-diffusion potential. The PD at the apical side is essentially generated by Na+ diffusion. 3. 3. Besides these cellular components, a transepithelial diffusion of Na+, likely to occur through paracellular pathways, also has to be taken into consideration when Na+ gradients are applied to the epithelium. 4. 4. The PD in the posterior gills can be satisfactorily explained considering diffusive movements of Cl− at the apical side and diffusive movements of K+ short-circuited by Cl− outward movements at the serosal side. 5. 5. The posterior gills are the site of independent active transports of Na+ and Cl−. Our results indicate that these processes implicate at least (1) amiloride sensitive Na+/H+ and SITS sensitive Cl~/HCOf antiporters at the apical side; and (2) the ouabain sensitive Na+/K+ exchange system at the serosal side.

Physiological aspects of NaCl movements in the gills of the euryhaline crab, Eriocheir sinensis, acclimated to fresh water

Abstract 1. 1. Transepithelial inward active transport of Na+ and Cl− are found in the posterior gills but not in the anterior ones. 2. 2. The posterior gills further show transepithelial passive movements of Cl− but not of Na+ while the anterior ones show transepithelial passive movements of Na+ and not of Cl−. 3. 3. In the anterior gills, the PD can be accounted for by diffusive Na+ fluxes at the aplcal side and Na+/K+ pump and leak system at the serosal one. 4. 4. In the posterior gills, the PD can be related to diffusive fluxes of Cl− at the aplcal side and diffusive outward movements of K+ and Cl− at the serosal one. 5. 5. In these gills, the transepithelial inward active movement of Na+ would be essentially related to the operations of aplcal Na+/H+ and serosal Na+/K+ pumps. Cl− would be moved IN at the aplcal side by a Cl−/HCO3− antiporter and driven OUT at the serosal one through Cl− channels following the K − diffusion potential generated by the Na+/K+ pump and leak system.

Na+ regulation and (Na++ K+)ATPase activity in the euryhaline fiddler crab Uca minax (Le conte)

Abstract 1. 1. Specific activity and kinetic characteristics of the (Na+ + K+)ATPase have been investigated in the gill epithelium of the hyper-hypoosmoregulator crab Uca minax. 2. 2. (Na+ +K+)ATPase activity is shown to be at least three times higher in the posterior gills. 3. 3. The kinetic study supports the hypothesis of the existence of two different (Na+ + K+)ATPases: the enzyme activity in the posterior gills could be involved in the transepithelial transport of Na+ while the activity of the anterior gills could be responsible for the intracellular regulation of Na+ and K+. 4. 4. Significant and specific changes in (Na+ +K+)ATPase activity occur upon acclimation to media of various salinities.

Effects of an hypo-osmotic shock on Na+, K+ and Cl− levels in isolated axons ofCarcinus maenas

SummaryApplication of an hypo-osmotic shock to isolated axons ofCarcinus maenas induces a decrease in the intracellular content of K+, Na+ and Cl−. The changes in Na+ and Cl− levels are only transitory while the K+ level reaches new steady-state value much lower than the control. The modification of K+ concentration cannot be ascribed only to a simple dilution process and it is proposed that the regulation of intracellular K+ plays an important role in limiting the swelling which occurs in this tissue.Hypo-osmotic conditions also induce an increase in Na+ permeability.The results are discussed in relation to changes in ion transport and interactions with intracellular organic compounds that could arise during the process of volume regulation.

OSMOREGULATION OF THE EURYHALINE CHINESE CRAB ERIOCHEIR SINENSIS. IONIC TRANSPORTS ACROSS ISOLATED PERFUSED GILLS AS RELATED TO THE SALINITY OF THE ENVIRONMENT

ABSTRACT Ionic distribution has been studied at the level of intact gills of euryhaline crabs Eriocheir sinensis adapted to fresh and sea waters. Transepithelial potential changes and ionic transports occuring during salinity changes across isolated perfused gills are discussed in relation to the crab osmoregulation. Changes in the activity of the (Na++K+)ATPase are also considered.

Cl− fluxes across isolated, perfused gills of the chinese crab Eriocheir sinensis (M.Edw.) acclimated to fresh water

Abstract 1. 1. The movements of Cl −1 have been studied in the so-called anterior and posterior gills of E. sinensis using radioactive 36 Cl −1 . 2. 2. The anterior gills hardly show any significant movements of Cl −1 . They thus have a very low (if any) permeability to that ion. On the contrary, the posterior gills show both passive fluxes and an active inward movement of Cl −1 . 3. 3. The Cl −1 influx in the posterior gills is largely sensitive to the amount of K + in the perfusion saline.

Physiological and ultrastructural studies of NaCl transport in crustaceans gills

Abstract This review concerns some new insights from ultrastructural studies combined with fluxes and transepithelial potential measurements on preparations of isolated, perfused gills of the euryhaline Chinese crab Eriocheir sinensis. The chinese crab E. sinensis is a strong hyperosmoregulator which has two completely different types of gills. The three anterior pairs of gills have a very thin, respiratory epithelium. The three posterior ones have an epithelium characteristic of salt‐transporting tissues. The permeability to Na+ of the anterior gills is relatively high and can be regulated in two different modes: a) a ≪long‐term mode≫ related to long‐term acclimation to sea water or to fresh water b) an ≪immediate mode≫ related to the Na+ concentration in the external medium. Both types of modulation result in a decrease in permeability at low external salinity. The permeability to Na+ of the posterior gills is always extremely low, whatever the salinity of the medium. The active uptake of salt is only e...

The effect of cytochalasin B on the volume regulation response of isolated axons of the green crab Carcinus maenas submitted to hypo-osmotic media

Abstract 1. 1. Cytochalasin B (5 × 10 −5 M) inhibits the volume regulation response of isolated axons of C. maenas submitted to a hypo-osmotic medium. 2. 2. The compound blocks both the rapid swelling limitation phase and the subsequent, much slower, volume readjustment phase. 3. 3. The reported observations are consistent with the idea that the elastic properties and mechanical resistance of different cell structures play an important part in cell volume maintenance and regulation.

Effects of high hydrostatic pressures on the activity of the membrane ATPases of some organs implicated in hydromineral regulation.

1. The effects of high hydrostatic pressures have been studied on the ATPases extracted from tissues implicated in iono- and osmoregulation of a frog and various teleostean fishes. Pressure affects enzyme activity in the same qualitative way, whatever the tissue and the species considered. 2. The Mg2+ ATPase activity is maximally enhanced at 250 kg/cm2. A slight inhibition is observed at higher pressures up to 1000 kg/cm2. 3. The (Na+ + K+)ATPase is little affected by low pressures but strongly inhibited at 500 kg/cm2 and more. 4. The results are discussed in terms of pressure effects on the recently described protein-lipid interaction linked to ATPase activity.