Hydrolysis of DMPC or DPPC by pancreatic phospholipase A2 is slowed down when (perfluoroalkyl) alkanes are incorporated into the liposomal membrane.

The effect of the incorporation of linear (perfluoroalkyl)alkanes (CmF2m + 1CnH2n + 1, FmHn) into liposomes made of DMPC or DPPC on the activity of porcine pancreatic phospholipase A2 was investigated. A large decrease in enzyme activity and modifications of the kinetic profile, especially at and above the phospholipid's phase transition temperature, were observed; both depend on the relative lengths of the phospholipid's fatty acid chains and of the Hn segment of the FmHn molecule. With DMPC Hn must have a minimum of 10 carbon atoms to be effective, as in F6H10, F8H10 and F4H12; F8H8 had no significant hydrolysis-rate-reducing effect. With DPPC Hn must have a minimum of 12 carbon atoms, as in F4H12, while F8H8, F6H10 and F8H10 were ineffective. The absence of effect when C10H22 or C16H34 was incorporated establishes that the fluorinated segment, although its length (from C4 to C8) is not crucial, is required to hinder hydrolysis by PLA2, indicating that this segment plays an important role in structuring the liposomal membrane.

Effects of ambient ion concentrations on gill ATPases in fresh water eel,Anguilla anguilla.

Branchial activities of Na(+),K(+)-ATPase (ouabain sensitive), Mg(2+) ATPase (ouabain insensitive) and kinetic analysis of high and low affinity Ca(2+) ATPase were measured inAnguilla anguilla that had been acclimated to demineralized water (DW, Ca < 10 µM), freshwater (FW, Ca = 2 mM), and Low calcium freshwater (L-Ca, Ca = 0.9 mM). Na(+),K(+)-ATPase activity decreased while ouabain insensitive activity increased when ambient Ca(2+) decreased. Two kinetic forms of Ca(2+) ATPase could be resolved in each environmental condition. The stimulation coefficients of both sites or enzymes were not affected by ambient Ca(2+) concentrations. The maximal velocity of both the high and the low affinity Ca(2+) ATPase was increased when external Ca(2+) was decreased during acclimation. The low affinity Ca(2+) ATPase and the Mg(2+) stimulated enzyme could be a non specific enzyme accepting either Ca(2+) or Mg(2+). Results are compared with previous results in the literature and in relation to the branchial morphology and ionic exchanges in fish.

Ca2+-stimulated ATPase activities in the gill of the eel: interactions of Mg2+ ions.

Enriched plasma membrane preparations of the branchial epithelium of freshwater-adapted eels were used to study adenosine triphosphatase (ATPase) activities insensitive to ouabain and responding to Ca2+ and Mg2+. Ca2+ induced ATP hydrolysis; two kinetics were observed in the presence or absence of chelators, one with a high-affinity site (0.3 microM) and one with a lower affinity site (10-20 microM). The high-affinity Ca2+ site or enzyme had a prerequisite for Mg2+ (endogenous Mg2+ being sufficient to satisfy the Mg2+ need) but was inhibited by exogenous Mg2+ (Ki0.5 less than 10 microM Mg2+). The low-affinity site or enzyme appears to have kinetic parameters comparable to those found for Mg2+-induced ATP hydrolysis. In the absence of Ca2+ ligands and with no exogenous Mg2+, the two Ca2+ sites or enzymes can be considered stimulated. The results are discussed in relation to the branchial ion environment and transport ion capacities.

Extraintestinal calcium uptake in the killifish, Fundulus heteroclitus.

Extraintestinal calcium influxes were measured in the killifish, Fundulus heteroclitus, in solutions with different calcium concentrations, from distilled water level (near 0) to seawater level (approximately 12 mM). The extraintestinal influx is modified by the concentration of calcium in the medium during the adaptive period. In freshwater-adapted fish, calcium depletion resulted in an increase in calcium uptake. Such an adaptation was not observed in calcium-depleted fish in artificial calcium-deficient seawater. Calcium depletion in either medium seems to increase the calcium permeability. No correlation was found between Ca-ATPase activity in the gill tissue and calcium uptake.

Separation by velocity sedimentation of the gill epithelial cells and their ATPases activities in the seawater adapted eel Anguilla anguilla L.

The separation of cell populations by sedimentation was carried out on heterogeneous suspensions of branchial cells of the seawater adapted eel Anguilla anguilla. The cell sedimentation rates vary mainly in relation to size and permit the separation of enriched fractions of chloride cells and respiratory cells. The method is described and discussed. The homogeneity of the separated populations was checked by microscopy and particle counting. An enrichment of 95% by volume concentration of the two main cell types was obtained. The separated cells had good viability (85-95% viable). This was controlled by Trypan blue exclusion tests. The adenosine triphosphatase activities of the different cell populations were measured and compared.

Cl- -HCO3- dependent ATPase in gills of freshwater and seawater adapted eels (Anguilla anguilla L.).

The gills of both seawater and freshwater adapted eels have an ATPase activity which is stimulated by anions in the presence of Mg2+. Plasma membranes were distinguished from mitochondrial membranes with specific enzyme markers, the membrane fractions separated on a discontinuous sucrose gradient, and the ATPase activity of the plasma membranes studied. Activation by the anions of Cl- or HCO3- followed Michaelis-Menten kinetics and was competitively inhibited by SCN-. The Cl- and HCO3- activation characteristics were determined: no differences between the plasma membrane ATPase activities of freshwater and seawater-adapted fishes were observed. Maximal activity measurements after solubilization of the enzymes by Triton X 100 confirmed these findings. The function of a membrane anion-dependent ATPase in the brachial epithelium of euryhaline fish is discussed.

Cl--HCO3--ATPase in gills of the rainbow trout: evidence for its microsomal localization.

The intracellular localization of a Cl--HCO3--ATPase, which is inhibited by SCN-, was studied in the gills of the rainbow trout, Salmo gairdneri. This activity can be measured in the absence of contamination by mitochondria (i.e., in the absence of succinate dehydrogenase or cytochrome c oxidase activities). The distribution of the 5'-nucleotidase and of the ATPase stimulated by Cl- and HCO3- after sucrose density gradient centrifugation of the microsomal fraction was compared. Because those activities cannot be separated, it is postulated that the anion-stimulated ATPase is located in the plasma membrane. The activation of this microsomal anion ATPase by chloride has been studied extensively. The possible role of the Cl--HCO3--ATPase of trout gills in the Cl-/HCO3- exchange and in the regulation of the internal acid-base balance is discussed.

[Energy metabolism in the liver of rats fed a diet contaminated with dithiocarbamates]. / Métabolisme energétique du foie chez des rats recevant un régime contaminé par des dithiocarbamates

Young male rats, Wistar CF strain, weighing about 100 g, were fed during 14 days with a well-balanced diet, but containing either 275 p.p.m. nabame, either 600 p.p.m. thirame or 3 600 p.p.m. zinebe. The animals given the non-contaminated diet were the controls. On the evening before the experiment, they were all fasted and some of them, forced to walk during 18 hours in a restraint wheel. On the morning of the experiment, some of the rats which have not been working were placed in a cold room at + 4 degrees C, and some others were given an i.p. injection of 2,6 g glucose per kg body weight. The animals were then killed, those that received the glucose treatment 30 mn after the injection, the cold-exposed rats 90 mn after the beginning of their exposure. The redox and energy potentials of the liver tissue were determined after the enzymatic assay of the following liver metabolites : lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, ATP, ADP, AMP, inorganic phosphate. The thirame group rats had the smallest body weight and the lowest food intake. All the pesticides-exposed animals has a higher liver weight than predicted by their body weight. The pesticides-containing diets decreased liver lactate concentration and the lac/pyr ratio. Thirame was the more efficient and it partly impaired the glucose induced increase of the cytoplasmic redox potential, as estimated from the variation of the lac/pyr ratio. The pesticide-containing diets also lowered the liver concentrations of beta-hydroxybutyrate, acetoacetate, and their ratio. Last the pesticides, which but slightly modified the liver contents in adenine nucleotides and inorganic phosphate in the fasting state, increased the ATP fall following cold exposure and decreased the net ATP synthesis produced by glucose administration. The thirame diet was the more efficient in our experimental conditions, the zinebe diet the least one. It was concluded in our discussion that dietary dithiocarbamates either induced a hyperthyroidic status in the animal, or acted themselves as thyroxin-like compounds, because the liver metabolism was more directed towards heat production than towards that of chemical energy available for syntheses.