Assessing the hydrogeological resilience of a groundwater-dependent Mediterranean peatland: Impact of global change and role of water management strategies.

Mediterranean peatlands remain largely under-documented, except for detailed biological data such as fauna and flora taxa lists, and yet are increasingly threatened by water withdrawal and agriculture practices. This lack of information, particularly on their hydrogeological functioning, makes it impossible to evaluate their response to changing climate conditions. A pilot study on a representative Mediterranean peatland on the island of Corsica (France) was conducted to evaluate recharge modalities in the peatland using a coupled water-level monitoring, geochemical and isotope multi-tracing approach (electric conductivity, major ions, δ18O, δ2H, 3H, 87Sr/86Sr). The goal was to understand how water budgets in peatland ecosystems were maintained throughout the year, especially during the summer. Despite the remarkable stability of the peatland water level, the recharge contributions of varied water bodies through an alluvial aquifer vary significantly from one season to another. An end-member mixing analysis (EMMA) indicates that the peatland is mainly recharged by an alluvial aquifer. During fall-winter, the alluvial aquifer on which the peatland depends is recharged by the rainfall, a river, and shallow groundwater (colluvium). During spring-summer, water supply is provided mostly by a river, shallow, and deep groundwater (fractured granite). However, this specific hydrogeological functioning is not taken into account by environmental management policies making peatlands vulnerable to anthropogenic and climatic pressures. Thus, their actual status regarding water and aquatic environment management policies is discussed to provide recommendations for better consideration and preservation.

Retention of thrombin by polytetrafluoroethylene: influence on the adsorption of fibrinogen/fibrin.

Beads of polytetrafluoroethylene were used to investigate adsorption of thrombin and the influence of the adsorbed protease on a subsequent deposition of fibrinogen. Adsorption of active thrombin was not detected by a specific fluorogenic substrate unless > 0.1 units/ml had been applied. Adsorption was considerably improved by albumin, which protected soluble thrombin from inactivation by hydrophobic surfaces. Retention of active thrombin was optimal at ca. 0.1% albumin and decreased at higher concentrations. After incubation with plasma, negligible thrombin activity was detected at the polytetrafluoroethylene beads by the fluorogenic substrate. However, repeated incubation with fresh plasma samples resulted in adsorbed activity rising with each step. This result suggested that thrombin activity should also accumulate at a polytetrafluoroethylene surface in vivo if fresh blood is permanently flowing past. Adsorbed thrombin improved the subsequent retention of fibrinogen, monitored by an antibody technique. Concomitantly, fibrinopeptides A, AP and AY were slowly released whilst fibrinopeptide B was not detectable before 24 h.

Monoclonal antibodies and peptide mapping reveal structural similarities between the subunits of the glycine receptor of rat spinal cord.

The glycine receptor of rat spinal cord is an oligomeric membrane glycoprotein of molecular mass 250,000 daltons that contains three polypeptides of 48,000, 58,000, and 93,000 daltons. Monoclonal antibodies (mAbs) were prepared against the affinity-purified glycine receptor protein by using 125I-labeled receptor preparations for the detection of positive hybrids. From nine monoclonal antibodies obtained, six recognized denatured receptor polypeptides blotted to nitrocellulose paper. Two of these antibodies bound to more than one glycine receptor polypeptide: mAb GlyR 4a stained the 48,000- and 58,000-dalton polypeptides, and mAb GlyR 7a stained the 48,000- and 93,000-dalton polypeptides. Common antigenic determinants thus are shared by the different subunits of the glycine receptor. Complementary results were obtained by peptide mapping of 125I-labeled glycine receptor polypeptides with various proteases. A set of peptide fragments of the same apparent molecular mass was produced from the different glycine receptor polypeptides by using V8 protease, chymotrypsin, and elastase. These data suggest that the subunits of the glycine receptor have significant homology within their primary structure and may have evolved from a common ancestor receptor polypeptide.

Purification and characterization of the glycine receptor of pig spinal cord.

A large-scale purification procedure was developed to isolate the glycine receptor of pig spinal cord by affinity chromatography on aminostrychnine agarose. After an overall purification of about 10 000-fold, the glycine receptor preparations contained three major polypeptides of Mr 48 000, 58 000, and 93 000. Photoaffinity labeling with [3H]strychnine showed that the [3H]strychnine binding site is associated with the Mr 48 000 and, to a much lesser extent, the Mr 58 000 polypeptides. [3H]Strychnine binding to the purified receptor exhibited a dissociation constant KD of 13.8 nM and was inhibited by the agonists glycine, taurine, and beta-alanine. Gel filtration and sucrose gradient centrifugation gave a Stokes radius of 7.1 nm and an apparent sedimentation coefficient of 9.6 S. Peptide mapping of the [3H]strychnine-labeled Mr 48 000 polypeptides of purified pig and rat glycine receptor preparations showed that the strychnine binding region of this receptor subunit is highly conserved between these species. Also, three out of six monoclonal antibodies against the glycine receptor of rat spinal cord significantly cross-reacted with their corresponding polypeptides of the pig glycine receptor. These results show that the glycine receptor of pig spinal cord is very similar to the well-characterized rat receptor protein and can be purified in quantities sufficient for protein chemical analysis.