Effects of decreased atmospheric deposition on the sulfur budgets of two Dutch moorland pools

The chemical composition of surface waters of two Dutch moorland pools and of incident precipitation, was monitored from 1982 to 1990. For this period, sulfur and water budgets were calculated using a hydrochemical model developed for well-mixed non-stratifying lakes. Total atmospheric deposition of S decreased significantly after 1986 at both locations. A model describing the sulfur budget in terms of input, output and reduction/oxidation processes predicted a fast decrease of pool water SO₄ ²⁻ concentrations after a decrease of atmospheric input. However, SO₄ ²⁻ concentrations in the surface water was lowered only slightly or remained constant. Apparently a source within the lake caused the unexpectedly high SO₄ ²⁻ concentrations. The possible supply of SO₄ ²⁻ from the sediment through regulation by (K-)Al-SO₄ containing minerals or desorption of SO₄ ²⁻ from positively charged surfaces in the sediment was evaluated. Solubility calculations of pore water with respect to alunite, basaluminite and jurbanite indicated that SO₄ ²⁻ concentration was not regulated by these minerals. It is suggested here (1) that desorption of SO₄ ²⁻ from peaty sediments may account for the estimated SO₄ ²⁻ supply provided that the adsorption complex is periodically recharged by partial oxidation of the upper bottom sediments and (2) that because of exposure of a part of the pool bottom to the atmosphere during dry summers and subsequent oxidation of reduced S, the amount of SO₄ ²⁻ may be provided which complements the decreasing depositional SO₄ ²⁻ input. In future research these two mechanisms need to be investigated.     

Sulfate reduction and S-oxidation in a moorland pool sediment

In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO₄ ^2– reduction rates in the sediment, (2) depletion of SO₄ ^2– in the overlying water column and (3) release of³⁵S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO₄ ^2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core³⁵SO₄ ^2– injection. Rates of SO₄ ^2– consumption in the overlying water were estimated by changes in SO₄ ^2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m^–2 d^–1. Rates of SO₄ ^2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m^–2 d^–1 (November) to 0.43–1.81 mmol m^–2 d^–1 (July, August and April). Maximum rates of oxidation to SO₄ ^2– in July 1990 estimated by combination of SO₄ ^2– reduction rates and rates of in situ SO₄ ^2– uptake in the enclosed water column were 10.3 and 10.5 mmol m^–2 d^–1 at an organic rich and at a sandy site respectively.Experiments with³⁵S^2– and³⁵SO₄ ^2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO₄ ^2– and (2) the presence of mainly non SO₄ ^2–-S derived from reduced S transported from the sediment into the overlying water. A³⁵S^2– tracer experiment showed that about 7% of³⁵S^2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author     

Perspectives of pluripotent stem cells in livestock

The recent progress in derivation of pluripotent stem cells(PSCs)from farm animals opens new approaches not only for reproduction,genetic engineering,treatment and conservation of these species,but also for screening novel drugs for their efficacy and toxicity,and modelling of human diseases.Initial attempts to derive PSCs from the inner cell mass of blastocyst stages in farm animals were largely unsuccessful as either the cells survived for only a few passages,or lost their cellular potency;indicating that the protocols which allowed the derivation of murine or human embryonic stem(ES)cells were not sufficient to support the maintenance of ES cells from farm animals.This scenario changed by the innovation of induced pluripotency and by the development of the 3 inhibitor culture conditions to support na?ve pluripotency in ES cells from livestock species.However,the long-term culture of livestock PSCs while maintaining the full pluripotency is still challenging,and requires further refinements.Here,we review the current achievements in the derivation of PSCs from farm animals,and discuss the potential application areas.     

The Active and the Inactive Form of the hAT1 Receptor Have an Identical Ligand-Binding Environment: An MPA Study on a Constitutively Active Angiotensin II Receptor Mutant

Several models of activation mechanisms were proposed for G protein-coupled receptors (GPCRs), yet no direct methods exist for their elucidation. The availability of constitutively active mutants has given an opportunity to study active receptor conformations within acceptable limits using models such as the angiotensin II type 1 (AT₁)¹ receptor mutant N111G-hAT₁ which displays an important constitutive activity. Recently, by using methionine proximity assay, we showed for the hAT₁ receptor that TMD III, VI, and VII form the ligand-binding pocket of the C-terminal amino acid of an antagonistic AngII analogue. In the present contribution, we investigated whether the same residues would also constitute the ligand-binding contacts in constitutively activated mutant (CAM) receptors. For this purpose, the same Met mutagenesis strategy was carried out on the N111G double mutants. Analysis of 43 receptors mutants in the N111G-hAT₁ series, photolabeled and CNBr digested, showed that there were only subtle structural changes between the wt-receptor and its constitutively active form.     

Multifactorial diversity sustains microbial community stability

Maintenance of a high degree of biodiversity in homogeneous environments is poorly understood. A complex cheese starter culture with a long history of use was characterized as a model system to study simple microbial communities. Eight distinct genetic lineages were identified, encompassing two species: Lactococcus lactis and Leuconostoc mesenteroides. The genetic lineages were found to be collections of strains with variable plasmid content and phage sensitivities. Kill-the-winner hypothesis explaining the suppression of the fittest strains by density-dependent phage predation was operational at the strain level. This prevents the eradication of entire genetic lineages from the community during propagation regimes (back-slopping), stabilizing the genetic heterogeneity in the starter culture against environmental uncertainty.     

Regulation of VEGF in the reproductive tract by sex-steroid hormones

Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis. In adults, angiogenesis is an infrequent event in the normal tissue except in the female reproductive tract where angiogenesis occurs frequently during the cyclical repair and regeneration of the endometrium as well as in the ovary. Little is known about angiogenesis in the male reproductive tract. The role of VEGF in controlling reproductive tract physiology and the role of hormones in regulating this key regulator of angiogenesis is not well understood. Since reproductive tract physiology is largely under sex-steroid regulation, we have reviewed some recent studies describing the role of sex-steroid hormones in regulating VEGF. We have also included studies on the role of sex-steroids in regulating VEGF and angiogenesis in endometrial, breast and prostate pathologies. We have provided an extensive review of the classical VEGF and VEGF receptors with examples drawn from numerous studies in the literature using diverse biological systems to encourage similar studies in the area of reproductive tract physiology. It is speculated that such studies will provide insights into understanding the role of VEGF in reproductive tract development, causes of infertility, and cancer. Such knowledge would allow us to target VEGF for improving human reproductive tract abnormalities, for enhancing implantation and fertility, and for designing drugs for treatment of endocrine dependent cancers.     

A model for the regulation of cerebral oxygen delivery

On the basis of the assumption that oxygen delivery across theendothelium is proportional to capillary plasmaPO₂, a model is presented that linkscerebral metabolic rate of oxygen utilization(CMR_O2) to cerebral blood flow(CBF) through an effective diffusivity for oxygen (D) of the capillarybed. On the basis of in vivo evidence that the oxygen diffusivityproperties of the capillary bed may be altered by changes in capillaryPO₂, hematocrit, and/or bloodvolume, the model allows changes in D with changes in CBF. Choice inthe model of the appropriate ratio of   (D/D)/(CBF/CBF)determines the dependence of tissue oxygen delivery on perfusion.Buxton and Frank (J. Cereb. Blood Flow. Metab. 17: 64-72, 1997) recently presented alimiting case of the present model in which  = 0. In contrast to thetrends predicted by the model of Buxton and Frank, in the current modelwhen > 0, the proportionality between changes in CBF andCMR_O2 becomes more linear, and similardegrees of proportionality can exist at different basal values ofoxygen extraction fraction. The model is able to fit the observedproportionalities between CBF and CMR_O2 for a large range ofphysiological data. Although the model does not validate any particularobserved proportionality between CBF andCMR_O2, generally values of(CMR_O2/CMR_O2)/(CBF/CBF) close to unity have been observed across ranges of graded anesthesia inrats and humans and for particular functional activations in humans.The model's capacity to fit the wide range of data indicates that theoxygen diffusivity properties of the capillary bed, which can bemodified in relation to perfusion, play an important role in regulatingcerebral oxygen delivery in vivo.

     

Survey of Argentine Health Researchers on the Use of Evidence in Policymaking

Objective

In this study, Argentine health researchers were surveyed regarding their perceptions of facilitators and barriers to evidence-based policymaking in Argentina, as well as their publication activities, and research environment satisfaction.

Methods

A self-administered online survey was sent to health researchers in Argentina. The survey questions were based on a preceding qualitative study of Argentine health researchers, as well as the scientific literature.

Results

Of the 647 researchers that were reached, 226 accessed the survey, for a response rate of 34.9%. Over 80% of researchers surveyed had never been involved in or contributed to decision-making, while over 90% of researchers indicated they would like to be involved in the decision-making process. Decision-maker self-interest was perceived to be the driving factor in the development of health and healthcare policies. Research conducted by a research leader was seen to be the most influential factor in influencing health policy, followed by policy relevance of the research. With respect to their occupational environment, researchers rated highest and most favourably the opportunities available to present, discuss and publish research results and their ability to further their education and training. Argentine researchers surveyed demonstrated a strong interest and willingness to contribute their work and expertise to inform Argentine health policy development.

Conclusion

Despite Argentina’s long scientific tradition, there are relatively few institutionalized linkages between health research results and health policymaking. Based on the results of this study, the disconnect between political decision-making and the health research system, coupled with fewer opportunities for formalized or informal researcher/decision-maker interaction, contribute to the challenges in evidence informing health policymaking in Argentina. Improving personal contact and the building of relationships between researchers and policymakers in Argentina will require taking into account researcher perceptions of policymakers, as highlighted in this study.