Twelve testable hypotheses on the geobiology of weathering

Critical Zone (CZ) research investigates the chemical, physical, and biological processes that modulate the Earth's surface. Here, we advance 12 hypotheses that must be tested to improve our understanding of the CZ: (1) Solar-to-chemical conversion of energy by plants regulates flows of carbon, water, and nutrients through plant-microbe soil networks, thereby controlling the location and extent of biological weathering. (2) Biological stoichiometry drives changes in mineral stoichiometry and distribution through weathering. (3) On landscapes experiencing little erosion, biology drives weathering during initial succession, whereas weathering drives biology over the long term. (4) In eroding landscapes, weathering-front advance at depth is coupled to surface denudation via biotic processes. (5) Biology shapes the topography of the Critical Zone. (6) The impact of climate forcing on denudation rates in natural systems can be predicted from models incorporating biogeochemical reaction rates and geomorphological transport laws. (7) Rising global temperatures will increase carbon losses from the Critical Zone. (8) Rising atmospheric P(CO2) will increase rates and extents of mineral weathering in soils. (9) Riverine solute fluxes will respond to changes in climate primarily due to changes in water fluxes and secondarily through changes in biologically mediated weathering. (10) Land use change will impact Critical Zone processes and exports more than climate change. (11) In many severely altered settings, restoration of hydrological processes is possible in decades or less, whereas restoration of biodiversity and biogeochemical processes requires longer timescales. (12) Biogeochemical properties impart thresholds or tipping points beyond which rapid and irreversible losses of ecosystem health, function, and services can occur.

Solution conformation of gramicidin S: An intramolecular nuclear Overhauser effect study

The solution conformation of gramicidin S in deuterated dimethyl sulfoxide was investigated by using the intramolecular nuclear Overhauser effect experiment. Experimental Overhauser enhancements were compared with predicted values for each of the nine most-stable conformations (M1-M9) calculated by Dygert et al. on the basis of energy-minimization procedures [Dygert, M., Gō, N. & Scheraga, H. A. (1975) Macromolecules 8, 750-761]. By using statistical hypothesis testing, the three lowest-energy conformations (M1, M2, and M3) were shown to give the best fit with the experimental data. All other conformations (M4-M9) were found to be inconsistent with the experimental data.

Oxytocin analogs with substitutions in postions 3 and 4

Synthesis and biological properties are reported for some analogs of oxytocin with replacements of the isoleucine residue in position 3, i.e., (3-proline)oxytocin and(3-D-alanine)oxytocin, and the glutamine residue in position 4, i.e., (4-D-alanine)-oxytocin and (4-D-leucin)oxytocin. (3-Proline)oxytocin exhibited smaller than0.02 U/MG oxytocic activity, 0.005 plus or minus smaller than 0.001 U/mg rat pressor activity and 0.003 plus or minus 0.0001 U/mg antidiuretic activity. (3-D-Alanine)oxytocin had no agonistic activity in the bioassays tested except for the rat antidiuretic assay (smaller than 0.0005 U/mg). The 4-D-alanine analog showed 0.05 plus or minus 0.003 U/mg oxytocic activity, 0.07 plus or minus 0.01 U/mg avian vasodepressor activity, and smaller than 0.001 U/mg rat antidiuretic activity. (4-D-Leucine)oxytocin possessed 0.001 plus or minus U/mg rat pressor activity, and showed slight inhibitory properties in the oxytocic and avian vasodepressor assays, inhibiting the oxytocin response in the latter assay by about 60% at a girnibe-to-analog ratio of 1:5000. The activity profiles of the analogs are compared to that of oxytocin and are discussed on the basis of the proposed solution conformation of oxytocin.

Effects of natural cross-linkers on the stability of dentin collagen and the inhibition of root caries in vitro

PURPOSE

To evaluate the effects of dentin collagen modifications induced by various cross-linkers on the stability of collagen matrix and the inhibition of root caries.

MATERIALS AND METHODS

The following cross-linkers were tested: 5% glutaraldehyde (GA), 0.5% proanthocyanidin (PA), 0.625% genipin (GE). In the first experiment, cross-linker-treated demineralized human root dentin was digested with bacterial collagenase, centrifuged, and the supernatants were subjected to amino acid analysis to determine collagen content. The residues were analyzed by SDS-PAGE and hydroxyproline analysis. In the second experiment, bovine root surfaces were conditioned with phosphoric acid, treated with the cross-linkers, incubated with Streptococcus mutans and Lactobacillus acidophilus for 1 week and the root caries inhibition was evaluated with confocal microscopy. Lastly, the ability of the bacteria to colonize the root surface was evaluated. In this experiment slabs of bovine root were treated with the cross-linkers and incubated in a suspension of S. mutans and L. acidophilus. The slabs were washed, resuspended in water, glucose was added, and the pH measured.

RESULTS

While all collagen was digested with collagenase in the control groups, only a small proportion was solubilized in the GA-, PA-, and GE-treated groups. The root caries was significantly inhibited by treatment with PA or GA. Drops in pH in the cross-linker-treated groups were essentially the same as in the untreated group.

CONCLUSION

Naturally occurring cross-linkers, especially PA, could be used to modify root dentin collagen to efficiently stabilize collagen and to increase its resistance against caries.

T-kininogen can either induce or inhibit proliferation in Balb/c 3T3 fibroblasts, depending on the route of administration

T-kininogen (T-KG) is a precursor of T-kinin, the most abundant kinin in rat serum, and also acts as a strong and specific cysteine proteinase inhibitor. Its expression is strongly induced during aging in rats, and expression of T-KG in Balb/c 3T3 fibroblasts results in inhibition of cell proliferation. However, T-KG is a serum protein produced primarily in the liver, and thus, most cells are only exposed to the protein from the outside. To test the effect of T-KG on fibroblasts exposed to exogenous T-KG, we purified the protein from the serum of K-kininogen-deficient Katholiek rats. In contrast to the results obtained by transfection, exposure of Balb/c 3T3 fibroblasts to exogenously added T-KG leads to a dose-dependent increase in [3H]-thymidine incorporation. This response does not require kinin receptors, but it is clearly mediated by activation of the ERK pathway. As a control, we repeated the transfection experiments, using a different promoter. The results are consistent with our published data showing that, under these circumstances, T-KG inhibits cell proliferation. We conclude that T-KG exerts opposite effects on fibroblast proliferation, depending exclusively on the way that it is administered to the cells (transfection versus exogenous addition).

The anticholinergic drug propiverine inhibits the protein kinase C activity in the rat urinary bladder

There is ample evidence that non-cholinergic protein kinase C (PKC) mediated signal transduction pathways are involved into regulation of bladder smooth muscle contractions. To evaluate whether the anticholinergic and calcium modulating drug propiverine exerts intracellular effects by inhibition of the PKC, male inbred LEW 1A rats were pretreated with 0.6, 2, 6 and 60 mg/kg body weight for 5 days. Furthermore, competition assays with partially purified PKC were performed with propiverine in vitro. The activities of the membrane-bound and soluble PKC were assessed by 32P enrichment of lysine-rich histone.

RESULTS

The active, membrane-bound PKC decreased by about 60% accompanied by increase of the soluble form after propiverine in doses above 0.6 mg/kg. 100 nM of the drug inhibited the PKC also in vitro whereas the propiverine metabolites M5 and M6 and atropine were without any effect.

CONCLUSIONS

Propiverine was identified to be an inhibitor of the protein kinase C. Its contribution to the noncholinergic control of hyperactive detrusor smooth muscle cells needs further investigation.

Compact sources as the origin of the soft γ-ray emission of the Milky Way

The Milky Way is known to be an abundant source of gamma-ray photons, now determined to be mainly diffuse in nature and resulting from interstellar processes. In the soft gamma-ray domain, point sources are expected to dominate, but the lack of sensitive high-resolution observations did not allow for a clear estimate of the contribution from such sources. Even the best imaging experiment revealed only a few point sources, accounting for about 50% of the total Galactic flux. Theoretical studies were unable to explain the remaining intense diffuse emission. Investigating the origin of the soft gamma-rays is therefore necessary to determine the dominant particle acceleration processes and to gain insights into the physical and chemical equilibrium of the interstellar medium. Here we report observations in the soft gamma-ray domain that reveal numerous compact sources. We show that these sources account for the entirety of the Milky Way's emission in soft gamma-rays, leaving at most a minor role for diffuse processes.

Blood viscosity and platelet function in patients with obstructive sleep apnea syndrome treated with nasal continuous positive airway pressure

Patients with obstructive sleep apnea syndrome (OSA) have a high incidence of cardiovascular events. We measured whole blood viscosity at high (94.5 s(-1)) and low (0.1 s(-1)) shear rate, hematocrit, fibrinogen, and platelet hemostatic function (PTA-100) at 7-8 p.m. and 7-8 a.m. in 8 controls and 13 patients, once with the established nasal continuous positive airway pressure (NCPAP) treatment and once without. OSA patients had a higher plasma viscosity (1.37+/-0.11 vs. 1.19+/-0.11 mPa.s in the evening, p<0.05) and fibrinogen (2.61+/-0.49 vs. 2.11+/-0.29 g/l, p<0.05) than controls, without diurnal difference, and similar values with or without NCPAP. Whole blood viscosity and hematocrit were similar in controls and patients before and after a night with or without NCPAP. Platelet activity was significantly higher in the morning than in the evening in controls and patients with or without NCPAP. We conclude that blood viscosity and platelet activity are similar in controls and patients with OSA on a long-term treatment with NCPAP, which is not worsened by a single night without NCPAP. The increase of plasma viscosity and fibrinogen in OSA patients as well as the general increase of platelet aggregation in the morning may contribute to the increased incidence of cardiovascular events.

Influence of propiverine on hepatic microsomal cytochrome p450 enzymes in male rats

The bladder spasmolytics propiverine was shown to induce hepatic cytochrome P450 (P450) and aminopyrine and aniline oxidation in rats. To characterize the type of enzyme induction and its dose dependence, activities of seven hepatic microsomal P450-dependent monooxygenases were measured in 72 male LEW1A albino rats (body weight 236-295 g) after oral treatment with 0.5, 2, 6, and 60 mg/kg of propiverine hydrochloride for 5 days and compared with the effects of 40 mg/kg beta-naphthoflavone, 10 mg/kg phenobarbital, and 20 mg/kg dexamethasone (each group, n = 8). CYP2B expression was measured by Western blotting. Furthermore, the inhibitory potency of propiverine on P450 enzymes was evaluated in competition assays with three most specific monooxygenases. Results show that Propiverine induced several monooxygenases and CYP2B expression dose dependently. The effects were well comparable with a phenobarbital-type inducer with 60 mg/kg being equipotent to 10 mg/kg phenobarbital. Furthermore, propiverine in low concentrations inhibited pentylresorufin O-dealkylase (for CYP2B) in vitro. In conclusion, propiverine is a phenobarbital-type inducer on hepatic P450 enzymes in rats in doses about 100-times above the therapeutic doses in man.

Influence of prestorage leucocyte depletion and storage time on rheologic properties of erythrocyte concentrates

BACKGROUND AND OBJECTIVES

Rheological blood properties were studied during storage.

MATERIALS AND METHODS

Blood viscosity, erythrocyte morphology and ATP levels were determined in filtered samples (Leukotrap WB filter system) and their unfiltered counterparts during storage with saline-adenine-glucose-mannitol (SAG-M) for 42 days.

RESULTS

Prestorage leucocyte depletion decreased blood viscosity at a high shear rate and reduced the degree of anisocytosis of erythrocytes. During storage, erythrocytes underwent a time-dependent echinocytic shape transformation, which increased the suspension viscosity at high and low shear rates. On day 42, high shear viscosity in filtered units remained lower than in unfiltered counterparts, the mean cellular volume and red blood cell distribution width (RDW) were lower and erythrocytic ATP levels were higher.

CONCLUSIONS

Prestorage leucocyte depletion by Leukotrap WB filters improves biophysical properties of erythrocyte concentrates throughout storage, which is, however, outweighed by a time-dependent echinocytic shape transformation and deterioration of these properties.

T-kininogen inhibits fibroblast proliferation in the G(1) phase of the cell cycle

By using synthetic protease inhibitors, several investigators have demonstrated that cysteine proteinases are required for cell proliferation. Kininogens are potent and specific physiological inhibitors of cysteine proteinases. We have used several mouse fibroblast-derived cell lines that express biologically active T-kininogen under the control of the mouse metallothionein promoter to test its effect on cell proliferation. Our results indicate that expression of T-kininogen results in diminished proliferative capacity, as measured by reduced cell numbers, both in logarithmically growing cultures and in G(0) cells induced to proliferate in response to serum. Furthermore, both fluorescence-activated cell sorting (FACS) analysis and incorporation of radioactive precursors into DNA suggest that the cells are unable to progress from G(0) through the S phase of the cell cycle in response to serum stimulation. However, we find that T-kininogen-expressing cell lines are still capable of responding to growth factors present in the serum, both by activating the ERK pathway and by expressing early genes, such as c-Fos and c-Jun. Thus, our results suggest that inhibition of cysteine proteinases by T-kininogen leads to inhibition of cell proliferation between the G(1) and S phases of the cell cycle.

No influence of C-peptide, insulin, and glucagon on blood viscosity in vitro in healthy humans and patients with diabetes mellitus

The influence of the hormones most involved in glucose homeostasis, C-peptide, insulin and glucagon on blood viscosity was tested in vitro. Whole blood (adjusted to haematocrit 45%) from healthy volunteers (n=24) and patients with diabetes mellitus (n=17) was incubated with 10(-7)-10(-10) M C-peptide, insulin or glucagon. None of these peptide hormones, neither at physiological nor at supraphysiological levels, had an influence on high (94.5 s(-1)) or low (0.1 s(-1)) shear rate viscosity. The small group of diabetic patients had a higher plasma viscosity and increased blood viscosity at 94.5 s(-1), which is in agreement with earlier studies, but decreased viscosity at low shear rate. We conclude that C-peptide, insulin and glucagon have no direct effect on blood viscosity in vitro. It is, therefore, unlikely that microvascular disturbances seen with either deficiency or excess of these hormones is due to haemorheological factors.

Effects of high-altitude exposure on vascular endothelial growth factor levels in man

Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen and permeability factor that is inducible by hypoxia. Its contribution to high-altitude illness in man is unknown. We measured VEGF levels in 14 mountaineers at low altitude (490 m) and 24 h after their arrival at high altitude (4,559 m). At high altitude, VEGF increased from [mean (SEM)] 32.5 (9.2) to 60.9 (18.5) pg.ml(-1) (P < 0.004) in the arterial blood, and from 15.9 (2.9) to 49.3 (15.9) pg.ml(-1) (P= 0.0001) in the mixed venous blood. Whereas at low altitude venous and arterial VEGF levels were not statistically different from each other (P= 0.065), the VEGF concentration was significantly lower in venous than in arterial blood samples at high altitude (P=0.004). The pulmonary capillary VEGF concentration remained unchanged at high altitude [14.8 (2.5) vs 17.1 (5.4) pg.ml(-1), P=0.85]. VEGF levels in the nine mountaineers who developed symptoms of acute mountain sickness (AMS), and in the six subjects who had radiographic evidence of high-altitude pulmonary edema were similar to those in subjects without symptoms. VEGF was not correlated with either AMS scores, mean pulmonary arterial pressures, arterial partial pressure of O2, or alveolar-arterial O2 gradients. We conclude that VEGF release is stimulated at high altitude, but that VEGF is probably not related to high-altitude illness.

Epistemology at work: the ontological relationship between feminist methods, intersubjectivity and nursing research--a research exemplar

This article explores the importance of strong epistemological and ontological links in nursing research by examining the design and process of a recent research project. The research topic concerns the relationship between self-concept and nursing practice. In this article, the authors demonstrate that commitment to a methodologically consistent process and the necessary associated epistemological and ontological positions provides a depth and structure to nursing research. It is the authors' belief that such consistency within research acts to strengthen the research process, and consequently strengthens nursing's research base and knowledge.