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PubMed1984

The kinetic mechanism by which CCCP (carbonyl cyanide m-chlorophenylhydrazone) transports protons across membranes.

We demonstrate that a simple kinetic model describes the transport of protons across lipid bilayer membranes by the weak acid CCCP (carbonyl cyanide m-chlorophenylhydrazone). Four parameters characterize this model: the adsorption coefficients of the anionic and neutral forms of the weak acid onto the interface (beta A and beta HA) and the rate constants for the movement of A- and HA across the membrane (kappa A and kappa HA). These parameters were determined by equilibrium dialysis, electrophoretic mobility, membrane potential, membrane conductance, and spectrophotometric measurements. From these equilibrium and steady state measurements on diphytanoyl phosphatidylcholine/chlorodecane membranes we found that beta A = beta HA = 1.4 10(-3) cm, kappa A = 175 s-1 and kappa HA = 12,000 sec-1. These parameters and our model describe our kinetic experiments if we assume that the protonation reactions, which occur at the interfaces, remain at equilibrium. The model predicts a single exponential decay of the current in a voltage-clamp experiment. The model also predicts that the decay in the voltage across the membrane following an intense current pulse of short duration (approximately 50 nsec) can be described by the sum of two exponentials. The magnitudes and time constants of the relaxations that we observed in both voltage-clamp and charge-pulse experiments agree well with the predictions of the model for all values of pH, voltage and [CCCP].

Biological Transport↗
PubMed1987

How do protons cross the membrane-solution interface? Kinetic studies on bilayer membranes exposed to the protonophore S-13 (5-chloro-3-tert-butyl-2'-chloro-4' nitrosalicylanilide).

A simple carrier model describes adequately the transport of protons across lipid bilayer membranes by the weak acid S-13. We determined the adsorption coefficients of the anionic, A-, and neutral, HA, forms of the weak acid and the rate constants for the movement of A- and HA across the membrane by equilibrium dialysis, electrophoretic mobility, membrane potential, membrane conductance, and spectrophotometric measurements. These measurements agree with the results of voltage clamp and charge pulse kinetic experiments. We considered three mechanisms by which protons can cross the membrane-solution interface. An anion adsorbed to the interface can be protonated by a H+ ion in the aqueous phase (protolysis), a buffer molecule in the aqueous phase or water molecules (hydrolysis). We demonstrated that the first reaction cannot provide the required flux of protons: the rate at which H+ must combine with the adsorbed anions is greater than the rate at which diffusion-limited reactions occur in the bulk aqueous phase. We also ruled out the possibility that the buffer is the main source of protons: the rate at which buffers must combine with the adsorbed anions is greater than the diffusion-limited rate when we reduced the concentration of polyanionic buffer adjacent to the membrane-solution interface by using membranes with a negative surface charge. A simple analysis demonstrates that a hydrolysis reaction can account for the kinetic data. Experiments at acid pH demonstrate that the transfer of H+ from the membrane to the aqueous phase is limited by the rate at which OH- combines with adsorbed HA and that the diffusion coefficient of OH- in the water adjacent to the bilayer has a value characteristic of bulk water. Our experimental results demonstrate that protons are capable of moving rapidly across the membrane-solution interface, which argues against some mechanisms of local chemiosmosis.

Kinetics↗
PubMed1985

The effect of pH and urine dilution on the electrophoretic mobility of uric acid crystals.

As a result of a continuing programme to understand better the uric acid stone treatment and prophylaxis, an investigation of the effect of pH and urine dilution on the surface charge of uric acid crystals was undertaken. A microelectrophoretic technique was employed to characterize the nature of the surface charge and the electrokinetics of uric acid crystals both in natural and synthetic urines under different conditions of pH and dilution. Both dilution and alkalization reduced the specific conductance of urine and increased the electrophoretic mobility (zeta potential) of uric acid crystals. The presence of cationic additives in diluted urine altered the zeta potential of uric acid crystals. Such findings suggest that proper control of the pH level and urine dilution as well as the surface charge at the solid-liquid interface represent an important factor in the uric acid stone prophylaxis.

Crystallization↗
PubMed2003

A first look at platinum in road-deposited sediments and roadside soils, Honolulu, Oahu, Hawaii.

Platinum (Pt) has become globally distributed by anthropogenic inputs, primarily from automobile emissions resulting from degradation of catalytic converters. These inputs are greatest in urban areas, with the major sinks being road sediments and roadside soils. Limited data are available on the distribution of Pt in the environment. No data for Pt in road-deposited sediments are presently available from the United States, and only a few studies offer a limited perspective of Pt in urban soils in the United States. This investigation represents the first study in the United States to characterize Pt concentrations and enrichment ratios in both road sediments and roadside soils in an urban (nonindustrialized) basin in Honolulu, Hawaii. Two independent analytical techniques-cathodic stripping voltammetry and lead-fire assay followed by ICP-AES-were used to quantify Pt in environmental media. Data from 10 road sediments confirm Pt contamination, with a median concentration of 33 ng g(-1) and a range of 15-160 ng g(-1). Upper soil horizons in roadside areas also exhibited contamination, with a median Pt value of 14 ng g(-1) (range 2-160 ng g(-1)), but significantly lower than road sediments. Computation of robust enrichment ratios using baseline soil, geology, and tree bark data indicated that road sediments had a median Pt enrichment of 9 (range 4-46), upper soil horizons a median of 4, and lower horizons 1.1. The latter were not found to differ significantly from Pt baseline concentrations. However, several roadside sites exhibited significant enrichment with depth, which may indicate potential Pt mobility in this environment. These data support a substantial loading of Pt in the urban environment of Hawaii. Further work is required to characterize the distribution of other autocatalyst-associated noble metals palladium (Pd) and rhodium (Rh) in the environment.

Cities↗
PubMed2004

Diel variation in ammonia excretion, glutamine levels, and hydration status in two species of terrestrial isopods.

Terrestrial isopods (suborder Oniscidea) excrete most nitrogen diurnally as volatile ammonia, and ammonia-loaded animals accumulate nonessential amino acids, which may constitute the major nocturnal nitrogen pool. This study explored the relationship between ammonia excretion, glutamine storage/mobilization, and water balance, in two sympatric species Ligidium lapetum (section Diplocheta), a hygric species; and Armadillidium vulgare (Section Crinocheta), a xeric species capable of water-vapor absorption (WVA). Ammonia excretion (12-h), tissue glutamine levels, and water contents were measured following field collection of animals at dusk and dawn. In both species, diurnal ammonia excretion exceeded nocturnal excretion four- to fivefold while glutamine levels increased four- to sevenfold during the night. Most glutamine was accumulated in the somatic tissues ("body wall"). While data support the role of glutamine in nocturnal nitrogen storage, potential nitrogen mobilization from glutamine breakdown (162 micromol g(-1) in A. vulgare) exceeds measured ammonia excretion (2.5 micromol g(-1)) over 60-fold. This may serve to generate the high hemolymph ammonia concentrations (and high P(NH3)) seen during volatilization. The energetic cost of ammonia volatilization is discussed in the light of these findings. Mean water contents were similar at dusk and dawn in both species, indicating that diel cycles of water depletion and replenishment were not occurring.

Adaptation, Physiological↗
PubMed2005

[Potentials of elderly migrants].

Re-migration and immigration are the causes for the continual fluctuation within the migrant population. It is, however, currently foreseeable that the elderly migrant population living in Germany will steadily increase. Because of the large degree of heterogeneity among the elderly migrant population in Germany, the following report will be limited to a discussion of those groups of migrant workers, who originate from former recruiting countries. These groups will constitute the majority of elderly migrants in the coming years. Among the first generation of migrants, some groups have extensive ethnic social networks. This is mostly the case with respect to the migrants from Turkey. These have access to their own ethnic infrastructure, and, due to this fact, there is little need for the initiation of social contacts outside their own ethnic context. Generally, they prefer, as do other elderly foreign workers, to remain in their cultural niches with their own religious institutions and migrant organizations. In comparison to the German population, the families of the first generation of migrants have more children and live more often in multigenerational households. Under the conditions of migration and in a foreign cultural context, the family fulfills a function of social-emotional support. Migrants possess a high potential for mobility. They commute between their homeland and the land of immigration. For some, this is a transitional strategy in order to reach a final decision, either to return to their homeland or to stay in Germany. For others, it is a long-term solution that enables them to make use of each country's respective advantages.

Age Distribution↗
PubMed1989

Effects of endothelin on sodium transport mechanisms: potential role in cellular Ca2+ mobilization.

The effects of endothelin on cellular Ca2+ mobilization were examined in cultured rat vascular smooth muscle cells (VSMC). Endothelin (10(-8)M) induced a rapid transient increase of [Ca2+]i from 77 +/- 3 to 104 +/- 5 nM (p less than .05) in VSMC. Preincubation (60 min) with endothelin (2 x 10(-6)M) increased basal [Ca2+]i from 77 +/- 3 to 105 +/- 8 nM (p less than .05). Preincubation with endothelin also enhanced vasopressin (10(-7)M)-stimulated peak levels of [Ca2+]i (528 +/- 20 nM vs 969 +/- 21 nM, p less than .01). Endothelin (10(-7)M) induced an intracellular alkalinization (7.18 +/- 0.03 vs 7.37 +/- 0.04, p less than .01) which was blocked by pretreatment with amiloride. The biphasic effects of endothelin on [Ca2+]i were similar to those of an endogenous inhibitor of Na-K-ATPase that we examined in a previous study. Therefore, we examined the effects of endothelin on Na-K-ATPase in an enzyme preparation from hog cerebral cortex. At high concentrations, endothelin (10(-5)M) inhibited Na-K-ATPase in vitro. Thus, endothelin may exert its vasoconstrictor effects at least in part via alterations of cellular Ca2+ mobilization in VSMC. While the rapid transient increase of [Ca2+]i appears to reflect intracellular Ca2+ mobilization, the sustained effect on [Ca2+]i may be related to an increase of intracellular sodium mediated by inhibition of Na-K-ATPase and/or more likely by stimulation of the Na+/H+-antiport.

Animals↗
PubMed1987

Effects of a phorbol ester on rat aortic contraction and calcium influx in the presence and absence of BAY k 8644.

Phorbol esters like phorbol-12,13-dibutyrate (PDB) exert potent contractile effects on rat aorta. In the present study, we determined whether phorbol esters alter contraction by augmenting calcium influx through calcium channels. Isometric tensions and calcium influx (using 45Ca) were measured in rat aortic rings exposed to PDB in the presence and absence of BAY k 8644, a calcium channel agonist. We found that PDB alone caused significant increases in isometric tension. The addition of 100 nM BAY k 8644 enhanced the PDB-induced rat aortic contraction which was inhibited as well as reversed by the calcium channel antagonist, nitrendipine. In the presence of PDB alone, calcium influx was significantly increased only after an extended time (30 min) of isometric contraction. In the presence of BAY k 8644, however, PDB caused a significant increase in calcium influx during shorter periods (10 min) of isometric contraction. We also found that the biologically inactive phorbol, 4-alpha-phorbol, did not potentiate the effects of BAY k 8644 on either contraction or calcium influx. These results indicate that PDB may induce rat aortic contraction via activation of protein kinase C which in the presence of a calcium channel agonist can potentiate the mobilization of calcium through nitrendipine-sensitive calcium channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1993

Mobility in pyruvate dehydrogenase complexes with multiple lipoyl domains.

High-field NMR studies were carried out with genetically-reconstructed pyruvate dehydrogenase (PDH) complexes of Escherichia coli containing from zero to nine lipoyl domains per lipoate acetyltransferase (E2p) subunit. The only significant differences between the NMR spectra were the increasing intensities of the signals derived from the lipoyl domains and their associated linkers, and the much enhanced signal from the E3-binding domain and its linker in complexes that are devoid of lipoyl domains. The results suggest an explanation for the presence of three lipoyl domains per E2p subunit in the wild-type PDH complex, based on its greater inherent mobility, and potentially more efficient active-site coupling, than any of the other complexes.

Acetyltransferases↗
PubMed1992

The role of the village midwife in detection of high risk pregnancies and newborns.

The preliminary findings of a prospective study of perinatal, neonatal and maternal mortality carried out in a rural community of Sudan are reported. Out of 6275 deliveries monitored over a period of 3 years, 150 stillbirths, 167 neonatal deaths and 27 maternal deaths were observed. An intervention program to upgrade the skills of the village midwives started in the middle of the second year. There was a 25% reduction in the risk of unfavorable outcome of pregnancy (i.e. stillbirth and neonatal death) in the third year relative to the first 2 years. Peer review of the 40 village midwives who took part in the study revealed their tremendous potentials in mobilization of mothers as well as participation in primary health care. Their role in detection of high risk pregnancies and newborns cannot be overemphasized.

Adolescent↗
PubMed1991

Trace elements in street and house dusts: sources and speciation.

The sources and speciation of trace elements in street and house dusts are reviewed. Soil is a major component of both dusts, but a number of elements are enriched in both materials. These include Pb, Zn, Cu, Cd, As, Sb, Cr, Ca, Na, Au, Cl and Br. They arise from a number of contributing and polluting sources. In the case of house dust, some elements, such as Cu, Co, As, Sb, Zn, Cd, Au, Cl, C and Pb, are produced in the house. There are a number of problems associated with the determination of the speciation of trace elements in dusts. These include the low concentrations of many of the elements, and the interpretation of the results from selective sequential extractions. The mobility and potential availability of the trace elements from dust lies in the order Cd greater than Zn, Pb greater than Mn, Cu greater Fe.

Air Pollutants↗
PubMed1996

C6-ceramide maintains elevated cytosolic calcium levels in activated platelets.

The effects of cell-permeable C2 and C6-ceramides on human platelet responses were investigated. In thrombin-activated platelets, C6(5-30 microM) potentiated Ca2+ mobilization and Ca2+ influx, and decreased the rate of removal of Ca2+ from cytosol. The effect of C2 was not significant. Phorbol ester or calyculin A inhibition of thrombin-induced rises in platelet [Ca2+]i was attenuated by C6. Assays show that C6 either prolonged the generation, or retarded the metabolism of inositol trisphosphates. Previous studies indicate that protein kinase C (PKC) acts in a negative feedback manner by inhibiting phosphatidylinositol breakdown, accelerating inositol trisphosphate metabolism, and increasing Ca2+ pump activity. C6 may counter these PKC effects indirectly. The synthetic ceramides inhibited platelet aggregation weakly and had no effect on pleckstrin (p47) phosphorylation. Recently we reported that C2 but not C6 inhibits superoxide generation and store-regulated Ca2+ influx in neutrophils at similar concentrations. Cellular differences in ceramide metabolism or ceramide-sensitive enzymes and their substrates may account for the disparate results.

Blood Platelets↗
PubMed1996

Cytosolic phospholipase A2 (cPLA2) and lipid mediator release in the brain.

The Ca(2+)-sensitive 85 kDa cytosolic PLA2 (cPLA2) is a receptor-regulated enzyme that may initiate the cascade of events leading to the production of free fatty acids and lysophospholipids for subsequent conversion to eicosanoids and PAF. At least two early events are necessary for full activation of cPLA2: (1) increased concentration of cytosolic free Ca2+ promoting association of cPLA2 with its membrane phospholipid substrate and (2) phosphorylation by stimulated proline-directed kinases converting cPLA2 into an enzyme of enhanced catalytic efficiency. Moreover, pro-inflammatory cytokines, such as IL-1 and TNF may induce de novo synthesis of cPLA2 thus further potentiating the mobilization of arachidonic acid and subsequent production of eicosanoids and PAF. Increased levels of fatty acids and PLA2-derived products, including eicosanoids and PAF are amongst the hallmarks of cerebral ischemia and reperfusion, and thought to mediate pathophysiological alterations and cellular processes which may lead to cell injury and death. There is substantial evidence to indicate that cPLA2 is present in the brain and appears most abundant in astrocytes. Therefore, cPLA2 may be an important component in the cascade of events leading to acute and delayed destructive cellular processes in the brain and accordingly represents an attractive target for the development of novel therapies to prevent brain damage triggered by ischemic and inflammatory insults.

Animals↗
PubMed2005

Distribution and partition of heavy metals in surface and sub-surface sediments of Naples city port.

The aim of the study was to delineate the extent of heavy metal pollution in the marine sediments within the port of Naples. Total metal contents from twenty surface sediments were compared with those from a long sediment core representing the natural geochemical baseline. Enrichment factors were computed for each metal and for each site in order to assess the polluting metals and the degree of pollution at each site. Results revealed that heavy metal pollution is mainly localized in the port area devoted to shipbuilding activities and in the south-east sector, which is under the influence of petroleum refineries. Data from sequential extractions indicate that metals from anthropogenic sources are mainly Cd, Zn, Cr and Cu and are potentially more mobile than those inherited from geological parent material.

Arsenic↗
PubMed2005

Glyphosate adsorption in soils compared to herbicides replaced with the introduction of glyphosate resistant crops.

Use of glyphosate resistant crops was helpful in addressing observed increases in environmental contamination by herbicides. Glyphosate is a broad-spectrum herbicide, and its behaviour-as well as that of other herbicides-in soils is an important consideration for the overall environmental evaluation of genetically resistant crop introduction. However, few data have been published comparing glyphosate behaviour in soil to that of the herbicides that would be replaced by introduction of glyphosate resistant crops. This work compares glyphosate adsorption in soil with that of other herbicides frequently used in rape (trifluralin and metazachlor), sugarbeet (metamitron) and corn (sulcotrione). Herbicide adsorption was characterised in surface soils and in the complete soils profiles through kinetics and isotherms using batch equilibration methods. Pedological and molecular structure factors controlling the adsorption of all five herbicides were investigated. Glyphosate was the most strongly adsorbed herbicide, thus having the weakest potential for mobility in soils. Glyphosate adsorption was dependent on its ionisable structure in relation to soil pH, and on soil copper, amorphous iron and phosphate content. Trifluralin adsorption was almost equivalent to glyphosate adsorption, whereas metazachlor, metamitron and sulcotrione adsorption were lower. Trifluralin, metazachlor and metamitron adsorption increased with soil organic carbon content. Sulcotrione was the least adsorbed herbicide in alkaline soils, but its adsorption increased when pH decreased. Ranking the adsorption properties among the five herbicides, glyphosate and trifluralin have the lowest availability and mobility in soils, but the former has the broadest spectrum for weed control.

Adsorption↗
PubMed2026

Electron shuttles facilitate methane-dependent arsenate reduction in paddy soils.

Methane-dependent arsenate reduction (M-AsR) occurs widely in paddy soils and can substantially enhance arsenic mobilization, posing potential ecological risks. However, the role of electron shuttles in this process remains poorly understood. In this study, we investigated the influence of anthraquinone-2,6-disulfonate (AQDS) on M-AsR in paddy soils. Fourteen-day incubation showed that 1 mmol/L AQDS facilitated 50.88 % of arsenate reduction and 31.31 % of methane oxidation. Quantitative polymerase chain reaction analysis revealed that AQDS significantly increased the abundance of functional genes associated with arsenate reduction (arrA, arsC) and anaerobic methane oxidation (mcrA) (P < 0.05). Microbial community analysis revealed that AQDS addition enriched Cloacibacterium, Sphingorhabdus, and Methylocystis, while decreasing the relative abundance of Methylobacter and Methylomonas. These findings indicate that electron shuttles facilitate M-AsR by modulating functional microbial populations, providing valuable insights into arsenic biogeochemistry and the coupled cycling of methane and arsenic in paddy soils.

Methane↗
PubMed2006

Leachability of heavy metals and arsenic from slags of metal extraction industry at Angleur (eastern Belgium).

At Angleur (eastern Belgium), a 53,000 m3 dump site, related to former Zn extraction, contains high concentrations of heavy metals and arsenic associated with minerals such as arsenopyrite (FeAsS), franklinite (ZnFe2O4) and willemite (Zn2SiO4). Eight representative samples were investigated by means of a modified availability test, which pointed towards a considerable availability of Cd, Pb and Zn. In addition a detailed analysis of leaching behaviour as a function of pH was performed by means of a pH(stat) leaching test. The results of this test were supported by modelling predictions with MINTEQA2. pH(stat) titration results also allowed determination of the acid neutralising capacity, making it possible to predict heavy metal release upon acidification, assuming a worst-case scenario. On a short- to medium-long term (+/-100 years) a release of 900 mg/kg Zn has to be expected upon assumed natural acidification. However, a leaching test performed at the natural pH (i.e. pH 8 for the sample studied) indicates that heavy metal release is very limited and far below the European limit values for slag material on dumps category 1. Therefore, despite the elevated total heavy metal and As concentrations on the site, leaching is relatively low under present environmental conditions. Moreover, the slag material has a rather elevated pH (6.5-8) and no acid mine drainage is produced. Glass phases seem very important in controlling heavy metal mobility since potential reactive minerals that are locked up in a silicate matrix are protected against leaching.

Arsenic↗