Short-term Exposure Experiments Research Articles

A mechanistic model for the uptake of waterborne strontium in the common carp (Cyprinus carpio L.).

The release of radioactive strontium to the environment is of concern due to the strong accumulation of this calcium resembling element in the bone and other tissues. To predict the effects of changes in environmental conditions on the uptake of Sr2+ and Ca2+ by freshwater fish, a Michaelis-Menten type model is introduced that accounts for the effects of chemical speciation, hydrogen ion activity, and metal ion competition. The uptake kinetics were characterized in vivo from short-term exposure experiments using the common carp (Cyprinus carpio) as the model organism. Fish were exposed to a wide range of waterborne Sr2+ (0.2-10,000 microM) and Ca2+ (10-10,000 microM) concentrations and water pH (5.0-8.5). Strontium uptake by the whole body of fish increased with increasing Sr2+ activity, displaying saturation kinetics, but decreased significantly with increasing Ca2+ and H+ activities in the water. Likewise, calcium uptake by the fish decreased with increasing Sr2+ and H+ activities in the water. The model fitted to the pooled data explains 97.5% of the variation in Sr2+ uptake and 86% in Ca2+ uptake over the wide range of exposure conditions and reveals that Sr2+ and Ca2+ inhibit each other completely competitively, while H+ inhibits the uptake of both metal ions in a partially noncompetitive way. This model can be used as a mechanistic tool to predict the uptake of these metals in carp under variable conditions.

Effects of Cu2+, Ni2+, Pb2+, Zn2+ and pentachlorophenol on photosynthesis and motility in Chlamydomonas reinhardtii in short-term exposure experiments

BackgroundHeavy metals, especially copper, nickel, lead and zinc, have adverse effects on terrestrial and in aquatic environments. However, their impact can vary depending on the nature of organisms. Taking into account the ability of heavy metals to accumulate in sediments, extended knowledge of their effects on aquatic biota is needed. In this context the use of model organisms (often unicellular), which allows for rapid assessment of pollutants in freshwater, can be of advantage. Pentachlorophenol has been extensively used for decades as a bleaching agent by pulp- and paper industry. Pentachlorophenol tends to accumulate in the nature. We aim to determine if photosynthesis and motility can be used as sensitive physiological parameters in toxicological studies of Chlamydomonas reinhardtii, a motile green unicellular alga. It is discussed if photosynthesis and motility can be used as sensitive physiological parameters in toxicological studies.ResultsThe concentrations studied ranged from 0.1 to 2.0 mg l-1 for copper, nickel, lead and zinc, and from 0.1 to 10.0 mg l-1 for pentachlorophenol. Exposure time was set to 24 h. Copper and pentachlorophenol turned out to be especially toxic for photosynthetic efficiency (PE) in C. reinhardtii.ConclusionCopper and pentachlorophenol turned out to be especially toxic for PE in C. reinhardtii. Zinc has been concluded to be moderately toxic while nickel and lead had stimulatory effects on the PE. Because of high variance, motility was not considered a reliable physiological parameter when assessing toxicity of the substances using C. reinhardtii.

MRP3, an organic anion transporter able to transport anti-cancer drugs.

The human multidrug-resistance protein (MRP) gene family contains at least six members: MRP1, encoding the multidrug-resistance protein; MRP2 or cMOAT, encoding the canalicular multispecific organic anion transporter; and four homologs, called MRP3, MRP4, MRP5, and MRP6. In this report, we characterize MRP3, the closest homolog of MRP1. Cell lines were retrovirally transduced with MRP3 cDNA, and new monoclonal antibodies specific for MRP3 were generated. We show that MRP3 is an organic anion and multidrug transporter, like the GS-X pumps MRP1 and MRP2. In Madin-Darby canine kidney II cells, MRP3 routes to the basolateral membrane and mediates transport of the organic anion S-(2,4-dinitrophenyl-)glutathione toward the basolateral side of the monolayer. In ovarian carcinoma cells (2008), expression of MRP3 results in low-level resistance to the epipodophyllotoxins etoposide and teniposide. In short-term drug exposure experiments, MRP3 also confers high-level resistance to methotrexate. Neither 2008 cells nor Madin-Darby canine kidney II cells overexpressing MRP3 showed an increase in glutathione export or a decrease in the level of intracellular glutathione, in contrast to cells overexpressing MRP1 or MRP2. We discuss the possible function of MRP3 in (hepatic) physiology and its potential contribution to drug resistance of cancer cells.

Measurement of crustacean hyperglycaemic hormone levels in the edible crab Cancer pagurus during emersion stress

The effects of emersion stress upon circulating hyperglycaemic hormone (CHH) levels in the edible crab Cancer pagurus were investigated using a highly specific and sensitive radioimmunoassay, with an antiserum directed against HPLC-purified C. pagurus CHH. Emersion resulted in hyperglycaemia and immediate hypoxia, as shown by rapid hyperlactaemia. CHH levels increased dramatically during the first hour of emersion, from almost undetectable levels to around 17 pmol l-1, thereafter increasing to around 30 pmol l-1 after 4 h of emersion. Short-term air exposure experiments demonstrated that significant increases in CHH levels (up to 3.5 pmol l-1) could be detected during the first 15 min of emersion. Although CHH appears to be fairly stable in haemolymph in vitro, injected CHH was cleared extremely rapidly from the haemolymph in vivo. The results suggest that emersion results in rapid, massive and prolonged exocytosis of CHH from the sinus gland. The sensitivity of the assay and the utility of this crab model may be useful in further studies to elucidate the control of CHH release in crustaceans.

Importance of ammonium and nitrate to the performance of herb-layer species from deciduous forests in Southern Sweden

Experiments were performed on the effect on growth and uptake of nitrogen given as NH 4 and/or NO 3 in a nutrient solution (pH 4.2) of a composition similar to that of the rhizosphere soil solution of an acidic beech forest but lacking Al. Seven treatments (0.2 and 0.4 mM NH 4 and NO 3, respectively, and 0.1 + 0.1, 0.2 + 0.2, 0.4 + 0.4 mM of NH 4 + NO 3) were used in a flowing solution culture without recirculation. The seven species tested have ecological distributions which range from very acid soils with low nutrient levels and nitrogen mainly present as NH 4, to less acidic and nitrifying soils. In the solution experiment, species occurring in very acidic soils had small preferences for nitrogen form or combination ( Deschampsia flexuosa, Carex pilulifera, Milium effusum), while Aegopodium podagraria of less acidic soils preferred NO 3. The other three species, Poa nemoralis, Bromus benekenii and Carex sylvatica, grew best in a mixed solution. Results of a short-term (2–24 hr) exposure experiment showed that all species had a higher nitrogen uptake from NH 4 in the solo and mixed solutions. Total N uptake was, however, similar for the solo NH 4 and mixed solutions for all species except D. flexuosa and C. pilulifera, which had the highest N uptake with solo NH 4. It was concluded that none of the species studied grew best when NH 4 was supplied as the sole N source. This may restrict the distribution of species in very acid soils, where nitrification may be lacking.

On the role of blood proteins for uptake, distribution, and clearance of waterborne lipophilic xenobiotics by fish: A linear system analysis

Pharmacokinetic and toxicokinetic system parameters in fish, like gill uptake and elimination efficiencies and mean body residence times of waterborne nonmetabolizing organic xenobiotics, are defined within the framework of linear input-output response theory. Quantitative estimates of these parameters derive from combining (i) a refined flow-limited approach of the countercurrent gill model with (ii) available correlation data of the steady state bioconcentration factor (BCF s) as well as (iii) the blood/water partition coefficient (β) with the octanol/water partition coefficient (K ow) of the chemical compound. Predictions from the model are compared to empirical results on short and long term exposure experiments with the rainbow trout ( Oncorhynchus mykiss).

In vitro activity of the benzotriazene dioxide SR 4233 against human tumour colony-forming units

SR 4233 (3-amino-1,2,4-benzotriazine 1,4-dioxide) is a novel bioreductive agent selectively toxic to hypoxic cells. It is active as a radiation sensitiser in vitro. Using a human tumour cloning system we have studied the effects of SR 4233 against freshly explanted human tumour specimens under hypoxic and non-hypoxic culture conditions. For hypoxic conditions, final concentrations of SR 4233 of 10.0–500 μmol/l were used in short-term (1 h) exposure experiments. Final concentrations in non-hypoxic experiments ranged from 10 to 1350 μmol/l. 25 tumour specimens were tested under each culture condition. Of those, 14 (56%) were evaluable. The most common tumour types recruited included ovarian, non-small cell lung, and breast cancer. A moderate concentration-dependent increase in the frequency of inhibited tumour specimens under non-hypoxic conditions was observed with zero out of 10 sensitive specimens at 10 μmol/l as compared with five out of 14 (36%) sensitive specimens at 500 μmol/l ( P < 0.02). However, when hypoxic conditions were used SR 4233 had a profound antitumour activity, (two out of 14 specimens sensitive at 10 μmol/l compared with 10 out of 10 specimens sensitive at 500 μmol/l, P < 0.00005). We conclude that SR 4233 is active against tumour colony-forming units in vitro and that its antitumour activity is greatly increased against hypoxic tumour cells.

Effects of long- and short-term exposure to carbaryl on survival, growth and reproduction of Daphnia ambigua

In laboratory experiments a cladoceran, Daphnia ambigua, was exposed for six instars to the insecticide carbaryl at five different concentrations (1, 2, 3, 4, 5 μg litre −1) or received short-term (10-h) exposure to 5 μg carbaryl litre −1 at different life stages of the animal. In the long-term exposure experiments carbaryl at 1 μg litre −1 did not have any detectable effects on the animals, whereas 2 μg litre −1 reduced the survival, growth and reproduction of the animals, and higher concentrations killed all the animals examined before they grew to the fifth instar. These results indicate that the range of sublethal concentrations of carbaryl for D. ambigua is narrow. In the short-term exposure experiments the animals did not suffer any damage when they were exposed to the chemical during the egg stage. However, their growth and egg production were reduced when the short-term exposure was conducted during the life stages from the final embryo stage to the third instar. The effect was most marked when the animals were treated during the first instar, indicating that this is the stage when the animals are most sensitive to the chemical.

The effect of iron source on formation and persistence of root iron pools in cereals

Five chelated iron sources have been applied to barley and maize to investigate the effect of differing chemical form on the formation and persistence of root apoplastic Fe pools. Short-term Fe exposure (barley) experiments indicated that the charged state of the Fe complex was the most important factor regulating the initial formation and magnitude of the apoplastic pool. Longer term experiments (maize), incorporating a period of Fe deprivation, produced more complex results. Differences in plant growth during the experiment produced changes in the magnitude of the root Fe pool; these interacted with the chemical form of the applied Fe to regulate the release, utilisation and hence the ultimate size of the apoplastic pool produced by each Fe source. It is concluded that such experiments are poor indicators of the potential performance of novel chelated Fe sources.

SO2-Induced changes in the polyribosomal profiles of the gametophyte of the moss tortula ruralis

Aqueous SO2 (0.5-2.0 mM), in short-term exposure experiments (30-120 min.), causes a rapid loss of integrity of the polyribosomes in the moss Tortula ruralis. This effect is concentration- and exposure time-dependent and appears to be unattributable to an SO2-induced pH change.

Effects of sublethal concentrations of mercuric chloride on ammonium-limitedSkeletonema costatum

The effect of sublethal additions of mercuric chloride on the marine diatomSkeletonema costatum (Grev.) Cleve grown in NH4-limited chemostats and batch cultures was assessed. In short-term Hg exposure experiments (up to 5 h), the effect of Hg on ammonium uptake rates was studied by simulatneously perturbing the culture with 5 μM NH4 Cl and Hg concentrations ranging from 0.04 to 5.52 nM HgCl2. The threshold of Hg toxicity occurred between 1.8 and 3.7 nM, based on a decrease in ammonium uptake rates. When the NH4-limited culture was starved of ammonium for 30 h, the threshold of Hg toxicity decreased about an order of magnitude to 0.2 nM. In long-term Hg exposure experiments (679.5 h), NH4-limited continuous cultures were semi-continuously exposed to 0.37 and 3.68 nM HgCl2. After 4 days, the cell density in the Hg-treated chemostats began to drastically decline. After about 16 days these populations recovered, even though Hg additions continued. At the end of the experiment (26 days), cell densities had reached the levels observed at the beginning of the experiment. The reason for the recovery is unknown, but several possibilities are discussed. Ammonium uptake rates determined during the time-course of this long-term Hg exposure, indicated that these NH4-limited cultures exhibited a significant loss in their ability to take up ammonium at low concentrations (e.g. 1 μM). Thus, mercury pollution may seriously decrease the ability of a species to utilize the limiting nutrient during periods of seasonal nutrient limitation.

Site of inhibitory action of isoniazid in the synthesis of mycolic acids in Mycobacterium tuberculosis

The cellular mycolate synthetase activity of Mycobacterium tuberculosis H37Ra was previously shown to be very sensitive to isoniazid (Wang, L., and K. Takayama. 1972. Antimicrob. Agents Chemother. 2: 438-441). We have now examined the question of how isoniazid inhibits the synthesis of mycolic acids. The saponifiable 14-C-labeled lipids of control and isoniazid-treated cells (1.0 mug/ml, 60 min) were compared on a Sephadex LH-20 column, and it appeared that the synthesis of the intermediate-sized fatty acids was partially inhibited. These fatty acids were fractionated as their methyl esters by Sephadex LH-20 column chromatograp-y and gas-liquid (6% Dexsil) chromatography. Mass sectral analysis of the fractionated lipids revealed several series of fatty acids: fraction II, C39-C56; fraction III, C27-C40. The long-chain fatty acids in three kinds of isoniazid-treated cells were examined: (a) long-term exposure (48 hr, 0.5 mug/ml), (b) short-term exposure (60 min, 1.0 mug/ml), and (c) variable exposure at low concentration (0-90 min, 0.2 mug/ml). Both long- and short-term exposure experiments showed that isoniazid inhibited the synthesis of saturated fatty acids greater than C26 and of unsaturated fatty acids greater than C24. The variable-exposure experiment at low isoniazid concentration showed that the syntheses of mycolic acids and long-chain fatty acid fractions II and III were inhibited to the same extent. These fatty acids may thus be precursors of mycolic acids.

Bacterial contamination of organic dusts: effects on pulmonary cell reactions.

The influence of water extracts from different organic dusts on the number of free lung cells was studied in short-term exposure experiments. A large increase in the number of leukocytes was found 24 hours after exposure to extracts from cotton and hay. The number of macrophages was not affected. The increase was greater when the dusts were incubated at 37 C and 100% relative humidity prior to the preparation of the extract. This procedure caused an increase in the number of bacteria. When different bacterial species were studied endotoxin-producing strains were found to cause the largest effect.