The interaction of gadolinium complexes with isolated rat hepatocytes

The lanthanide metal, gadolinium, is currently used in contrast agents for magnetic resonance imaging. We have performed a study of the interaction between isolated rat hepatocytes and ¹⁵³Gd complexed to diethylene-triamine pentaacetic acid (DTPA) or to DTPA-albumin conjugates. The study shows that isolated hepatocytes are able to take up both types of ¹⁵³Gd complexes. The ¹⁵³Gd-DTPA-albumin complexes are apparently taken up by pinocytosis, and possibly receptor-mediated endocytosis and/or adsorptive endocytosis, whereas the uptake mechanism of ¹⁵³Gd-DTPA is unknown. The ¹⁵³Gd-DTPA-albumin complexes, but not the ¹⁵³Gd-DTPA complex, are degraded by the cell. The degradation is inhibited by ammonium chloride. Gadolinium is slowly released back to the medium after loading of the cells with both complex types. In the experiments reported here no evidence of any adverse effects on the hepatocyte resulting from exposure to the ¹⁵³Gd-complexes were observed.     

Physical map of the bacteriophage L (Salmonella typhimurium)

Abstract A circular restriction map of the genome of the phage L ( Salmonella typhimurium ) has been constructed with five restriction endonucleases, Eca I, Eco RI, Bam HI, Bgl I, and Pst I. The Eco RI fragments of phage-L DNA were cloned into pACYC184, and the resulting recombinant plasmids pL1, pL2,…,pL7 were introduced into Salmonella typhimurium . The genes present on the fragments cloned were identified by the marker rescue experiments with the L-phage amber mutants. A physical gene map of the L genome obtained in this way was compared with that of P22.     

Metal-directed affinity labeling of zinc(II), cobalt(II) and cadmium(II) horse liver alcohol dehydrogenases

The active site metal in horse liver alcohol dehydrogenase has been studied by metal-directed affinity labeling of the native zinc(II) enzyme and that substituted with cobalt(II) or cadmium(II). Reversible binding of bromoimidazolyl propionic acid to the cobalt enzyme blueshifts the visible absorption band originating from the catalytic cobalt atom at 655 to 630 nm. Binding of imidazole to the cobalt(II) enzyme redshifts the 655 nm band to 667 nm. Addition of bromoimidazolyl propionic acid blueshifts this 667 nm band back to 630 nm. This proves direct binding of the label to the active site metal in competition with imidazole. The affinity of the label for the reversible binding site in the three enzymes follows the order Zn ? Cd ? Co. After reversible complex formation, bromoimidazolyl propionic acid alkylates cysteine-46, one of the protein ligands to the active site metal. The nucleophilic reactivity of this metal-mercaptide bond in each reversible complex follows the order Co ? Zn ? Cd.     

Effects of lead and cadmium on chemical composition and total water content of the pupal parasitoid, Pimpla turionellae

The parasitoid Pimpla turionellae L. (Hymenoptera, Ichneumonidae) was fed on Cd, Pb and Cd+Pb-contaminated food (33g Cd, 82g Pb and 33g Cd+82g Pb per gram food fresh weight, respectively). Significant decrease in the total lipid and protein content was found along with an increase in the water content particularly in Cd-contaminated parasitoids.     

Why the evolution of resistance to anthropogenic toxins normally involves major gene changes: the limits to natural selection

Standard population genetic theory suggests that adaptation should normally be achieved by the spread of many genes each of small effect (polygenes), and that adaptation by major genes should be unusual. Such models depend on consideration of the rates of acquisition of adaptation. In practice, adaptation to pollutants and anthropogenic toxins has most frequently been achieved by the spread of major genes. A simple model is developed to explain this discrepancy, in which the determining factor is not the rate of spread, but the maximum response achievable under the two contrasting models of polygenic or major gene inheritance. In the short term, for a given mean and genetic variance, characters in which the additive genetic variance is produced by the segregation of many genes of small effect at intermediate gene frequencies are unable to produce as large a response to directional selection as characters in which the variance is caused by genes of large effect at low frequency. If the target for selection is a long way from the mean prior to selection (as it may well be for adaptation to novel anthropogenic stresses) then adaptation can only be achieved by species possessing major genes. The model is discussed with reference to the example of heavy metal tolerance in plants.     

Heavy metals (Cu and Zn) in recent sediments of Llangorse Lake,Wales: non-ferrous smelting,Napoleon and the price of wheat — a palaeoecological study

Elevated concentrations of Cu and Zn have been found in the upper part of three sediment cores collected from Llangorse Lake, in south Wales. Palaeomagnetic evidence from one of the cores and ²¹⁰Pb analysis of another, suggests that the increase in sediment Cu and Zn concentrations began during the eighteenth century. A sharp increase in the concentrations of these metals in the sediment profile appears to have occurred during the latter part of the eighteenth century and these concentrations remained high until the mid to late nineteenth century.The absence of known ore deposits and industry around the lake suggests that the lake and catchment soils were increasingly contaminated by long-range aerial transport of emissions from the expanding activity of Cu and Zn smelters located some 80 km upwind in the Swansea area during the Industrial Revolution. Evidence from agricultural crop returns indicates a significant increase in the amount of land devoted to tillage in the catchment, particularly to cereal production, during the late eighteenth and the first half of the nineteenth century which included the Napoleonic Wars. This agricultural shift appears to coincide with increased concentrations of Cu and Zn in the lake sediments. It is suggested that newly ploughed soils, contaminated with metals for many years by long-range aerial transport from the Swansea area, eroded, and were carried into the lake by catchment run-off and added to the sediment burden of Cu and Zn. A subsequent decline of Cu and Zn emissions due to the collapse of the non-ferrous smelting industry and reduced soil erosion because of a 50% reduction of tillage due to an agricultural depression in the second half of the 19th century may explain the fall in Cu and Zn concentrations in the upper part of the sediment profile. The most recent sediments (20th century) show the increase in heavy metals characteristic of many lakes around the world.     

Measuring maximum root growth instead of longest root elongation in metal tolerance tests for grasses (Agrostis capillaris,Agrostis delicatula and Agrostis castellana)

Longest root elongation diminished significantly in the three species tested from 6 mm d^-1 to 3 mm d^-1 in 3 weeks. During this period S.D. increased considerably (from 49% to 112%, A. castellana), and accounted on the average for 68% (A. capillaris) till 94% (A. castellana) of the mean. Maximum root growth stabilized at 6 mm d^-1 and showed less variation in the measurements (S.D. 52% of the mean). Growth of the originally longest root approaches zero in all three species, in accordance with the natural cease of growth of roots in grasses fascicular root system. Measuring maximum root growth instead of longest root elongation is proposed for testing metal tolerance of grasses in sequential experiments.     

Root-microbial effects on plant iron uptake from siderophores and phytosiderophores

Collaborative experiments were conducted to determine whether microbial populations associated with plant roots may artifactually affect the rates of Fe uptake and translocation from microbial siderophores and phytosiderophores. Results showed nonaxenic maize to have 2 to 34-fold higher Fe-uptake rates than axenically grown plants when supplied with 1 μM Fe as either the microbial siderophore, ferrioxamine B (FOB), or the barley phytosiderophore, epi-hydroxymugineic acid (HMA). In experiments with nonsterile plants, inoculation of maize or oat seedlings with soil microorganisms and amendment of the hydroponic nutrient solutions with sucrose resulted in an 8-fold increase in FOB-mediated Fe-uptake rates by Fe-stressed maize and a 150-fold increase in FOB iron uptake rates by Fe-stressed oat, but had no effect on iron uptake by Fe-sufficient plants. Conversely, Fe-stressed maize and oat plants supplied with HMA showed decreased uptake and translocation in response to microbial inoculation and sucrose amendment. The ability of root-associated microorganisms to affect Fe-uptake rates from siderophores and phytosiderophores, even in short-term uptake experiments, indicates that microorganisms can be an unpredictable confounding factor in experiments examining mechanisms for utilization of microbial siderophores or phytosiderophores under nonsterile conditions.     

Developmental variation in copper,zinc and metallothionein mRNA in brindled mutant and nutritionally copper deficient mice

The concentrations of copper, zinc and metallothionein-I (MT-I) mRNA were determined in the liver, kidney and brain of the brindled mutant mouse from birth until the time of death. Despite accumulation of copper in the kidney of the mutant, MT-I mRNA concentrations were normal. There was no difference between the MT-I mRNA in the brain of mutant and normal in the first 10 days of life, but after day 10 metallothionein mRNA levels were increased in the mutant. The concentration of copper was very low in the liver of the mutant, and on day 6 after birth the metallothionein mRNA was also reduced by about 50%. This reduction was not seen in copper-deficient 6-day-old pups, despite very low hepatic copper levels. This suggests that the lower hepatic MT-I mRNA in the day 6 brindled mouse was not simply due to the reduction in hepatic copper and also that hepatic copper is not regulating metallothionein gene expression the liver of neonatal mice. After day 12 hepatic MT-I mRNA levels were elevated in mutant and in copper deficient mice, both of which die at 14 to 16 days. These increases and the increase in brain MT-I mRNA in older mutant mice are likely to be caused by stress. Overall the results support the conclusions that the brindled mutation does not cause a constitutive activation of the metallothionein genes, and that the differences in metallothionein mRNA between mutant and normal are most probably secondary consequences of the mutation.