Uptake and binding of cadmium and mercury to metallothionein in rat hepatocyte primary cultures

The administration of inorganic Cd and Hg in vivo has been shown to result in markedly different metal concentrations in rat liver. Primary cultures of rat hepatocytes were utilized to gain insight into the dispositional differences between these chemically similar metals. Hepatocyte monolayer cultures were exposed to several concentrations of Cd or Hg (3, 10 and 30μm) in serum-containing medium for 30min. The cells were then washed and incubated in fresh medium for the remainder of the experiment. Hepatocytes exposed to Cd accumulated significantly more metal than hepatocytes exposed to equimolar concentrations of Hg. In cells exposed to 3μm-Cd there was an initial loss of Cd from the hepatocytes when placed in fresh medium, followed by a gradual re-uptake of metal, concomitant with increased binding to metallothionein. In hepatocytes exposed to 3 and 10μm-Cd, 87 and 77% of the intracellular Cd was bound to metallothionein within 24h. Loss of Hg from hepatocytes pulsed with 30μm-Hg was also observed upon the addition of fresh medium and continued for the duration of the experiment. No time-dependent increase in Hg binding to metallothionein was observed. A maximum of about 10% of the intracellular Hg was found associated with metallothionein in hepatocytes exposed to 30μm-Hg. Studies utilizing [³⁵S]cysteine incorporation indicated significant increases in the amount of metallothionein synthesized in hepatocytes exposed to 3 and 10μm-Cd (300% of control value) and 30μm-Hg (150% of control value) 24h after metal pulsing. Time-course studies revealed a 6–12h lag in metallothionein synthesis, followed by a significant elevation in [³⁵S]cysteine incorporation into metallothionein between 12 and 24h. These studies suggest that (a) isolated hepatocytes differentiate between Cd and Hg and preferentially accumulate the former, and (b) Cd strongly stimulates the induction of, and preferentially binds to, metallothionein, whereas Hg induces weakly, and does not preferentially bind to, metallothionein.     

INCREASE IN SIZE AND CELL NUMBER OF LATERAL ROOT PRIMORDIA IN THE PRIMARY OF INTACT PLANTS AND IN EXCISED ROOTS OF PISUM SATIVUM AND VICIA FABA

Increase in cell number, and in anlage volume and length have been investigated during the development of lateral root primordia in roots of intact plants of Pisum sativum and Vicia faba and in excised roots of both species cultured in White's medium supplemented with 2% sucrose. With the exception of primordia in excised roots of Vicia, the general equation which best described increase in each aspect of primoridium growth measured against time was that for exponential growth. When the times necessary for cell number and primordium volume and length to double were determined at intervals over the period of development studied, however, they were found to vary. Similarly, estimates of the size of the proliferative fraction of cells at different times during anlage development indicated that this index of meristematic activity also fluctuated over the developmental period investigated, i.e., increase in cell number and in primordium volume and length do not occur in a truly exponential fashion as the primordia increase in size and cell number. One difference between anlage development in the roots of intact plants and in those grown in culture was that whereas the former primordia completed their development and emerged as lateral roots over the period of the investigation, the latter did not. Moreover, cell doubling time and anlage volume and length doubling times were longer, and the proliferation fraction of cells lower, over the whole period of, and at intervals during, primordium development in the excised roots compared with the results obtained for the roots of the corresponding intact plants.     

Anaerobic Oxidation of Acetylene by Estuarine Sediments and Enrichment Cultures

Acetylene disappeared from the gas phase of anaerobically incubated estuarine sediment slurries, and loss was accompanied by increased levels of carbon dioxide. Acetylene loss was inhibited by chloramphenicol, air, and autoclaving. Addition of ¹⁴C₂H₂ to slurries resulted in the formation of ¹⁴CO₂ and the transient appearance of ¹⁴C-soluble intermediates, of which acetate was a major component. Acetylene oxidation stimulated sulfate reduction; however, sulfate reduction was not required for the loss of C₂H₂ to occur. Enrichment cultures were obtained which grew anaerobically at the expense of C₂H₂.     

Equilibria of the anomeric and ring forms of ammonium 3-deoxy-d-manno-octulosonate in deuterium oxide

The tautomeric composition of a solution of ammonium 3-deoxy-d-manno-octulosonate (KDO, 1a) in D₂O at 28° was assessed by means of ¹³ C-F.t.-n.m.r. spectroscopy. The results revealed the presence of 6?0 and 11 % of the α and β anomers of the pyranose, and 20 and 9 % of the two furanoses, and suggested, but did not unequivocally prove, that the major furanose form is the α anomer. To facilitate interpretation of the spectral results for 1, ammonium 3,5-dideoxy-d-arabino(or ribo)-octulosonate (3a) was prepared by the reaction of 5-deoxy-d-erythro-pentose with sodium oxalacetate at pH 11. A chromatographically homogeneous, noncrystalline sample of 3 was obtained by lyophilization, and characterized as its (4-nitrophenyl)hydrazone (m.p. 162-163°). The ¹³C-n.m.r. spectrum of a solution of 3a in D₂O revealed it to be substantially all in the α-pyranose form. No signals were obtained for the possible 1,4-lactone of 3. As the 1,5-lactone and furanose forms are impossible for 3, it exhibited no signals analogous to those attributed to furanoid 1. On the basis of these results for 3, the two lactone forms of 1 were excluded from consideration, and the three pairs of ¹³C-n.m.r. signals observed at ≈45, 86, and 104 p.p.m. were assigned to the furanose forms of 1.     

Effect of Ca2+ and Mg2+ upon the reassociation byEscherichia coli of material released by ethylenediaminetetraacetate

Parameters involved in reconstitution of the outer membrane permeability described by Brunner, Caputo, and Treick [3] were examined. The most efficient reconstitution was obtained when divalent cations accompanied the addition of exogenous outer membrane material. Studies indicated that the effectiveness of Ca²⁺ or Mg²⁺ to promote reassociation of outer membrane material, and subsequent protection against actinomycin D, was dependent upon the strain ofEscherichia coli. More specifically, the data suggest that the effectiveness of the different divalent cations in promoting reassociation was determined by the relative amounts of F1 and F2 fractions released by ethylenediaminetetraacetate (EDTA). Reconstitution was shown by cell survival to be as high as 25% and dependent upon the total amount of material released from the outer membrane by EDTA. Between 50 and 80% of the bound material could be removed from the cells by subsequent EDTA treatment.     

Social organization of confined male collared lemmings (Dicrostonyx groenlandicus Traill)

This study describes and quantifies the social organization and agonistic behaviour of adult male collared lemmings (Dicrostonyx groenlandicus) in an indoor enclosure. Five groups of four lemmings were observed during separate 8-day tests. Experimental design permitted an increase in group size while density remained constant. When in groups of two, males established stable dominant-subordinate relationships and, when in groups of four, they formed stable non-linear dominance hierarchies. For either group size, frequency of agonistic behaviour declined over time. Habituation, formation of dominance relationships and spatio-temporal partitioning of space are suggested as possible explanations of this decline. Percentage of initial body weight lost during the experiments varied inversely with social rank. Possible causes of this weight loss are discussed. Social relationships in this study are discussed in light of field observations of male lemming home range distribution.