Cadmium,mercury, and lead effects on gill tissue of freshwater crayfishProcambarus clarkii (girard)

Intermolt adult crayfishP. clarkii were used for this work. After acclimatation to laboratory conditions crayfish were exposed to sublethal concentrations of cadmium, mercury, and lead for 96 h. Gills of control and exposed crayfish were removed and ATPase activity and oxygen uptake rate were determined. Structural damage of gill filaments was also observed. Gill tissue respiration rates were measured for individual crayfish using a Gilson differential respirometer. Lead causes a decrease of gill oxygen uptake, but neither cadmium nor mercury seems to affect it at the concentrations employed. Although all metals studied alter gill filament structure, lead damage is the most apparent. In the same way, significant differences in gill ATPase activity owing to metal exposure were only observed in lead treated crayfish.     

Mutual contact of murine erythroleukemia cells activates depolarizing cation channels, whereas contact with extracellular substrata activates hyperpolarizing Ca2+-dependent K+ channels

This study deals with the modulation of the plasma membrane potential (delta psi p) of murine erythroleukemia (MEL) cells by cell-substratum or cell-cell contact. delta psi p was determined by measuring the distribution of tetraphenylphosphonium (TPP+) across the plasma membrane; it appeared strongly, and inversely, influenced by the two types of cell contacts. Contact with the culture surface produced a delta psi p hyperpolarization directly proportional to average distance among the ideal centers of the cells on this surface (d) within the range 10-80 microns. A detailed mathematical analysis of the function delta psi p = f(d) is presented, as well as experiments involving the use of ionophores (valinomycin and A23187) and the conditioning of the culture surface. We concluded that the d-dependent hyperpolarization (dDH) was the result of a complex interplay between the activating properties of substratum on Ca2+-dependent K+ channels (KCa) and some substratum-adherent factors that are shed by MEL cells and antagonize KCa activation (substratum-attached cellular factors = SACF). By contrast, contact of the cells with each other, obtained by incubating MEL cells at d smaller than the average cell diameter (phi = 10 microns), produced a marked delta psi p depolarization. This intercellular contact-dependent depolarization (ICDD) was unaffected by valinomycin; it was abolished by substituting Na+ in the external medium with a nondiffusible cation (choline), which shows that ICDD was sustained by Na+ influxes, probably mediated by stretch-activated (s.a.) cation channels.     

HIV-1-specific B cell activation. A major constituent of spontaneous B cell activation during HIV-1 infection

B cell activation is a well known consequence of HIV-1 infection, and seropositive subjects show high numbers of spontaneously activated Ig-secreting cells in circulation. To better define the importance of the HIV-1-specific response in this phenomenon, we first studied whether in vitro spontaneous anti-HIV-1 antibody production was accompanied by reactivation of memory B lymphocytes. Unstimulated PBL from HIV-1-infected individuals with prior history of hepatitis B and/or EBV infection did not consistently show spontaneous in vitro synthesis of anti-hepatitis B core Ag or anti-EBV antibodies; in addition, PWM-induced synthesis of anti-hepatitis B virus and anti-EBV antibodies was decreased compared to HIV-1-seronegative subjects. Moreover, in comparing the frequencies of activated HIV-1-specific B cell precursors and activated Ig-secreting precursors in limiting dilution experiments, a sizable fraction (20 to 40%) of circulating cells spontaneously secreting Ig produced antibody against HIV-1 determinants. The ratio between the two frequencies fitted in very well with the amount of Ig removed from unstimulated culture supernatants after HIV-1-specific antibody absorption with solid-phase HIV-1. These findings indicate that B cell activation during HIV-1 infection is mainly oriented toward a specific response to HIV-1 determinants; the possible relevance of this phenomenon to lymphomagenesis in AIDS patients is discussed.     

Calcofluor- and lectin-binding exocellular polysaccharides of Azospirillum brasilense and Azospirillum lipoferum.

Extracellular polysaccharides synthesized by Azospirillum brasilense and A. lipoferum were shown on agar plates and liquid flocculating cultures. The six strains used in this work expressed a mucoid phenotype, yielding positive calcofluor fluorescence under UV light. The calcofluor-binding polysaccharides were distributed between the capsular and exopolysaccharide fractions, suggesting exocellular localization. No calcofluor fluorescence was observed in residual cells after separation of the capsular and exopolysaccharide fractions. Cellulose content was significantly higher in flocculating than in nonflocculating cultures. Failure to induce flocculation by addition of cellulose (100 mg/ml) to nonflocculating cultures, together with the sensitivity of flocs to cellulase digestion, suggested that cellulose is involved in maintenance of floc stability. Different A. brasilense and A. lipoferum strains bound to a wheat lectin (fluorescein isothiocyanate-wheat germ agglutinin), indicating the occurrence of specific sugar-bearing receptors for wheat germ agglutinin on the cell surface. The biochemical specificity of the reaction was shown by hapten inhibition with N-acetyl-D-glucosamine. All six strains failed to recognize fluorescein isothiocyanate-soybean seed lectin under our experimental conditions. We conclude that azospirilla produce exocellular polysaccharides with calcofluor- and lectin-binding properties.     

Gastric cytoprotection by pirenzepine is not mediated by catecholamines

The effects of pirenzepine (in a dose of 25.0 mg X kg-1) and atropine (2.5 mg X kg-1) were studied on the development of gastric ulceration produced by pylorus ligation, polymyxin B and absolute ethanol, as well as on the gastric secretory responses and plasma level of noradrenaline. It was found that: (1) pirenzepine significantly decreased the development of ulcer formation produced by pylorus ligation, polymyxin B and absolute ethanol without any antisecretory response; (2) atropine inhibited gastric acid secretion, but no effect was obtained on ulcus produced by pylorus ligation, polymyxin B and absolute ethanol; (3) the plasma level of noradrenaline could be decreased by atropine and pirenzepine, although the difference did not reach statistical significance. It has been concluded that catecholamines are not involved in the gastric cytoprotective mechanism of pirenzepine.     

Humoral immune response to equine chorionic gonadotropin in ewes: association with major histocompatibility complex and interference with subsequent fertility.

In dairy ewes, the use of eCG as a convenient hormone for the induction of ovulation is necessary for out-of-season breeding and artificial insemination (AI). In this report we show the presence of anti-eCG antibodies in plasma of treated ewes. The major histocompatibility complex (MHC) was involved in the individual variability of the humoral immune responses to eCG. We found significant associations between the anti-eCG response phenotype and some MHC class II alleles. The low immune response phenotype was associated with one MHC class II allele only in Lacaune ewes, and the high immune response phenotype was associated with one MHC class II allele both in Manech and in Lacaune ewes. In herds, the impact of residual anti-eCG antibodies on subsequent fertility after AI seems minimal because of an indirect elimination of high-responder ewes from AI breeding. Therefore, the true magnitude of the association between residual anti-eCG antibody concentration and fertility has been underestimated. An additional experiment without any high-responder female elimination showed a significant correlation between high residual antibody concentrations and lower lambing rate after AI at a fixed time, possibly because of a delayed preovulatory LH surge. The results suggest that anti-eCG antibody concentration is one risk factor for infertility after AI.     

News & Notes: Correlation of Resistance to the Alkaloid Lycorine with the Degree of Suppressiveness in Petite Mutants of Saccharomyces cerevisiae

In previous papers (Del Giudice et al. Curr Genet 8:493–497, 1984; Massardo et al. Curr Genet 17:455–457, 1985) we have shown that strains of Saccharomyces cerevisiae that are devoid of mitochondrial DNA (rho ^o) are resistant to the alkaloid lycorine isolated from Amaryllis plants, whereas strains containing mitochondrial DNA (rho ⁻ , mit ⁻ , or rho ⁺ ) are sensitive to this drug. In addition, we were able to show that the so-called hypersuppressive petites, whose mitochondrial genomes consist of short regions of DNA containing an ori sequence, show intermediate resistance. In this paper, we demonstrate that the degree of suppressiveness of a rho ⁻ mutant correlates with the degree of resistance to lycorine. Received: 20 September 1996 / Accepted: 10 January 1997     

Phylogenetic relationships among Malagasy lemurs as revealed by mitochondrial DNA sequence analysis

Systematics and evolution of Malagasy lemurs has been analyzed using morphological characters, fossil evidence, ecological/ethological data, and chromosomal banding patterns. Recent developments in DNA technology have provided evolutionary biologists with additional and powerful tools for making phylogenetic inference. In the last years several studies concerning highly repeated DNA sequences (hrDNA) provided new insights about the systematic relationships among the different species of Lemuridae and Cheirogaleidae. Here, a reconstruction of molecular phylogeny of extant Malagasy lemurs based on the comparison of cytochrome-b mitochondrial DNA sequences is presented. With the Polymerase Chain Reaction (PCR) and direct sequencing of amplified DNA fragments, both the phylogenetic range and resolving power of comparative analysis can be extended. These techniques allow to gather sequence data useful to evaluate the pattern of molecular evolution offering opportunities for phylogenetic purposes. A 290-bp fragment of cytochrome-b gene has been amplified and sequenced from the following species:Tupaia glis, Galago alleni, Daubentonia madagascariensis, Indri indri, Varecia variegata, Eulemur fulvus, Eulemur coronatus, Eulemur rubriventer, Eulemur mongoz, Eulemur macaco, Lemur catta, andHapalemur griseus griseus. The phylogenetic trees obtained show the relationships among the Eulemur species and confirm the karyological and hrDNA results of a separated clade forL. catta/Hapalemur. The separation ofVarecia variegata from the other genus of the family Lemuridae is discussed.     

Studies of genetic effects in the D7 strain of Saccharomyces cerevisiae under different conditions of pH

The genetic effects of variation in pH in culture media and in suspension tests were examined in a diploid strain (D7) of the yeast, Saccharomyces cerevisiae. Deviation from the normal pH of 6.24 in the liquid culture medium, has a significant effect on cellular growth and on mitotic gene conversion at the trp5 locus. Frequencies of reversion at the ilv I-92 locus and of mitotic crossing-over at the ade2 locus are not significantly influenced. Suspension tests, performed using phosphate buffer (pH 5.8), strongly confirm the original results. Our data suggest that the increase in mitotic gene conversion under various conditions of pH is due to a specific effect of pH itself on the cells of S. cerevisiae. In fact, increases were obtained using the same pH in both cellular growth and non-growth conditions. The maximum effect detected with both procedures was obtained at pH 5.8; in the growth test, at this pH, gene conversion frequency appeared to be most pronounced, being about 10 times higher than that of the control. These results suggest that pH exerts its specific action both on growing and non-growing yeast cells, and the difference in induction of genetic effect between these two conditions is probably due to a time factor.