Lead effect on the oxidation resistance of erythrocyte membrane in rat triton-induced hyperlipidemia

The anemia observed in severe chronic lead poisoning is in part attributable to alterations in the erythrocyte physicochemical properties. Since they are partly related to the membrane lipid composition, the aim of the present study was to determine the effects of a triton-induced hyperlipidemia on the resistance to oxidation of erythrocyte membranes in lead-treated Wistar rats. Our results showed that triton administration to lead-treated rats induced an increase in erythrocyte choline phospholipid levels together with a significant decrease in the erythrocyte membrane lipid resistance to oxidation. These results led us to suggest that anemia in lead poisoning is linked to interactions between lead present in the membrane and plasma phospholipids. Their increase in rat hyperlipidemia induced by triton resulted in a decrease in the membrane resistance to oxidation and finally in an erythrocyte fragility leading to their destruction.     

Topography of the E site on the Escherichia coli ribosome.

Three photoreactive tRNA probes have been utilized in order to identify ribosomal components that are in contact with the aminoacyl acceptor end and the anticodon loop of tRNA bound to the E site of Escherichia coli ribosomes. Two of the probes were derivatives of E. coli tRNA(Phe) in which adenosines at positions 73 and 76 were replaced by 2-azidoadenosine. The third probe was derived from yeast tRNA(Phe) by substituting wyosine at position 37 with 2-azidoadenosine. Despite the modifications, all of the photoreactive tRNA species were able to bind to the E site of E. coli ribosomes programmed with poly(A) and, upon irradiation, formed covalent adducts with the ribosomal subunits. The tRNA(Phe) probes modified at or near the 3' terminus exclusively labeled protein L33 in the 50S subunit. The tRNA(Phe) derivative containing 2-azidoadenosine within the anticodon loop became cross-linked to protein S11 as well as to a segment of the 16S rRNA encompassing the 3'-terminal 30 nucleotides. We have located the two extremities of the E site-bound tRNA on the ribosomal subunits according to the positions of L33, S11 and the 3' end of 16S rRNA defined by immune electron microscopy. Our results demonstrate conclusively that the E site is topographically distinct from either the P site or the A site, and that it is located alongside the P site as expected for the tRNA exit site.     

Occurrence ofBacillus popilliae and two nematode pathogens in populations ofAmphimallon solstitialis (Col.: Scarabaeidae) near darmstadt,Germany

Populations of the June beetle,Amphimallon solstitialis (Coleoptera: Scarabaeidae), were sampled from grasslands near Darmstadt, Germany, and found to be infected by a number of diseases and parasitic nematodes. Several milky diseased larvac were found, andBacillus popilliae type A 1 isolated as the causative agent. The bacterium readily infected healthy larvae ofA. solstitialis when administeredper os in the laboratory, but was not infective to larvae ofMelolontha hippocastani by this route. A large mermithid nematode was found parasitising 10% of theA. solstitialis larvae at one site andHeterorhabditis bacteriophora was found infecting larvae at the other.

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Résumé Des populations deAmphimallon solstitialis (Col.: Scarabaeidae) ont été échantillonnées dans deux prairies distinctes près de Darmstadt (Allemagne) et se sont révélées infestées par des maladies et des nématodes parasites. Plusieurs larves dans chaque site étaient infectées par la maladie laiteuse etBacillus popillae, type A1 a été isolé comme étant l'agent responsable. La bactérie infeste facilement des larves saines deA. solstitialis quand elle est administrée par voie orale au laboratoire mais n'a pas d'effet infectieux pour les larves deMelolontha hippocastani par cette même voie. Un grand nématode mermithide a été trouvé parasite de 10% des larves deA. solstitialis sur un seul site, mais comme seuls les jeunes ont été trouvés, la détermination à l'espèce n'a pu être faite.Heterorhabditis bacteriophora était responsable de l'infection de 1,5% des larves sur seulement un site. Plusieurs larves deA. solstitialis présentaient une couleur ambrée, identique à celle trouvée sur le scarabéeCostelytra zealandica infecté parSerratia spp., et ne se nourrissaient pas de carotte au laboratoire. Les bactéries isolées à partir de ces larves ne provoquent aucun effet visible quand elles sont données en nourriture à des larves saines.

     

Different internal metabolites trigger the induction of glycolytic gene expression in Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, the sugar-induced expression of various genes coding for glycolytic enzymes is triggered by increases in the concentrations of different internal metabolites. Here, we show that the induction of the glycolytic isoenzyme enolase 2 is strictly dependent on the abilities of different mutant strains to increase the level of glucose-6-phosphate after the addition of sugars. In contrast, the induction of alcohol dehydrogenase I is dependent on increasing concentrations of metabolites in the late stages of glycolysis.     

Separate Determination of the Electrical Properties of the Tonoplast and the Plasmalemma of the Giant-Celled Alga Valonia utricularis: Vacuolar Perfusion of Turgescent Cells with Nystatin and Other Agents

In the giant-celled marine algae Valonia utricularis the turgor-sensing mechanism of the plasmalemma and the role of the tonoplast in turgor regulation is unknown because of the lack of solid data about the individual electrical properties of the plasmalemma and the vacuolar membrane. For this reason, a vacuolar perfusion technique was developed that allowed controlled manipulation of the vacuolar sap under turgescent conditions (up to about 0.3 MPa). Charge-pulse relaxation studies on vacuolarly perfused cells at different turgor pressure values showed that the area-specific resistance of the total membrane barrier (tonoplast and plasmalemma) exhibited a similar dependence on turgor pressure as reported in the literature for nonperfused cells: the resistance assumed a minimum value at the physiological turgor pressure of about 0.1 MPa. The agreement of the data suggested that the perfusion process did not alter the transport properties of the membrane barrier. Addition of 16 μm of the H⁺-carrier FCCP (carbonylcyanide p-trifluoromethoxyphenyhydrazone) to the perfusion solution resulted in a drop of the total membrane potential from +4 mV to −22 mV and in an increase of the area-specific membrane resistance from 6.8 × 10⁻² to 40.6 × 10⁻²Ωm². The time constants of the two exponentials of the charge pulse relaxation spectrum increased significantly. These results are inconsistent with the assumption of a high-conductance state of the tonoplast (R. Lainson and C.P. Field, J. Membrane Biol. 29:81–94, 1976). Depending on the site of addition, the pore-forming antibiotics nystatin and amphotericin B affected either the time constant of the fast or of the slow relaxation (provided that the composition of the perfusion solution and the artificial sea water were replaced by a cytoplasma-analogous medium). When 50 μm of the antibiotics were added externally, the fast relaxation process disappeared. Contrastingly, the slow relaxation process disappeared upon vacuolar addition. The antibiotics cannot penetrate biomembranes rapidly, and therefore, the findings suggested that the fast and slow relaxations originated exclusively from the electrical properties of the plasmalemma and the tonoplast respectively. This interpretation implies that the area-specific resistance of the tonoplast is significantly larger than that of the plasmalemma (consistent with the FCCP data) and that the area-specific capacitance of the tonoplast is unusually high (6.21 × 10⁻² Fm⁻² compared to 0.77 × 10⁻² Fm⁻² of the plasmalemma). Thus, we have to assume that the vacuolar membrane of V. utricularis is highly folded (by a factor of about 9 in relation to the geometric area) and/or contains a fairly high concentration of mobile charges of an unknown electrogenic ion carrier system. Received: 22 October 1996/Revised: 16 January 1997     

Neural and smooth muscle development in the chicken gizzard

The development of the autonomic ganglia of Auerbach's plexus and gizzard smooth muscle was studied in chicken embryos. Nervous system and smooth-muscle-specific antibodies were employed in immunofluorescence stainings on tissue sections to investigate the temporal and spatial frame of neural and muscular differentiation in relation to each other. Subserosal clusters of neural cells were clearly demonstrable at embryonic day 5 (ED5), the earliest stage analysed, with the monoclonal antibody El (SGIII-1). Fine nerve fibres (ED6) and, later, large axon bundles projecting from subserosal neuron clusters towards the lumen were followed and found to reach the luminal border by ED11. Already in early development the area of the future laminar tendons on the ventral and dorsal surface of the gizzard was devoid of neuroblasts, and nerve fibres were not extending to the muscle-tendon borderline until ED16. Double stainings with antibodies to smooth muscle myosin (SMM) and El revealed that SMM expression, taken as an indicator for muscle differentiation, followed neural growth. It was first detectable in close apposition to the differentiating neuroblasts in the caudal and cranial portion of the gizzard at ED6. With further development, myosin expression proceeded inward towards the lumen in a wave which followed the ingrowth of E1-positive nerve fibres from the prospective Auerbach plexus. Neuromuscular differentiation deviated from this pattern in the lateral tendon area where nerve growth was delayed and myosin expression preceeded the arrival of E1-positive nerve fibres. The findings suggest that the gizzard could serve as a model system for the analysis of potential early nervous system imprints on smooth premuscle mesenchyme differentiation.     

Involvement of alpha 1- and alpha 2-adrenergic receptors in the hypothalamo-pituitary-ovarian axis of the domestic fowl, Gallus domesticus

The alpha 1-adrenergic receptor ligand, 3H-WB4101, and the alpha 2-adrenergic receptor ligand, 3H-para-aminoclonidine, were utilized at a 1.0 nM incubation concentration to determine relative alpha 1-and alpha 2-adrenergic receptor binding by cell membranes from selected tissues within the brain, ovary and oviduct of the domestic fowl. Significant specific alpha 1-adrenergic binding was observed in the hypothalamus, anterior pituitary, pineal, cerebrum and cerebellum but only the cerebrum had significant alpha 2-receptor binding. Significant levels of alpha 1-adrenergic binding were observed in the granulosa cells of the three largest ovarian follicles and in the postovulatory follicle. Significant specific alpha 2-adrenergic binding was measured in the infundibulum, magnum, isthmus and shell gland of the oviduct. The physiological implications of alpha-adrenergic receptors in these tissues are discussed.