Cationic amino acid transport by two renal epithelial cell lines: LLC-PK1 and MDCK cells

LLC-PK1 and MDCK cells take up cationic amino acids (lysine and arginine) by a specific sodium independent transport system. Uptake is inhibited by ornithine in LLC-PK1 and MDCK cells either in the presence or absence of sodium and by glutamine or homoserine in MDCK cells in the presence of sodium. Trans-stimulation of uptake occurs in the presence of intracellular cationic amino acids. Experiments with valinomycin or with different extracellular potassium concentrations suggest that uptake is dependent on the membrane potential of these cells. These transport features are similar to those previously ascribed to a transport system denominated y+ in other cells. Further experiments suggested that this carrier system is localised to the basolateral membrane in each cell type.     

PMA induces the ligand-independent internalization of CR1 on human neutrophils

Phorbol myristate acetate (PMA) has been reported to confer on the C3b receptor (CR1) of neutrophils a capacity for phagocytosis of particles bearing C3b without the involvement of other membrane receptors. In the present study, we employed a monoclonal antibody, YZ-1, that is specific for CR1 to assess the effect of PMA on plasma membrane expression of CR1, total cellular CR1, and internalization of CR1 by neutrophils. PMA had a biphasic effect on the membrane expression of CR1 by purified neutrophils, with 4 ng/ml inducing a 60% increment in receptor expression, and higher concentrations causing up to a 70% decrement. PMA-dependent increases in CR1 expression were not accompanied by corresponding changes in total cellular CR1 and were preempted by treatment of cells with formyl-methionyl-leucyl-phenylalanine (FMLP). PMA-induced decreases in CR1 expression by neutrophils, as measured by binding of indirectly fluoresceinated or radiolabeled YZ-1, or of 125I-labeled dimeric C3b, were maximal with 20 to 30 ng/ml PMA, and occurred within 30 min of incubation at 37 degrees C. The PMA-dependent down-regulation of CR1 by neutrophils was not associated with a comparable decrease in total cellular CR1, and this response was observed to occur also with monocytes but not with peripheral blood lymphocytes. By tagging neutrophil CR1 with 125I-YZ-1 Fab and monitoring accessibility to Protease, intracellular CR1 (inaccessible) was discriminated from receptor on plasma membrane (accessible). Internalization of CR1 occurred within 5 min after addition of PMA to neutrophils, was dose dependent, and involved up to two-thirds of the tagged receptors. Therefore, PMA caused internalization of CR1 by neutrophils in the absence of ligand, indicating that this response was independent of a transmembrane signal generated by a C3b-CR1 interaction.     

Differential susceptibility of cultured neural cells to the human coronavirus OC43.

By using cell-type-specific markers and neural cultures derived from various areas of the nervous system, it has been possible to identify various interactions between OC43 virus and mouse oligodendrocytes, neurons, astrocytes, and fibroblasts. Neurons derived from dorsal root ganglia produced viral antigen and infectious virus. Astrocytes and fibroblasts both produced viral antigen but not infectious virus. Oligodendrocytes produced neither infectious virus nor viral antigen. Human embryo brain cells, including astrocytes, were susceptible to OC43 infection but did not produce infectious virus.     

Characterization of virulent and avirulent A/chicken/Pennsylvania/83 influenza A viruses: potential role of defective interfering RNAs in nature.

In April 1983, an influenza virus of low virulence appeared in chickens in Pennsylvania. Subsequently, in October 1983, the virus became virulent and caused high mortality in poultry. The causative agent has been identified as an influenza virus of the H5N2 serotype. The hemagglutinin is antigenically closely related to tern/South Africa/61 (H5N3) and the neuraminidase is similar to that from human H2N2 strains (e.g., A/Japan/305/57) and from some avian influenza virus strains (e.g., A/turkey/Mass/66 [H6N2]). Comparison of the genome RNAs of chicken/Penn with other influenza virus isolates by RNA-RNA hybridization indicated that all of the genes of this virus were closely related to those of various other influenza virus isolates from wild birds. Chickens infected with the virulent strain shed high concentrations of virus in their feces (10(7) 50% egg infective dose per g), and the virus was isolated from the albumin and yolk of eggs layed just before death. Virus was also isolated from house flies in chicken houses. Serological and virological studies showed that humans are not susceptible to infection with the virus, but can serve as short-term mechanical carriers. Analysis of the RNA of the viruses isolated in April and October by gel migration and RNA-RNA hybridization suggested that these strains were very closely related. Oligonucleotide mapping of the individual genes of virulent and avirulent strains showed a limited number of changes in the genome RNAs, but no consistent differences between the virulent and avirulent strains that could be correlated with pathogenicity were found. Polyacrylamide gel analysis of the early (avirulent) isolates demonstrated the presence of low-molecular-weight RNA bands which is indicative of defective-interfering particles. These RNAs were not present in the virulent isolates. Experimental infection of chickens with mixtures of the avirulent and virulent strains demonstrated that the avirulent virus interferes with the pathogenicity of the virulent virus. The results suggest that the original avirulent virus was probably derived from influenza viruses from wild birds and that the virulent strain was derived from the avirulent strain by selective adaptation rather than by recombination or the introduction of a new virus into the population. This adaptation may have involved the loss of defective RNAs, as well as mutations, and thus provides a possible model for a role of defective-interfering particles in nature.     

Tobacco single-copy DNA is highly homologous to sequences present in the genomes of its diploid progenitors

Summary We compared the single-copy DNA sequences of the tetraploid tobacco plant, Nicotiana tabacum, with those of its diploid progenitors N. sylvestris and N. tomentosiformis. We observed that 65% of N. sylvestris and N. tomentosiformis single-copy DNA fragments reacted with each other using moderately stringent hybridization conditions (60° C, 0.18 M Na⁺). An additional 10% sequence homology was detected when the hybridization temperature was reduced by 10° C. The thermal stability of interspecific single-copy DNA duplexes indicated that they were approximately 6% more mispaired than homologous single-copy DNA duplexes. In contrast, we observed almost no single-copy DNA divergence between N. tabacum and its diploid progenitors. Greater than 99% of N. sylvestris and N. tomentosiformis single-copy DNAs reacted with N. tabacum DNA using moderately stringent hybridization conditions. The thermal stability of these duplexes indicated that they contained no more sequence mismatch than homologous single-copy duplexes. Together, our results show that significant single-copy DNA sequence divergence has occurred between the diploid N. sylvestris and N. tomentosiformis genomes. However, by applying our experimental criteria these single-copy DNAs are indistinguishable from their counterparts in the hybrid N. tabacum nucleus.     

10 nm RecA protein filaments formed in the presence of Mg2+ and ATP gamma S may contain RNA

Summary Filaments formed by the polymerization of RecA protein along DNA in the presence of Mg²⁺ and adenosine 5-0-(3-thiotriphosphate) (ATPS) are seen by electron microscopy to have a 10 nm diameter with a 9 nm helical repeat. When certain preparations of apparently pure RecA protein are incubated with Mg²⁺ and ATPS in the absence of nucleic acid for extended times, very long filaments with the same 10 nm diameter and 9 nm axial repeat are seen. We show here that these long 10 nm filaments can contain RNA which is present as a contaminant of the RecA protein and poly(A) which is synthesized during the incubations by an activity that is apparently polynucleotide phosphorylase. RecA protein purified by a procedure developed in this laboratory did not contain RNA and did not form these very long 10 nm filaments. However, when exogenous RNA was added to this protein, 10 nm filament formation was observed.     

Effect of Unilateral Decortication on Choline Acetyltransferase Activity in the Nucleus Basalis and Other Areas of the Rat Brain

Acetyl-coenzyme A: choline O-acetyltransferase (EC 2.3.1.6) (ChAT) enzyme activity was measured in the nucleus basalis and other microscopically identified brain areas at various times after unilateral cortical lesions were made in the rat. Initially, a significant decrease in ChAT activity was detected in the nucleus basalis ipsilateral to the lesion. However, after 120 days ChAT activity had apparently recovered, as levels of the enzyme at that time were not significantly different from control values. No changes in ChAT activity could be detected in any of the other brain areas similarly studied. The significance of these findings and their relationship to the morphological changes seen in neurones of the nucleus basalis after cortical lesions are discussed.     

Inhibition of chlorophyll synthesis inHordeum vulgare by 3-amino 2,3-dihydrobenzoic acid (gabaculin)

Gabaculin (3-amino 2,3-dihydrobenzoic acid) is shown to be a very potent inhibitor of chlorophyll formation inHordeum vulgate. Exposure of leaf segments to 30/M gabaculin results in an 80% inhibition of chlorophyll synthesis, and this is paralleled by a decrease in carotenoid. Dual-inhibitor studies with dioxoheptanoic acid, which is an inhibitor of inolaevulinic acid dehydratase, show that gabaculin inhibits an earlier step than dioxoheptanoic acid and affects -aminolaevulinic acid synthesis rather than its subsequent metabolism.     

The oral assimilation of radiomanganese by the mouse

The metabolism of orally administered radiomanganese was studied in mice. Assimilation of absorbed manganese (Mn) was determined using whole body counting techniques. When⁵⁴MnCl₂ was administered, 2.7% of the dose was retained after 10 d compared with 1.2% from the⁵⁴Mn-nitrilotriacetate (NTA) complex. However, this difference was accounted for by the rapid and persistent adsorption of the Mn onto the teeth of the lower jaw when fed as the ionic salt at pH 2.0 compared with the NTA-chelate fed at pH 9.0. Once corrected for the amount adsorbed onto the teeth, the biodistribution and relative specific activity of the assimilated radiomanganese into a variety of tissues were similar for both forms of the metal.     

The influence of oxygen concentrations on denitrification in soil

Summary The influence of different O₂ concentrations on denitrification was studied in an agricultural soil. In both nitrate and nitrite amended soil, denitrification was not observed until the O₂ concentration decreased to 0.20 and 0.21 mol/ml, respectively. Denitrification was not observed in soil samples with O₂ concentrations above 0.28 mol/ml in the gas phase. These findings suggest that a completely anoxic environment is not required for denitrification to occur in soil.