Transport of methionine in Trypanosoma brucei brucei

African trypanosomes live free in the bloodstream and central nervous system of mammalian hosts and also within the midgut of the tsetse fly vectors which transmit them. The parasite plasma membrane represents the interface between both hosts and parasite, and trypanosomes accumulate many essential metabolites via specific transport processes. L-Methionine uptake by procyclic and bloodstream forms of Trypanosoma brucei has been measured and shown to be mediated by a transporter presenting similar characteristics in both forms of the parasite. The carrier shows, in both forms, a relatively high affinity for methionine (Km ca. 30 microM). The effect of inhibitors of ion gradients across the membrane indicated that the uptake process is likely to be dependent upon a proton motive force. Various methionine analogues were tested against the transporter and these have demonstrated that the recognition depends on the motif common to all amino acids, and an electronegative group at the position of the sulphur atom separated from the alpha-carbon atom by a two carbon spacer.     

Relationships among ragweed skin tests and both allergen specific and nonspecific nasal provocation.

Twenty-six patients with ragweed-induced allergic rhinitis were evaluated prior to the onset of seasonal symptoms. Ragweed skin tests and nasal challenges were performed 2 weeks after histamine nasal provocation. A correlation between ragweed skin tests and nasal challenges was detected (r = .4867, P much less than .01). Histamine challenges did not correlate with either of the other variables. A properly performed skin test predicts nasal reactivity to the same allergen. A clinical role for nonspecific nasal provocation could not be determined.     

Effect of antibody-induced modulation of measles (SSPE) virus membrane proteins on beta-adrenergic receptor-mediated adenylate cyclase activity

The effect of measles virus antiserum on the expression of viral glycoproteins on the membranes of measles (SSPE) persistently infected C6 rat glioma cells was studied. There was a gradual loss of virus membrane antigen from these cells until no antigen was detectable 18 days after initiation of antiserum treatment. At this stage approximately 25% of cells still displayed intracellular virus antigen which was also lost after further cell passages. There was an accompanying recovery of the previously reported disrupted catecholamine-dependent beta-adrenergic receptor-stimulated cAMP synthesis in antiserum-treated cells which coincided with the loss of viral antigen from the membrane. This was determined to be due to a recovery of fluoride-stimulated activity of the cAMP synthesising adenylate cyclase enzyme to normal values. Thus we demonstrate that the impairment of this important cell function was due to insertion of viral antigen in the cell membrane rather than its accumulation in the cytoplasm.     

In vitro activity of E-4868, a new trifluoroquinolone,compared to six similar compounds

The compound E-4868 (Laboratorios Dr. Esteve) is a trifluoro, 7-azetidinyl quinolone with properties resembling those of other fluoroquinolones. Its activity in vitro was compared to that of six other similar drugs against more than 700 nosocomial isolates using standard methods. The MIC50s of E-4868 for enteric bacilli ranged from 0.015 to 0.25 µg/ml, being highest forProvidencia spp.Pseudomonas aeruginosa strains were two-fold more susceptible to E-4868 than to ofloxacin. MICs of E-4868 forHaemophilus influenzae, Moraxella catarrhalis and pathogenicNeisseria spp. were all 0.12 µg/ml. E-4868 was equal in activity to or eight-fold more active than ciprofloxacin against gram-positive cocci. The MICs of E-4868 for pneumococci were all 0.5 µg/ml but anaerobes such asBacteroides fragilis were generally less susceptible (MIC90, 4 µg/ml). There was almost complete cross-resistance to several other fluoroquinolones. Resistant mutants were selected by a multiple passage technique but the rate of mutation to resistance was very low (< 10^–8) at an 8 x MIC.     

Comparison of arsenic-induced cell transformation, cytotoxicity, mutation and cytogenetic effects in Syrian hamster embryo cells in culture

Sodium arsenite and sodium arsenate were observed to inducemorphological transformation of Syrian hamster embryo cellsin a dose-dependent manner. A linear dose-dependence with aslope of 1 was observed with both compounds when the data wereplotted on a log-log graph. The trivalent sodium arsenite was> 10-fold more potent than the pentavalent sodium arsenate.The compounds also exhibited toxicity; however, transformationwas observed at non-toxic as well as toxic doses. At low doses,enhanced colony-forming efficiency of the cells was observed.To understand the mechanism of arsenic-induced transformation,the genetic effects of the two arsenicals were examined overthe same doses that induced transformation. No arsenic-inducedgene mutations were detected at two genetic loci. However, celltransformation and cytogenetic effects, including endoreduplication,chromosome aberrations, and sister chromatid exchanges wereinduced by the arsenicals with similar dose-responses. Theseresults support a possible role for chromosomal changes in arsenic-inducedtransformation.     

Changes in stem cell populations of rat tracheal epithelial cell cultures at an early stage in neoplastic progression

The development of transformed colonies and concomitant changes in proliferative and nonproliferative cell compartments were studied in rat tracheal epithelial (RTE) cell cultures following exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Primary RTE cells were plated onto 3T3 feeder layers and treated with MNNG (0.25 micrograms/ml) or solvent. Seven days later, the feeder cells were removed to select for enhanced growth variants, which are the transformants of the RTE cell system, usually scored 5 weeks after carcinogen exposure. Most of the RTE cell colonies, which originally formed during the first 7 days of culture, disappeared within 2 weeks after feeder cell removal in control and MNNG-treated cultures. In control cultures, about 3% of the original colonies persisted, while in MNNG-treated cultures, a larger percentage (approximately 9%) of the colonies persisted. These percentages remained constant from 3 to 7 weeks. Based on colony size, cell density, and cell morphology, the persistent colonies were classified into transformed colonies (large colony size, high cell density, high nuclear:cytoplasmic ratio) and untransformed colonies (small size, low cell density, low nuclear:cytoplasmic ratio). In the MNNG-treated cultures, about 50% of all persistent colonies showed transformed morphology. Their frequency remained unchanged between 3 and 7 weeks of culture. In contrast, only 10 to 15% of the persistent colonies in control cultures showed transformed morphology at 3 weeks, but that proportion increased steadily between 3 and 7 weeks. These data suggest that, in control cultures, transformed colonies developed spontaneously as a function of time within untransformed colonies. Autoradiographic studies with [3H]thymidine showed that labeling indices in the early "normal" RTE cell colonies between Days 4 and 7 of culture were very high, ranging between 75 and 90%. In contrast, the labeling indices of persistent colonies, both those without and those with transformed morphology, were low, i.e., between 18 and 25%, indicating that a major proportion of cells was either noncycling or cycling very slowly. The relative compartment sizes of cells with stem cell characteristics and of cells with characteristics of transformed stem cells were estimated before and after transformed colonies appeared.(ABSTRACT TRUNCATED AT 400 WORDS)     

Rapid isolation of human kininogens

A rapid, two-step procedure is described for the isolation of both "high molecular weight" (H-) and "low molecular weight" (L-) plasma kininogens from a single sample of plasma. Affinity chromatography on carboxymethyl-papain-Sepharose is used, together with high-resolution anion exchange chromatography.     

Spectrophotometric evaluation of carboxyhemoglobin in blood of mice after exposure to marijuana or tobacco smoke in a modified Walton horizontal smoke exposure machine

Carboxyhemoglobin (COHb) values were determined in mice exposed to varying amounts of marijuana and tobacco cigarette smoke utilizing a spectrophotometric technique. Mice were exposed to smoke inhalation in a modified Walton horizontal smoke exposure machine, whereby rodents can be exposed to multiples of 1-min smoke exposure cycles. Smoke exposure was intermittent; during the first 30 sec of each 1-min cycle, the subjects were exposed to smoke diluted either 1:10 or 1:5 with air. During the second half of the cycle the animals were given fresh air. There was a positive linear relationship between COHb values obtained and the number of puffs of marijuana smoke administered via either 2, 4, 6, or 8 "puffs" of marijuana smoke. COHb levels in plasma did not increase in animals given multiple 8-puff episodes of smoke daily as long as a 60-min period was interposed between smoking episodes. COHb values in mice exposed to tobacco smoke were significantly higher than those in mice receiving equal numbers of exposures to marijuana smoke. Mean COHb values of mice receiving 8 consecutive puffs of marijuana smoke were 18.6 and 22.0% saturation, but CO was rapidly cleared from the blood. This rapid clearance suggests that the binding affinity of CO for mouse hemoglobin may be be weaker than that of human hemoglobin. Mice similarly exposed to 6 or 8 puffs of tobacco smoke had mean COHb values of 24.6 and 28.5% saturation, respectively. No acute lethal effects were observed in mice receiving multiple daily episodes of 8 puffs per episode of marijuana smoke, whereas mice exposed to a single 8-puff episode of tobacco smoke suffered about 50% acute lethal effects.