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At least 811 records · Page 45Linked to original sources
PubMed1986

The detection of various color combinations under different chromatic ambient illuminations.

Our purpose was to reveal the effects of ambient illumination color and various foreground/background color pairings on a choice reaction time task performed on a color CRT. Six men and two women with normal color vision served as observers in a four-alternative forced choice procedure. A small (18' visual angle) colored circle appeared in the center of one of the unmarked quadrants of the screen. The observer's task was to respond as quickly as possible to this target by pressing one of four buttons corresponding to its location. We found that target colors that were opponent to the background colors were most quickly detected. Detection was enhanced by maximizing both brightness and chromatic contrast, but brightness contrast was much more effective. Chromatic ambient lighting which was a log unit dimmer than the target luminance had no effect on performance.

Choice Behavior↗
PubMed1994

"Hot spots" of chromium accumulation at bifurcations of chromate workers' bronchi.

To investigate the mechanisms underlying respiratory tract carcinogenesis in chromate workers, we measured the concentration of chromium in samples of tissues from 50 bronchial bifurcations and other bronchial tissue obtained at autopsy, or during surgical procedures, from 9 exchromate workers known to be at risk of developing lung cancer. The mean duration of exposure was 21 years and the average time between cessation of exposure and death/surgery was 15 years. The area of the tissue samples was measured by image analysis and the chromium concentration determined by neutron activation analysis. Chromium concentrations ranged from 0.04 to 39 x 10(-10) g/microns tissue thickness/mm2 and in 80% of the cases the concentrations were greater at bifurcations than in neighboring epithelial tissue. The mean concentration ratios between bifurcations and adjacent areas were 1.5 (n = 1) in the trachea, 3.0 (n = 9) in the main bronchi, 3.6 (n = 22) in lobar bronchi, and 10.9 (n = 3) in subsegmental bronchi. Our results demonstrated long-term retention of chromium in the bronchial walls of chromate workers and also that chromium concentrations were higher at airway bifurcations than elsewhere, thus providing solid evidence for a deposition "hot spot" concept.

Aged↗
PubMed1995

Luminance and chromatic contrast effects on reading and object recognition in low vision: a review of the literature.

This paper reviews the literature on the effects of luminance and chromatic contrast on reading and object recognition in low vision. The general consensus is that whereas luminance contrast can enhance reading and object recognition for some low vision subjects, chromatic contrast does not aid low vision reading but may be useful in low vision object recognition. Although providing useful theoretical results, the experimental designs have so far been remote from the conditions that low vision patients may experience in the home and work environment. Suggestions are made for an 'ideal' experimental design and details of current research, using conditions more likely to be experienced by low vision subjects in everyday life, are given. This research makes use of a recently developed instrument, the Intuitive Colorimeter.

Cognition↗
PubMed1998

Isolation of chromatic and achromatic mechanisms: a new approach.

The purpose of this study was to optimise the testing paradigm for isolating the contributions of chromatic and achromatic mechanisms to the human spectral sensitivity function. Spectral sensitivity was determined for a test spot size of 1.2 deg presented with various spatial and temporal masks on a large, 10 deg background field of moderate intensity (1000 td) and colour temperature, CT = 2700 K. Sinusoidal temporal presentation (1 Hz) and a masking annulus of between 3 and 10 min of arc surrounding the test spot, was found to be most effective in separating chromatic from achromatic mechanisms. Square-wave (1 Hz) temporal presentation combined with the annulus was slightly less selective. The presence of the annulus did not affect the shape of flicker detection at 25 Hz which is a measure of the luminosity (achromatic) spectral sensitivity function.

Color Perception↗
PubMed1984

Use of sodium chromate Cr51 in diagnosing childhood idiopathic pulmonary hemosiderosis.

The diagnosis of idiopathic pulmonary hemosiderosis (IPH) may be elusive. A 6-year-old boy had microcytic hypochromic anemia and a hemolytic component. Hemosiderin-laden macrophages were not found in the gastric aspirate. He had no pulmonary signs or symptoms. Extensive hematologic and roentgenologic investigations failed to reveal the cause of the anemia. Quantitative serial scintigraphic scanning showed significant (35%) pulmonary sequestration of autologous erythrocytes labeled with sodium chromate Cr51. The half-life of the RBCs was moderately decreased (half-life, 15 days; normal, 25 to 35 days). An open-lung biopsy specimen confirmed the diagnosis of IPH. A diagnosis of IPH should be considered when children have iron deficiency anemia and pulmonary signs or symptoms. Organ sequestration studies may be helpful in equivocal cases.

Anemia, Hypochromic↗
PubMed1993

High-risk notification of chromate and bichromate production workers.

A high-risk notification program is in progress for 4,862 former chromate and bichromate production workers. A previous mortality study of this cohort found a 29-fold increase in mortality for respiratory cancer. The increase was greater in black than white workers (80-fold vs. 15-fold). The cohort was compiled from Social Security Administration records. Notification was performed mainly using addresses on file with the Internal Revenue Service. At this time, 68% of the cohort has either been determined to have died or has been contacted. A description of the various steps of notification is included. This project has demonstrated that it is possible to perform high-risk notification in an economical manner even in the absence of employer personnel records or current addresses. The methodology used in this project is generalizable to other cohorts.

Chemical Industry↗
PubMed2003

Modeling chromate reduction in Shewanella oneidensis MR-1: development of a novel dual-enzyme kinetic model.

Chromate (Cr(VI)) reduction tests were performed with nitrate- and fumarate-grown stationary phase cultures of Shewanella oneidensis MR-1 (henceforth referred to as MR-1) and disappearance of Cr(VI) was monitored over time. A rapid initial decrease in Cr(VI) concentration was observed, which was followed by a slower, steady decrease. These observations appear to be consistent with our previous results indicating that Cr(VI) reduction in MR-1 involves at least two mechanisms (Viamajala et al., 2002b). Modeling of metal reduction kinetics is often based on single-enzyme Michaelis-Menten equations. However, these models are often developed using initial rates and do not always match actual reduction profiles. Based on the hypothesis that multiple Cr(VI) reduction mechanisms exist in MR-1, a model was developed to describe the kinetics of Cr(VI) reduction by two parallel mechanisms: (1) a rapid Cr(VI) reduction mechanism that was deactivated (or depleted) quickly, and (2) a slower mechanism that had a constant activity and was sustainable for a longer duration. Kinetic parameters were estimated by fitting experimental data, and model fits were found to correspond very closely to quantitative observations of Cr(VI) reduction by MR-1.

Cell Culture Techniques↗
PubMed2003

Chromate tolerance caused by reduced hydroxyl radical production and decreased glutathione reductase activity in Schizosaccharomyces pombe.

The stable Cr(VI)-tolerant chr1-66T mutant of Schizosaccharomyces pombe, which carries one simple gene mutation responsible for Cr(VI) tolerance, accumulated and reduced the chromate anion (CrO(4)(2-)) significantly more slowly than did its parental strain 6chr(+). The mutant chr1-66T proved to be sensitive to oxidative stressors such as H(2)O(2), menadione, tert-butyl hydroperoxide and Cd(2+). Both the Cr(VI) tolerance and the oxidative stress sensitivity were attributed to a decreased specific glutathione reductase activity. These effects were also enhanced with a decrease in the specific mitochondrial Mn-SOD activity.

Chromates↗
PubMed1998

Effects of smoking, aromatic amines, and chromates on CD4+ and CD8+ T lymphocytes in male workers.

To investigate effects of smoking, aromatic amines (AAs), and chromates (CRs) on T lymphocyte subpopulations, we measured CD3+, CD4+, and CD8+ T lymphocytes in the peripheral blood of 33 nonexposed workers, 25 AA-use workers, 27 AA-production workers, and 19 CR workers (all subjects were males). The number of CD4+ T lymphocytes in smokers of nonexposed workers was significantly larger than that of the nonsmokers; also, the numbers of CD4+ and CD3+ T lymphocytes in smokers of each group of AA-production and AA-use workers were significantly larger than those in nonsmokers. Number of CD4+ and CD3+ T lymphocytes in nonsmokers of AA-production and CR workers were significantly smaller than those in nonsmokers of nonexposed workers; the number of CD8+ T lymphocytes in nonsmokers of CR workers was significantly smaller than that in nonsmokers of nonexposed workers. The cross-sectional study suggests that (1) smoking increases CD4+ (and CD3+) T lymphocytes in all categories of workers except for CR workers; (2) exposure to CRs and AAs decreases CD4+ (and CD3+) T lymphocytes; (3) the magnitude of decrease in CD4+ T lymphocytes is large among CR workers, intermediate among AA-production workers, and small among AA-use workers regardless of smoking status; and (4) exposure to CRs also decreases CD8+ T lymphocytes.

Adult↗
PubMed1999

Cytotoxicity, apoptosis, and in vitro DNA damage induced by potassium chromate.

Cr(6+) is a known human cytotoxic and carcinogenic agent that requires intracellular reduction for activation. We have analyzed the cytotoxic and DNA binding properties of K(2)CrO(4) (Cr(6+)) in comparison with those of Cl(3)Cr (Cr(3+)). The results indicate that K(2)CrO(4) exhibits higher cytotoxicity than Cl(3)Cr in several human and murine cell lines. The cytotoxic activity of K(2)CrO(4) is also indicated by the fact that is able to produce cell killing through apoptosis in cisplatin-resistant cells transformed by H-ras oncogene. Moreover, in vitro DNA binding experiments show that, in the presence of ascorbate (the major intracellular reductant of Cr(6+)), K(2)CrO(4) induces both interstrand cross-links and strand breaks. Because the chromate anion is by itself unreactive toward DNA, these data suggest that the cytotoxicity of K(2)CrO(4) may be associated with the DNA binding of reactive intermediate chromium species resulting from reduction of Cr(6+).

Animals↗
PubMed1992

Evidence for intrarenal kallikrein storage during chromate-induced acute renal failure in rat.

During the course of chromate-induced acute renal failure (ARF), urinary kallikrein excretion (UKE), a serine protease of distal tubule origin in the normal animal was decreased but tissue kallikrein concentration (TK) was increased, suggesting intracellular accumulation. Severe morphological lesions were observed in proximal tubular cells which showed brush border damage, numerous vesicles, necrosis and liquefaction of cytoplasmic material. Less marked changes were also present in distal tubules: large apical vacuoles and swollen mitochondria. Compared to normal rats, using the peroxidase-anti-peroxidase (PAP) method for light microscopy, greater kallikrein immunoreactivity was detected along the apical pole in distal tubules, on the membrane and in the cytoplasm as well as in the glomerulus. By immunoelectron microscopy, kallikrein was found in the connecting apical area, along the luminal, basolateral and basement membranes, in some vesicles, in Golgi apparatus and on ribosomes bound to endoplasmic reticulum. In the glomerulus, kallikrein was observed along the luminal surface of endothelial cell. After 14 days a progressive recovery of renal function, tissue morphology and UKE towards control values was observed. The presence of immunoreactive kallikrein in the glomerulus observed only during ARF confirmed the previous demonstration of kallikrein mRNA in the glomerulus. The cellular accumulation results more likely from a dysfunction of a general secretory mechanism due to cell membrane alteration than from a specific inhibition of kallikrein production and secretion.

Acute Kidney Injury↗
PubMed1995

Hexavalent-chromium reduction by a chromate-resistant Bacillus sp. strain.

Bacillus strain QC1-2, isolated from a chromium-polluted zone, was selected by its high ability to both tolerate and reduce hexavalent chromium [Cr(VI)] to less-toxic trivalent chromium [Cr(III)]. Cell suspensions of strain QC1-2 rapidly reduced Cr(VI), in both aerobic and anaerobic conditions, to Cr(III) which remained in the supernatant. Cr(VI) reduction was dependent on the addition of glucose but sulfate, an inhibitor of chromate transport, had no effect. Studies with permeabilized cells and cell extracts showed that the Cr(VI) reductase of strain QC1-2 is a soluble NADH-dependent enzyme.

Aerobiosis↗
PubMed1990

Chromate reduction in Streptomyces.

Streptomyces species 3M grew in peptone yeast extract medium with 1000 micrograms/ml K2Cr2O7. Incubation of the chromate with different cell fractions in the presence of NADH and NADPH resulted in a decrease of Cr6+ in the reaction mixture. The level of Cr6+ was reduced by 82.7% by a particulate cell fraction obtained by centrifugation at 105,000 x g for 1 h, in the presence of NADH. The reducing enzyme was associated with this cell fraction. The enzyme was constitutive and reduced Cr6+ to Cr3+.

Chromates↗
PubMed1994

The ambiguous effect of ascorbic acid on chromate induced proteinuria in rats.

The influence of ascorbic acid (AA, 5 g/kg body weight) on chromate (Cr, 10 mg/kg) induced proteinuria, which is a sensitive parameter of its nephrotoxicity, was investigated in adult female Wistar rats. The concentrations of Cr and ascorbic acid (AA) were determined in renal tissue. Cr nephrotoxicity is related to its intracellular reduction from Cr(VI) to Cr(III). Proteinuria was completely prevented by enhancement of extracellular reduction of Cr(VI) to Cr(III) followed by rapid renal excretion when Cr and AA were given concomitantly. With an interval up to 1 h between Cr and AA, proteinuria was decreased probably by the radical scavenging function of AA. At an interval of 3 h AA enhanced Cr toxicity by increased intracellular Cr reduction. If the interval was increased to 5 h or if Cr was given 24 h after AA, no influence of AA could be detected. Our results confirm that AA is a very effective reductant of Cr which can influence Cr nephrotoxicity in very high concentrations. It depends on the interval between Cr and AA administration whether or not there is a beneficial effect of AA in Cr nephrotoxicity.

Animals↗
PubMed1996

Contribution to the mechanism of chromate nephrotoxicity in developing rats: EPR investigations.

The effect of 2 mg and 1 mg Na2Cr2O7 (Cr)/100 g body wt. on renal function was investigated in 10- and 55-day-old rats, respectively. These doses were followed by equal Cr concentrations in the renal tissue of both age groups. Confirming previous data we found lower nephrotoxicity in young than in adult rats. The concentration of glutathione (GSH) and the activity of glutathione reductase (GSSG reductase) in renal tissue of adult rats were diminished by buthionine sulfoximine (BSO) and lomustine (CCNU) administration, respectively. In these animals Cr nephrotoxicity was decreased significantly. Lower nephrotoxicity was accompanied by slower disappearance of Cr(VI) from renal tissue homogenate in vitro. The time course of Cr(VI) reduction demonstrated by the signal intensity of Cr(V), as recorded by electron spin resonance (EPR) spectroscopy in the supernatant of renal tissue homogenate, enabled us to follow the reduction of Cr(VI) to Cr(III) via Cr(V). Maximally reached Cr(V) concentrations lowest in young rats, did not differ significantly in adult control and BSO and BSO + CCNU treated rats. Further reduction of Cr(V) to Cr(III) which appeared most rapidly in adult rats, was delayed by pretreatment with BSO and CCNU. From our results we concluded that (1) reduction of Cr(VI) was more related to the concentration of GSH than to the activity of GSSG reductase, (2) the formation of Cr-GSH-complexes with GSH oxidation seemed to be the first step of Cr(VI) metabolism, and (3) the stabilization of reactive Cr(V) by GSH seemed to be decisive for the preventive effect of BSO and CCNU as well as for age differences in chromate nephrotoxicity.

Age Factors↗
PubMed2003

The 79,370-bp conjugative plasmid pB4 consists of an IncP-1beta backbone loaded with a chromate resistance transposon, the strA-strB streptomycin resistance gene pair, the oxacillinase gene bla(NPS-1), and a tripartite antibiotic efflux system of the resistance-nodulation-division family.

Plasmid pB4 is a conjugative antibiotic resistance plasmid, originally isolated from a microbial community growing in activated sludge, by means of an exogenous isolation method with Pseudomonas sp. B13 as recipient. We have determined the complete nucleotide sequence of pB4. The plasmid is 79,370 bp long and contains at least 81 complete coding regions. A suite of coding regions predicted to be involved in plasmid replication, plasmid maintenance, and conjugative transfer revealed significant similarity to the IncP-1beta backbone of R751. Four resistance gene regions comprising mobile genetic elements are inserted in the IncP-1beta backbone of pB4. The modular 'gene load' of pB4 includes (1) the novel transposon Tn 5719 containing genes characteristic of chromate resistance determinants, (2) the transposon Tn 5393c carrying the widespread streptomycin resistance gene pair strA-strB, (3) the beta-lactam antibiotic resistance gene bla(NPS-1) flanked by highly conserved sequences characteristic of integrons, and (4) a tripartite antibiotic resistance determinant comprising an efflux protein of the resistance-nodulation-division (RND) family, a periplasmic membrane fusion protein (MFP), and an outer membrane factor (OMF). The components of the RND-MFP-OMF efflux system showed the highest similarity to the products of the mexCD-oprJ determinant from the Pseudomonas aeruginosa chromosome. Functional analysis of the cloned resistance region from pB4 in Pseudomonas sp. B13 indicated that the RND-MFP-OMF efflux system conferred high-level resistance to erythromycin and roxithromycin resistance on the host strain. This is the first example of an RND-MFP-OMF-type antibiotic resistance determinant to be found in a plasmid genome. The global genetic organization of pB4 implies that its gene load might be disseminated between bacteria in different habitats by the combined action of the conjugation apparatus and the mobility of its component elements.

Bacterial Proteins↗