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L Stankova

Publications and source records attributed to L Stankova.

At least 19 recordsLinked to original sources
PubMed1992

Pentylenetetrazol-induced seizures in rats: an ontogenetic study.

A quantitative description of motor seizures induced by pentylenetetrazol (PTZ, metrazol) was performed. Seizures were induced by PTZ in doses from 40 to 120 mg/kg s.c. in 477 male albino rats of the Wistar strain 7 to 90 days old. Two patterns of seizures were elicited: minimal, i.e. predominantly clonic seizures of facial and forelimb muscles with preserved righting ability, and major, i.e. generalized tonic-clonic seizures with a loss of righting reflex. Minimal seizures could be reliably elicited since the age of 18 days; the CD50 for these seizures did not significantly differ with age. Major seizures were elicited regularly at all developmental stages studied. Their CD50 did not significantly differ among 7-, 12- and 25-day-old rat pups but the value for 18-day-old rats was smaller and for adult animals larger than these three age groups.

Aging↗
PubMed1991

The effect of cyanide on vitamin C uptake by human polymorphonuclear leukocytes.

1. Cyanide inhibited the uptake of vitamin C by human polymorphonuclear leukocytes (PMNs). 2. Preincubation of PMNs with cyanide had no effect on cytochalasin B-inhibitable uptake of dehydroascorbic acid (DHA) (the reversibly oxidized and transportable form of vitamin C). 3. Preincubation of DHA with cyanide resulted in inhibition of DHA uptake. 4. Vitamin C uptake was decreased by cyanide to the same degree as it was by glutathione (GSH), which effectively reduces DHA to ascorbic acid. The effects of cyanide and GSH were not additive. 5. The data are consistent with the hypothesis that cyanide inhibition of vitamin C uptake represents the chemical elimination of extracellular DHA rather than the inhibition of active transport in these cells.

Animals↗
PubMed1989

Gyrate atrophy of the choroid and retina: characterization of mutant ornithine aminotransferase and mechanism of response to vitamin B6.

The purpose of this study was to characterize the mutant enzyme in nine patients with gyrate atrophy of the choroid and retina associated with ornithine aminotransferase (OAT) deficiency, to elucidate the mechanism of response to pyridoxine in four pyridoxine-responsive patients, and to determine the extent of genetic heterogeneity in both groups of patients. We have measured the apparent Km for pyridoxal phosphate (PLP) in fibroblast mitochondria and the heat stability of OAT at 45 degrees C in the presence and absence of PLP, using a sensitive radiochemical assay. The apparent Km for PLP was higher in pyridoxine-responsive patients than in nonresponsive patients whose apparent Km for PLP was normal. In contrast, the apparent Km for ornithine was normal in the seven patients studied. Surprisingly, the responsive patient with mildest clinical disease had the highest Km for PLP. However, she had the most stable enzyme, which presumably contributed to her milder phenotype. Western blot analyses of mitochondrial proteins, using antibody to human OAT, indicated clearly detectable OAT protein in pyridoxine-responsive patients and in two of five nonresponders, but low or undetectable levels in the other three patients. These data clarify the mechanism of pyridoxine response and indicate heterogeneity within as well as between the pyridoxine-responsive and the nonresponsive patients with gyrate atrophy.

Atrophy↗
PubMed1988

Effect of monosaccharide on dehydroascorbic acid uptake by placental membrane vesicles.

Dehydroascorbic acid (DHA), the oxidized form of vitamin C, is transported across the microvillous surface of the human placental syncytiotrophoblast by the D-glucose transporter. The existence of this mechanism suggests that maternal hyperglycemia may influence placental transfer of vitamin C. Therefore, we examined the effect of monosaccharides, equilibrated across the membrane, on the uptake of 0.5 mmol/L DHA by placental membrane vesicles. Relative to uptake in the absence of monosaccharide, the rate of DHA uptake was enhanced by up to 90% in the presence of 3-O-methyl-D-glucose equilibrated across the membrane. Comparable results were obtained with D-glucose and D-galactose. An inward-directed monosaccharide concentration gradient inhibited DHA uptake. However, with elevated equilibrium concentrations of monosaccharide, the magnitude of such uptake inhibition was reduced. Relative to DHA uptake at normal blood glucose concentrations (5 mmol/L), the results suggest that moderate maternal hyperglycemia does not alter, but that severe hypo- or hyperglycemia decreases, placental uptake of DHA from the maternal circulation.

3-O-Methylglucose↗
PubMed1986

Role of monosaccharide transporter in vitamin C uptake by placental membrane vesicles.

Dehydroascorbic acid (DHA), the reversibly oxidized form of vitamin C, was taken up much more rapidly than L-glucose into membrane vesicles prepared from the maternal face of the human placental syncytiotrophoblast. DHA uptake was sensitive to inhibition by cytochalasin B and was independent of a sodium concentration gradient. At equilibrium, the concentration of DHA in the vesicles did not exceed that of the medium. DHA and the D-glucose analogue, 3-O-methyl-D-glucose (3-O-MG) appeared to compete with one another for the transporter. The 3-O-MG and DHA inhibitory constants were indistinguishable. Vesicles loaded with a high concentration of 3-O-MG and suspended in low 3-O-MG displayed a marked, transitory enhancement of DHA, but not L-glucose uptake. These findings suggest that DHA is taken into the first cellular boundary of the placenta between maternal and fetal circulations by the sodium-independent monosaccharide transporter. In contrast to DHA, L-ascorbic acid, the reversibly reduced form of vitamin C, was taken into these vesicles much more slowly. This uptake was not affected by cytochalasin B nor by a sodium concentration gradient; it appeared to occur by simple diffusion.

3-O-Methylglucose↗
PubMed1984

Plasma ascorbate concentrations and blood cell dehydroascorbate transport in patients with diabetes mellitus.

Rates of dehydroascorbate uptake by blood granulocytes and mononuclear cells are slower, and plasma ascorbate concentrations are lower, among persons with diabetes mellitus than in nondiabetic subjects. These measurements do not correlate with one another or with simultaneously measured plasma glucose or glycosylated hemoglobin; they do not differ with type of diabetes or mode of treatment. In those diabetic granulocytes that exhibit slow dehydroascorbate uptake, maximal velocity (Vmax) transport rates for dehydroascorbate, 2-deoxyglucose, and 3-O-methylglucose are decreased, each to the same degree, while Km values for transport of these ligands are not different from those observed in nondiabetic cells. Since diffusion of these ligands is facilitated by a common transporter, these observations may reflect decreased numbers of glucose transporters in the plasma membranes of some diabetic leukocytes.

3-O-Methylglucose↗
PubMed1983

Interaction between glucose and dehydroascorbate transport in human neutrophils and fibroblasts.

Dehydroascorbate (DHA) competitively inhibits the uptake of 2-deoxy-D-glucose and of 3-O-methyl-D-glucose by human blood neutrophils; 2-deoxyglucose and 3-O-methylglucose competitively inhibit dehydroascorbate uptake. Ratios of Km to Kl are near unity for each of these ligands. Exposure of cultured human fibroblasts to insulin enhances cytochalasin B-inhibitable uptake of DHA and of 2-deoxyglucose, both to the same degree. These observations suggest that DHA transport is mediated by glucose transport systems in human neutrophils and fibroblasts.

3-O-Methylglucose↗
PubMed1983

Dehydroascorbate uptake as an in vitro biochemical marker of granulocyte differentiation.

We tested the hypothesis that the rate of cellular uptake of dehydroascorbate in cultures of developing granulocyte-macrophage progenitors in vitro would serve as a biochemical marker of neutrophil maturation. Suspension cultures of low-density, nonadherent, T-lymphocyte-depleted bone marrow cells from eight normal volunteers were cultured in medium containing 10% human placental conditioned medium and were harvested at intervals over 14 days. The harvested cells were tested for their ability to take up dehydroascorbate. Mean cellular uptake rate increased 12-fold by Day 10, at which time the cells had differentiated to neutrophils. Uptake increased by less than 2-fold in cells which had been induced to differentiate to mature mononuclear phagocytes with 12-O-tetradecanoylphorbol-13-acetate. Additional studies using HL-60 cells induced to differentiate with dimethyl sulfoxide or 12-O-tetradecanoylphorbol-13-acetate support the view that a major increase in dehydroascorbate uptake in cultured granulopoietic progenitors is a manifestation of a neutrophil differentiation.

Ascorbic Acid↗
PubMed1981

Human cell dehydroascorbate reductase. Kinetic and functional properties.

Dehydroascorbate reductase (glutathione: dehydroascorbate oxidoreductase, EC 1.8.5.1) activity was examined in crude cytosol extracts of human cells. In blood neutrophil and lymphocyte extracts, the Km at pH 6.85 for dehydroascorbate was 1.3 mM, and for reduced glutathione 3.8 mM. Rates of dehydroascorbate uptake by intact human neutrophils, monocytes, lymphocytes and cultured fibroblasts were proportional to cytosol dehydroascorbate reductase activities. Dehydroascorbate reduction during dehydroascorbate uptake by these cells may be entirely enzymatic.

Cells, Cultured↗
PubMed1980

Biphasic radiosensitization of human lymphocytes by diethyldithiocarbamate: possible involvement of superoxide dismutase.

A biphasic radiosensitization of human lymphocytes by diethyldithiocarbamate (DDC), a metal chelator, was observed. The first phase occurred at 10(-5) M and the second at 10(-3) MDDC. The biphasic radiosensitization coincided with the previously reported biphasic toxicity of DDC. Inhibition of superoxide dismutase (SOD) occurred only in the second phase, suggesting that it may be a contributing cause of this phase. The mechanism of the first radiosensitization phase is not known. The radiation survival curves indicated the presence of at least two lymphocyte populations differing in their radiosensitivity and representing 40 per cent and 60 per cent of the cells. Both cell populations were biphasically radiosensitized by DDC.

Cell Survival↗
PubMed1980

Glutathione-dependent dehydroascorbate reduction: a determinant of dehydroascorbate uptake by human polymorphonuclear leukocytes.

Dehydroascorbate uptake and reduction are impaired in normal human polymorphonuclear leukocytes (PMN) preincubated with N-ethylmaleimide, and in glutathione reductase-deficient cells. We conclude that human PMN dehydroascorbate reduction is glutathione-dependent, and that dehydroascorbate reduction appears to be a necessary condition for cellular dehydroascorbate uptake.

Ascorbic Acid↗
PubMed1977

Effect of zinc on peritoneal macrophages in vitro.

Rat peritoneal macrophages incubated in a medium with 10% autologous serum showed 50% inhibition of O2 consumption by 0.4 mM zinc only when activated by yeast. Zinc ions had no effect on resting macrophages. The inhibitory efficiency of zinc depended on the ratio of yeast particles to macrophages; with more activated cells, the inhibition was less. The multiple-shaped intact macrophages changed into rounded cells in the presence of 0.1 and 0.5 mM Zn2+ as shown by photomicrography and scanning electron microscopy. When the incubation medium was replaced by zinc-free medium, cells recovered and became irregularly shaped. The reversibility of zinc effect on cell morphology corresponded with uptake and release of zinc by macrophages. The presence of serum in the medium interfered with the magnitude of zinc uptake by macrophages. We conclude that besides already reported effects of zinc on mast cells, platelets, and granulocytes, zinc ions also inhibit some functions of macrophages.

Animals↗
PubMed1977

Inhibition of some functions of polymorphonuclear leukocytes by in vitro zinc.

In granulocytes isolated by dextran sedimentation from dog blood, the O2 consumption, phagocytosis of yeast particles, and E. coli killing were tested in Tris-guffered saline medium with additions of Zn++, Mg++, and other divalent cations and in the presence or absence of plasma. Zn++ inhibited all three cell functions in a concentration-related manner only in the presence of 1.2 mM Mg++. Without Mg++ in the medium the lower concentrations of Zn++ (17 to 67 muM) were stimulatory; 83 muM Zn++ concentration was inhibitory. A close association was found between the inhibitory effect of Zn++ and the actual content of zinc in the cell: (1) the uptake of zinc from the medium was minimal during the first minute, where no Zn++ effect on cell functions was manifest, (2) when zinc-loaded cells with inhibited activity were washed and reincubated for at least 15 minutes in zinc-free medium, almost 95 per cent of the zinc was washed out and cell activity was normalized. This indicated reversibility of the zinc effect, (3) in the presence of increasing concentrations of autologous plasma in the medium, the effect of zinc was proportionally less pronounced and at the same time uptake of zinc by cells was decreased. Of the six divalent cations studied at 50 muM concentration and in the presence of Mg++, only Zn++ was inhibitory, Se and Co were inactive, and Mn and Cu stimulated O2 consumption of latex-activated granulocytes. We conclude that zinc ions, in the presence of Mg++ in the medium, inhibit various functions of dog peripheral granulocytes and this effect is closely associated with zinc uptake by the cells. The effect is reversible and specific for this metal.

Animals↗