Biomedical subjects
Publications and source records attributed to V A Iurkiv.
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It has been demonstrated that histamine induces in rabbit small intestine an ATPase activity which is stimulated by NaCl or NaHCO3. The Na+/HCO3- (C1-)-stimulated ATPase activity, unlike the Mg2+,HCO3(-)-ATPase activity, has a pH optimum at pH 6.2, is inhibited by ethacrynic acid (10(-4) M) and bivalent metal ions (but not 10(-2) M thiocyanate). The substrate specificity of Na+/HCO3- (C1-)-ATPase and its regulation by Ca2+ ions has been studied. The feasible role of the enzyme in secretion is discussed.
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It was shown that "mouse" toxin of Yersinia pestis injected into the rat tail vein (LD100) caused a 2-fold decrease in the glycogen content in the liver and the glucose content in the blood. The Bmax of beta-adrenoceptors as well as basal, forskolin, 5-guanylyl imidodiphosphate, fluoride and glucagon-stimulated liver adenylate cyclase (AC) activities did not change in all periods of intoxication. After 5 hours of intoxication isoproterenol had no effect on AC; however, the cAMP content was increased 1.5 times in comparison with control. These data suggest that plague intoxication has no effect on cAMP-dependent regulation of glycogenolysis and gluconeogenesis in the liver. The action mechanism of toxin(s) on carbohydrate metabolism in also unrelated to the decrease in Bmax for alpha 1 adrenergic receptors in liver membranes, whose number increased 1.3 and 1.5 times after 1 and 2 hours of intoxication.
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Thermostable protein factor (20000 Da) was prepared from Yersinia pestis avirulent strain EV 1290. This protein inhibited the aggregation of human platelets as well as elevation of [Ca2+], induced by different agonist. The action of this protein on platelets is accompanied by elevation of cellular cGMP levels. This factor activated guanylate cyclase suspension of human platelets. The data indicate that this protein factor of Y. pestis may possibly release in circulation during decay of bacteria and can change the physiological activity of human blood cells and contribute to the pathogenesis of plague.
Yersinia pestis toxin (fraction II by E. Baker) (YPT) inhibited the aggregation of human platelets as well as elevation of [Ca2+], induced by different agonists (ADP, PAF, Thrombin). Agonist-induced Ca2+ mobilization and Ca2+ influx were dose-dependently inhibited by the toxin. The effect was rapid, developing during the first minute of incubation with toxin. In contrast to murine lethal protein (MLP), the platelet-inhibiting activity was thermostable and was eliminated in the course of MLA purification from YPT. These data indicate that Yersinia pestis component, unlike MLP, could influence the Ca(2+)-dependent processes in human platelets.
Influence of intravenous administration to rats of murine toxin of Y. pestis (1 mg/ml, LD100) on the number of potential-operated Ca(2+)-channels, alpha- and beta-adrenergic and M1-cholinergic receptors of plasma membranes and heart contractility function has been studied in rats. The number of Ca(2+)-channels in plasma membranes and contractility of heart decreased by 50% in 1 hour after the i.v. administration of toxin and further decreased up to the lethal end. During the agonal stage of the shock desensitization of beta-adrenergic receptors has been discovered, while alpha-adrenergic and M1-cholinergic receptors remained unchanged throughout the experiments.
Influence of intravenously administered to rats murine toxin of Y. pestis in the dose of I mg/ml (LD100) on the regulatory properties of heart plasma membranes adenylate cyclase (AC) has been studied during the intoxication. It has been shown that basal, fluoride,- and 5-guanylyl imidodiphosphate-stimulated AC activity remained unchanged during the intoxication. Stimulation of AC by isoproterenol, glucagon and histamine did not change during the first two hours and significantly decreased after 5 hours of intoxication. Affinity of AC for the investigated hormones did not change through the experiments.
Patients with meningococcal infection, meningitis and with a mixed form of the disease were demonstrated to have unbalance in the redox system of glutathione during the all disease periods till the clinical recovery. Activation of glutathione peroxidases to hydrogen peroxide and tertiary butyl hydroperoxide in erythrocytes was coupled, during the whole disease, with unbalance of the time-course of changes in the interrelated enzymes--superoxide dismutase and glutathione peroxidase to hydrogen peroxide, while in neutrophils, the balance of those enzymes remained unimpaired. Glutathione transferase activity appeared reduced both in erythrocytes and neutrophils. Potential mechanisms by which the redox system of glutathione and superoxide dismutase may be deranged in meningococcal infection are under discussion.
A study was made of the time-course of changes in the activity of the enzymic antioxidant system of blood platelets from patients with meningococcemia and meningitis (mixed form) of medium gravity. As a result a steady unbalance in the redox system of glutathione was established: a decrease of glutathione reductase activity and rise of the activity of glutathione peroxidases to hydrogen peroxide and tertiary butyl hydroperoxide until the clinical recovery. The patients with meningococcal meningitis and with the mixed form of medium gravity manifested impairment of the interrelations between superoxide dismutase and glutathione peroxidase to hydrogen peroxide, with that impairment being eliminated by the end of the disease. Potential mechanisms by which the enzymic antioxidant system is impaired in meningococcal infection are discussed.
It was demonstrated, that the lethal in vitro suppressed the phagocytic activity of peritoneal mononuclear phagocyte (Mph) and enhanced the level activity of glutathione peroxidase to H2O2 (GP-H2O2) in Mph of resistant to anthrax BALB mice. In Mph BALB the authors observed dependent-dose enhancement of GP-H2O2 activity and reduction of the ratio of level glutathione reductase (GR) to GP-H2O2 (GR/GP-H2O2). The enhancement of activity GR-H2O2 in Mph CBA was not dependent on the doses of toxin. The coefficient GR/GP-H2O2 was similar to the control. The mechanisms of hereditary resistance to anthrax were discussed.
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Complexes of lipopolysaccharide (LPS) B of Salmonella typhimurium with human low density lipoproteins (LDL) formed during in vitro coincubation via spontaneous incorporation of LPS (complex LDL-LPS) or through the incorporation stimulated by the serum protein fraction (LPS/LDL complex) were studied. The LPS/LDL complex was shown to maximally bind 0.24 mg of LPS per 1 mg of LDL protein, whereas the LDL-LPS complex contained only 0.07 mg of LPS per 1 mg of LDL protein. The observed incorporation of LPS into LDL particles was not possibly associated with a transfer of lipids or proteins from high density lipoproteins to LDL. The insertion of LPS was probably accompanied by the expulsion of a small portion of phosphatidylcholine molecules from the outer monolayer of LDL into the aqueous medium and by an increase in the phosphatidylethanolamine concentration in LDL. Simultaneously, the level of esterified cholesterol in the LPS/LDL complex decreased, and the concentrations of free cholesterol and triacylglycerols showed a rise. The level of free fatty acids in the LPS/LDL complex increased more than twofold compared with intact LDL. The enhancement of LPS incorporation did not result in the insertion of any serum proteins into LDL, in which apoB-100 remained the major apolipoprotein (ca. 90%); apoB-100 fragments made up to 5-7%, whereas apoE and apoC contained altogether ca. 3-5%. It is suggested that the LPS/LDL complex obtained can bind to three types of cell receptors, i.e., apoB/E receptors, LPS receptors and scavenger receptors of macrophages (monocytes); the increased level of free fatty acids in the LPS/LDL complex may accelerate its subsequent catabolism.
Complexes of Salmonella typhimurium lipopolysaccharide toxin (LPS) with low density lipoproteins (LDL) containing various amounts of LPS were prepared in vitro. The 31P-NMR spectra showed that in the LDL-LPS complexes as well as in native LDL all phosphate groups of phospholipids are accessible to the paramagnetic shift reagent, Pr3+. Besides, the low frequency mobility of phospholipid phosphates in the complex is diminished. It was supposed that the phospholipid molecules in the LDL/LPS complex as in native LDL form a monolayer structure on the surface of LDL. The intrinsic fluorescence spectra of tryptophan residues of the apoprotein (apo B-100) revealed that the incorporation of LPS molecules into LDL particles is accompanied by minor changes in the conformation and orientation of the apo B molecule. As a result of these changes, certain fragments become exposed to a more hydrophilic environment and become more accessible to fluorescence quenchers. The use of charged (I-, Cs+) and uncharged (acrylamide) quenchers permitted to identify in the apo B molecule different tryptophan residues, some of which are localized in the vicinity of negatively charged groups, whereas others are neighbouring positively charged groups. It is suggested that the LPS molecules incorporated into LDL particle do not screen the apo B molecule to such an extent that it would hinder the LDL/LPS complex binding to apo B/E cellular receptors.
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The preincubation of isolated washed human platelets with lipopolysaccharide toxin (LPS) from Salmonella typhimurium (10 min, 37 degrees) speeds up the thrombin-induced aggregation. Besides, LPS-pretreatment was shown to alter the turnover of polyphosphoinositides stimulated by thrombin and significantly elevated concentrations of diacylglycerol and thromboxane B2 in comparison with control platelets. However, LPS does not influence on the lipid fluidizing effect of thrombin action as testifies by ESR spectroscopy with doxyl-stearic acids as spin-probes. An LPS pretreatment of platelets that induces no aggregation by itself is proposed might transform cells into a state of hidden activation" associated with the accumulation of such products as diacylglycerol and precursors of thromboxane B2. Addition of thrombin to such "preactivated" platelets could cause a more effective aggregation.