Determination of pralidoxime chloride in pharmaceutical dosage forms by isotachophoresis.
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Chemistry, Pharmaceutical↗
Biomedical subjects
R Popovic
Publications and source records attributed to R Popovic.
Mercury inhibition at the donor side of photosystem II is reversed by chloride.
Mercury is an environmental contaminant that strongly inhibits photosynthetic electron transport, photosystem II being the most sensitive target. We investigated in greater detail the effect of mercury using photosystem II submembrane fractions of higher plants. Oxygen evolution was strongly inhibited and variable chlorophyll fluorescence was severely quenched by mercury. Chloride, an inorganic cofactor known to be essential for the optimal function of photosystem II, significantly reversed the inhibitory effect of mercury. However, calcium, another essential cofactor, showed no reversal capacity. It is concluded that on the donor side of PSII, mercury exerts its action by perturbing chloride binding and/or function. Considering the exceptional affinity of mercury for sulfhydryl groups of proteins, the results suggest the implication of cystein residue(s) in maintaining structural and functional integrity of photosystem II.
Chlorides↗
Atrial natriuretic peptide release in response to different positive end-expiratory pressure levels.
OBJECTIVE: To assess the influence of different positive end-expiratory pressure (PEEP) levels on plasma atrial natriuretic peptide concentrations. DESIGN: Prospective, randomized study. SETTING: Intensive care unit of a university hospital. PATIENTS: Twenty-seven patients who were mechanically ventilated due to acute respiratory failure. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: The patients were randomized into three groups: in each group, a defined PEEP level (5, 10, or 15 cm H2O, respectively) was applied, alternating with zero PEEP (0 cm H2O) in consecutive order (reversal experiment). Blood samples for the determination of atrial natriuretic peptide concentrations were drawn from the pulmonary artery and the radial artery catheters. There were no decreases in atrial natriuretic peptide concentrations with a PEEP of 5 cm H2O, but significant decreases could be shown for PEEP values of 10 and 15 cm H2O. The patients of all groups were subjected to PEEP levels of 5, 10, 15, and 20 cm H2O in randomized order (step experiment). The data demonstrated a significant inverse correlation between changes in PEEP levels and changes in plasma atrial natriuretic peptide concentrations. CONCLUSION: The data suggest that the release of atrial natriuretic peptide is influenced by a PEEP of > or = 10 cm H2O, while a PEEP of < or = 5 cm H2O does not disturb this cardiac endocrine function.
Adult↗
Study of dependency between culture growth and photosynthetic efficiency measured by fluorescence induction in Selenastrum capricornutum inhibited by copper.
Fluorescence parameters were reported earlier to be reliable indicators in the determination of heavy metal toxicity in algal cultures (Samson and Popovic, 1988). In this report, the effects of copper on Selenastrum capricornutum culture growth and photosynthetic efficiency were studied at different copper concentrations. By using the complementary area of variable fluorescence kinetics and the cell counting method, we determined the level of toxicity at different copper concentrations and the ability of algal populations to adapt to inhibitory effects. Algae exposed to copper concentrations higher than 0.5 mg/liter were incapable of recovering biochemical and physiological processes related to photosynthesis after 96 hr. A recovery process in algal culture intoxicated with 0.5 mg/liter was revealed only by fluorescence induction phenomena. Here, the authors justify the use of fluorescence induction parameters in the investigation of copper stress effects on algal populations and their short-term adaptation phenomena.
Cell Division↗
Extremely prolonged half-life of prostacyclin in plasma causative for bleeding in an uremic patient?
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Aged↗
[DEXA (dual-energy x-ray absorptiometry) and DPA (dual photon absorptiometry) in densitometry of the femoral neck: correlation of the measurements of three commercially available instruments].
The bone mineral density measurements of three different instruments at the femoral head were compared using 12 cadaver specimens. Two of these instruments were operated by x-rays (dual energy x-ray absorptiometry = DEXA), whereas one system was based on a gadolinium source (dual photon absorptiometry = DPA). Although excellent correlation between the measurements was obtained (r greater than 0,9), the measurements of one of the DEXA-instruments were significantly higher than the measurements of the two other systems. We conclude that a comparison of bone mineral density measurements obtained on different densitometry instruments may pose problems. Follow-up examinations should be done on one single densitometry unit.
Absorptiometry, Photon↗
Protective role of CaCl2 against Pb2+ inhibition in Photosystem II.
The Pb2+ treatment of Photosystem II (PS II) membrane fragments, either intact or depleted in 17 and 23 kDa extrinsic polypeptides, inhibits PS II activity. When CaCl2 was present in the assay, the Pb2+ inhibition was significantly reduced in both types of PS II membranes, suggesting a protective role of CaCl2 against Pb2+ inhibition. However, in either case, the degree of PS II inhibition by Pb2+ was higher in the protein depleted than in intact PS II. It showed that the loss of endogenous Ca2+ induced by polypeptide depletion causes the PS II to be more susceptible to Pb2+. The interaction of Pb2+ with CaCl2 in protein-depleted PS II was competitive. Our results suggest that Pb2+ competes for binding to the Ca2(+)- and Cl- active sites in the water-splitting complex. Since Pb2+ inhibition of PS II activity cannot be reversed by CaCl2 but can be reversed by diphenylcarbazide, we conclude that Pb2+ induced inhibition of PS II activity was mediated via the water-splitting system.
Binding, Competitive↗
Determination of four apparent mercury interaction sites in photosystem II by using a new modification of the Stern-Volmer analysis.
We used the Stern-Volmer method to analyze the mercury fluorescence quenching effect in the green alga Dunaliella tertiolecta. To this end, we introduced a new modification of the Stern-Volmer equation on the basis of the Lineweaver-Burk analysis used to characterize allosteric enzyme activity. This modification was useful to determine the Stern-Volmer constant, the parameter indicating the fraction of PSII fluorescence susceptible to the mercury quenching effect (Fs), and to estimate the apparent number of mercury binding sites (Napp = 3.72) on PSII which affect the variable fluorescence. This value of Napp indicates the possibility of four mercury binding sites in the PSII complex. We suggested that this may be related to the mercury inhibition of the oxygen-evolving complex containing four Mn active sites.
Binding Sites↗
Removal of the 33, 23 and 18 kDa extrinsic proteins of photosystem II by sulfite treatment at alkaline pH.
We found that sulfite incubation of photosystem II submembrane fractions can induce selective depletion of the 18, 23 and 33 kDa polypeptides of the PSII oxygen evolving complex. When the sulfite treatment was done at pH 8.0, the 18 and 23 kDa proteins were removed efficiently from the PSII oxygen evolving complex. Under the same conditions, the 33 kDa subunit remained bound (even when 2 M sodium sulfite was used). However, in more alkaline conditions (pH 9.8), we show extensive removal of the 33 kDa in the presence of a low sulfite concentration (50 mM). The different extraction affinity for the 18, 23 and 33 kDa of the photosystem II complex was interpreted to mean that the 33 kDa polypeptides are bound to photosystem II by both electrostatic and hydrogen bonding forces.
Chlorophyll↗
Use of algal fluorescence for determination of phytotoxicity of heavy metals and pesticides as environmental pollutants.
The phytotoxicity of heavy metals and pesticides was studied by using the fluorescence induction from the alga Dunaliella tertiolecta. The complementary area calculated from the variable fluorescence induction was used as a direct parameter to estimate phytotoxicity. The value of this parameter was affected when algae were treated with different concentrations of mercury, copper, atrazine, DCMU, Dutox, and Soilgard. The toxic effect of these pollutants was estimated by monitoring the decrease in the complementary area, which reflects photosystem II photochemistry. Further, the authors have demonstrated the advantage of using the complementary area as a parameter of phytotoxicity over using variable fluorescence yield. The complementary area of algal fluorescence can be used as a simple and sensitive parameter in the estimation of the phytotoxicity of polluted water.
Chlorophyll↗
Atrial natriuretic peptide decrease during spontaneous breathing with continuous positive airway pressure in volume-expanded healthy volunteers.
We examined the effect of spontaneous breathing with continuous positive airway pressure (CPAP) on the plasma concentrations of immunoreactive (ir) alpha-atrial natriuretic peptide (ANP). In three experiments, each of 11 healthy male volunteers performed CPAP at 20, 10 and 0 cm H2O for 2 h during continuous volume loading. Samples were drawn from a peripheral vein. Plasma concentrations of irANP were determined by a sensitive radioimmunoassay. Significantly lower concentrations of irANP were observed during 20 cm H2O CPAP than at 10 and 0 cm H2O. The concentrations of irANP did not differ significantly when individuals breathing with CPAP at 10 and at 0 cm H2O were compared. Our data suggest that CPAP at 20 cm H2O lowers the release of ANP in volume-expanded subjects. We hypothesize that this phenomenon may contribute to the fluid retention and renal dysfunction observed frequently during high CPAP levels. The decline in plasma concentrations of irANP may be the result of atrial compression by the distended lungs and of reduced venous return to the heart during CPAP.
Adult↗
A new method for the separation of the constant and the variable fluorescence of chlorophyll a in in vivo.
The constant fluorescence of chlorophyll a in alga Dunaliella tertiolecta was estimated by a method of the least square regression applied to the linearized form of the equation y = axb. The value of the constant fluorescence obtained by this method was compared by the values estimated with simple linear extrapolation. Constant fluorescence, evaluated by the simple linear extrapolation of 10 ms of the initial variable fluorescence, was 50% higher than the value obtained by the method of the least square regression. We demonstrated that the estimation of constant fluorescence by the least square regression is a more correct method and provides a better comparison of results from different laboratories. This method offers a simple way to determine and separate constant fluorescence from variable fluorescence in the total yield of chlorophyll a fluorescence in "in vivo" conditions. Furthermore it facilitates the interpretation of the variable fluorescence phenomena in "in vivo".
Chlorophyll↗
A new medium improves sampling for determination of platelet factor 4 in human plasma.
The determination of alpha-granule specific platelet proteins in human plasma is a valuable indicator of in-vivo release and platelet activation provided that an artificial in-vitro release during sampling can be avoided. A new sampling medium (M) has been compared with the commercially available ones for the sampling and the subsequent determination of platelet factor 4 and beta-thromboglobulin. M allows blood withdrawal at room temperature (22 degrees C) (3.49 +/- 0.7 ng/ml) without any difference to 4 degrees C (3.47 ng/ml) up to a 30 minutes sedimentation period. However, after 40 minutes there is a significant (p less than 0.01) increase, amounting at 22 degrees C (13.30 ng/ml) and at 4 degrees C 6.68 ng/ml. The addition of prostacyclin (PGI2) in-vitro as well as blood withdrawal from volunteers infused with PGI2 at a rate of 5 ng/kg/min did not alter the values of M-preserved samples, whereas in the commercially available ones, PGI2 caused a decrease. A comparison of radioimmunoassay and enzyme immunoassay exhibited no significant difference in the absolute values. Beta-thromboglobulin was assayed as control. The findings indicate M being optimal for the sampling of platelet factor 4, but not for other alpha-granule release products. Thus, there is again evidence, that the alpha-granule products are not released to an equal extent upon a certain stimulus. Furthermore, it seems likely, that various substances inhibit their liberation from the platelet to a differing extent.
Adult↗
Photosynthetic action spectra of the energy storage in bundle sheath cells of Zea mays.
Photosynthetic action spectra (Formula: see text), (Carpentier, R., Larue, B. and Leblanc, R. (1984) Arch. Biochem. Biophys. 228, 534-543.), from 400 to 750 nm were studied in bundle sheath cells of maize. Photosynthetic action spectra in the presence of 10 mM ascorbate or 4 mM ribose-5-phosphate were increased and shifted through all the spectra. After the addition of 10 microM DCMU photosynthetic action spectra were remarkably diminished. On the basis of these results we suggest that the role of PSII in BS chloroplasts will be to prevent the overoxidation of PSI. It appears that in addition to PSII some endogen electron donor may regulate the PSI activity in bundle sheath cells.
Chloroplasts↗
Study of Energy Storage Processes in Bundle Sheath Cells of Zea mays.
Photochemical energy storage in isolated bundle sheath cells from Zea mays was examined. Photoacoustic spectroscopy was used in this study to monitor energy storage processes. The presence of methyl viologen or addition of substrates which activated carbon fixation, prevented energy storage processes through the electron transport system. The energy storage was inhibited completely by dibromothymoquinone (DBMIB) and DCMU, inhibitors of noncyclic electron flow. However, the reductants such as dithiothreitol and ascorbate increased the energy storage. It was concluded that photosystem (PS) I may be reduced by some electron donor(s) other than water and that PSII only partially participates in PSI reduction. It is postulated that the role of PSII is to regulate PSI electron transport and prevent its overoxidation. In the presence of high level of malate, photoacoustic spectroscopy indicated a low energy storage which may be due to induction of energy utilization in carbon assimilation.
Journal Article↗
Mechanical ventilation with the esophageal tracheal combitube (ETC) in the intensive care unit.
Mechanical ventilation in critically ill patients is usually performed with the conventional endotracheal airway. The esophageal tracheal combitube (ETC) is a new device for cardiopulmonary resuscitation, conceived to bridge the gap between hospital and prehospital phases. The ETC may be used in esophageal and endotracheal positions. The authors report six patients who were ventilated with the ETC in the esophageal obturator position for 2-8 h after emergency ventilation. Blood gas data showed adequate ventilation with the ETC during the observation period. Data suggest that mechanical ventilation with the ETC is possible for several hours after cardiopulmonary resuscitation. This might be helpful during the initial post-arrest period, when replacement of the ETC by a conventional endotracheal airway might destabilize a vulnerable patient.
Aged↗
Prostacyclin formation around human abdominal aortic ostia.
Earlier studies have demonstrated an age dependent effect in the extent of sudanophilic and atherosclerotic lesions around aortic ostia in men. As prostacyclin may be a key determinant in the development of atherosclerosis we examined its formation around abdominal aortic ostia (coeliac, superior mesenteric and inferior mesenteric arteries) in-vitro. Prostacyclin formation was higher distal to the orifice as compared to proximal areas, but without reaching the level of significance. Prostacyclin formation was always higher in females than in males and in nonsmokers than in smokers, showing the greatest difference distal to the ostium, but again without significance. From the limited number of vessels examined, no trend for an age dependency can be noted. The relation between prostacyclin generation and morphological data is discussed.
Adolescent↗
Electron Transport-Dependent Chlorophyll-a Fluorescence Quenching by O(2) in Various Algae and Higher Plants.
A comparison of chlorophyll-a fluorescence in brown algae (Macrocystis integrifolia, Fucus vesiculosis), green algae (Scenedesmus obliquus, Ulva sp.) and higher plants (bean, corn) show differences in the relative fluorescence intensities and induction time courses which characterize each type of plant. These differences are not reflected in either the maximum fluorescence emission in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (F(max)) or the nonvariable fluorescence (F(o)). Constancy of F(o) and F(max) suggests functional similarities of photosystem II and associated antennae pigments in the various classes of plants. The time course differences are observed only in the absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and appear, therefore, to be electron transport dependent. During induction, the peak in fluorescence (F(p)) is much lower in all of the algae studied than in the higher plants. Exogenous O(2) strongly quenches F(p) in all plants studied and our data indicate that the low F(p) in the algae can be partially accounted for by endogenous O(2) quenching.
Journal Article↗