Presence Of Low Concentrations Research Articles

K252a modulates the expression of nerve growth factor-dependent capsaicin sensitivity and substance P levels in cultured adult rat dorsal root ganglion neurones.

K252a, an inhibitor of trk phosphorylation and nerve growth factor signal transduction in PC12 cells, blocked nerve growth factor-induced responses in cultured adult rat dorsal root ganglion sensory neurones. The nerve growth factor-dependent appearance of capsaicin sensitivity and accumulation of the neuropeptide substance P were inhibited when dorsal root ganglion neurones were grown in the presence of low concentrations (100 nM) of K252a. At higher concentrations (3 microM), however, K252a stimulated the development of capsaicin sensitivity and the accumulation of substance P even in the absence of nerve growth factor. By using a wide dose range, therefore, we showed that K252a could either inhibit or mimic nerve growth factor's actions on sensory neurones. These results may explain the apparent paradox in the literature that some groups show a blocking effect of K252a on nerve growth factor-dependent survival of dorsal root ganglion sensory neurones, whereas other report that K252a can substitute for nerve growth factor or other trophic factors and promote neuronal survival.

Bistability and its regulation by serotonin in the endogenously bursting neuron R15 in Aplysia.

1. Previous computational studies of models of neuron R15 in Aplysia have indicated that several distinct modes of electrical activity may coexist at a given set of parameters, that this multistability can be modulated by transmitters such as serotonin (5-HT) and that brief perturbations of the membrane potential can induce persistent changes in the mode of electrical activity. To test these predictions, the responses of R15 neurons to injections of brief (1.5 s) current pulses were recorded intracellularly in the absence and presence of 5-HT. 2. In the absence of 5-HT, brief perturbations induced abrupt transitions in the electrical activity from bursting to beating. Such transitions were observed in approximately 20% of the cases. The duration of beating activity varied from several seconds to tens of minutes. In the presence of low concentrations (1 microM) of 5-HT, both the probability of mode transitions and the duration of induced beating activity increased significantly. 3. These results indicate that at least two stable modes of electrical activity can coexist in R15 neurons and that this bistability can be regulated by 5-HT. In general, these conclusions agree with the results from analyses of mathematical models of R15. Although the function of these dynamic properties in R15 is speculative, our results, interpreted on the background of the model, support the notion that nonlinear dynamical properties of individual neurons can endow them with richer forms of information processing than has generally been appreciated.

Aggregation Behavior of Water Soluble Bis(benzothiazolylidene)squaraine Derivatives in Aqueous Media†

Two new water soluble squaraine dyes, bis[3-(p-carboxybenzyl)benzothiazol-2-ylidene]squaraine (Sq1) and bis[3-(carboxymethyl)benzothiazol-2-ylidene]squaraine (Sq2), have been synthesized and their photophysical properties have been characterized. Sq1 and Sq2 form dimer aggregates in water that have absorption bands blue-shifted to those of the monomeric forms. Aggregate formation is more preferred in D2O than in H2O. In the presence of low concentrations (<3 × 10-4 M) of poly(vinylpyrrolidone) (PVP), enhancement in aggregate formation of Sq1 is observed, whereas that of Sq2 remains unaffected. Higher concentration (>3 × 10-4 M) of PVP leads to the disruption of the aggregate and formation of a new species with absorption bands red-shifted to those of the corresponding monomers. The nature of these interactions has been investigated. It is proposed that hydrophobic interaction between the chromophoric units is the major driving force for the formation of the H-type (sandwich) aggregates in water. The red-shifted species are attributed to the monomeric forms, microencapsulated in a hydrophobic environment provided by PVP. Picosecond laser flash photolysis studies of the aggregates show clear evidence for the breakup of the aggregate from the excited state to yield an excited state−ground state monomer pair that rapidly recombines to reform the ground state dimer.

STREPTOCOCCAL PYROGENIC EXOTOXINS A (SpeA) AND C (SpeC) STIMULATE THE PRODUCTION OF INDUCIBLE NITRIC OXIDE SYNTHASE (iNOS) PROTEIN IN RAW 264.7 MACROPHAGES

Streptococcal pyrogenic exotoxins A (SpeA) and C (SpeC) are members of a family of superantigens produced by group A streptococci that appear to play a key role in the pathogenesis of streptococcal toxic shock syndrome. Since it is known that nitric oxide (NO) and tumor necrosis factor (TNF) are largely responsible for the shock and multiple organ dysfunction of Gram-negative sepsis, we hypothesized that SpeA and/or SpeC could trigger the production of inducible nitric oxide synthase (iNOS) and/or TNF by murine macrophages. We exposed RAW 264.7 macrophages to increasing concentrations of SpeA or SpeC alone and in combination with recombinant murine interferon-gamma (rIFN gamma) for 16-24 h. We found that both SpeA and SpeC triggered iNOS production in the presence of low concentrations of rIFN gamma, while neither provoked iNOS accumulation in the absence of rIFN gamma. Neither SpeA nor SpeC (with or without rIFN gamma) reproducibly induced TNF production by these murine macrophages. These data indicate that two streptococcal exotoxins up-regulate iNOS production by murine macrophages and suggest that nitric oxide production may play an important role in the pathogenesis of streptococcal toxic shock syndrome.

Enhancement of the stress response by low concentrations of arsenite in arsenite-pretreated Reuber H35 hepatoma cells.

The present study is aimed at determining whether the induction of heat-shock protein (hsp) synthesis, heat-shock mRNAs, and tolerance development after arsenite application has been sensitized to low concentrations of arsenite in Reuber H35 rat hepatoma cells. Using a step-down arsenite treatment, consisting of a 1-hr pretreatment with 100 or 300 microM followed by an incubation with a lower concentration (1-10 microM), H35 cells were shown to exhibit increased sensitivity to low concentrations of sodium arsenite shortly after exposure to the high arsenite concentration, but not any longer when the low concentration was applied 4 hr after pretreatment. In this paper it is shown that exposure of H35 cells to sodium arsenite concentrations of 100 or 300 microM for 1 hr rapidly changes the sensitivity toward a second arsenite treatment with respect to the induction of the heat-shock response. It was observed that under conditions of enhanced sensitivity, an additional increase occurred in hsp synthesis as well as in hsp mRNA (as exemplified by hsp68 mRNA behavior) when low concentrations of arsenite were applied to arsenite pretreated cells. Since no effect of these low concentrations was observed in nonpretreated cells, the effect of step-down treatment results in a higher effect than could be expected based on summation. Furthermore, in sensitized cultures, cells are able to develop a higher level of tolerance in the presence of low concentrations of arsenite. It can be concluded that during a transient period of enhanced sensitivity, low concentrations of the original stressor are able to enhance hsp synthesis and to induce a higher level of tolerance in comparison with control cultures that are sensitized but not incubated in the presence of low concentrations of the original stressor.

Possible involvement ofL-glycero-phosphoryl-ethanolamine in the phospholipid methylation pathway

It is usually accepted that GPEtn is only an intermediate in glycerophospholipid degradation. However, some years ago J. P. Infante published a review-hypothesis concerning the possible involvement of GPEtn and GPCho in the biosynthesis of acyl-specific glycerophospholipids in mammalian tissues. This paper reports the results obtained by incubating brain cortex slices in the presence of labeled GPEtn. GPEtn enters the cells and the radioactivity of the precursor is found in both PE and PC. When these results were compared with those obtained by incubating brain slices in the presence of 3H-Etn, a significantly higher amount of radioactivity was found in PC, mainly after short incubations in the presence of low concentrations of the precursors. The slopes of the methylated forms of PE further underline the above differences found by comparing the results obtained with the two precursors. The results presented in this paper suggest a possible role of GPEtn in phospholipid biosynthesis and methylation pathway of PE.

Initiation of embryogenesis from cultured barley microspores: a further investigation into the toxic effects of sucrose and glucose

The toxic effects of sucrose and glucose upon Hordeum vulgare L. ev Igri microspore cultures were investigated. It was concluded from this study that: -microspores could be cultured in the presence of low concentrations of glucose without any deleterious effects upon cell viability, but the microspores did not form embryos or calluses. -microspores died when incubated in the presence of 40 mM glucose during the first 2 of days of incubation, but, if glucose was added after this period, cells went on to produce embryos or calluses. -the toxic effects of sucrose upon cultured microspores were irreversible after 6 h from the start of incubation. Implications of these results on underlying causes of cell death in the presence of sucrose and glucose are discussed.

Poliovirus‐1 adsorption onto and desorption from montmorillonite in seawater. Survival of the adsorbed virus

Abstract It is an acknowledged fact that most viruses in the aquatic medium are present in an aggregated form or adsorbed to particulate matter and especially clay matter. This adsorption is a parameter that must be taken into account when dealing with the natural inactivation of viruses in an aquatic medium. The adsorption of poliovirus‐1 in seawater was examined on Na‐montmorillonite. It proved to be a quick (less than 30 min) and mass phenomenom depending on the Na‐montmorillonite concentration. As a matter of fact, whereas more than 99.9% of viruses are adsorbed in less than 30 min in the presence of 500 mg.l‐1 of Na‐montmorillonite, the adsorption percentage under the same conditions is yet around 70% with a concentration of 3 mg.l‐1. A comparison between the survival durations of poliovirus‐1, be it free or adsorbed onto Na‐montmorillonite in a seawater with a salinity of 33 g.l‐1 at 25°C, showed that the survival duration was not significantly increased in the presence of low concentrations (3 and ...

Barium ions fail to support neurotransmission at a central synapse

Synaptic transmission in the CA1 area of the hippocampal slice preparation in vitro was studied in bathing media containing different levels of divalent cations. Transmission was abolished by replacing the normal levels (2.5 mM) of Ca 2+ with 3 mM Mg. Transmission was not permanently restored by subsequent addition of Ba 2+ but added Ca 2+ was effective. Transient reappearance of synaptic currents were seen when Ba 2+ was added at a time when contaminating levels of Ca 2+ were still present, but neurotransmission waned as [Ca 2+] e declined with protracted washout. In accordance with this interpretation, Ba 2+ potentiated the transmission observed in the presence of low concentrations (0.25 mM) of Ca 2+. Little evidence was found for Ba 2+ effects at axonal sites but the potentiation of synaptic transmission by Ba 2+ could be accounted for in terms of a blockade of terminal K-channels.

The stabilization of a human IgM monoclonal antibody with poly(vinylpyrrolidone).

An IgM anti-group B Streptococcus monoclonal antibody (4B9) was found to undergo irreversible heat-induced aggregation at 50 degrees C. A variety of excipients was tested for their ability to inhibit antibody aggregation. The amount of 4B9 aggregation, which was determined by analysis on a size-exclusion HPLC, was significantly reduced in the presence of low concentrations [between 0.1 and 1.0% (w/v)] of poly(vinylpyrrolidone) (PVP) molecules ranging in molecular weight from 10 to 40 kDa. When the PVP concentration was greater than 1.0%, antibody aggregation was enhanced, and with the highest molecular weight PVP, antibody precipitation occurred. HPLC was used to show that more PVP was associated with the 4B9 at 50 degrees C than at 25 degrees C. Differential scanning calorimetry revealed that PVP concentrations greater than 2.0% decreased the antibody thermal transition temperature. Enzyme-linked immunosorbent assays were used to assess the effects of PVP on the antigen binding capacity of 4B9 and on 4B9 quantitation. At 4 degrees C, PVP solutions of up to 5.0% had no effect on either 4B9 quantitation or antigen binding. At 50 degrees C, however, less 4B9 was detected in the 5.0% PVP solution. The heat stabilization of the 4B9 antibody by low concentrations of PVP can be explained by a weak binding of PVP to the native protein. The PVP may sterically interfere with protein-protein interactions, thus reducing aggregation. Higher concentrations of PVP lead to protein aggregation and precipitation, probably by a volume-exclusion mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser-assisted optical rotational cell analyser (L.O.R.C.A.); II. Red blood cell deformability: Elongation index versus cell transit time

Red blood cell deformability was measured under normal and experimental conditions with the Laser-assisted Optical Rotational Cell Analyser (LORCA). Results were compared to simultaneously performed filtration measurements using the Cell Transit Analyser (CTA). The deformability parameters of the two methods were Elongation Index (EI) and mean Cell Transit Time (CIT), respectively. Aside from instrumental and intra-individual reproducibility, normal values, the effect of sample aging and of changing medium osmolality are reported. Furthermore, the respective sensitivities were determined using red blood cells with slightly impaired deformability. Both heat treatment and incubation in the presence of low concentrations of glutaraldehyde are used to manipulate the deformability of the entire red cell population. It is concluded that minor defects in red blood cell deformability are detected more easily by the laser technique than by filtration. Even when the absolute differences in EI are small, they can be significant due to the very high reproducibility of the ektacytometric technique. Differentiation between a decreased deformability of the entire RBC population and the presence of a small (i.e., 5% or higher) subpopulation of rigid cells can be achieved with the LORCA by combining the measured EI-values with visual inspection of the diffraction pattern. Finally, no significant correlation was found between the results of both techniques applied to blood from 525 patients with various diseases.

Purification and characterization of the high molecule weight microtubule associated proteins from neonatal rat brain.

The changes in the levels of microtubule-associated proteins (MAPs) during advanced embryonic stages, neonatal and adult organisms reflect the importance of these cytoskeletal proteins in relation to the morphogenesis of the central nervous system. MAP-1B is found in prenatal brains and it appears to have the highest levels in neonatal rat brains, being a developmentally-regulated protein. In this research, a fast procedure to isolate MAP-1B, as well as MAP-2 and MAP-3 from neonatal rat brains was designed, based on the differential capacity of poly L-aspartic acid to release MAPs during temperature-dependent cycles of microtubule assembly in the absence of taxol. The high molecular weight MAP-1B was recovered in the warm supernatants after microtubular protein polymerization in the presence of low concentrations of polyaspartic acid. Instead, MAP-2 and a 180 kDa protein with characteristics of MAP-3 remained associated to the polymer after the assembly. Further purification of MAP-1B was attained after phosphocellulose chromatography. Isolation of MAP-2 isoforms together with MAP-3 was achieved on the basis of their selective interactions with calmodulin-agarose affinity columns. In addition, MAP-2 and MAP-3 were also purified on the basis of their capacities to interact with the tubulin peptide beta-II (422-434) derivatized on an Affigel matrix. However, MAP-1B did not interact with the beta-II tubulin fragment, but it showed interaction with the Affigel-conjugated beta-I (431-444) tubulin peptide. The different MAPs components were characterized by western blots using specific monoclonal antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Matrix effects of potassium chloride and phosphoric acid in argon inductively coupled plasma atomic emission spectrometry

Changes in analyte emission intensity in the presence of low concentrations of potassium chloride and phosphoric acid were studied in inductively coupled plasma atomic emission spectrometry. It has been shown that both matrices can cause significant depressant effects on the relative emission intensities of Sr, Mg, Mn, Fe, Cu and Zn under normal analytical operating conditions and that the lowering of intensity was more pronounced for KCl than for H3PO4 at the same analyte to matrix concentration ratio. The matrix effects can be corrected by increasing the power supplied to the plasma, which was found to correlate with the excitation energy of the emission line.

Platelet-derived growth factor stimulates hyaluronate but not proteoglycan synthesis by human gingival fibroblasts in vitro.

The effect of PDGF-BB on human gingival fibroblasts was monitored in an in vitro system. PDGF was found to be mitogenic for these cells, although it required the presence of low concentrations of fetal calf serum to be active. Proteoglycan and hyaluronate synthesis was analyzed by labeling newly synthesized macromolecules with [35S]-sulfate or [3H]-glucosamine, respectively. Identification of specific glycosaminoglycans was achieved by selective enzymatic or chemical degradations. It was found that cells cultured in the presence of PDGF showed no discernible differences in proteoglycan synthesis relative to the control cultures. There were no alterations in amounts of proteoglycans synthesized, types of sulfated glycosaminoglycans synthesized, or relative hydrodynamic sizes of the proteoglycans. In contrast to the proteoglycans, hyaluronate synthesis was significantly increased in the presence of PDGF. The increase in [3H]-glucosamine incorporation into newly synthesized hyaluronate correlated with an increase in the activity of the enzyme hyaluronate synthetase but could not be accounted for entirely by changes in the specific activity of sugar nucleotide precursors, which did alter slightly under differing culture conditions. It is concluded from these results that PDGF stimulates gingival fibroblasts to proliferate and is associated with a differential effect of proteoglycan and hyaluronate synthesis. These observations may correlate with the observed early events associated with wound healing and repair.

Radio-label and mass determinations of inositol 1,3,4,5-tetrakisphosphate formation in rat cerebral cortical slices: differential effects of myo-inositol.

To investigate the effects of increasing concentrations of myo-inositol (inositol) on receptor stimulated [3H]inositol polyphosphate formation in the absence of lithium, slices of rat cerebral cortex were incubated with various concentrations of [3H]inositol (1 to 30 microM). Carbachol stimulated formation of [3H]inositol trisphosphate (InsP3) and [3H]inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) increased several fold when the inositol concentration was increased reaching a plateau at approximately 12 microM inositol. Time course studies revealed that in the presence of low concentrations of inositol (1 microM), [3H]InsP3 and [3H]Ins(1,3,4,5)P4 formation in response to carbachol stimulation increased slowly over a 10 to 20 min time period, whereas in the presence of 4 and 12 microM inositol, carbachol stimulated [3H]InsP3 and [3H]Ins(1,3,4,5)P4 formation was rapid and essentially complete within 3 to 5 min after carbachol addition. Although the carbachol dose response in 12 microM inositol had a much greater maximal efficacy, there was no change in potency. Similar to the effects of carbachol on [3H]Ins(1,3,4,5)P4 formation from prelabeled phosphoinositides, muscarinic receptor stimulation increased Ins(1,3,4,5)P4 mass formation by seven fold. Furthermore, Li+ (8 mM) completely inhibited carbachol stimulated increases in Ins(1,3,4,5)P4 mass formation. In contrast to the effects of increasing inositol on carbachol stimulated formation of radiolabeled inositol phosphates, increasing inositol had no effect upon mass formation of Ins(1,3,4,5)P4. These results show that when measuring inositol polyphosphate formation by the radiolabeling technique in the absence of Li+, increasing the inositol concentration greatly increases the stimulated component of [3H]InsP3 and [3H]Ins(1,3,4,5)P4 formation. However, this inositol induced increase in agonist stimulated Ins(1,3,4,5)P4 formation is not reflected as an increase in mass formation.

Removal of geosmin and methylisoborneol from drinking water by adsorption on ultrastable zeolite-Y

Geosmin and 2-methylisoborneol (MIB) were removed from solutions in freshwater (100–180 ng/l) by adsorption on US-Y zeolite (SiO 2/Al 2O 3 = 80). The zeolite can be re-used by burning off the adsorbed organics. Adsorption efficiency for geosmin and MIB was not reduced by water hardness or the presence of low concentrations (5 mg C/l) of humic acid.

Cauliflower Mosaic Virus Particles Alter the Sensitivity of Arabidopsis thaliana Seedlings to 2,4-D

Summary Seed obtained from Arabidopsis thaliana plants can be germinated on agar plates and seedlings remain viable in the presence of low concentrations of the growth substance 2,4-D. However, when seed obtained from plants infected with cauliflower mosaic virus (CaMV) was similarly germinated in 2,4-D, seedlings developed cotyledons but then rapidly bleached and senesced. Bleached plants were also observed when purified particles of CaMV were mixed with seed obtained from healthy plants and germinated in 0.23-2.3 μM 2,4-D. The growth substance alone was found to cause bleaching only when increased above 2.3 μM. The effect of CaMV and 2,4-D on Arabidopsis was still observed after UV-inactivation of virus particles suggesting that the effect was caused by a change in the sensitivity of Arabidopsis to 2,4-D rather than virus replication.

Synergistic and molecular interactions between the formamidine amitraz and copper(II) sulfate, used against the mite Varroa jacobsoni O., a parasite of the honeybee Apis mellifera L.

Toxicological field assays have shown that the shock-treatment efficacy of the formamidine pesticide amitraz, used against the parasitic mite Varroa jacobsoni, is synergistically improved by the administration of copper(II) sulfate through feeding of the honeybees. Amitraz is autoxidized and this process is accompanied by chemiluminescence. The emission is enhanced in the presence of low concentrations of H2O2. A dose-related inhibition of the chemiluminescence by CuSO4 was observed; consistent with the formation of copper-amitraz complexes evidenced in vitro. The results suggest the possibility that a protection of amitraz by cupric ions might be at the origin of the enhancement of its toxicity and thus makes a contribution to the observed synergy.

Effect of caffeine and zinc on DNA and protein synthesis of neonatal rat cardiac muscle cell in culture.

The effect of caffeine and/or zinc on DNA and protein synthesis of purified neonatal-rat ventricular cardiac myocytes was studied. Caffeine (0.2-2 mM) inhibited both DNA and protein synthesis of the cells. Addition of EDTA in the growth medium inhibited both DNA and protein synthesis. Without caffeine and in the presence of lower concentrations of caffeine (0.2 mM) in the growth medium, 10 microM of zinc concentration reversed DNA synthesis, which was inhibited by the chelating agent (EDTA). Higher concentrations of caffeine (2 mM) in the growth medium completely abolished sensitivity of cardiac myocytes to zinc. Additional zinc supplementation to the growth medium of cardiac myocytes did not alter the rate of protein synthesis. The present results suggest that the effect of caffeine on cardiac myocytes may be associated with the zinc-dependent enzymes involved in DNA synthesis.

Effects of sub-MICs of antibiotics on cell surface characteristics and virulence of Pasteurella multocida.

The effects of sub-MICs of certain antibiotics, namely, penicillin G, tetracycline, and trimethoprim-sulfamethoxazole, on the cell surface characteristics and the virulences of two toxigenic isolates of Pasteurella multocida representing capsular types A and D were evaluated. Expression of proteins, in particular, outer membrane proteins and iron-regulated proteins, was not affected by exposure of bacterial cells to low concentrations of antibiotics. However, exposition of surface antigens was modified by sub-MICs of the antibiotics tested. The lipopolysaccharide profile of one isolate (capsular type D) was altered by penicillin G. Sub-MICs of penicillin G and tetracycline diminished the virulence of the capsular type A isolate and adherence to porcine tracheal rings of the capsular type D isolate. Production of dermonecrotic toxin was not affected by sub-MICs of the antibiotics tested. Our results indicate that growth of P. multocida in the presence of low concentrations of antibiotics seems to have, depending on the isolate, profound effects on cell surface characteristics, with concomitant effects on adherence or virulence. Our results also indicate that production of dermonecrotic toxin, an important virulence factor of P. multocida isolates associated with porcine atrophic rhinitis, was not affected by sub-MICs of the antibiotics studied.