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PubMed2003

The nacre protein perlucin nucleates growth of calcium carbonate crystals.

Atomic force microscopy (AFM) in aqueous solution was used to investigate native nacre of the marine snail Haliotis laevigata on the microscopic scale and the interaction of purified nacre proteins with calcium carbonate crystals on the nanoscopic scale. These investigations were controlled by scanning electron microscopy (SEM), light microscopy (LM) and biochemical methods. For investigations with AFM and SEM, nacre was cleaved parallel to the aragonite tablets in this biogenic polymer/mineral composite. Multilamellar organic sheets consisting of a core of chitin with layers of proteins attached on both sides lay between the aragonite layers consisting of confluent aragonite tablets. Cleavage appeared to occur between the aragonite tablet layer and the protein layer. AFM images revealed a honeycomb-like structure to the organic material with a diameter of the 'honeycombs' equalling that of the aragonite tablets. The walls of the structures consisted of filaments, which were suggested to be collagen. The flat regions of the honeycomb-like structures exhibited a hole with a diameter of more than 100 nm. When incubated in saturated calcium carbonate solution, aragonite needles with perfect vertical orientation grew on the proteinacous surface. After treatment with proteinase K, no growth of orientated aragonite needles was detected. Direct AFM measurements on dissolving and growing calcite crystals revealed a surface structure with straight steps the number of which decreased with crystal growth. When the purified nacre protein perlucin was added to the growth solution (a super-saturated calcium carbonate solution) new layers were nucleated and the number of steps increased. Anion exchange chromatography of the water-soluble proteins revealed a mixture of about 10 different proteins. When this mixture was dialysed against saturated calcium carbonate solution and sodium chloride, calcium carbonate crystals precipitated together with perlucin leaving the other proteins in the supernatant. Thus perlucin was shown to be a protein able to nucleate calcium carbonate layers on calcite surfaces, and in the presence of sodium chloride, is incorporated as an intracrystalline protein into calcium carbonate crystals.

Calcium Carbonate↗
PubMed2004

Improved wet bonding of methyl methacrylate-tri-n-butylborane resin to dentin etched with ten percent phosphoric acid in the presence of ferric ions.

The objective of this study was to determine the influence of dissolved dentinal substances in demineralized dentin on the hybridization of resin for bonding to dentin. It was hypothesized that these substances, including polyelectrolytes, significantly change the substrates, which could then be assessed by the addition of Na(+), Ca(2+), or Fe(3+) in 10% phosphoric acid. Bovine dentin specimens were etched for 10 s with a solution of 10% phosphoric acid (control) or of 22.0 mM dissolved sodium chloride (10P-Na), calcium chloride (10P-Ca), or ferric chloride (10P-Fe). The specimens were then rinsed, blot-dried, and primed three times with 5% 4-methacryloyloxyethyl trimellitate anhydride in acetone for 60 s. Methyl methacrylate-tri-n-butylborane resin was then applied. The tensile bond strength of each of the dumbbell-shaped specimens was then measured. The fractured surfaces and modified cross-sections were examined by scanning electron microscopy. The cross-sections were soaked in 6N HCl for 10 s and then in 1% sodium hypochlorite for 30 min to determine the resin content in the hybridized specimens. Shrinkage of the demineralized dentins upon drying was assessed by atomic force microscopy. The tensile bond strengths were 10.8 +/- 4.5 (control), 15.0 +/- 7.0 (10P-Na), 19.3 +/- 5.5 (10P-Ca), and 27.8 +/- 8.1 (10P-Fe) MPa. The atomic force microscopy studies showed that Fe(3+) minimized the shrinkage by drying for 10 s but Ca(2+) and Na(+) did not decrease the shrinkage the same as the control. The results support the hypothesis that the monomer permeability of wet demineralized dentin is effectively improved by dissolving ferric ions in the phosphoric acid, resulting in a greater bond strength and higher resin content in the hybridized dentin. The dissolved dentinal substances, including the polyelectrolytes, had a significant influence on the characteristics of the demineralized dentin, changing the degree of hybridization and bonding.

Animals↗
PubMed2000

Sandbed Consolidation with Mineral Precipitation.

A new method has been developed to prevent sand reentrainment during oil production from unconsolidated or poorly consolidated reservoir formations. Consolidation of the zformation around the well is achieved through in situ precipitation of a sparingly soluble salt, namely, calcium phosphate. Control of the depth of salt formation is achieved by alternating injection, mixing, and reaction of two aqueous solutions of calcium chloride and potassium phosphate. Calcium phosphate crystals precipitate and grow on the grain surfaces, forming sufficiently uniform coatings. The formation of relatively uniform coatings on the grains causes an acceptably small decrease of the permeability, which is a feature of primary importance for oil production. The grains are gradually "cemented" with bridges of calcium phosphate crystallites and form a consolidated and still porous structure. As a result, the rate of hydrocarbon production for the problematic reservoir can be increased considerably without undesirable reentrainment of sand. The proposed method for consolidation has been successfully tested in sandbeds. Several series of experiments have been carried out under diverse conditions to establish the optimum parameter values for the implementation of this method. A set of optimum conditions at 25 degrees C were determined and these conditions gave satisfactory consolidation with permeability loss of ca. 60% of the initial value. The conditions of precipitation were chosen so that the precipitated phase was octacalcium phosphate [Ca(4)H(PO(4))(3).2.5H(2)O], along with its byproduct hydroxyapatite [Ca(5)(PO(4))(3)OH]. Experiments were also carried out at 70 degrees C and have shown that it is feasible to consolidate loose sandpacks at oil reservoir conditions. Copyright 2000 Academic Press.

Journal Article↗
PubMed1994

Adventitious redox-active metals in Krebs-Henseleit buffer can contribute to Langendorff heart experimental results.

Adventitious redox-active metals in Krebs-Henseleit buffer exhibit a significant enhancement of damage to isolated rat hearts. Using atomic absorption spectroscopy, it was determined that Krebs-Henseleit buffer contains substantial amounts of contaminating iron and copper. Significant copper contamination was found in ACS Reagent grade sodium chloride and sodium bicarbonate; iron contamination in sodium chloride, potassium chloride, sodium bicarbonate, and calcium chloride. Chelating resin treatment of individual reagents was found to decrease copper content of Krebs-Henseleit buffer from 0.32 to 0.17 microM. Using salicylate as a probe for .OH formation, it was determined that considerable amounts of this radical are formed when 0.25 mM ascorbate is added to the buffer indicating significant metal-catalysed autoxidation. Isolated rat hearts, perfused with non-chelexed Krebs-Henseleit buffer plus 0.25 mM ascorbate for 60 min, sustained moderate injury with developed systolic pressure, +dP/dtmax and -dP/dtmax decreased by 30 to 35% by the end of experiment. Hearts perfused with chelating resin-treated Krebs-Henseleit buffer sustained no significant injury within the same time frame. Furthermore, it was observed that hearts perfused with non-chelexed Krebs-Henseleit buffer accumulate significant amounts of copper depending on the amount of contamination and length of perfusion. Significant effects on post-ischemic end diastolic pressure were observed in hearts perfused with a Krebs-Henseleit buffer subsequently found to be contaminated with high levels of copper. These results clearly demonstrate that adventitious redox-active transition metals may be a confounding factor in experimental results. Further, it is recommended that all perfusion media be routinely examined for adventitious metals and treated if deemed necessary.

Animals↗
PubMed1999

Inhibition by cAMP of calcium-activated chloride currents in cultured Sertoli cells from immature testis.

We have characterized a Ca2+-dependent Cl- current (ClCa) in cultured Sertoli cells from immature rat testis by using the whole cell recording patch-clamp technique. Cells dialyzed with pipette solutions containing 3 mm adenoside-triphosphate (ATP) and 1 microM free Ca2+, exhibited outward currents which were inhibited by 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) and anthracene-9-carboxylic acid (9-AC) but insensitive to tetraethylammonium (TEA). Dialysis of cells with pipette solutions containing less than 1 nm free Ca2+ strongly reduced the currents indicating that they were Ca2+ dependent. With cells dialyzed with Cs+ glutamate-rich pipette solutions containing 0.2 mm EGTA, 10 microM ionomycin induced outward currents having properties of Ca2+-activated Cl- currents. With ATP-free pipette solution, the magnitude of currents was not modified suggesting the direct control by Ca2+. By contrast, addition of 0.1 mm cAMP in the pipette solution or the superfusion of cells by a permeant analogue of cAMP strongly reduced the currents. These results may suggest that ClCa is inhibited by cAMP-dependent protein kinase. Finally, our results do not agree with the model of primary fluid secretion by exocrine cells, but are in agreement with a hyperpolarizing effect of cAMP in primary culture of Sertoli cells and the release of a low Cl- and bicarbonate-rich primary fluid by these cells.

Adenosine Triphosphate↗
PubMed2004

A study of dilational rheological properties of polymers at interfaces.

Viscoelastic properties of two polymers, partially hydrolyzed polyacrylamide and partially hydrolyzed modified polyacrylamide, widely used in chemical flooding in the petroleum industry, were investigated at three interfaces, water-air, water-dodecane, and water-crude oil, by means of a dilational method provided by I.T. Concept, France, at 85 degrees C. Polymer solutions were prepared in brine with 10,000 mg/l sodium chloride and 2000 mg/l calcium chloride. It has been shown that the viscoelastic modulus increases with the increment of polymer concentration in the range of 0-1500 mg/l at the water-air interface. Each polymer shows different viscoelatic behavior at different interfaces. Generally speaking, values of the viscoelastic modulus (E), the real part (E'), and the imaginary part (E") at the crude oil-water interface for each polymer are lower than at the air-water or water-dodecane interface. The two polymers display different interfacial properties at the same interface. Polymer No. 2 gives more viscous interfaces than polymer No. 1. All the information obtained from this paper will be helpful in understanding the interfacial rheology of ultra-high-molecular-weight polymer solutions.

Journal Article↗
PubMed1998

Use of reversed polarity and a pressure gradient in the analysis of disaccharide composition of heparin by capillary electrophoresis.

A capillary electrophoresis method with reversed polarity, combining both the application of a voltage and a pressure gradient between the buffer vials, was developed for the analysis of eight heparin-derived delta-disaccharides obtained by enzymatic depolymerization. A 60 mM formic acid buffer at pH 3.40 was selected as running electrolyte, with an applied voltage of -15 kV and an over-imposed pressure gradient (3.45.10(-3) MPa) for 6 min from inlet to outlet starting at 20 min. Figures of merit such as run-to-run and day-to-day precision, and limits of detection were established. The electrophoretic method was applied to the analysis of depolymerization products of different kinds of heparins. The composition of the depolymerization buffer was selected in order to reduce baseline distortions in the electrophoretic separation, thus a buffer solution containing 20 mM Tris, 50 mM sodium chloride, and 3 mM calcium chloride at pH 7.10 was used. Percentages of molar disaccharide compositions for unfractionated heparins from porcine, bovine and ovine intestinal mucosa, and bovine lung were determined. In addition, low-molecular-mass heparins from bovine and porcine intestinal mucosa were analysed as well.

Animals↗
PubMed2005

Dissipation-enhanced quartz crystal microbalance studies on the experimental parameters controlling the formation of supported lipid bilayers.

We report on the investigations of the transformation of spherically closed lipid bilayers to supported lipid bilayers in aqueous media in contact with SiO(2) surfaces. The adsorption kinetics of small unilamellar vesicles composed of dimyristoyl- (DMPC) and dipalmitoylphosphatidylcholine (DPPC) mixtures on SiO(2) surfaces were investigated using a dissipation-enhanced quartz crystal microbalance (QCM-D) as a function of buffer (composition and pH), lipid concentration (0.01-1.0 mg/mL), temperature (15-37 degrees C), and lipid composition (DMPC and DMPC/DPPC mixtures). The lipid mixtures used here possess a phase transition temperature (T(m)) of 24-33 degrees C, which is close to the ambient temperature or above and thus considerably higher than most other systems studied by QCM-D. With HEPES or Tris.HCl containing sodium chloride (150 mM) and/or calcium chloride (2 mM), intact vesicles adsorb on the surface until a critical density ((c)) is reached. At close vesicle contact the transformation from vesicles to supported phospholipid bilayers (SPBs) occurs. In absence of CaCl(2), the kinetics of the SPB formation process are slowed, but the passage through (c) is still observed. The latter disappears when buffers with low ionic strength were used. SPB formation was studied in a pH range of 3-10, yet the passage through (c) is obtained only for pH values above to the physiological pH (7.4-10). With an increasing vesicle concentration, (c) is reached after shorter exposure times. At a vesicle concentration of 0.01-1 mg/mL, vesicle fusion on SiO(2) proceeds with the same pathway and accelerates roughly proportionally. In contrast, the pathway of vesicle fusion is strongly influenced by the temperature in the vicinity of T(m). Above and around the T(m), transformation of vesicles to SPB proceeds smoothly, while below, a large number of nonruptured vesicles coexist with SPB. As expected, the physical state of the membrane controls the interaction with both surface and neighboring vesicles.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1975

Brdicka currents observed with bovine serum albumin and completely reduced bovine serum albumin in the presence of urea.

In ammonia buffers of varying composition and pH, native bovine serum albumin and completely reduced bovine serum albumin, denoted by p(SH)35, yield quite different Brdicka current-voltage (i-E) curves, but they are identical in the presence of 5 mM calcium chloride. This means that in the presence of calcium, bovine serum albumin becomes completely reduced to p(SH)35. In 8 M urea and ammonia buffers the Brdicka i-E patterns of serum albumin and p(SH)35 are identical even in the absence of calcium, the effect of calcium on the first wave being negligible while calcium slightly increases the second wave. The maximum polarographic effect is attained at urea concentrations of about 5-6 M. Quite generally, the appearance of a second Brdicka wave is attributed to complexation of Co(II) with S- and a group of ligands that is different on the second than on the first wave. The effect of calcium on Brdicka currents of bovine serum albumin in the absence of urea is attributed to an orientation of the protein on the surface of the electrode such that all disulfide groups are reduced and with other ligands can complex with Co(ii). Denaturation of bovine serum albumin in buffers with a pH less than 10.5, and which are 8 M in area, is (polarographically) completely reversible if dilution is made within 15 minutes after preparation. Changes in Brdlcka I-E patterns upon longer aging at varying pH are attributed-in part at least-to dimerization of the denatured protein by interaction of pS- in one molecule with -S-S-in another.

Ammonia↗
PubMed1976

Sodium and calcium ions in the control of temperature set-point in the pigeon.

1 The effect of altering the ionic balance of the cerebrospinal fluid (CSF) on cloacal temperature of unanesthetized pigeons kept at room temperature (20-25 degrees C) was examined by injection or infusion of solutions of different ionic composition into a cannulated lateral cerebral ventricle. 2 An increase in the concentration of calcium ions caused a fall in temperature and behavioural sedation. The effects were the same whether the calcium was present as calcium chloride or as the calcium disodium salt of ethylenediamine tetra-acetic acid (CaNa2EDTA). 3 When the concentration of sodium ions in the CSF perfusate was increased by addition of NaCl or that of calcium ions was decreased by addition of Na2EDTA a rise in temperature was often produced but this was not consistent. NaCl sometimes had either no effect or lowered the temperature. Na2EDTA while producing a rise when first injected failed to do so when repeated a few hours, 24 h and often 72 h later. Prolonged infusion of either agent caused intense behavioural excitement leading to death. 4 Potassium ions, like sodium ions, caused a rise in temperature but only when infused continuously. Behavioural excitement was only rarely observed. 5 Magnesium produced a fall in temperature. The concentration required was much higher than that of calcium but the hypothermia was more prolonged suggesting a slower elimination of the magnesium ions from the CSF. Magnesium ions caused tremors, nystagmus and ataxia as opposed to sedation caused by calcium. 6 All these were central effects as they were not obtained when the substances were injected intravenously. 7 Since changes in body temperature of the pigeon produced by injection of calcium or sodium ions into the CSF were similar to those seen in various species of mammal, it is concluded that the relative concentration of these ions within the brain plays an important role in establishing the temperature setpoint in both birds and mammals.

Animals↗
PubMed1996

Activation of potassium currents by inhibitors of calcium-activated chloride conductance in rabbit portal vein smooth muscle cells.

1. The conventional whole-cell recording technique was used to study the effects of the chloride channel inhibitors ethacrynic acid, anthracene-9-carboxylic acid (A-9-C) and indanyloxyacetic acid (IAA) on membrane currents in rabbit portal vein smooth muscle cells at a holding potential of 0 mV. 2. Using a pipette solution that contained 1 x 10(-4) M 1,2-bis (2-aminophenoxy)-ethane-N,N,N,N,-tetraacetic acid (BAPTA) and a normal bathing solution the addition of ethacrynic acid (2 x 10(-4) M to 1 x 10(-3) M) inhibited spontaneous transient outward currents (STOCs) and evoked a concentration-dependent current at a holding potential of 0 mV. A similar current was activated by IAA (5 x 10(-4) M to 1 x 10(-3) M) but not by A-9-C (1-5 x 10(-3) M) at a holding potential of 0 mV. 3. The amplitude of the current evoked by ethacrynic acid and IAA was linearly related to potential between -30 and 0 mV and displayed outward rectification at positive potentials. The current induced by A-9-C was evident only at potentials positive to +20 mV. 4. Glibenclamide (1 x 10(-5) M) abolished the current evoked by ethacrynic acid and IAA at potentials negative to +10 mV and partially inhibited the current positive to +10 mV. The glibenclamide-insensitive current at positive potentials was completely inhibited by 1 x 10(-3) M TEA. The A-9-C-evoked current was insensitive to glibenclamide and abolished by 1 x 10(-3) M TEA. 5. The glibenclamide-sensitive current activated by ethacrynic acid was not sustained and declined to control levels in the continued presence of ethacrynic acid. However, the outwardly rectifying current recorded at +50 mV was well maintained over the same period. 6. Outwardly rectifying currents evoked by ethacrynic acid and A-9-C were observed with a pipette solution containing 1 x 10(-2) M BAPTA in cells bathed in Ca-free extracellular solution containing 5 x 10(-4) M BAPTA and 1 x 10(-5) M cyclopiazonic acid. 7. It is concluded that all three chloride-channel blockers activated an outwardly rectifying, TEA-sensitive current. Moreover, ethacrynic acid and IAA evoked an additional glibenclamide-sensitive current which was present at all potentials between -30 and +50 mV.

Animals↗
PubMed1995

Effects of the antihypertensive drug captopril on human salivary secretion rate and composition.

The effects of the antihypertensive drug captopril on salivary secretion rate and composition was evaluated in 24 healthy adults (18-46 yr) according to a double-blind, cross-over design. Unstimulated and paraffin-chewing stimulated whole saliva and 3% citric acid stimulated parotid and submandibular-sublingual (SM-SL) secretion were collected at 10.30 a.m. (about 2h after intake of breakfast) on day 0 (baseline values), day 1 (experimental acute values) and day 7 (experimental chronic values) in each treatment period. In 8 of the subjects, also morning samples were collected at 7.30 a.m., with the test subjects in a fasting condition. Whole saliva was assessed for flow rate and for concentrations of sodium, potassium, chloride, calcium and phosphate. In addition, parotid and SM-SL secretion were assessed for concentrations of total protein, hexosamine, sialic acid, lactoferrin and salivary IgA and for activities of amylase, lysozyme and salivary peroxidase. During treatment with the angiotensin converting enzyme inhibitor captopril, the secretion rates tended to increase for unstimulated and paraffin-chewing stimulated whole saliva and for parotid secretion. For salivary composition, no alterations were observed in any of the collected secretions.

Adolescent↗
PubMedDate not supplied

Trace element contamination of total parenteral nutrition. 1. Contribution of component solutions.

BACKGROUND: Trace elements have been shown to contaminate total parenteral nutrition (TPN) solutions. METHODS: This study used the multi-elemental technology of inductively coupled plasma-mass spectrometry to demonstrate the extent to which trace elements were present in amounts above (ie, as contaminants) or below expected levels in eight TPN component solutions. RESULTS: Of the 66 trace elements scanned, there were 12 trace element contaminants in amounts >1 microg/L (zinc, copper, manganese, chromium, selenium, boron, aluminum, titanium, barium, vanadium, arsenic, and strontium) in the eight component solutions studied. Trace element contaminants were present in all solutions, and different trace elements contaminated the solutions at various concentrations. Component solutions of amino acid, potassium chloride, calcium gluconate, and sodium chloride contained the greatest numbers of trace element contaminants, whereas the lowest numbers were present in sterile water and magnesium sulfate. Interlot and intermanufacturer variations were apparent. Measured concentrations of trace elements in the multi-trace element additive solution also were higher than the labeled values. A comparison of the amounts of contaminated trace elements delivered by a typical TPN mixture relative to the amounts typically absorbed by the gastrointestinal tract indicates that the inadvertent delivery of trace elements from contaminated TPN solutions may be substantial. CONCLUSIONS: All eight components tested were contaminated with trace elements not intended to be present in the product, and similarly, the multi-trace element component contained trace elements either above or below that which the label claimed.

Drug Contamination↗
PubMed2004

Adsorption of divalent cations on DNA.

The distribution of divalent ions in semidilute solutions of high-molecular-mass DNA containing both sodium chloride and strontium chloride in near-physiological conditions is studied by small-angle x-ray scattering and by small-angle neutron scattering. Both small-angle neutron scattering and small-angle x-ray scattering reveal a continuous increase in the scattering intensity at low q with increasing divalent ion concentration, while at high q the scattering curves converge. The best fit to the data is found for a configuration in which DNA strands of cross-sectional radius 10 angstroms are surrounded by a counterion sheath of outer radius approximately 13.8 angstroms, independent of the strontium chloride concentration. When the strontium chloride is replaced by calcium chloride, similar results are obtained, but the thickness of the sheath increases when the divalent salt concentration decreases. These results correspond in both cases to partial localization of the counterions within a layer that is thinner than the effective Debye screening length.

Adsorption↗