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PubMed2004

Effects of filler size, water, and alcohol on hardness and laboratory wear of dental composites.

Three UEDMA/TEGDMA (50:50 by weight) based dental composites were made, each with filler loadings of 53 vol.%. The three composites contained silane-treated filler particles with average particle diameters of 1.5, 3.0, or 10.0 microm. Twelve specimens per composite were mounted on wear wheels and run through 200,000 cycles in an ACTA wear machine. Six of these specimens per material were worn in slurries consisting of 30 g ground Millet seed shells and 120 g ground rice mixed with 275 mL water. The remaining six specimens were worn in similar 25% ethanol-water slurries. The composite wear profiles were recorded with a profilometer and used to calculate the wear. Hardness values of the composites were also measured both before and after storage for 2 weeks in either water or in a 25% ethanol water solution. The wear and hardness values from the measurements were analyzed using ANOVA. The wear analysis showed that the finer composites (1.5 microm filler diameter) wore the least and the coarsest composites (10 microm filler diameter) the most. The wear was significantly higher in the ethanol water slurry than in the water slurry. The hardness value of the coarsest composite decreased more than the finest composite during storage in water or 25% ethanol water. The hardness decrease was most pronounced in the alcohol solution.

Aluminum Oxide↗
PubMedDate not supplied

Beneficial effects of human serum albumin on stability and functionality of alginate microcapsules fabricated in different ways.

A key engineering challenge in designing microcapsules made from biocompatible alginate is maintaining adequate exchange of nutrients and oxygen between the entrapped cells and the environment, while simultaneously avoiding swelling and subsequent failure of the microcapsule. Approval for the use of alginate in pharmaceutical and/or biomedical applications also strictly requires that the components of the microcapsule material must meet the safety criteria of the ASTM and FDA. Incorporation of foetal calf serum (FCS) into the microcapsules for stabilization is not in accordance with the guidelines affirmed by these organizations. FCS should be substituted by microcapsule-stabilizing additives that are medically approved. In this communication, it is shown that 10% FCS can be replaced by 1% human serum albumin (i.e. by an agent for which medical approval is granted) without compromising effects on long-term in vitro stability. Furthermore, it is demonstrated that human serum albumin (HSA) significantly enhances cell survival and, particularly, insulin secretion of encapsulated rat islets over a time period of 3 weeks when incubated in culture medium. Thus, HSA-stabilized microcapsules made from UHV(Lam) alginate are apparently a promising system for immunoisolation of cells, particularly when alginate is cross-linked by injection of BaCl(2) crystals into the alginate droplets. Slight adjustments of the alginate concentration can tailor the microcapsule permeability to the released therapeutic factor.

Alginates↗
PubMed2005

Ionotropic alginate beads for controlled intestinal protein delivery: effect of chitosan and barium counter-ions on entrapment and release.

Alginate beads containing the model protein haemoglobin (Hb) were prepared by coagulation with various counter-ions to improve the controlled release of the protein. The effect of Ba(2+) and Ca(2+) ions and of the polycationic polysaccharide chitosan was investigated. Coagulation with Ba(2+), Ca(2+) and/or chitosan showed differences in the swelling index of the beads, in the encapsulation efficiency of Hb entrapment and in the release of the entrapped protein. Chitosan in the coagulation fluid markedly enhanced the encapsulation efficiency of the Hb. Release studies were conducted in simulated gastric fluid (SGF pH approximately or equal to 1.2) and subsequently in simulated intestinal fluid (SIF ) at 37 degrees C. Beads were stable in the gastric fluid but released their protein upon transfer to intestinal fluid. The release coincides with the burst and disintegration of beads. Rate of protein release from the beads was affected by the Ba(2+) and chitosan concentration in coagulation fluid.

Alginates↗
PubMed2005

Selenate removal from sulfate containing aqueous solutions.

The performance of selenium remediation agents, mainly gamma alumina sorbents and zerovalent metals is greatly inhibited in the presence of large concentrations of sulfate found in selenium-rich agricultural drainage water. It is therefore imperative to remove sulfates from these contaminated waters, prior to their treatment for selenium removal. This paper presents data on enhanced selenium removal resulting from a two stage process involving the use of barium chloride in the first stage followed by a selenium remediation agent in the second. Barium chloride is known to stoichiometrically precipitate out sulfates. In addition to the sulfate removal from the contaminated solutions, a significant amount of selenate immobilization in the precipitated solids was achieved. When a loading of 15 g l(-1) of BaCl2, was employed, 100% selenate removal from an aqueous solution (containing 1 mg l(-1) selenate, 4 g l(-1) of sulfate and 2.5 g l(-1) of chloride) was achieved by the use of BaCl2, alone. Bimetallic NiFe particles, gamma alumina and activated carbon were employed to further remove selenium in the second stage. A solution containing 1 mg l(-1) and 4 g l(-1) of selenate and sulfate, respectively, when treated sequentially with 10 g l(-1) of BaCl2 and NiFe powder showed 100% selenium removal.

Adsorption↗
PubMedDate not supplied

In vivo properties of potassium channels in cerebral blood vessels during diabetes mellitus.

OBJECTIVE: While potassium (K+) channels are important in basal tone and dilatation of large and small cerebral vessels, the effect of diabetes mellitus on K+ channels remains unclear. The goal of this study was to identify the influence of diabetes on responses of cerebral vessels to inhibition/activation of K+ channels. METHODS: The authors measured in vivo responses of pial arterioles and the basilar artery to inhibition/activation of K+ channels in nondiabetic and diabetic rats using intravital microscopy. RESULTS: Pial arterioles from nondiabetic and diabetic rats constricted to barium chloride (BaCl2) and 4-aminopyridine (4-AP). However, the magnitude of vasoconstriction to BaCl2 was greater in nondiabetic than in diabetic rats. Tetraethylammonium (TEA) did not alter diameter of pial arterioles in nondiabetic or diabetic rats. In addition, dilatation of pial arterioles to KCl and NS-1619 was less in diabetic compared to nondiabetic rats. The basilar artery from nondiabetic and diabetic rats constricted in a similar manner to BaCl2 and 4-AP. In contrast, vasoconstriction to TEA was greater in diabetic than nondiabetic rats. Similar to that reported for pial arterioles, dilatation of the basilar artery to KCl and NS-1619 was less in diabetic than nondiabetic rats. CONCLUSIONS: Inward-rectifier (Kir) and voltage-dependent (Kv), but not calcium-activated (Kca), K+ channels are active under basal conditions in pial arterioles, while Kir, Kv, and Kca are active under basal conditions in the basilar artery of nondiabetic and diabetic rats. In addition, activation of Kir and Kca channels produces less cerebral vasodilatation in diabetic compared to nondiabetic rats. These findings provide new and important information regarding the influence of diabetes on the role of K+ channels in the regulation of cerebral vascular diameter.

Animals↗
PubMed1994

Intracellular pH modulates the availability of vascular L-type Ca2+ channels.

L-type Ca2+ channel currents were recorded from myocytes isolated from bovine pial and porcine coronary arteries to study the influence of changes in intracellular pH (pHi). Whole cell ICa fell when pHi was made more acidic by substituting HEPES/NaOH with CO2/bicarbonate buffer (pHo 7.4, 36 degrees C), and increased when pHi was made more alkaline by addition of 20 mM NH4Cl. Peak ICa was less pHi sensitive than late ICa (170 ms after depolarization to 0 mV). pHi-effects on single Ca2+ channel currents were studied with 110 mM BaCl2 as the charge carrier (22 degrees C, pHo 7.4). In cell-attached patches pHi was changed by extracellular NH4Cl or through the opened cell. In inside-out patches pHi was controlled through the bath. Independent of the method used the following results were obtained: (a) Single channel conductance (24 pS) and life time of the open state were not influenced by pHi (between pHi 6 and 8.4). (b) Alkaline pHi increased and acidic pHi reduced the channel availability (frequency of nonblank sweeps). (c) Alkaline pHi increased and acidic pHi reduced the frequency of late channel re-openings. The effects are discussed in terms of a deprotonation (protonation) of cytosolic binding sites that favor (prevent) the shift of the channels from a sleepy to an available state. Changes of bath pHo mimicked the pHi effects within 20 s, suggesting that protons can rapidly permeate through the surface membrane of vascular smooth muscle cells. The role of pHi in Ca2+ homeostases and vasotonus is discussed.

Ammonium Chloride↗
PubMed1995

Single calcium channel behavior in native skeletal muscle.

The purpose of this study was to use whole-cell and cell-attached patches of cultured skeletal muscle myotubes to study the macroscopic and unitary behavior of voltage-dependent calcium channels under similar conditions. With 110 mM BaCl2 as the charge carrier, two types of calcium channels with markedly different single-channel and macroscopic properties were found. One class was DHP-insensitive, had a single-channel conductance of approximately 9 pS, yielded ensembles that displayed an activation threshold near -40 mV, and activated and inactivated rapidly in a voltage-dependent manner (T current). The second class could only be well resolved in the presence of the DHP agonist Bay K 8644 (5 microM) and had a single-channel conductance of approximately 14 pS (L current). The 14-pS channel produced ensembles exhibiting a threshold of approximately -10 mV that activated slowly (tau act approximately 20 ms) and displayed little inactivation. Moreover, the DHP antagonist, (+)-PN 200-110 (10 microM), greatly increased the percentage of null sweeps seen with the 14-pS channel. The open probability versus voltage relationship of the 14-pS channel was fitted by a Boltzmann distribution with a VP0.5 = 6.2 mV and kp = 5.3 mV. L current recorded from whole-cell experiments in the presence of 110 mM BaCl2 + 5 microM Bay K 8644 displayed similar time- and voltage-dependent properties as ensembles of the 14-pS channel. Thus, these data are the first comparison under similar conditions of the single-channel and macroscopic properties of T current and L current in native skeletal muscle, and identify the 9- and 14-pS channels as the single-channel correlates of T current and L current, respectively.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2000

Ion interactions in the high-affinity binding locus of a voltage-gated Ca(2+) channel.

The selectivity filter of voltage-gated Ca(2+) channels is in part composed of four Glu residues, termed the EEEE locus. Ion selectivity in Ca(2+) channels is based on interactions between permeant ions and the EEEE locus: in a mixture of ions, all of which can pass through the pore when present alone, those ions that bind weakly are impermeant, those that bind more strongly are permeant, and those that bind more strongly yet act as pore blockers as a consequence of their low rate of unbinding from the EEEE locus. Thus, competition among ion species is a determining feature of selectivity filter function in Ca(2+) channels. Previous work has shown that Asp and Ala substitutions in the EEEE locus reduce ion selectivity by weakening ion binding affinity. Here we describe for wild-type and EEEE locus mutants an analysis at the single channel level of competition between Cd(2+), which binds very tightly within the EEEE locus, and Ba(2+) or Li(+), which bind less tightly and hence exhibit high flux rates: Cd(2+) binds to the EEEE locus approximately 10(4)x more tightly than does Ba(2+), and approximately 10(8)x more tightly than does Li(+). For wild-type channels, Cd(2+) entry into the EEEE locus was 400x faster when Li(+) rather than Ba(2+) was the current carrier, reflecting the large difference between Ba(2+) and Li(+) in affinity for the EEEE locus. For the substitution mutants, analysis of Cd(2+) block kinetics shows that their weakened ion binding affinity can result from either a reduction in blocker on rate or an enhancement of blocker off rate. Which of these rate effects underlay weakened binding was not specified by the nature of the mutation (Asp vs. Ala), but was instead determined by the valence and affinity of the current-carrying ion (Ba(2+) vs. Li(+)). The dependence of Cd(2+) block kinetics upon properties of the current-carrying ion can be understood by considering the number of EEEE locus oxygen atoms available to interact with the different ion pairs.

Animals↗
PubMed1971

Divalent ions and the surface potential of charged phospholipid membranes.

Phospholipid bilayer membranes were bathed in a decimolar solution of monovalent ions, and the conductance produced by neutral carriers of these monovalent cations and anions was used to assess the electric potential at the surface of the membrane. When the bilayers were formed from a neutral lipid, phosphatidylethanolamine, the addition of alkaline earth cations produced no detectable surface potential, indicating that little or no binding occurs to the polar head group with these ions. When the bilayers were formed from a negatively charged lipid, phosphatidylserine, the addition of Sr and Ba decreased the magnitude of the surface potential as predicted by the theory of the diffuse double layer. In particular, the potential decreased 27 mv for a 10-fold increase in concentration in the millimolar-decimolar range. A 10-fold increase in the Ca or Mg concentration also produced a 27 mv decrease in potential in this region, which was again due to screening, but it was necessary to invoke some specific binding to account for the observation that these cations were effective at a lower concentration than Ba or Sr. It is suggested that the ability of the alkaline earth cations to shift the conductance-voltage curves of a nerve along the voltage axis by 20-26 mv for a 10-fold increase in concentration may be due to essentially a screening rather than a binding phenomenon.

Aniline Compounds↗
PubMed1991

Whole-cell and single channel K+ and Cl- currents in epithelial cells of frog skin.

Whole-cell and single channel currents were studied in cells from frog (R. pipiens and R. catesbiana) skin epithelium, isolated by collagenase and trypsin treatment, and kept in primary cultures up to three days. Whole-cell currents did not exhibit any significant time-dependent kinetics under any ionic conditions used. With an external K gluconate Ringer solution the currents showed slight inward rectification with a reversal potential near zero and an average conductance of 5 nS at reversal. Ionic substitution of the external medium showed that most of the cell conductance was due to K and that very little, if any, Na conductance was present. This confirmed that most cells originate from inner epithelial layers and contain membranes with basolateral properties. At voltages more positive than 20 mV outward currents were larger with K in the medium than with Na or N-methyl-D-glucamine. Such behavior is indicative of a multi-ion transport mechanism. Whole-cell K current was inhibited by external Ba and quinidine. Blockade by Ba was strongly voltage dependent, while that by quinidine was not. In the presence of high external Cl, a component of outward current that was inhibited by the anion channel blocker diphenylamine-2-carboxylate (DPC) appeared in 70% of the cells. This component was strongly outwardly rectifying and reversed at a potential expected for a Cl current. At the single channel level the event most frequently observed in the cell-attached configuration was a K channel with the following characteristics: inward-rectifying I-V relation with a conductance (with 112.5 mM K in the pipette) of 44 pS at the reversal potential, one open and at least two closed states, and open probability that increased with depolarization. Quinidine blocked by binding in the open state and decreasing mean open time. Several observations suggest that this channel is responsible for most of the whole-cell current observed in high external K, and for the K conductance of the basolateral membrane of the intact epithelium. On a few occasions a Cl channel was observed that activated upon excision and brief strong depolarization. The I-V relation exhibited strong outward rectification with a single channel conductance of 48 pS at 0 mV in symmetrical 112 mM Cl solutions. Kinetic analysis showed the presence of two open and at least two closed states. Open time constants and open probability increased markedly with depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

The PC6B cytoplasmic domain contains two acidic clusters that direct sorting to distinct trans-Golgi network/endosomal compartments.

The mammalian proprotein convertases (PCs) are a family of secretory pathway enzymes that catalyze the endoproteolytic maturation of peptide hormones and many bioactive proteins. Two PCs, furin and PC6B, are broadly expressed and share very similar cleavage site specificities, suggesting that they may be functionally redundant. However, germline knockout studies show that they are not. Here we report the distinct subcellular localization of PC6B and identify the sorting information within its cytoplasmic domain (cd). We show that in neuroendocrine cells, PC6B is localized to a paranuclear, brefeldin A-dispersible, BaCl(2)-responsive post-Golgi network (TGN) compartment distinct from furin and TGN38. The 88-amino acid PC6B-cd contains sorting information sufficient to direct reporter proteins to the same compartment as full-length PC6B. Mutational analysis indicates that endocytosis is predominantly directed by a canonical tyrosine-based motif (Tyr(1802)GluLysLeu). Truncation and sufficiency studies reveal that two clusters of acidic amino acids (ACs) within the PC6B-cd contain differential sorting information. The membrane-proximal AC (AC1) directs TGN localization and interacts with the TGN sorting protein PACS-1. The membrane-distal AC (AC2) promotes a localization characteristic of the full-length PC6B-cd. Our results demonstrate that AC motifs can target proteins to distinct TGN/endosomal compartments and indicate that the AC-mediated localization of PC6B and furin contribute to their distinct roles in vivo.

Amino Acid Motifs↗
PubMed1989

Effects of ketamine on isolated human bronchial preparations.

The bronchodilator effects of ketamine were examined in human bronchial preparations contracted maximally with histamine, acetylcholine, barium chloride or potassium chloride. Antagonism between ketamine and either histamine or acetylcholine was examined also. Ketamine caused bronchial relaxation irrespective of the constricting agent, and exerted a partial and non-competitive antagonism to histamine and acetylcholine. Propranolol and indomethacin did not inhibit the effect of ketamine, excluding the involvement of beta activation and of prostaglandins.

Acetylcholine↗
PubMed1985

Mechanism of hydralazine-induced relaxation of arterial smooth muscle.

The effect of hydralazine on contractile responses by various agents has been studied in isolated rat tail artery strips. Hydralazine caused dose-dependent relaxation of contractions produced by 10(-7) mol.litre-1 noradrenaline (N); 10(-7) mol.litre-1 5-HT or 100 mmol.litre-1 KCl, suggesting that the relaxation response is non-specific. CaCl2 dose-response (in the presence of 10(-5) mol.litre-1 N; 10(-5) mol.litre-1 5-HT or 100 mmol.litre-1 KC1) was significantly inhibited by 5 X 10(-4) mol.litre-1 hydralazine in the order: KCl greater than 5-HT greater than N. Hydralazine also inhibited BaCl2 dose-response curve (in K+-depolarised strips); maximal contraction to BaCl2 was depressed by 87%. In other experiments, hydralazine significantly depressed (by 20%) the phasic contractile response to N due to mobilisation of calcium from a membrane-bound pool. D 600, a calcium entry blocker, also caused dose-dependent relaxation of contractile responses to all three agents studied; and inhibited CaCl2 and BaCl2 dose-response curves in K+-depolarised media, as well as depressed the phasic contractile response to N in Ca-free media by 17%. These results suggest that in the rat tail artery, hydralazine interferes with Ca2+ influx, as well as release from a membrane-bound pool.

Animals↗
PubMed1991

Role of the inward rectifier IK1 in the myocardial response to hypoxia.

STUDY OBJECTIVE: The aim was to assess the contribution of the inward rectifier IK1 to the electrical responses of the myocardium to hypoxia: action potential shortening, maintenance of resting potential, and myocardial K loss. DESIGN: Hypoxia induced changes of gK1 were inferred from the effects of 40 microns Ba2+ on action potential duration, resting potential, and cellular K content of normoxic and hypoxic rabbit hearts paced at 2.5 Hz and perfused at 33 degrees C and constant coronary flow of 20 ml.min-1. The components (diffusion generated and Na pump related) of the resting potential (Vr) were separated by exposure to 10(-4) M ouabain. The effects of varying the extracellular K concentration (Ko) were also examined. EXPERIMENTAL MATERIAL: New Zealand rabbits were heparinised and anaesthetised and the hearts rapidly excised and perfused in the Langendorff manner. MEASUREMENTS AND MAIN RESULTS: The membrane potential was measured with standard glass microelectrodes and the cellular content of K and Na estimated from determinations of total electrolyte and water content and volume of the inulin space of the tissue. In normoxia, Ba2+ caused a slight depolarisation at Ko below 10 mM and lengthened the action potential duration at 95% repolarisation (APD95) without altering the plateau duration. In hypoxia, Ba2+ caused further depolarisation and markedly reduced the APD95 shortening at normal Ko. The Vr v Ko relationship was considerably flattened and the diffusion component of Vr became insensitive to changes in Ko between 1.5 and 10 mM. Concomitantly, the Na pump related fraction of Vr increased under Ba2+. Barium also attenuated myocardial K loss induced by hypoxia. CONCLUSION: Our data suggest that an increase in the IK1 current underlies the maintenance of Vr in hypoxia despite the decrease in the transmembrane K gradient and contributes to the action potential shortening, speeding up the late repolarisation. The inwardly rectifying K channels would also be involved in the increased efflux of K+. In contrast, the decrease in plateau duration is probably caused by another K current system, less sensitive to Ba2+. Finally, the contribution of electrogenic Na pumping to Vr becomes critical for the maintenance of the resting potential under conditions of decreased resting permeability.

Action Potentials↗
PubMed2002

Trap spectroscopy by the glow rate technique using bleaching of colour centres.

An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF3:Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F(A) and F centres, leading to both the hopping migration and recombination of F centres and the thermoactivated dissociation of the F(A) centres.

Barium Compounds↗
PubMed2002

Optically stimulated luminescence in an imaging plate using BaFi:Eu.

BaFI:Eu phosphors are fabricated using a new method of synthesis: liquid phase synthesis, in which the phosphor particles are formed through the association of Ba2+ ions, F-ions and Eu2+ ions in solution. An intense optically stimulated luminescence (OSL) peak at about 410 nm is observed by stimulating X ray irradiated BaFI:Eu phosphor with about 550-750 nm light. It is found that the peak wavelength of the optically stimulation spectrum is about 690 nm. This result suggests that the semiconductor laser can be used as the stimulating light source. It is also found that the OSL intensity is increased with increasing the X ray dose. The BaFI:Eu phosphor as a photostimulable material for the imaging plate of a computed radiography system provides the following advantages; (1) high X ray absorption coefficient, (2) high monodispersion in size which would contribute to sharp images, (3) high OSL and thus low luminescence mottle and (4) high DQE (detective quantum efficiency).

Barium Compounds↗
PubMed2002

Thermoluminescence of photostimulable materials after X irradiation below room temperature.

Thermoluminescence glow peaks in the temperature range 100 to 400 K are investigated for BaFX (X = Cl, Br) crystals after X irradiation at 100 K. A prominent glow peak of BaFCl around 210 K is found to be composed of a few recombination roots, that is, the peak corresponds to the recombination of hole trapped centres such as an O- centre and a dissociated Cl2- centre with the F (F-) centre and the O2--F(Cl-) pair defect. Another small glow peak around 270 K is likely to occur from thermal dissociation of the O2- -F(Cl-) pair defect. The main glow peak of BaFBr:O2- at 170 K may be attributed to a recombination of an O- centre with the F(Br-) centre.

Barium Compounds↗
PubMed2006

Barium dithionate as an EPR dosemeter.

Electron paramagnetic resonance (EPR) dosimetry is growing in popularity and this success has encouraged the search for other dosimetric materials. Previous studies of gamma-irradiated barium dithionate (BaS(2)O(6) x 2H(2)O) have shown promise for its use as a radiation dosemeter. This work studies in greater detail several essential attributes of the system. Special attention has been directed to the study of EPR response dependences on microwave power, irradiation temperature, minimum detectable dose and post-irradiation stability.

Barium Compounds↗