Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Potassium Compounds”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed1991

Variables influencing the clot lysis assay of streptokinase.

Clot lysis induced by streptokinase has been studied and the influences of pH and the concentrations of plasminogen, fibrinogen and buffer composition investigated. Variations in the concentrations of plasminogen strongly effect the SK apparent activity, maxima being obtained at different plasminogen concentrations linearly dependent on the concentration of fibrinogen. Buffer composition and pH also effect the apparent activity and the maxima obtained are dependent on the fibrinogen concentration. Analytical conditions are discussed and suitable sample and reagent volumes, as well as concentrations of the reactants and buffer environment, are suggested.

Blood Coagulation Tests↗
PubMed1993

Mechanical fatigue of a feldspathic dental procelain.

Ceramics are known to undergo chemical static fatigue in the presence of moisture at ambient temperatures. However, until recently, it has been assumed that ceramic materials do not undergo mechanical fatigue. This study, using an indentation technique, demonstrated the existence of mechanically induced cyclic fatigue in a feldspathic dental porcelain under ambient conditions. Growth rates (dc/dN) were consistent with the Paris Law, which is a power law function of the applied stress intensity range (delta K) governing mechanical fatigue phenomena. A Paris exponent m of the order of 4, and a constant C of the order of 2 x 10(-6) were calculated. The susceptibilities of a range of dental ceramics to mechanical fatigue, and the possible interaction between mechanical and chemical static fatigue must be investigated so that materials and techniques giving ceramic prostheses the longest possible lifetimes can be identified.

Aluminum Silicates↗
PubMed1993

Dynamic fatigue of feldspathic porcelain.

Several studies (Sherrill and O'Brien, 1974; Southan and Jørgensen, 1974; Jones, 1983) have shown that stress corrosion fatigue occurs in dental porcelains. Morena et al. (1986) reported on an assessment of slow crack growth parameters for dental ceramics. The purpose of the study reported here was to evaluate the fatigue parameters of a model experimental porcelain using dynamic fatigue testing. This test procedure makes use of several constant stressing rates to perform strength tests. Dynamic stress testing was first described by Evans (1974) and later defined as a distinct test modality by Ritter (1978). From such data, the fatigue parameters can be calculated. These fatigue parameters, n and sigma f0, are, respectively, the crack growth exponent from the crack velocity expression and a materials constant which is dependent on the test environment and the inert (moisture-free) strength. The model porcelain was made from 60% component 1 and 40% component 3 according to the Weinstein patent (Weinstein, et al., 1962). The biaxial flexure strength of 300 specimens 1 mm thick was tested in 37 degrees C water by testing 50 samples at each of 6 constant stressing rates: 100, 10, 1, 0.1, 0.01, and 0.001 MPa/s. One hundred specimens were tested in a moisture-free environment at 100 MPa/s using a servo-mechanical testing machine. A commercial porcelain (Jelenko Gingival-Lot # 2012, Jelenko Dental Health Products, Armonk, NY, USA) was chosen as a reference material. One hundred twenty specimens were tested using the same procedures as those used for the model porcelain; however, only 20 samples were tested for 5 stressing rate groups and an inert group.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Silicates↗
PubMed1990

Paradoxical effect of bicarbonate on cytoplasmic pH.

The effect of an abrupt rise in bicarbonate concentration on cytoplasmic pH was studied in human platelets suspended in a Tyrode's buffer. Addition of bicarbonate raised extracellular pH but simultaneously caused pronounced cytoplasmic acidification. This effect may be due to combination of bicarbonate with hydrogen ions in extracellular fluid to form carbonic acid, which is converted by carbonic anhydrase to water and carbon dioxide. Bicarbonate ions do not diffuse rapidly across cell membranes, whereas carbon dioxide is highly diffusible and can combine with water in the cytoplasm, forming carbonic acid and reducing the intracellular pH. In accord with this explanation cytoplasmic acidification by bicarbonate was antagonised by acetazolamide (an inhibitor of carbonic anhydrase). Cytoplasmic acidification could contribute to adverse effects of intravenous sodium bicarbonate in patients with severe acidaemia. These findings add weight to the body of opinion that such treatment is both illogical and dangerous.

Acetazolamide↗
PubMed1991

Partitioning of beta-galactosidase fusion proteins in PEG/potassium phosphate aqueous two-phase systems.

Four different beta-galactosidase fusion proteins have been partitioned in poly(ethylene glycol) (PEG) 4000/potassium phosphate aqueous two-phase systems. The partition coefficients (K) of staphylococcal protein A-beta-galactosidase (SpA beta gal) (K = 3.5) and staphylococcal protein A-streptococcal protein G-beta-galactosidase (AG beta gal) (K = 2.8) were compared with the partition coefficients of their constituent molecules, beta-galactosidase, SpA, and protein AG. It was found that by fusing beta-galactosidase to the smaller proteins SpA and protein AG, their partition coefficients were increased four to five times. Experimental data were fitted into, and found to agree with, the Albertsson partition model of interacting molecules. The compatibility with PEG and potassium phosphate of beta-galactosidase, SpA, and two different versions of the SpA beta gal protein, displayed as precipitation curves, showed a relationship to the protein partition coefficients in PEG/potassium phosphate systems. High solubility in one phase component was accompanied by preferential partitioning to the phase rich in the same component in the PEG/potassium phosphate system. Also, a changed linker region in SpA beta gal resulted in a more soluble protein. This, together with the improved K values of the target proteins by fusion, shows that it is possible to use beta-galactosidase as an affinity handle.

Cloning, Molecular↗
PubMed1991

Influence of system and molecular parameters upon fractionation of intracellular proteins from Saccharomyces by aqueous two-phase partition.

The interaction of molecular characteristics of proteins with the physicochemical properties of PEG-phosphate aqueous two-phase systems has been studied. This has involved characterization of protein molecular weight, charge, and hydrophobicity and study of PEG molecular weight and concentration, phosphate concentration, and pH. System characterization has been conducted in the context of limited stage fractionation procedures for protein recovery from baker's yeast. Results are presented which show that the degree of purification achieved is dependent on macromolecular surface properties rather than system operating conditions. A simple conceptual model of partitioning in PEG-phosphate aqueous two-phase systems is presented which is applicable in the rational design of fractionation procedures and serves to limit the amount of empirical experimentation necessary for the establishment of practical operations.

Electrophoresis, Polyacrylamide Gel↗
PubMed1996

Chemical and morphological analysis of explanted polyurethane vascular prostheses: the challenge of removing fixed adhering tissue.

During in vivo experiments to evaluate the biocompatibility and biostability of alternative biomaterials, the ideal protocol for the handling and preservation of the explanted material is often compromised in order to meet the needs of both the pathologist and the materials scientist. Explants surrounded by tissue are often fixed in formalin or glutaraldehyde to facilitate later pathological and histological analysis, but the subsequent removal of such fixed tissue from thermally sensitive and less chemically stable polymers, such as polyurethanes, poses major problems for the materials scientist, who does not wish to modify the chemical, physical or morphological characteristics of the underlying biomaterial. The present study has attempted to find a solution to this problem by exposing virgin specimens of the microporous polyurethane Vascugraft vascular prosthesis to six different cleaning conditions, all known to be effective in removing fixed tissue. These conditions included the use of 20% aqueous potassium hydroxide solution for 48 h at room temperature, 5% sodium bicarbonate solution for 5 min at the boil, and 9, 10, 11 and 12N hydrochloric acid for 48 h at room temperature. The appearance and chemical properties of the virgin and treated specimens were compared using electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, gel permeation chromatography for molecular weight and differential scanning calorimetry techniques. The use of temperatures close to the boil resulted in the formation of a translucent, rubbery material with gross changes in the microporous and microfibrous structure. The strongly acidic and alkaline conditions caused a loss in the surface carbonate group content. In addition, 12N hydrochloric acid reduced the molecular weight and urethane content. Consequently, 9N hydrochloric acid is recommended as the cleaning agent of choice for removing fixed tissue from this type of microporous polyurethane. Control experiments on virgin material should also be included in any cleaning protocol.

Adhesiveness↗
PubMed1986

Effect of different salt leachates on the movement of some phosphorus containing pesticides in soils using thin layer chromatography.

The influence of pH, leachates of alkaline and saline salts, inorganic fertilizers, and surfactants on the movement of eight organophosphorus pesticides, viz., DDVP, diazinon, Ekatin, Folithion, malathion, metasystox, parathion methyl, and Rogor has been studied using soil thin layer chromatographic techniques. The variation in the movement of pesticides under different solvent amendments are expressed in terms of Rf, RB, and RM values and are explained on the basis of adsorption and leachability.

Carbonates↗
PubMed1981

An improved GCMS method to measure tele-methylhistamine.

The presence of tele-methylhistamine (t-MH), the metabolite of histamine in rat brain, and its relationship to putative histaminergic transmission have been the subjects of recent work. We modified the GCMS method of Hough et al. (1979) to enhance both sensitivity and reproducibility. The substitution of KOH for NaOH to extract t-MH considerably improved the recovery. Evaporation of the extract in 0.2 N HCl, as used in the earlier method, reduced the formation of heptafluorobutyryl derivative; substitution with 0.01 N HCl more than doubled the recovery of the derivative. The derivatization procedure itself was changed, the new method exhibiting significantly improved reproducibility. Standard curve of t-MH obtained at different times after derivatization were indistinguishable. The modified method is capable of measuring less than 1 pmole of t-MH. The t-MH content found in nine rat brain regions agree with previously reported values.

Animals↗
PubMed1979

Estimation of polymerization efficiency in the formation of polyacrylamide gel, using continuous optical scanning during polymerization.

The Ferguson plot and 'quantitative' gel electrophoresis (based on the Ferguson plot) depend on a knowledge of accurate gel concentrations. The easiest way to estimate accuracy of gel concentrations, in terms of the degree of completion of the polymerization reaction which gives rise to a gel, is by spectrophometry. Making use of the apparatus for continuous optical scanning of polyacrylamide gels, the extent and rate of polymerization of cross-linked polyacrylamide were estimated by measuring the absorbance at 275 nm of the reaction mixture subsequent to free radical initiation of polymerization. Under appropriate conditions of monomer concentration, initiator levels and temperature, absorbance decreased monotonically after a lag period of 10 min, and after 20--30 min of reaction the absorbance reached a plateau value which provided a measure of polymerization efficiency. Application of a standard curve of absorbance vs. monomer concentration allowed one to quantitate concentrations of residual monomer throughout the course of polymerization. Under a set of arbitrary polymerization conditions (e.g. 6--20% total gel concentration), the reaction went to 63--96% completion. The rate of polymerization was approximately proportional to the square of the monomer concentration (2nd-order reaction kinetics). Absorbance decrease subsequent to the initiation of the polymerization reaction appeared suitable as a measure of efficiency of polymerization since: (a) absorbance spectra of monomers at 0.5 %T and residual monomers in a 10 %T gel, at a time when polymerization seemed terminated, coincided; (b) values of residual monomer obtained were reasonable (10--30%); (c) bimolecular reaction kinetics were found, in agreement with expectation; and (d) absorbance of incomplete polymerization mixtures, deficient in either initiators or monomers, was constant with time.

Acrylamides↗
PubMed1980

An improved approach to histofluorescence using the SPG method for tissue monoamines.

A modification of the SPG histofluorescence method for the visualization of monoamines in tissues using cryostat sections is described. This modification has let to consistent standardization of the fluorescent intensity from one tissue section to another while also eliminating a cumbersome step in the procedure. The present procedure results in highly rapid and sensitive visualization of dopamine-, noradrenaline- and serotonin-containing neurons and their axonal varicosities. Processing time from fresh tissue to microscopic examination requires less than 15 min.

Axonal Transport↗
PubMed1995

Effects of K+, pH and glutamate on 45Ca kinetics in hippocampal brain slices.

Altered calcium homeostasis is likely to play a pathogenetic role in cerebral ischemia. In order to further understand which factors associated with ischemia contribute to disturbances of calcium metabolism, the influence of 3 isolated insults, 8 mM K+, pH 6.1 and 1 mM glutamate, on total tissue calcium were studied by analysis of steady-state kinetics of 45Ca in 500 microns hippocampal brain slices. 45Ca kinetics were analyzed with 2 bi-exponential models by non-linear least-squares analysis. Tissue wet weight/protein was measured simultaneously. Each experimental condition produced a unique tissue response. Raising K+ had no effect on tissue water but increased the rate of uptake of Ca2+ into the larger, rapidly equilibrating tissue Ca2+ space. Acidosis reduced tissue water and the amount of Ca2+ in the slowly equilibrating compartment due to enhanced efflux from that space. Glutamate increased tissue water in a time-dependent manner and increased the influx and amount of Ca2+ in the slowly equilibrating space. Combined insults revealed minimal interaction between K+ and acidosis or glutamate, but glutamate with acidosis worsened tissue injury. We discuss the relationship of this technique to other methods for studying tissue calcium and the significance of the observations regarding ischemia.

Animals↗
PubMed1989

Quantitative methods for assessing a synergistic or potentiated genotoxic response.

The problem of assessing chemical interactions in studies of genotoxicity is discussed. Attention is focused on assessing possible synergism or potentiation when the observed genotoxic response is binary (yes-no). Different forms of enhancement are distinguished based upon different assumptions on the genotoxic activity of the experimental treatments. A generalized linear statistical model is considered that links the probability of the binary response to the doses, and data-analytic strategies are described for detecting synergy and potentiation in factorially designed experiments. This approach is illustrated with a series of analyses of various genotoxicity data-sets.

Aminacrine↗
PubMed1986

Potassium chromate potentiates frameshift mutagenesis in E. coli and S. typhimurium.

Possible comutagenic effects of chromate on frameshift mutagenesis were studied in bacterial assays. In these experiments, cells were treated with potassium chromate and 9-aminoacridine either singly or in combination. Results were analyzed to detect synergistic, additive and antagonistic responses. Data from these investigations show a clear potentiation of 9-aminoacridine-induced mutagenesis in the presence of chromate in S. typhimurium strain TA1537. Results from cell viability assays shows that the effect is not due to a toxicity artifact. Similar results are obtained in E. coli strains 343/358 (repair-proficient parental strain), 343/415 (recA-deficient), and 343/435 (mismatch-repair-deficient). These data indicate the neither induction of recA-protein nor inhibition of mismatch repair is involved in the action of chromate. In E. coli strain 343/447 (DNA polymerase I deficient), the potentiation was observed at lower concentrations of chromate. This finding suggests that polymerase I functions in recovery of cells from 9-aminoacridine-induced DNA damage and that its absence allows some of this damage to be dealt with in a manner which promotes mutagenesis in the presence of chromate. One possible explanation of these findings is that chromate and 9-aminoacridine react chemically to produce a unique mutagen and that damage caused by this mutagen is repaired via some excision process. However, no reaction between chromate and 9-aminoacridine could be detected by TLC under conditions similar to those in the bacterial assays, even at very high concentrations of both agents. Thus, it seems most likely that the potentiation is due to some action of chromate on repair and/or replication at sites of 9-aminoacridine intercalation. Chromate appears, then, to have significant comutagenic actions in bacterial systems.

Aminacrine↗
PubMed1987

Mutagenic activity of fluorides in mouse lymphoma cells.

The L5178Y mouse lymphoma cell forward-mutation assay was used to test for the mutagenic activity of sodium and potassium fluoride at the thymidine kinase locus. Mutants were detected by colony formation in soft agar in the presence of trifluorothymidine. Mutagenic and toxic responses were observed in the concentration range of 300-600 micrograms/ml with both sodium and potassium fluoride. Approximately 3-fold increases in mutant frequency were observed for concentrations in the 500-700 micrograms/ml range that reduced the relative total growth to approximately 10% in the absence or presence of a rat-liver S9 activation system. A sample of 30% sodium fluoride-70% sodium bifluoride (NaHF2) induced a similar mutagenic response but was more toxic with respect to the fluoride concentration. A specificity for fluoride ions in causing mutagenesis was indicated by the fast that much higher concentrations of sodium or potassium chloride were necessary to cause toxicity and increases in the mutant frequency. The possible involvement of chromosomal changes was signaled by the predominant increase in the small colony class of mutants.

Animals↗