Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cations”

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 253 records · Page 14Linked to original sources
PubMed1996

Ionic permeability of, and divalent cation effects on, two ATP-gated cation channels (P2X receptors) expressed in mammalian cells.

1. Complementary DNAs for the ATP-gated ion channel subunits P2X1 (from human bladder) and P2X2 (from rat phaeochromocytoma (PC12) cells) were used to express the receptors in human embryonic kidney cells by stable transfection, and in Chinese hamster ovary cells by viral infection. 2. Membrane currents evoked by ATP were recorded by the whole-cell patch clamp method. The reversal potential of the current was measured with various intracellular and extracellular solutions and used to compute the relative permeability of the P2X receptor channels. 3. There was no difference between the two receptors with respect to their permeability to monovalent organic cations. The relative permeabilities (PX/PNa) were 2.3, 1.0, 1.0, 0.95, 0.72, 0.5, 0.29, 0.16, 0.04 and 0.03 for guanidinium, potassium, sodium, methylamine, caesium, dimethylamine, 2-methylethanolamine, tris(hydroxymethyl)-aminomethane, tetraethylammonium and N-methyl-D-glucamine, respectively (values for P2X2 receptor). 4. The calcium permeability of P2X1 receptors was greater than that of P2X2 receptors. Under biionic conditions (112 mM calcium outside, 154 mM sodium inside), PCa/PNa values were 3.9 and 2.2, respectively (corrected for ionic activities). 5. ATP-evoked currents in cells expressing the P2X2 receptor were strongly inhibited when the extracellular calcium concentration was increased (0.3-30 mM); the action of ATP could be restored by increasing the ATP concentration. ATP-evoked currents in cells expressing the P2X1 receptor were not inhibited by such increases in the extracellular calcium concentration.

Adenosine Triphosphate↗
PubMed2002

Artificial neural networks for modeling electrophoretic mobilities of inorganic cations and organic cationic oximes used as antidote contra nerve paralytic chemical weapons.

Electrophoretic mobility of various analytes can be modeled and thus also predicted using artificial neural networks (ANNs) evaluating experiments done according to a suitable experimental design. In contrast to response surfaces modeling which can be used to predict optimal separation conditions, ANNs combined with experimental design were shown to be efficient for modeling and prediction of optimal separation conditions, while no explicit model and any knowledge of the physicochemical constants is needed. Methodology has been developed and demonstrated on separation of inorganic cations and organic oximes while various additives (methanol, complexation agent), pH or buffer concentration were followed. In our approach proposed the number of experiments necessary to find optimal separation conditions can be reduced significantly.

Antidotes↗
PubMed2005

How does DNA compaction favor chiral selectivity with cationic species? Higher selectivity with lower cationic charge.

A single-molecule study on giant DNA compaction by enantiomeric dications and tetracations demonstrates that strong chiral discrimination in DNA compaction is manifested only if the positive charge on enantiomeric multications is relatively low. The increase in cationicity of the chiral compaction agent inevitably leads to an increase in nonspecific electrostatic interactions and quenching of chiral discrimination in the DNA-folding phase transition.

Bacteriophage T4↗
PubMed1995

Luminal transport system for H+/organic cations in the rat proximal tubule. Kinetics, dependence on pH; specificity as compared with the contraluminal organic cation-transport system.

The efflux of radiolabelled organic cations from the tubular lumen into proximal tubular cells was investigated by using the stop-flow microperfusion method. The efflux rate increased in the sequence: N1-methylnicotinamide (NMeN+) < cimetidine < tetraethylammonium (TEA+) < N-methyl-4-phenylpyridinium (MPP+). Preloading the animals by i.v. infusion or pre perfusion of the peritubular capillaries with NMeN+ increased the efflux rate of MPP+. Luminal efflux was also augmented when the tubular solution was made alkaline with HCO3- or phosphate, whereby HCO3- is more effective than phosphate. Replacement of Na+ by Cs+ showed no effect. With i.v. preloading the animals with NMeN+ and with 25 mM HCO3- in the luminal perfusate the 2-s efflux follows kinetics with a Michaelis constant Km = 0.21 mmol/l and maximal flux Jmax = 0.42 pmol.cm-1.s-1 and a permeability term with P = 37.7 microns2.s-1. Comparing the apparent luminal inhibitory constant values for MPP+ (Kil,MPP+) with the apparent contraluminal Kicl,NMeN+ values of substrates of homologous series, it was found that (1) limitation by molecular size occurs at the contraluminal cell side earlier than at the luminal cell side; (2) affinity increases with hydrophobicity of the substrates at the luminal cell side, with a steeper or equal slope than at the contraluminal cell side; (3) affinity increases with basicity (i.e. pKa values) at the luminal cell side with a steeper slope than at the contraluminal cell side. Taken together, substrates with low hydrophobicity and low basicity interact at the luminal cell side more weakly than at the contraluminal cell side. On the other hand large, hydrophobic substrates have, at the luminal cell side, a higher affinity than at the contraluminal cell side. Many substrates, however, have equal affinity at the luminal and contraluminal cell sides.

Animals↗
PubMed1989

Detection of cationic and non-cationic markers in the rat glomerulus by electron probe analysis.

Acidic glycans (glomerular polyanion substances) in the rat kidney were visualized ultrastructurally by three cationic markers: colloidal iron, ruthenium red, and polyethylenimine-phosphotungstic acid (PEI-PTA). Heavy metal atoms (Fe, Ru and W) were detected in ultrathin sections by energy-dispersive electron probe microanalysis (EPMA). Characteristic peaks of the locally bound elements were obtained in spectra derived from the dense structures seen by transmission electron microscopy (TEM)--i.e. the glycocalyx of podocytes and/or the polyanion sites in the lamina rara externa of the glomerular basement membrane. Weaker signals were emitted by some extraglomerular structures. This finding may reflect a low concentration of glycans in structures lacking apparent density by TEM, and/or incomplete specificity of the markers, partial dislocation of reactive substances or the presence of an endogenous element (Fe). Experimental argyrosis was elicited by the peroral administration of silver nitrate. Dense Ag precipitates were seen chiefly in the lamina densa and characteristic peaks of silver were displayed in this site by EPMA, and was best demonstrated in non-contrasted sections. A single i.v. injection of Ag proteinate failed to produce glomerular pigmentation. The only dense granular product in tubular cells yielded characteristic peaks of Fe (endogenous siderosomes) but EPMA excluded detectable amounts of silver.

Animals↗
PubMed2004

Novel methylcellulose-immobilized cation-exchange precolumn for on-line enrichment of cationic drugs in plasma.

We developed a novel methylcellulose-immobilized strong cation-exchange (MC-SCX) precolumn for direct analysis of drugs in plasma. MC-SCX consists of silica gel with a methylcellulose outer-surface and a 2-(4-sulfophenyl) ethyl phase inner-surface. The MC-SCX precolumn was evaluated by direct analysis using pyridoxine, atenolol and sulpiride spiked in plasma, using a column-switching HPLC system. Each drug was retained and enriched on MC-SCX using an acidic mobile phase, which resulted in good linearity, sufficient reproducibility, intra- and inter day precision, and accuracy in analytical ion-pair LC with trifluoroacetic acid. The analytical methods for model drugs were applied to pharmacokinetics of atenolol and sulpiride in rats.

Animals↗
PubMed2005

Spectrophotometric studies of anionic dye-cationic surfactant interactions in mixture of cationic and nonionic surfactants.

The interaction between an anionic dye C.I. Reactive Orange 16 (RO16) and a cationic surfactant dodecylpyridinium chloride (DPC) in mixtures of DPC and nonionic surfactants poly(oxyethylene)ethers (C(m)POE(n); m = 12, 16 and 18, n = 4, 10 and 23) are investigated spectrophotometrically in a certain micellar concentration range. The spectrophotometric measurements of dye-surfactant systems are carried out as function of mole fraction of surfactant at four different temperatures. For this reason, a typical system was occurred at 1.0 x 10(-2) mol l(-1) for surfactants and at 1.0 x 10(-4) mol l(-1) for dye concentrations. The formation of DPC-RO16 complex in the C(m)POE(n) solutions of different mole fractions in its micellar concentration range have been determined and compared to those obtained in the binary mixtures. From the spectrophotometric measurements has been observed that the addition of nonionic surfactant in to the mixture of DPC-RO16, causes a significant increase of the value of absorbance. This increase explains that the stability of DPC-RO16 complex is reduced in the presence of nonionic surfactant micelles. It can be seen from results; in mixed surfactant solutions, there are DPC-C(m)POE(n) and RO16-C(m)POE(n) interactions in addition to DPC-RO16 interaction. Since the solubilizaton of the DPC-RO16 complex has been appeared in the C(m)POE(n) solution, our results support the conclusion that adding C(m)POE(n) influences the hydrophobic-hydrophilic balance of the studied complex. Furthermore effect of the alkyl chain length and the number of poly(oxyethylene) in nonionic surfactant on values of absorbance have been investigated.

Anions↗
PubMed1988

Cation binding sites on actin: a structural relationship between antigenic epitopes and cation exchange.

Divalent cations such as Mg2+ and Ca2+, which bind specifically to actin, induce conformational changes that affect its antigenic structure. The distribution of antigenic epitopes on the sequence shows that these structural modifications involve epitopes related to monomer-monomer interfaces. In the N-terminal part, the 1-7 acidic extremity is not affected, in contrast with sequence 18-28. The ability of polycations such as diamine to modify the actin structure at concentrations below 0.1 microM strengthens the hypothesis that in vivo these compounds act locally and specifically on actin polymerization.

Actins↗
PubMed2002

Sulfoacylated poly(styrene-divinylbenzene) copolymers as resins for cation chromatography. Comparison with sulfonated, dynamically coated and silica gel cation exchangers.

Most important properties of an ion chromatographic resin are influenced by the resin matrix, the type of functional group and the ion-exchange capacity. Highly crosslinked PS-DVB resins of 5 microm diameter have been functionalized by sulfoacylation, by sulfonation and by dynamic coating over a wide range of exchange capacities. These materials allow a study of the influence of different ion-exchange sites and capacities. The influence of the degree of functionalization on resin performance is completely reverse for sulfoacylated and sulfonated resins. The HETP values for all observed analytes (Cu, Pb, Zn, Ni, Co, Cd, Mn, Ca, Mg) in a tartaric acid elution system decrease for sulfoacylated resins with increasing capacity, for sulfonated resins with decreasing capacity. The performance of sulfoacylated exchangers is better than for dynamically coated ones and far better than for sulfonated resins. The performance of silica gel based cation-exchangers such as BioSil CAT is in most cases better than observed for sulfoacylated resins.

Cation Exchange Resins↗
PubMed1995

Novel NMDA antagonists: replacement of the pyridinium ring of 6,11-ethanobenzo[b]quinolizinium cations with heteroisoquinolinium cations.

Replacement of the pyridinium ring of 6,11-ethanobenzo[b]quinolizinium cations with thiazolium (4a and 4b) and N-methylimidazolium (4c and 4d) resulted in equipotent compounds in the [3H]TCP binding assay. The corresponding N-methyl-1,2,4-triazolium analogs were less potent in this assay. The thiazolium derivative 4b, with a Ki = 2.9 nM, is being evaluated as a possible neuroprotective N-methyl-D-aspartic acid (NMDA) antagonist.

Animals↗
PubMed2007

Lack of association between a cationic protein and a cationic fluorosurfactant.

Surface tension, 19F and 1H NMR spectroscopy, and cryotransmission electron microscopy are used to characterize the state of association in aqueous solutions of a fluorosurfactant CF3(CF2)nSO2NH(CH2)3-4N(CH3)3+ I- (n = 8, 6) with and without lysozyme added. In the absence of lysozyme, we find monomers, small aggregates, and large vesicles to coexist, with the individual fluorosurfactant molecules exchanging slowly (>1 ms) among those states. When both lysozyme and fluorosurfactant are present in the solution, they have no measurable influence on the physical state of the other. In contrast, a hydrogenated cationic surfactant with the same headgroup, hexadecyltrimethylammonium bromide, is shown to associate to lysozyme.

Cations↗
PubMed1998

Disulfide bonds in the extracellular calcium-polyvalent cation-sensing receptor correlate with dimer formation and its response to divalent cations in vitro.

Extracellular calcium/polyvalent cation-sensing receptors (CaR) couple to G proteins and contain highly conserved extracellular cysteine residues. Immunoblotting of proteins from rat kidney inner medullary collecting duct endosomes with CaR-specific antibodies reveals alterations in the apparent molecular mass of CaR depending on protein denaturation conditions. When denatured by SDS under nonreducing conditions, CaR migrates as a putative dimeric species of 240-310 kDa. This is twice the predicted molecular mass of the CaR monomer observed after SDS denaturation in the presence of sulfhydryl-reducing agents. In sucrose density gradients, Triton X-100-solubilized CaR sediments as a 220-kDa complex, not explainable by binding of G proteins to CaR monomers. Treatment of Triton-soluble CaR with divalent (Ca2+, Mg2+) and trivalent (Gd3+) metal ion CaR agonists, but not monovalent ions (Na+), partially shifts the electrophoretic mobility of CaR under reducing conditions from a predominantly monomeric to this putative dimeric species on immunoblots in a manner similar to their rank order of functional potency for CaR activation (Gd3+ >> Ca2+ > Mg2+). This Ca2+ effect is blocked by pretreatment with N-ethylmaleimide. We conclude that disulfide bonds present in CaRs mediate formation of dimers that are preserved in Triton X-100 solution. In addition, CaR exposure to Ca2+ induces formation of additional disulfide bonds within the Triton-soluble CaR complex.

Animals↗
PubMed2001

Molecular shape of the cationic lipid controls the structure of cationic lipid/dioleylphosphatidylethanolamine-DNA complexes and the efficiency of gene delivery.

Pyridinium amphiphiles, abbreviated as SAINT, are highly efficient vectors for delivery of DNA into cells. Within a group of structurally related compounds that differ in transfection capacity, we have investigated the role of the shape and structure of the pyridinium molecule on the stability of bilayers formed from a given SAINT and dioleoylphosphatidylethanolamine (DOPE) and on the polymorphism of SAINT/DOPE-DNA complexes. Using electron microscopy and small angle x-ray scattering, a relationship was established between the structure, stability, and morphology of the lipoplexes and their transfection efficiency. The structure with the lowest ratio of the cross-sectional area occupied by polar over hydrophobic domains (SAINT-2) formed the most unstable bilayers when mixed with DOPE and tended to convert into the hexagonal structure. In SAINT-2-containing lipoplexes, a hexagonal topology was apparent, provided that DOPE was present and complex assembly occurred in 150 mm NaCl. If not, a lamellar phase was obtained, as for lipoplexes prepared from geometrically more balanced SAINT structures. The hexagonal topology strongly promotes transfection efficiency, whereas a strongly reduced activity is seen for complexes displaying the lamellar topology. We conclude that in the DOPE-containing complexes the molecular shape and the nonbilayer preferences of the cationic lipid control the topology of the lipoplex and thereby the transfection efficiency.

Animals↗
PubMedDate not supplied

Receptor-mediated gene delivery to HepG2 cells by ternary assemblies containing cationic liposomes and cationized asialoorosomucoid.

Unilamellar cationic liposomes have been prepared from an equimolar mixture of 3beta[N',N'-dimethylaminopropane)-carbomoyl] cholesterol (Chol-T), a higher homologue of 3beta[N',N'-dimethylaminoethane)-carbomoyl] cholesterol (DC-Chol), and dioleoylphosphatidyl-ethanolamine. The DNA binding capabilities of Chol-T and Chol-T/DOPE liposomes have been demonstrated in lipid impregnated paper-DNA binding assays and gel retardation experiments, respectively. These liposomes have been combined with pRSVL plasmid DNA and N-ethyl-N'-(3-trimethylpropylammonium) carbodiimide iodide modified asialoorosomucoid (Me+ CDI urea-AOM) to generate ternary electrostatic assemblies intended for selective entry into cells displaying the galactose-specific lectin. This effect has been evaluated in the human hepatocellular carcinoma cell line HepG2 in which high levels of luciferase activity were achieved (up to 1.84 x 10(7) relative light units/mg protein) after transfection with complexes containing liposomes (1-3 microg), Me+CDI urea-AOM (2 microg), and DNA (0.5 microg) in 0.5 mL culture medium. Transfections conducted in the presence of free asialoorosomucoid afforded much lower luciferase activity (up to 1.5 x 10(5) relative light units/mg protein) confirming that DNA uptake was predominantly via asialoorosomucoid receptor-mediated endocytosis. We concluded therefore that modular complexes used in our study display the carbohydrate moiety of the glycoprotein component prominently, thus permitting interaction of terminal galactose units with their cognate receptors on the cell membrane.

Asialoglycoprotein Receptor↗
PubMed1994

Cation fluxes and cation channels in outer segment membranes of bovine retinal rods: contamination by antibiotics applied to cattle?

Membrane vesicles were prepared from intact rod outer segments (ROSs) isolated from bovine retinas and were examined for the presence of cation-selective conductances. We performed macroscopic flux measurements in an ensemble of ROS membrane vesicles and single-channel measurements after fusion of ROS membrane vesicles with planar bilayer membranes. Two K(+)-permeable conductances were observed, the well-established cyclic GMP (cGMP) gated channel and an apparently new K+ channel with some unusual properties. Flux and single-channel data showed that the new conductance passed K+, Rb+, and Cs+ equally well but was much less permeable to Na+, Li+ and protons. Single-channel measurements revealed a linear current-voltage relationship and three unitary conductance states of 15, 11, and 8 pS, using symmetric 150 mM KCl solutions. Measured macroscopic K+ fluxes varied considerably among different preparations, suggesting some unknown regulation of the channel; the variability appeared to arise from variation in the channel's open probability, not the unit conductance or the number of channels present. The recorded single-channel events and the selectivity data are remarkably similar to those reported for antibiotic channel-forming ionophore gramicidin. We believe that the variability in both macroscopic permeability experiments and single-channel experiments may reflect a variable contamination with gramicidin applied to the animals as the topical antibiotic V-Sporin.

Animals↗
PubMed1987

Cation-dependent and cation-independent stages in regulation of the vascular angiotensin receptor after alteration of sodium balance in the rat.

The role of cations in vascular angiotensin receptor regulation has been investigated by radioligand receptor assay using a cell membrane fraction derived from mesenteric arterial muscle of the rat. In arterial membrane fractions from normal rats, the apparent receptor density varied with the ambient [Ca++] over the range, 0-10 mM. Receptor densities of 50 +/- 4, 102 +/- 4, and 156 +/- 5 fmol/mg membrane protein were obtained in low (0 mM), normal (4.8 mM), and high (25 mM) [Ca++], respectively. After 2 days of sodium loading, sodium depletion, and converting enzyme blockade altered receptor densities were detected in normal assay but not in high [Ca++] or low [Ca++], indicating changes in the relationship between [Ca++] and apparent receptor density. Similar results were obtained after 12 days of sodium loading or converting enzyme blockade. After 12 days of sodium depletion, there was no difference in receptor density between normal and high [Ca++] (44 +/- 5 fmol/mg protein) and the value obtained in low [Ca++] (27 +/- 2 fmol/mg protein) was significantly below that for all other groups. No change in receptor affinity was observed. These results suggest that there are two stages in vascular angiotensin receptor regulation; an initial masking-unmasking process which involves Ca++, and with prolonged agonist occupancy, an actual loss of receptors.

Angiotensin II↗
PubMed2005

The release of 5-methylene-2-furanone from irradiated DNA catalyzed by cationic polyamines and divalent metal cations.

Release of 5-methylene-2-furanone (5-MF), a characteristic marker of DNA deoxyribose oxidative damage at the C1' position, was observed in significant quantities from X-irradiated DNA. This observation, which held for DNA irradiated either in aqueous solution or as a film, requires postirradiation treatment at 90 degrees C in the presence of polyamines and divalent metal cations at biological pH. The 5-MF product was quantified by using reverse-phase HPLC. The radiation chemical yield of 5-MF comprised more than 30% of the yield of total unaltered base release. Polylysine, spermine and Be(II) showed the strongest catalytic effect on 5-MF release, while Zn(II), Cu(II), Ni(II), putrescine and Mg(II) were substantially less efficient. We have hypothesized that the 5-MF release from irradiated DNA occurs through catalytic decomposition of the 2'-deoxyribonolactone (dL) precursor through two consecutive beta- and delta-phosphate elimination reactions. A stepwise character of the process was indicated by the S-shaped time course of 5-MF accumulation. If dL proves to be the precursor to 5-MF formation, it would then follow that dL is a very important lesion generated in DNA by ionizing radiation.

Catalysis↗