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 145 records · Page 8Linked to original sources
PubMed1984

The environment of the high-affinity cation binding site on actin and the separation between cation and ATP sites as revealed by proton NMR and fluorescence spectroscopy.

The lanthanide ions Lu3+ (diamagnetic) and Gd3+ (paramagnetic broadening probe) were used to displace Ca2+ from the high-affinity cation binding site on G-actin. The effects of these higher-affinity ions on the proton nuclear magnetic resonance spectrum of actin were recorded. The aliphatic proton envelope in the Gd-actin sample exhibited a complex array of changes due to the proximity of Gd to several aliphatic residues. No such changes were observed in the diamagnetic Lu-actin control spectrum. By contrast, the aromatic proton envelope remained largely unaffected in both Gd-actin and Lu-actin samples. However, the adenosine moiety on the actin-bound ATP became increasingly mobilized without the triphosphate chain being released from the ATP binding site. Maximum adenosine mobilization occurred with approximately 1 mol of lanthanide ion bound per mol of actin. The absence of changes in the aromatic proton envelope suggests that the high-affinity cation binding site is in a region well removed from the adenosine moiety of bound ATP as well as any aromatic side-chains. The separation of the ATP and cation sites was further explored using the fluorescent ATP analogues FTP and epsilon-ATP. Tb3+ bound to the high-affinity cation site was found to be separated by 16 A from the FTP chromophore bound to the nucleotide binding site on actin. Since this distance is greater than can be accommodated on a model of the Tb-ATP complex, we conclude that the sites are physically separate. This conclusion was further reinforced by experiments involving the quenching of epsilon-ATP fluorescence by Mn2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1983

Cation exchange--a common mechanism in the storage and release of biogenic amines stored in granules (vesicles)? I. Comparative studies on the uptake of sodium and biogenic amines by the weak cation (carboxyl) exchangers Amberlite IRC-50 and Sephadex C-50 and by biogenic (granule-enriched) materials in vitro.

Studies on the uptake and storage of sodium and biogenic amines (phenylethylamine, noradrenaline, histamine) by two weak cation-exchangers, IRC-50 and Sephadex C-50, and by biogenic granule-enriched preparations demonstrated that the synthetic and biogenic materials had several common characteristics. They showed similar concentration- and pH-dependence and fitted the same cation-exchange and receptor-binding equations. The observations were taken to support the view that the matrices of amine-storing granules have the properties of weak cation-exchangers, with carboxyls as the cation-binding groups.

Animals↗
PubMed1995

Effects of divalent cations on muscarinic receptor cationic current in smooth muscle from guinea-pig small intestine.

1. Effects of Mg2+ and Ca2+ on muscarinic receptor cationic current (Icat) in guinea-pig ileal smooth muscle cells have been studied using patch-clamp techniques (whole-cell recording). Icat was activated either by externally applied carbachol or, to bypass receptors, by intracellular GTP-gamma-S. 2. Independently of the main permeant cation the current-voltage (I-V) relation for Icat was U-shaped between the reversal potential (usually 0 mV) and very negative potentials such as -120 mV where current could be virtually lost. Adding Ca2+ to Ca(2+)- and Mg(2+)-free external solution reduced inward current and made it less U-shaped whereas adding Mg2+ reduced inward current and shifted more positively the potential at which maximum inward current occurred. 3. Activation of the conductance underlying Icat could be described by the Boltzmann relation which was shifted positively by adding Ca2+ or Mg2+. Extracellular Ca2+ also distorted the relation by increasing the slope factor; maximal conductance was reduced in all cases. Icat relaxation at negative potentials was accelerated by increasing Mg2+ and slowed down by Ca2+. 4. These data suggest the presence of fixed negative surface charges on or near the muscarinic receptor cationic channel, which allow its modulation through alteration of surface potential. Additional more direct ion binding to and blocking of the channel cannot be ruled out. Some additional effects of Ca2+ (if compared with Mg2+) could be explained on the assumption that the Ca(2+)-binding activation site known to be present on the internal side of the channel can be accessible to Ca2+ entering through the open channel during muscarinic receptor stimulation, as Ca2+ ions contribute to a limited extent to Icat. 5. We conclude that voltage-dependent gating of muscarinic receptor cationic channels is an intrinsic channel property and that Ca2+ and Mg2+ have strong modulatory effects.

Animals↗
PubMed1990

Erythrocyte cation permeability induced by mechanical stress: a model for sickle cell cation loss.

Human red blood cells were subjected to mechanical shearing in a Couette viscometer at 37 degrees C, using polyvinylpyrrolidone to increase the medium viscosity. At stresses greater than 300 dyn/cm2, movement of both Na and K down their concentration gradients was observed. The net rate of both monovalent cation fluxes appeared to be linear with applied stress in the range of 300-910 dyn/cm2. The applied shear forces caused no fragmentation of the cells. Observed hemolysis was slight. The observed cation fluxes are not a result of hemolysis because the amount of K released by the hemolyzed cells is quantitatively inadequate to account for the net K efflux, and there is a net uptake of Na by the stressed erythrocytes, which cannot be a consequence of hemolysis. The rates of net Na uptake and K efflux were nearly equal (ratio = 0.93 +/- 0.40, n = 6). The stress-induced permeabilities were reversible when shearing was halted. This work demonstrates the existence of cation permeability inducible in the red cell membrane by mechanical deformation, which may be a model for the sickling-induced monovalent cation exchange observed in deoxygenated sickle cells.

Anemia, Sickle Cell↗
PubMed2003

Asialoganglioside enhances the efficiency of gene transfection mediated by cationic liposomes with a cationic cholesterol derivative.

We investigated the transfection efficiency mediated by asialoganglioside-containing cationic liposomes. Previously we reported that monosialoganglioside GM(1) (GM(1a)) enhanced transfection efficiency. In this study, we investigated the effects of sialic acid in gangliosides on transfection efficiency. Two mammalian culture cell lines HeLa and HepG2 were transfected with luciferase plasmids (pGL3) using cationic liposomes which contain monosialoganglioside GM(1) (GM(1a)) or its asialic counterpart, asialoganglioside GM(1) (GA(1)). Both GM(1a) and GA(1) enhanced the efficiency of transfection mediated by cationic liposomes, and GA(1) exhibited higher efficiency than GM(1a) in both cell lines. Transfection efficiency of ganglioside-containing liposomes was also assessed by the effects of antisense oligonucleotides (AS-ODN) for bcl-2 gene, which suppresses apoptotic cell death. Western blotting analysis revealed that the expression of Bcl-2 was decreased by AS-ODN, and the reduction of protein expression in cells treated with GA(1)-containing liposomes was more remarkable than that with GM(1a)-containing liposomes. Furthermore, the induction rate of apoptosis was higher in cells treated with AS-ODN with GA(1)-containing liposomes. Together with the results obtained by luciferase assay mentioned above, the removal of sialic acid from ganglioside causes the enhancement of efficiency of transfection mediated by cationic liposomes.

Apoptosis↗
PubMed2006

Determination of ammonium cations and alkali and alkaline earth metal cations in jellyfish by capillary zone electrophoresis.

We developed a capillary zone electrophoresis method with indirect UV detection for determination of ammonium cations and alkali and alkaline earth metal cations in jellyfish. As the background electrolyte, a mixture of N-methylbenzylamine, citrate, and 18-crown-6 was used for the complete separation of all analyte cations. The limits of detection were 0.13 - 0.34 mg l(-1) at a signal-to-noise ratio of three. The values of the relative standard deviation of peak area were 3.2 - 4.9%. The proposed method successfully determined the above analyte cations in jellyfish for approximately 4 min.

Animals↗
PubMed1985

7Li, 31P, and 1H NMR studies of interactions between ATP, monovalent cations, and divalent cation sites on rabbit muscle pyruvate kinase.

The interactions between ATP, monovalent cations, and divalent cations on rabbit muscle pyruvate kinase have been examined using 7Li, 31P, and 1H nuclear magnetic resonance. Water proton nuclear relaxation studies are consistent with the binding of Li+ to the K+ site on pyruvate kinase with an affinity of 120 mM in the absence of substrates and 16 mM in the presence of P-enolpyruvate. Titrations with pyruvate demonstrate that pyruvate binds to the enzyme with an affinity of 0.65 mM in the presence of Li+ and 0.4 mM in the presence of K+. 7Li+ nuclear relaxation rates in solutions of pyruvate kinase are increased upon titration with the metal-nucleotide analogue, Cr(H2O)4ATP. Mn2+ EPR spectra were used to determined the distribution of the enzyme between the so-called isotropic and anisotropic conformations of the enzyme (Ash, D. E., Kayne, F., and Reed, G.H. Arch. Biochem. Biophys. (1978) 190, 571-577). Li-Cr distances of 5.6 and 11.0 A were calculated for the anisotropic and isotropic forms, respectively, in the absence or presence of pyruvate. When the divalent cation site on the enzyme was saturated with Mg2+, these distances increased to 6.7 and 9.5 A, respectively, regardless of the presence or absence of pyruvate. 31P nuclear relaxation studies with the diamagnetic metal-nucleotide analogue, Co(NH3)4ATP, indicated that addition of Mn2+ ion to the divalent cation site on the enzyme increased the longitudinal relaxation rates of all three phosphorus nuclei of the analogue. The 31P data indicate that the presence of pyruvate at the active site effects a decrease in the Mn-P distances, bringing Mn2+ and Co(NH3)4ATP closer together at the active site. The data also permit an evaluation of the role of the metal coordinated to the beta-P and gamma-P of ATP at the active site.

Adenosine Triphosphate↗
PubMed1984

Effects of divalent cations on the regulation of insulin-sensitive glucose transport and cAMP phosphodiesterase in adipocytes. Insulin-like effects of divalent cations.

Effects of divalent cations on the regulation of glucose transport and cAMP phosphodiesterase in isolated rat epididymal adipocytes were studied. EDTA (5 mM) moderately inhibited the binding of insulin to adipocytes in Krebs-Henseleit Hepes buffer. In the same buffer, A-23187 (an ionophore specific for divalent cations; 50 microM) plus EDTA (5 mM) almost completely blocked the insulin- or hydrogen peroxide-dependent stimulation of phosphodiesterase. This inhibition was not secondary to the loss of ATP. When cells that had been treated with A-23187 plus EDTA were washed and then exposed to 1-10 mM of divalent cations, the cellular phosphodiesterase activity was elevated. Mn2+ was most stimulatory, Mg2+ was next, and Ca2+ was least effective. The stimulatory effects were enhanced by insulin. In the presence of insulin, Mn2+ at 10 mM was less stimulatory than that at 1 mM. In regular Krebs-Henseleit Hepes buffer, Mn2+ greatly stimulated phosphodiesterase if cells were first exposed to A-23187. The Mn2+-dependent stimulation was blocked by treatment of cells with 2,4-dinitrophenol. Results essentially parallel to those described above were also obtained when the rate of glucose transport was determined. The above results indicate that divalent cations mildly support the extracellular binding of insulin to its receptor, facilitate the physiological actions of insulin, and mimic the hormone actions, presumably by stimulating an intracellular enzyme.

2,4-Dinitrophenol↗
PubMed2000

Polyamine triggering of exocytosis in Paramecium involves an extracellular Ca(2+)/(polyvalent cation)-sensing receptor, subplasmalemmal Ca-store mobilization and store-operated Ca(2+)-influx via unspecific cation channels.

The polyamine secretagogue, aminoethyldextran (AED), causes a cortical [Ca(2+)] transient in Paramecium cells, as analyzed by fluorochrome imaging. Our most essential findings are: (i) Cortical Ca(2+) signals also occur when AED is applied in presence of the fast Ca(2+) chelator, BAPTA. (ii) Extracellular La(3+) application causes within seconds a rapid, reversible fluorescence signal whose reversibility can be attributed to a physiological [Ca(2+)](i) transient (while injected La(3+) causes a sustained fluorescence signal). (iii) Simply increasing [Ca(2+)](o) causes a similar rapid, short-lived [Ca(2+)](i) transient. All these phenomena, (i-iii), are compatible with activation of an extracellular "Ca(2+)/(polyvalent cation)-sensing receptor" known from some higher eukaryotic systems, where this sensor (responding to Ca(2+), La(3+) and some multiply charged cations) is linked to cortical calcium stores which, thus, are activated. In Paramecium, such subplasmalemmal stores ("alveolar sacs") are physically linked to the cell membrane and they can also be activated by the Ca(2+) releasing agent, 4-chloro-m-cresol, just like in Sarcoplasmic Reticulum. Since this drug causes a cortical Ca(2+) signal also in absence of Ca(2+)(o) we largely exclude a "Ca(2+)-induced Ca(2+) release" (CICR) mechanism. Our finding of increased cortical Ca(2+) signals after store depletion and re-addition of extracellular Ca(2+) can be explained by a "store-operated Ca(2+) influx" (SOC), i.e., a Ca(2+) influx superimposing store activation. AED stimulation in presence of Mn(2+)(o) causes fluorescence quenching in Fura-2 loaded cells, indicating involvement of unspecific cation channels. Such channels, known to occur in Paramecium, share some general characteristics of SOC-type Ca(2+) influx channels. In conclusion, we assume the following sequence of events during AED stimulated exocytosis: (i) activation of an extracellular Ca(2+)/polyamine-sensing receptor, (ii) release of Ca(2+) from subplasmalemmal stores, (iii) and Ca(2+) influx via unspecific cation channels. All three steps are required to produce a steep cortical [Ca(2+)] signal increase to a level required for full exocytosis activation. In addition, we show formation of [Ca(2+)] microdomains (</=0.5 microm, </=33 msec) upon stimulation.

Animals↗
PubMed2001

Biodistribution and renal excretion of isomers of the cationic tracer, (99m)Tc diaminocyclohexane (DACH): biodistribution of cationic renal tracers.

The buildup of organic anions in the plasma in the uremic state can competitively inhibit the tubular extraction of para-aminohippurate or (131)I ortho-iodohippurate (OIH) and lead to spuriously low measurements of effective renal plasma flow (ERPF). This problem can be circumvented by the use of cationic tracers. The cationic renal tracer, (99m)Tc labeled diaminocyclohexane ((99m)Tc DACH), has a clearance of 80% of OIH in mice but its clearance in humans is relatively low, only 30% of OIH. The (99m)Tc DACH isomer(s) used in prior studies, however, was not clearly defined and may have consisted of a single isomer or a combination of isomers. Since the anionic isomers of some (99m)Tc renal tracers have been shown to have widely different clearances, the biodistribution and urine excretion of the (99m)Tc cis-, trans-S,S, trans-R,R and +/-trans-DACH isomers were compared in Sprague-Dawley rats at 10 minutes and 60 minutes postinjection to determine if one of the (99m)Tc DACH isomers may be a significantly better renal tracer than the others. The red cell binding of (99m)Tc +/- trans-DACH was also determined. All of the isomers showed a high degree of specificity for the kidney with minimal secretion into the gastrointestinal tract. Urine excretion of the 4 tracers, however, was only 38-48% that of OIH at 10 minutes and 66-84% that of OIH at 60 minutes. Red cell binding was 6.9%. Cationic renal tracers have the potential to provide a more accurate measurement of ERPF than anionic tracers. Based on the animal data, however, it is unlikely that any of the (99m)Tc DACH isomers will have a substantially higher clearance in humans than the form of (99m)Tc DACH originally tested. Development of alternative cationic renal tracers is warranted.

Animals↗
PubMed2005

Study of Hg22+ and complexes of NpO2+ and UO22+ in solution. examples of cation-cation interactions.

Density functional theory (BPW91/TZ2P) is used to explore the nature of cation-cation interactions (CCIs) that exist between two actinyl cations in solution. Solvation, which is modeled using COSMO, favors the complexes (ONpO-ONpO)2+ and (ONpO-OUO)3+ over separated NpO2+(aq) and UO2(2+)(aq) cations because of the quadratic dependence of solvation on charge. For (OUO-OUO)4+, solvation effects, even though very large, are unable to overcome intrinsic electrostatic repulsion between the units. The actinyl-actinyl complexes are T-shaped, with the oxygen of one unit coordinated to the actinide metal of the other unit. The association free energies of (ONpO-ONpO)2+ and (ONpO-OUO)3+ are calculated as -42.1 and -29.2 kcal/mol. Explicit consideration of the first solvation shell at the B3LYP/LANL2DZ level suggests that the free energies of binding may be overestimated. The Hg2(2+) dication, though not considered a "traditional" CCI, is very similar to the actinyl-actinyl interaction. The binding free energy of Hg2(2+) in solution is calculated as -16.0 kcal/mol.

Journal Article↗
PubMed2005

(Sensitized) photolysis of diazonium salts as a mild general method for the generation of aryl cations. Chemoselectivity of the singlet and triplet 4-substituted phenyl cations.

The photolysis of a series of 4-X-benzenediazonium tetrafluoroborates is studied in MeCN. Loss of nitrogen occurs from the singlet excited state with X=H, t-Bu, and NMe2 and leads to the singlet aryl cation. This adds to the solvent yielding the corresponding acetanilides. With other substituents, ISC competes with (X=Br, CN) or overcomes (X=COMe, NO2) fragmentation and the aryl cation is formed in part or completely in the triplet state. In neat MeCN, this either abstracts hydrogen from the solvent (in most cases inefficiently) or undergoes intersystem crossing to the more stable singlet that reacts as above. In the presence of pi nucleophiles (allyltrimethylsilane or benzene), the triplet aryl cation is efficiently trapped giving substituted allylbenzenes and biphenyls, respectively. By triplet sensitization by xanthone, the triplet cation and the products from it are obtained from the whole series considered. The direct or sensitized photodecomposition of diazonium fluoroborates, substituted with both electron-donating and -withdrawing substituents, in the presence of alkenes and arenes offers an access to an alternative arylation procedure.

Journal Article↗
PubMed2005

Chemistry of styrene (water)n clusters, n = 1-5: spectroscopy and structure of the neutral clusters, deprotonation of styrene dimer cation, and implication to the inhibition of cationic polymerization.

The styrene-water binary clusters SW(n), with n = 1-5 have been studied by the (one-color) resonant two-photon ionization technique using the resonance of styrene. The structures and energetics of the neutral clusters are investigated using a search technique that employs Monte Carlo procedure. The strong tendency for water molecules to form cyclic hydrogen-bonded structures is clearly observed in the SW(n) structures starting from n =3. The results indicate that the spectral shifts correlate with the interaction energies between styrene and the water subcluster (W(n)) within the SW(n) clusters. Evidence is presented that points to (1) the formation of a covalent bonded styrene radical cation dimer following the 193 nm MPI of styrene neutral clusters, (2) proton transfer from the styrene dimer cation to the water or methanol subcluster, resulting in the formation of protonated water or methanol clusters and a styrene dimer radical, and (3) extensive solvation of the styrene dimer radical within the protonated solvent molecules. The proton-transfer reactions may explain the strong inhibition effects exerted by small concentrations of water or methanol on the cationic polymerization of styrene. These results provide a molecular level view of the inhibition mechanism exerted by protic solvents on the cationic polymerization of styrene.

Journal Article↗
PubMed2005

Binding of monovalent metal cations by the p-sulfonatocalix[4]arene: experimental evidence for cation-pi interactions in water.

Gibbs free energies, enthalpies and entropies for the binding of Na+, K+, Rb+, Cs+, Ag+, Tl+ and NH4+ by the p-sulfonatocalix[4]arene in water are determined by microcalorimetry. Whereas no significant heat effect is detected with Na+ or Ag+, suggesting that these cations are not complexed, weak but selective binding is observed with the other cations. The whole set of thermodynamic parameters, which demonstrate that the cations bind inside the cavity of the calixarene, evidence the importance of the cation-pi interactions for these complexes in water.

Journal Article↗
PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗
PubMed2002

The voltage-independent cation channel in the plasma membrane of wheat roots is permeable to divalent cations and may be involved in cytosolic Ca2+ homeostasis.

A voltage-independent cation (VIC) channel has been identified in the plasma membrane of wheat (Triticum aestivum) root cells (P.J. White [1999] Trends Plant Sci 4: 245-246). Several physiological functions have been proposed for this channel, including roles in cation nutrition, osmotic adjustment, and charge compensation. Here, we observe that Ca(2+) permeates this VIC channel when assayed in artificial, planar lipid bilayers, and, using an energy barrier model to describe cation fluxes, predict that it catalyzes Ca(2+) influx under physiological ionic conditions. Thus, this channel could participate in Ca(2+) signaling or cytosolic Ca(2+) homeostasis. The pharmacology of (45)Ca(2+) influx to excised wheat roots and inward cation currents through the VIC channel are similar: Both are insensitive to 20 microM verapamil or 1 mM tetraethylammonium, but inhibited by 0.5 mM Ba(2+) or 0.5 mM Gd(3+). The weak voltage dependency of the VIC channel (and its lack of modulation by physiological effectors) suggest that it will provide perpetual Ca(2+) influx to root cells. Thus, it may effect cytosolic Ca(2+) homeostasis by contributing to the basal Ca(2+) influx required to balance Ca(2+) efflux from the cytoplasm through ATP- and proton-coupled Ca(2+) transporters under steady-state conditions.

Barium↗
PubMed2002

Interaction of double-chained cationic surfactants, dimethyldialkylammoniums, with erythrocyte membranes: stabilization of the cationic vesicles by phosphatidylcholines with unsaturated fatty acyl chains.

We studied the interaction of double-chained cationic surfactants, dimethyldialkylammoniums, (CH3)2N+(CnH2n+1)2, with the lipid bilayer of guinea-pig erythrocytes by observing the haemolysis, aggregation and shape change in the erythrocytes. In the presence of sonicated dispersions of the five dimethyldialkylammoniums tested (n = 10, 12, 14, 16 and 18), haemolysis was induced dose dependently, and at 0.1 mM or higher concentrations, haemolysis was induced more rapidly by dimethyldialkylammoniums with shorter alkyl chains. The cationic surfactants with longer alkyl chains, such as dimethyldipalmitylammonium, induced aggregation of the erythrocytes before haemolysis fully progressed. The vesicles of these long-chain dimethyldialkylammoniums in the presence of phosphatidylcholines with unsaturated fatty acyl chains markedly reduced the haemolysis rates. Furthermore, in the presence of phosphatidylcholines with unsaturated acyl chains the formation of tightly aggregated structures of several erythrocytes was observed. These findings, and analysis by spin label 5-doxylstearic acid, indicate that phosphatidylcholines enriched with unsaturated acyl chains stabilize the cationic vesicles of long-chain dimethyldialkylammoniums and the interaction with the lipid bilayer of erythrocyte membranes as cationic vesicles became prominent.

Animals↗
PubMed1993

Dual nature of the intracellular cations. Conductance of adsorbed intracellular cations in the region of microwave frequencies.

The majority of intracellular ions was "invisible" by classical conductance measurements over the regions of audio and radio frequencies. In the microwave region all the cations become "visible" in muscles. A non-invasive method is found to determine the cationic content of biological tissues. The better the physical condition of the muscle the greater the new parameter, the invisible cationic conductivity. 15% of the total cation content is released by thermal treatment that was probably associated with negative phosphate or carboxylate groups of the lipoid surface of the membrane structure. This K+ fraction in the frog muscle has been already discovered by three quite different methods.

Acoustic Stimulation↗