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 649 records · Page 36Linked to original sources
PubMed1998

Antitumor effect of diphtheria toxin A-chain gene-containing cationic liposomes conjugated with monoclonal antibody directed to tumor-associated antigen of bovine leukemia cells.

Monoclonal antibody c143 against tumor-associated antigen (TAA) expressed on bovine leukemia cells was conjugated to cationic liposomes carrying a plasmid pLTR-DT which contained a gene for diphtheria toxin A-chain (DT-A) under the control of the long terminal repeat (LTR) of bovine leukemia virus (BLV) in the multicloning site of pUC-18. The specificity and antitumor effects of the conjugates were examined in vitro and in vivo using TAA-positive bovine B-cell lymphoma line as the target tumor. In vitro studies with the TAA-positive cell line indicated that luciferase gene-containing cationic liposomes associated with the c143 anti-TAA monoclonal antibody caused about 2-fold increase in luciferase activity compared with cationic liposomes having no antibody, and also that the c143-conjugated cationic liposomes containing pLTR-DT exerted selective growth-inhibitory effects on the TAA-positive B-cell line. Three injections of pLTR-DT-containing cationic liposomes coupled with c143 into tumor-bearing nude mice resulted in significant inhibition of the tumor growth. The antitumor potency of the c143-conjugated cationic liposomes containing pLTR-DT was far greater than that of normal mouse IgG-coupled cationic liposomes containing pLTR-DT as assessed in terms of tumor size. These results suggest that cationic liposomes bearing c143 are an efficient transfection reagent for BLV-infected B-cells lymphoma cells, and that the delivery of the pLTR-DT gene into BLV-infected B-cells by the use of such liposomes may become a useful technique for gene therapy of bovine leukosis.

Animals↗
PubMed2006

Value of eosinophil cationic protein and tryptase levels in bronchoalveolar lavage fluid for predicting lung function impairment in anaesthetised, asthmatic children.

Bronchial hyperactivity, a key feature of active asthma in children, is a risk factor for respiratory adverse events in the peri-operative period. The presence of activated eosinophils in the lungs and mast cell degranulation can contribute to bronchial hyperreactivity. Eosinophil cationic protein is released by activated eosinophils and tryptase reflects mast cell degranulation. This study focused on the relationship of respiratory mechanics, eosinophil cationic protein and tryptase levels in bronchoalveolar lavage fluid in asthmatic and healthy children under general anaesthesia. We measured eosinophil cationic protein and tryptase levels in bronchoalveolar lavage fluid from 21 asthmatic and 21 healthy children following induction of general anaesthesia. Respiratory system resistance and dynamic compliance were measured during mechanical ventilation. Eosinophil cationic protein was more common in bronchoalveolar lavage fluid from asthmatics (12/21) than from controls (4/21, p = 0.01) and was present at higher levels (p = 0.002). Tryptase was also more common in the asthmatics (8/21 vs 1/21, p = 0.01). Respiratory resistance was significantly higher in asthmatic children with detectable eosinophil cationic protein levels than in those with undetectable eosinophil cationic protein levels (p = 0.019). Furthermore, 50% of the asthmatics with detectable eosinophil cationic protein exhibited bronchospasm after sampling their bronchoalveolar lavage fluid. These findings suggested that high levels of eosinophil cationic protein in the bronchoalveolar lavage fluid are associated with irritable airways, presumably secondary to airway inflammation, and this might be a useful marker for respiratory adverse events in the peri-operative period.

Airway Resistance↗
PubMed1999

Gating current studies reveal both intra- and extracellular cation modulation of K+ channel deactivation.

1. The presence of permeant ions can modulate the rate of gating charge return in wild-type human heart K+ (hKv1.5) channels. Here we employ gating current measurements in a non-conducting mutant, W472F, of the hKv1.5 channel to investigate how different cations can modulate charge return and whether the actions can be specifically localized at the internal as well as the external mouth of the channel pore. 2. Intracellular cations were effective at accelerating charge return in the sequence Cs+ > Rb+ > K+ > Na+ > NMG+. Extracellular cations accelerated charge return with the selectivity sequence Cs+ > Rb+ > Na+ = NMG+. 3. Intracellular and extracellular cation actions were of relatively low affinity. The Kd for preventing slowing of the time constant of the off-gating current decay (tau off) was 20.2 mM for intracellular Cs+ (Cs+i) and 358 mM for extracellular Cs+ (Cs+o). 4. Both intracellular and extracellular cations can regulate the rate of charge return during deactivation of hKv1.5, but intracellular cations are more effective. We suggest that ion crystal radius is an important determinant of this action, with larger ions preventing slowing more effectively. Important parallels exist with cation-dependent modulation of slow inactivation of ionic currents in this channel. However, further experiments are required to understand the exact relationship between acceleration of charge return and the slowing of inactivation of ionic currents by cations.

Cations↗
PubMed1985

Existence of sites for anions and divalent cations in the solubilized gamma-aminobutyric acid/benzodiazepine receptor complex.

This study evaluated the ability of gamma-aminobutyric acid (GABA), baclofen, monovalent anions, divalent cations, and various combinations thereof to protect solubilized benzodiazepine (BZ) receptors of types 1 and 2, when contained together on the complex, against heat inactivation. Neither anions, cations, nor GABA alone provided significant protection of solubilized BZ receptors against heat, but inclusion of monovalent anions or divalent cations together with 500 microM GABA did afford protection. Monovalent anions combined with GABA (500 microM) provided 50% to full protection. Divalent cations, such as CaCl2 (2.5 mM) or MgCl2 (2.5 mM) in the presence of GABA (500 microM) yielded 45% and 24% protection, respectively. Other divalent cations tested (Zn2+, Hg2+, Co2+, and Ni2+) were poor protectors, even when combined with GABA. Monovalent anions (200 mM NaCl) and divalent cations (5 mM CaCl2) when tested together provided no protection. Similarly, baclofen (the GABA-B agonist) provided no protection, either alone or together with anions or divalent cations. These results indicate that the independent but interacting recognition sites of GABA, BZ, anions, and divalent cations, previously detected in the membrane-bound state, are retained in the solubilized state.

Animals↗
PubMed2005

Action of extracellular divalent cations on native alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors.

The effects of divalent cations on Ca2+-impermeable containing (GluR2 subunit) MPA receptors of hippocampal pyramidal neurones isolated from rat brain was studied using patch-clamping. Ca2+, Mg2+, Mn2+, Co2+, Ni2+ and Zn2+ inhibited currents induced by kainate and glutamate. Inhibition was fast, reversible and voltage independent. The rank order of activities was Ni2+ > Zn2+ > Co2+ > Ca2+ > Mn2+ > Mg2+. Cyclothiazide (0.1 mm) significantly reduced inhibition by divalent cations and 6, 7 dinitroquinoxaline-2.3-dione (DNQX). However, high concentrations of Ni2+ and DNQX inhibited AMPA receptors even in the presence of cyclothiazide. The inhibitory effect of divalent cations as well as DNQX was counteracted by an increase in agonist concentration. In the presence of divalent cations the EC50 values of kainate and glutamate were increased, but the maximal response was not changed. An increase in agonist concentration induced a parallel shift in the concentration-inhibition curve for a divalent cation. These data suggest a competitive-like type of inhibition. However, an increase in agonist concentration reduced the inhibitory action of Ni2+ less than that of DNQX. This gave evidence against direct competition between divalent cations and AMPA receptor agonists. A 'complex-competition' hypothesis was proposed to explain the inhibitory action of divalent cations; it is suggested that divalent cations form ion-agonist complexes, which compete with free agonist for agonist-binding sites on AMPA receptors.

Algorithms↗
PubMed1986

Novel interactions of cations with dihydropyridine calcium antagonist binding sites in brain.

The effects of monovalent (Na+, Li+, K+, Rb+) and divalent (Ca2+, Mg2+, Mn2+) cations on dihydropyridine calcium antagonist binding sites in brain and cardiac membranes were investigated using a low ionic strength buffer (5 mM Tris-HCl, pH 7.4), and the dihydropyridine, [3H]-nitrendipine. At 25 degrees C, the monovalent cations Na+, Li+, and K+ (100 mM) but not Rb+ significantly decreased the apparent dissociation constant (KD) but had no effect on the maximum binding site capacity (Bmax) of [3H]-nitrendipine in brain. The divalent cations Ca2+, Mg2+, and Mn2+ (2 mM) significantly increased the Bmax, but did not affect the KD of [3H]-nitrendipine. The effects of cations were concentration-dependent (EC50 monovalent cations 10-25 mM; EC50 divalent cations 50-200 microM) and demonstrated brain region selectivity. The effect of Ca2+, but not Mg2+ or Mn2+ on [3H]-nitrendipine binding was described by a two-site model. At 25 degrees C, neither mono- nor divalent cations altered the characteristics of [3H]-nitrendipine binding to rat cardiac membranes. At 37 degrees C, Na+ (100 mM) but not K+ (100 mM) significantly increased the Bmax of [3H]-nitrendipine in rat brain membranes. Ca2+ (2 mM) significantly increased the Bmax of [3H]-nitrendipine binding to rat brain membranes to a greater extent than at 25 degrees C. Both Na+ and K+ had no effect on [3H]-nitrendipine binding to cardiac membranes, while Ca2+ (2 mM) significantly decreased the KD of [3H]-nitrendipine. It is suggested that the selective effects of mono- and divalent cations on [3H]-nitrendipine binding to rat brain and cardiac membranes may be associated with differences in the calcium current blocking activity of dihydropyridine calcium antagonists in brain and cardiac tissues.

Animals↗
PubMed1982

Cation-dependent binding of substrate to the folate transport protein of Lactobacillus casei.

Lactobacillus casei cells grown in the presence of limiting folate contained large amounts of a membrane-associated binding protein which mediates folate transport. Binding to this protein at 4 degrees C was time and concentration dependent and at low levels (1 to 10 nM) of folate required 60 min to reach a steady state. The apparent dissociation constant (K(d)) for folate was 1.2 nM at pH 7.5 in 100 mM K-phosphate buffer, and it varied by less than twofold when measured over a range of pH values (5.5 to 7.5) or in buffered salt solutions of differing ionic compositions. Conversely, removal of ions and their replacement with isotonic sucrose (pH 7.5) led to a 200-fold reduction in binding affinity for folate. Restoration of the high-affinity state of the binding protein could be achieved by the readdition of various cations to the sucrose medium. K(d) measurements over a range of cation concentrations revealed that a half-maximal restoration of binding affinity was obtained with relatively low levels (10 to 50 muM) of divalent cations (e.g., Ca(2+), Mg(2+), and ethylenediammonium(2+) ions). Monovalent cations (e.g., Na(+), K(+), and Tris(+)) were also effective, but only at concentrations in the millimolar range. The K(d) for folate reached a minimum of 0.6 nM at pH 7.5 in the presence of excess CaCl(2). In cells suspended in sucrose, the affinity of the binding protein for folate increased 20-fold by decreasing the pH from 7.5 to 4.5, indicating that protons can partially fulfill the cation requirement. These results suggest that the folate transport protein of L. casei may contain both a substrate- and cation-binding site and that folate binds with a high affinity only after the cation-binding site has been occupied. The presence of these binding sites would support the hypothesis that folate is transported across the cell membrane via a cation-folate symport mechanism.

Bacterial Proteins↗
PubMed2002

Permeant but not impermeant divalent cations enhance activation of nondesensitizing alpha(7) nicotinic receptors.

Neuronal alpha(7) nicotinic acetylcholine receptors (nAChRs) are permeable to Ca(2+) and other divalent cations. We characterized the modulation of the pharmacological properties of nondesensitizing mutant (L(247)T and S(240)T/L(247)T) alpha(7) nAChRs by permeant (Ca(2+), Ba(2+), and Sr(2+)) and impermeant (Cd(2+) and Zn(2+)) divalent cations. alpha(7) receptors were expressed in Xenopus oocytes and studied with two-electrode voltage clamp. Extracellular permeant divalent cations increased the potency and maximal efficacy of ACh, whereas impermeant divalent cations decreased potency and maximal efficacy. The antagonist dihydro-beta-erythroidine (DHbetaE) was a strong partial agonist of L(247)T and S(240)T/L(247)T alpha(7) receptors in the presence of divalent cations but was a weak partial agonist in the presence of impermeant divalent cations. Mutation of the "intermediate ring" glutamates (E(237)A) in L(247)T alpha(7) nAChRs eliminated Ca(2+) conductance but did not alter the Ca(2+)-dependent increase in ACh potency, suggesting that site(s) required for modulation are on the extracellular side of the intermediate ring. The difference between permeant and impermeant divalent cations suggests that sites within the pore are important for modulation by divalent cations.

Acetylcholine↗
PubMed1984

In situ formation of subepithelial immune complexes in the rabbit glomerulus: requirement of a cationic antigen.

In a previous study we examined the role of antigenic electrical charge as a factor influencing glomerular immune complex (IC) localization in the rabbit. From that study patterned after chronic serum sickness nephritis it was demonstrated that the administration of charge-modified cationic bovine serum albumin (BSA) of isoelectric point (pI) greater than or equal to 9.5 invariably resulted in heavy subepithelial deposits, whereas native BSA (anionic, pI 4.5) produced principally mesangial deposits. In order to investigate the mechanism by which the immune deposits formed, passive serum sickness was induced in New Zealand white rabbits by unilaterally perfusing kidneys of nonimmunized rabbits with five alternating cycles of saline, antigen and antibody, or immunized rabbits with saline and antigen alone. Localization of BSA and IgG along the glomerular basement membrane (GBM) occurred only after exposure to cationic BSA and antibody; nonimmunized animals perfused with cationic BSA and antibody to cationic BSA uniformly developed generalized, diffuse nearly linear deposits of IgG and BSA along the GBM. Similar deposits, which became progressively more granular after exposure to circulating antibody, were seen after the perfusion of cationic BSA alone into animals actively immunized with cationic or native BSA. Ultrastructural examination showed effacement of foot processes and isolated, irregular subepithelial and subendothelial deposits. Control perfusion employing alternating cycles of native BSA and anti-native BSA antibody, cationic BSA and normal sheep IgG, or native BSA alone in animals actively immunized with native or cationic BSA failed to develop glomerular IgG deposits. All control kidneys were normal on ultrastructural examination.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Cationization of catalase, peroxidase, and superoxide dismutase. Effect of improved intraarticular retention on experimental arthritis in mice.

Several enzymes and other proteins were made cationic either by coupling to polylysine or by shielding of anionic sites. These cationic proteins, all having an isoelectric point greater than 8.5 exhibited excellent retention in articular structures when injected in mouse knee joints. Autoradiography and histochemistry showed that cationic forms of catalase, superoxide dismutase, and horseradish peroxidase were firmly retained by synovial and cartilaginous tissues. The half-life of these enzymes in the joint is thus significantly extended compared with native enzymes. The native enzymes and their cationic derivatives were tested for antiinflammatory properties in mice, using antigen-induced arthritis and zymosan-induced arthritis. It was found that injection of cationic catalase or peroxidase induced a marked suppression of some parameters of the inflammatory response in both types of arthritis, as measured by 99m technetium pertechnetate uptake and leakage of 125I-labeled albumin. Native catalase and peroxidase were less, or not at all effective. Cationic superoxide dismutase or cationic nonenzyme proteins did not suppress inflammation. The observed suppression of two different types of inflammation (an immune and a nonimmune arthritis) by catalase and peroxidase suggests that elimination of peroxides contributes to the suppression of an inflammatory response. We would hypothesize that cationic enzymes offer the possibility for investigating the mechanisms of inflammation and, in addition, might be interesting from a therapeutical point of view.

Animals↗
PubMed2004

A novel cation-sensing mechanism in osteoblasts is a molecular target for strontium.

UNLABELLED: Defining the molecular target for strontium in osteoblasts is important for understanding the anabolic effects of this cation on bone. The current studies demonstrate that a G-protein-mediated response to strontium persists in osteoblasts that lack CASR, suggesting a predominant role for a novel cation-sensing receptor in mediating the osseous response to strontium. INTRODUCTION: Strontium has anabolic effects on bone and is currently being developed for the treatment of osteoporosis. The molecular target for strontium in osteoblasts has not been determined, but the existence of CASR, a G-protein-coupled receptor calcium-sensing receptor, raises the possibility that strontium actions on bone are mediated through this or a related receptor. MATERIALS AND METHODS: We used activation of a transfected serum response element (SRE)-luciferase reporter in HEK-293 cells to determine if CASR is activated by strontium. In addition, we examined strontium-mediated responses in MC3T3-E1 osteoblasts and osteoblasts derived from wild-type and CASR null mice to determine if other cation-sensing mechanisms are present in osteoblasts. RESULTS AND CONCLUSIONS: We found that strontium stimulated SRE-luc activity in HEK-293 cells transfected with full-length CASR but not in cells expressing the alternatively spliced CASR construct lacking exon 5. In contrast, we found that MC3T3-E1 osteoblasts that lack CASR as well as osteoblasts derived from CASR null mice respond to millimolar concentrations of strontium. The response to strontium in osteoblasts was nonadditive to a panel of extracellular cations, including aluminum, gadolinium, and calcium, suggesting a common mechanism of action. In contrast, neither the CASR agonist magnesium nor the calcimimetic NPS-R568 activated SRE activity in osteoblasts, but the response to these agonists was imparted by transfection of CASR into these osteoblasts, consistent with the presence of distinct cation-sensing mechanisms. Co-expression of the dominant negative Galphaq(305-359) minigene also inhibited cation-stimulated SRE activity in osteoblasts lacking known CASR. These findings are consistent with strontium activation of a novel Galphaq-coupled extracellular cation-sensing receptor in osteoblasts with distinct cation specificity.

Alternative Splicing↗
PubMed2006

Transfection activity of binary mixtures of cationic o-substituted phosphatidylcholine derivatives: the hydrophobic core strongly modulates physical properties and DNA delivery efficacy.

A combination of two cationic lipid derivatives having the same headgroup but tails of different chain lengths has been shown to have considerably different transfection activity than do the separate molecules. Such findings point to the importance of investigating the hydrophobic portions of cationic amphiphiles. Hence, we have synthesized a variety of cationic phosphatidylcholines with unusual hydrophobic moieties and have evaluated their transfection activity and that of their mixtures with the original molecule of this class, dioleoyl-O-ethylphosphatidylcholine (EDOPC). Four distinct relationships between transfection activity and composition of the mixture (plotted as percent of the new compound added to EDOPC) were found, namely: with a maximum or minimum; with a proportional change; or with essentially no change. Relevant physical properties of the lipoplexes were also examined; specifically, membrane fusion (by fluorescence resonance energy transfer between cationic and anionic lipids) and DNA unbinding (measured as accessibility of DNA to ethidium bromide by electrophoresis and by fluorescence resonance energy transfer between DNA and cationic lipid), both after the addition of negatively charged membrane lipids. Fusibility increased with increasing content of second cationic lipid, regardless of the transfection pattern. However, the extent of DNA unbinding after addition of negatively charged membrane lipids did correlate with extent of transfection. The phase behavior of cationic lipids per se as well as that of their mixtures with membrane lipids revealed structural differences that may account for and support the hypothesis that a membrane lipid-triggered, lamellar-->nonlamellar phase transition that facilitates DNA release is critical to efficient transfection by cationic lipids.

Cations↗
PubMed1994

Manipulation of dietary cation-anion difference on nutritionally related production diseases, productivity, and metabolic responses of dairy cows.

Dietary cation-anion difference has been defined as milliequivalents of (Na+K)-(Cl+S) per kilogram of DM and has a direct impact on blood acid-base metabolism. As this difference decreases, one or more of the following blood parameters change: increased H+, decreased HCO3-, and decreased pH. These changes are accompanied by reduced urinary HCO3- excretion and pH as compensatory mechanisms. Although other minerals have an impact on acid-base metabolism, the four minerals used in dietary cation-anion difference have the greatest effect. Manipulation of acid-base balance can be used to manipulate other biological functions to benefit health and productivity of cows. Low cation-anion difference prepartum can mitigate hypocalcemia peripartum via increased urinary Ca, blood-ionized Ca, and responsiveness to Ca homeostatic hormones. These changes reduced the incidence of paresis and increased productivity by reducing the severity and length of hypocalcemia in all cows (periparturient), regardless of the occurrence of paresis. Reduced cation-anion differences prepartum have been related to a reduced severity of udder edema, likely related to increased renal loss of water and unchanged water intake. However, the effects on acid-base balance cannot be ruled out because of effects on biochemical and transport processes. Elevated cation-anion difference in lactation has been shown to increase DMI and production and to mitigate the effects of heat stress. Because production and heat stress are acidogenic, elevated cation-anion difference improves blood-buffering capacity to cope with H+. In heat stress, elevated water intake with elevated cation-anion difference cannot be ignored. Other diseases related to metabolic acid, such as laminitis and ketoacidosis, may be influenced by elevated cation-anion difference in lactation; however, research in these areas has not been forthcoming.

Acid-Base Equilibrium↗
PubMed1999

Protective role for proteoglycans against cationic lipid cytotoxicity allowing optimal transfection efficiency in vitro.

A dependence on proteoglycans for cationic lipid-mediated gene transfer has been suggested in previous studies [Mislick and Baldeschwieler (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 12349-12354; Mounkes, Zhong, Cipres-Palacin, Heath and Debs (1998) J. Biol. Chem. 273, 26164-26170]. We have evaluated the mechanism of proteoglycan involvement in cationic lipid-mediated gene transfer. DNA plasmid uptake and gene expression were studied in wild-type Chinese hamster ovary (CHO) cells (CHO-K1), heparan sulphate-deficient CHO cells (pgsD-677) and proteoglycan-deficient CHO cells (pgsB-618). At an optimal ratio of cationic lipid to DNA, a substantial decrease in reporter gene expression was observed in proteoglycan-deficient cells compared with that in heparan sulphate-deficient and wild-type cells. However, there were no differences in reporter gene expression between the cell lines when transfected by electroporation. Moreover, all cell lines exhibited equal cationic-lipid-DNA complex uptake activities, as assessed by the measurement of intracellular (32)P-labelled and rhodamine-labelled DNA plasmid. An analysis of reflected-light images of wild-type and proteoglycan-deficient cells suggested that cationic lipids were preferentially toxic to proteoglycan-deficient cells. Cell-growth assays confirmed this, showing that cationic lipids exhibited a greater anti-proliferative activity in proteoglycan-deficient cells and in chlorate-treated wild-type cells than in the other cell lines. The growth-inhibitory effect of cationic lipids was abrogated by the addition of exogenous sulphated glycosaminoglycans. We conclude that the glycosaminoglycan part of proteoglycans serves a protective role against cationic lipid cytotoxicity, allowing optimal transfection efficiency in vitro.

Animals↗
PubMed2001

Modulation of alpha1beta1 integrin mediated adhesion of hepatocytes to collagen IV and laminin by divalent cations.

Cell matrix interactions play a critical role in hepatic development and regeneration after acute injury. These interactions are mediated by transmembrane receptors belonging mainly to the integrin family. We have tried to assess the role of divalent cations in mediating attachment of hepatocytes to matrix proteins like collagen IV (Col IV) and laminin (Ln). The three cations examined viz. Ca2+, Mg2+ and Mn2+ showed attachment promoting activity. Since alpha1beta1 integrin is a common receptor for col IV and LN in liver, the effect of cations in its binding to these matrix proteins was studied. Although cations in general enhanced the binding, different cations exhibited differential effect in promoting the binding for different ligands. Mg2+ ions were more effective in promoting the binding of alpha1beta1 integrin to col IV but Ca2+ proved to be more effective one for Ln. Kinetic analysis of binding in dot blot assays using different concentrations of cations showed that while Mg2+ was active at low concentrations Ca2+ and Mn2+ promoted the binding more at higher concentrations. Absence of competitive effect in binding studies showed that they bind at different sites on the receptor. Differential effects of cations in promoting the binding of alpha1beta1 integrin to Col IV and Ln suggest that changes in level of diffusible cations can modulate affinity of the common receptor alpha1beta1 integrin to its ligands and can influence adhesion of hepatic cells to different matrix proteins during hepatic development and regeneration.

Animals↗
PubMed2001

Extracellular polyvalent cation block of slow Na+ channels in Xenopus laevis oocytes.

Sustained depolarization of the Xenopus oocyte membrane elicits a slowly activating Na+ current, thought to be due to the opening of sodium selective channels. These channels are induced to become voltage gated by the depolarization. They show unconventional gating properties and are insensitive to tetrodotoxin (TTX). The present study was undertaken to evaluate the effect of extracellular multivalent cations (Ca2+, Co2+, Cd2+, La3+, Mg2+, Mn2+, Ni2+, Sr2+ and Zn2+) on these TTX-resistant channels, either on membrane potential responses or on current responses. Our data show that all the polyvalent cations used blocked Na+ channels in a concentration-dependent manner. The order of potency of the most efficient cations was Co2+ < Ni2+ < Cd2+ < Zn2+, the respective concentration required to cause a 50% decrease of Na+ current was 0.9+/-0.29; 0.47+/-0.15; 0.36+/-0.09 and 0.06+/-0.02 mmol/l. The comparison of the activation curves from controls and after treatment with the cations indicated a shift towards more positive voltages. These results can be interpreted as due to the screening effect of divalent cations together with an alteration of the Na+ channel gating properties. We also show that divalent cations blocked Na+ channels in an open state without interfering with the induction mechanism of the channels. The possibility that cation block was due to a possible interaction between cations and SH-groups was investigated, but a sulphydryl alkylating reagent failed to abolish Zn2+ block.

Alkylating Agents↗
PubMed2003

[Study on the defluoridation of drinking water with model-La cation exchange resin].

Model-La cation exchange resin was transformed from strong acid cation exchange resin, which was used for the defluoridation of drinking water. The 001 x 7 strong acid cation exchange resin was transformed into model-La cation exchange by soaking in the La(NO3)3 solution. The F- in the water was removed by model-La cation exchange resin under the optimum condition because it was combined into fluoride with the La3+ in the model-La cation exchange resin. The used resin was regenerated with the La(NO3)3 solution and was used to defluoridate many times. The optimum conditions of transform and defluoridation and regeneration were d(rasin) = 0.315-0.600 mm, V(rasin):V(regeneration) = 1:6, t(transform) = 48 h, T = 298.16 K(25 degrees C). The defluoridation capacity was 5.60 mg/g in column test, and 4.08 mg/g in batch test. The model-La cation exchange resin could be used for defluoridation for 8 times. The results suggest that the model-La cation exchange resin is a novel material of defluoridation. This method is easy to master and the pH value of the solution doesn't need to be regenerated that the cost of defluoridation can be reduced significantly and it can be used for a long time.

Cation Exchange Resins↗
PubMed1987

The pH gradient-dependent transport of organic cations in the renal brush border membrane. Studies with acridine orange.

Recent studies have suggested that there is an organic cation-proton exchange mechanism in the renal brush border membrane which may be responsible for the active secretion of organic cations by the kidney. In all of these studies, the movement of organic cations was specifically monitored in the presence of a proton gradient. In this study, the organic cation-proton exchange mechanism in renal brush border membrane vesicles was examined by studying the movement of protons in the presence of favorable gradients of the organic cation, tetraethylammonium (TEA). Using acridine orange, a pH-sensitive fluorescent probe, we demonstrated that in isolated brush border membrane vesicles prepared from rabbit renal cortex, the rate of proton efflux increased with increasing inwardly directed gradients of TEA, although the efflux was saturable. An outwardly directed TEA gradient could also accelerate the influx of protons. The rate of exchange of protons for TEA was slower than that for Na+. This slower rate appears to be due to a lower Vmax of the exchange of organic cations with protons. These data provide more direct evidence for an exchange of organic cations with protons or a cotransport of organic cations and hydroxyl ions in the renal brush border membrane.

Acridine Orange↗