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At least 937 records · Page 52Linked to original sources
PubMed1992

Influence of cation-anion balance on feed intake, body weight gain, and humoral response of dairy calves.

The objective of this study was to examine the influence of diets with varying cation-anion balance on performance and humoral responses in young, growing dairy calves. Twenty-eight Holstein and 4 Jersey female calves were blocked at 56 to 70 d after birth according to breed and age and assigned randomly to dietary treatments of 0, 21, 37, and 52 meq(Na + K) - Cl/100 g of dietary DM. Diets were based on cracked corn, dried brewers grains, and oats and were fed for 8 wk. Feed intake and average daily gain tended to increase quadratically, being highest for calves fed the +37-meq diet and lowest for those fed the 0-meq diet. Blood and urine pH increased linearly with increasing dietary cation-anion balance. Plasma Ca increased linearly, and Mg and Cl decreased linearly with increasing cation-anion balance. Plasma Na and P were unaffected by dietary treatments. Urinary Ca, Mg, and Cl excretions decreased linearly; urinary P, Na, and K excretion increased linearly with increasing dietary cation-anion balance. Blood pH increased linearly with increasing dietary cation-anion balance. Blood partial pressure of CO2 and HCO3 increased concurrently with increasing dietary cation-anion balance. Results indicate that altering cation-anion balance may impact DMI and average daily gain in the young ruminant.

Animal Feed↗
PubMed1975

Structural basis of cation exchange, complex formation and redox properties in chloragosomes.

Components of chloragosomes isolated from Octolasium transpadanum ROSA were separated by fractional extraction. The chemical composition of the fractions was determined and their effect on the anion- and cation-binding capability and on the lipophilic property of chloragosomes was studied. The acid-alcoholic extract of chloragosomes contained, among others, metalloporphyrins with 2 or 4 free -COOH groups; the residuum consisted of basic proteins. The metalloporphyrins and phosphatides gained by extraction with chloroform-methanol neutralize the basic groups of the chloragosome proteins, thus, an excess of free acidic groups develops, which is responsible for the polyanionic nature and cation exchange of chloragosomes. The apolar groups of phosphatides and carotenoids are responsible for the lipophilic nature of chloragosomes. Under experimental circumstances both in vivo and in vitro, organic cations were bound to chloragosomes, partially by a cation-exchange mechanism and partially by formation of more stable complexes. A small amount of anions may be absorbed by the bound cations. The diluted acidic extract of chloragosomes predominantly contain organic cations, in the present study riboflavin, flavin nucle0tide and thiamine were determined. Chloragosomes, owing to their structure, form complexes of varying stability with anions, cations and hydrophilic compounds equally. This feature explains their capability of cumulating trophic and toxic substances, while their redox activity is explained by their metalloporphyrin, flavin, thiamine and carotene content.

Chromatography, Paper↗
PubMed2003

[Influence of soybean-derived sterylglucoside and amphipathic polyethylene glycol on the cellular delivery and anisotropy of different cationic liposomes].

OBJECTIVE: To investigate the influences of different lipids on cellular delivery and fluidity of liposome membrane of cationic liposome. METHODS: The 3 beta [N-(N',N'-dimethylaminoethane) carbamoyl] cholesterol (DC-chol), a cationic lipid was synthesized, which is approved by FDA. Using fluorescein sodium (SF) as a model material, dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylethanolamine (DOPE) and cholesterol (ch) as help lipids, the DPPC/ch/DC-chol cationic liposomes, DOPE/ch/DC-chol cationic liposome and soybean-derived sterylglucoside (SG) or polyethylene glycol-distearoylphosphatidylethanolamine (PEG-DSPE) modified cationic liposomes were prepared, respectively. The neutral liposome DPPC/ch was also prepared. HepG2 2.2.15 was selected as an in vitro cell culture assay model to investigate the cellular delivery of different liposomes. The influences of different lipids on the fluidity of liposome membranes were investigated with the technique of fluorescence polarization. RESULTS: It is showed that the DC-chol has significant influences on the incorporation efficiencies (from 0.64% to 74.84%), cellular delivery (from 1.83% to 32.29%) and the fluidity of liposome membrane; SG can significantly increase the incorporation efficiency (from 52.60% to 63.37%), cellular delivery (from 20.18% to 47.48%) and fluidity of liposome membrane; PEG-DSPE can enhance the cellular delivery of cationic liposome (from 20.18% to 28.17%). CONCLUSION: DC-chol and SG can significantly increase the cellular delivery and fluidity of liposome membrane, PEG-DSPE can enhance the cellular delivery of cationic liposome.

Anisotropy↗
PubMed1992

Postnatal development of organic cation transport and mdr gene expression in mouse kidney.

The apical surface of the proximal tubular epithelium is the site of both P-glycoprotein localization and postulated active secretion of organic cations in the mammalian kidney. P-glycoprotein has been shown to act as a pleiotropic drug efflux pump across the cell membrane of tumor cells expressing the multidrug resistance phenotype, whereas the renal organic anion and organic cation secretory systems serve the function of pleiotropic drug transport across the proximal tubule epithelium. Because most known substrates for P-glycoprotein are organic cations, we tested the hypothesis that the physiological function of this protein in the kidney is to mediate renal organic cation secretion. In one approach, we compared the postnatal development of organic cation transport with that of kidney mdr gene expression. Cimetidine-sensitive uptake of classical substrates for renal secretion (N-methyl nicotinamide and tetraethylammonium) into kidney slices developed gradually in neonate mice, reaching adult capacity in 4 to 6 weeks. P-glycoprotein and its mRNA, as estimated by immunohistochemical methods and RNAse protection analysis, were undetectable at birth and were expressed abruptly at the adult level between 2 and 3 weeks of age. In another approach, classical inhibitors of renal organic cation secretion (cimetidine and cyanine 863) failed to reverse resistance to adriamycin in Chinese hamster ovary and P388 cell lines, which possess the phenotypic traits of multidrug resistance. These results suggest that the cimetidine-sensitive component of organic cation secretion is mediated by a protein other than the P-glycoprotein in the mammalian kidney.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

[Cationic liposomes enhance the inhibitory effects of antisense oligodeoxynucleotide on hepatitis B virus].

OBJECTIVE: To study the interaction between 3beta-[N-(N', N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-chol), a cationic lipid, and antisense oligodeoxynucleotide (asODN), and the cytotoxicity to HepG(2) 2.2.15 cells and the inhibitory effects of asODN cationic liposomes on hepatitis B virus. METHODS: Extract efficiency was used to estimate the interaction between DC-chol and asODN under different conditions; MTT was applied to examine the infection of DC-chol concentration on the cytotoxicity of treated cells; By ELISA technology, we examined the contents of HBsAg, and HBeAg in the culture medium, and evaluated the accelerate efficiency of neutral liposome and cationic liposomes to the inhibitory effects of asODN on hepatitis B virus, and the infection of charge ratio on the inhibitory effects of asODN cationic liposomes. RESULTS: When the charge ratio >0.6, DC-chol could efficiently extract the asODN from the aqueous phase; The alkaline condition and the presence of Na(+), Cl(-) ions prevented the efficient interaction between DC-chol and the asODN; DC-chol cationic liposomes had some toxicity to HepG(2) 2.2.15 cells, at low concentration (0.84-26.94 mg x L(-1)), and the toxicity of DC/chol was linear with the concentration of DC/chol; Within 1.25-5.00 micromol x L(-1), the inhibition efficacy of asODN was correlated to its concentration; liposomes could enhance the inhibition efficacy of asODN on hepatitis B virus, and cationic liposomes could enhance much more (from 60% to 95%). CONCLUSION: Surface-modified DC-chol cationic liposomes can efficiently enhance the anti-hepatitis B virus efficiency of asODN in vitro.

Dose-Response Relationship, Drug↗
PubMed1985

Activation of human blood platelets by arginine-vasopressin. Role of bivalent cations.

Arginine-vasopressin caused platelet activation, i.e., a shape change reaction and a rise in intracellular free Ca2+ ([Ca2+]i) only in the presence of certain bivalent cations. The EC50 of arginine-vasopressin (concentration causing half-maximal shape change) decreased with rising concentrations of Mn2+, Mg2+, or Ca2+ in the medium, but was at least an order higher with Ca2+ than with Mn2+ or Mg2+. The EC50 of the active bivalent cations (concentrations enabling 100 nM arginine-vasopressin to exert half-maximal shape change and rise in [Ca2+]i) varied with the individual cations, being by far the highest for Ca2+. The KD of [3H]arginine-vasopressin binding to platelet membranes and intact platelets markedly decreased when extracellular Mg2+ or Mn2+ were present, and the KD values were inversely related to the concentration of the cations. Ca2+ also lowered the KD values; however, the effect was less marked than that of Mg2+ or Mn2+ and, in physiological conditions, significant only in intact platelets. Vasopressin-1 antagonists counteracted arginine-vasopressin binding and the shape change reaction and [Ca2+]i rise induced by arginine-vasopressin. In the presence of Mn2+ in the medium, administration of arginine-vasopressin led to quenching of the intracellular fluorescence of 2-methyl-6-methoxy-8-nitroquinoline-loaded platelets, possibly due to influx of Mn2+. In conclusion, the dependency of the arginine-vasopressin-induced platelet activation on bivalent cations is at least partly due to an enhancement by these cations of the affinity of the vasopressin-1 receptor for arginine-vasopressin. Thereby, under physiological conditions, Mg2+ seems to be of primary importance. Other mechanisms may be involved, too, e.g., an enhancement by arginine-vasopressin of the influx of bivalent cations into the platelets.

Aminoquinolines↗
PubMed1994

P-glycoprotein and organic cation secretion by the mammalian kidney.

On the basis of physiological localization, broad substrate specificity and energy dependence, the role of the kidney P-glycoprotein was tested in the energy-dependent renal secretion of organic cations. P-glycoprotein-enriched vesicles from Cl 1D/VCR [a multidrug-resistant (MDR) cell line] displayed enhanced transport of the MDR drug vinblastine and the organic cation cimetidine but not of the organic cation tetraethylammonium (TEA) over that shown by vesicles prepared from the drug-sensitive parental line Cl 1D. An outwardly directed proton gradient stimulated TEA and cimetidine uptake by renal brush border membrane vesicles (BBMV) but this gradient did not enhance the uptake of these organic cations into Cl 1D/VCR vesicles. Vinblastine uptake was unaffected by the proton gradient in either vesicle preparation. An outwardly directed gradient of TEA enhanced the uptake of TEA into renal BBMV but did not do so in the case of Cl 1D/VCR vesicles. These data indicate that P-glycoprotein, which is normally energized by ATP hydrolysis, is incapable of catalyzing organic cation/proton exchange or organic cation/organic cation exchange, properties of the organic cation carrier of renal proximal tubule BBMV. The MDR substrates and modulators inhibited the uptake of vinblastine and cimetidine by Cl 1D/VCR vesicles and the uptake of cimetidine and TEA by renal BBMV. Several organic cations studied inhibited TEA and cimetidine uptake by renal BBMV but did not inhibit the uptake of vinblastine and cimetidine by Cl 1D/VCR vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Possible pathogenic role of cationic anti-DNA autoantibodies in the development of nephritis in patients with systemic lupus erythematosus.

Extensive studies in murine models of lupus nephritis have shown that cationic anti-DNA autoantibodies have nephritogenic potential. We have investigated whether cationic anti-DNA antibodies of IgG class are also produced in vivo in patients with active lupus nephritis. Antibodies against DNA in the sera from patients with SLE were purified by affinity chromatography on DNA-cellulose, followed by nonequilibrium pH gradient electrophoresis and SDS-PAGE. The highly cationic anti-DNA antibodies of IgG class were prominent in the nonequilibrium pH gradient electrophoresis-immunoblots of the antibodies from the patients with active lupus nephritis. Decreased proteinuria after successful treatment with prednisolone was associated with disappearance of the cationic anti-DNA antibodies in the circulation. The cationic anti-DNA antibodies did bind to heparan sulfate, which is a major glycosaminoglycan in glomerular basement membrane, much better than did neutral anti-DNA antibodies. The results suggest that the cationic anti-DNA autoantibodies may play a certain role in the development of lupus nephritis. Our study demonstrates the strong association between the presence of cationic anti-DNA antibody and the development of lupus nephritis in humans.

Adolescent↗
PubMed1998

Maitotoxin (MTX) activates a nonselective cation channel in Xenopus laevis oocytes.

Maitotoxin (MTX) may exert its toxic effect by activating ion conductances and has been shown to elicit a fertilization-like response in Xenopus laevis oocytes. In the present study we investigated the electrophysiological response of stage V-VI Xenopus oocytes to MTX using the two-microelectrode voltage-clamp technique. Membrane voltage (Vm) measurements demonstrated that MTX (50 pM to 1 nM) depolarized the oocytes from -49+/-7 to -14+/-1 mV. Subsequent replacement of bath Na+ by the impermeant cation NMDG (N-methyl-d-glucamine) shifted Vm from -14+/-1 to -53+/-5 mV (n=29). This indicates that MTX activates a cation conductance. Indeed, current measurements at a holding potential of -60 or -100 mV showed that within 10 s of MTX application an inward current component developed which was largely abolished by extracellular Na+ removal. After a 1-min application of 1 nM MTX the NMDG-sensitive current increased more than 100-fold from 0.14+/-0.03 microA to a peak value of 21+/-3 microA (n=11). The effect of MTX was concentration dependent with an EC50 of about 250 pM but only slowly reversible. Ion substitution experiments indicated that the stimulated conductance was nonselective for monovalent cations with a slight preference for NH4+ (2.1) > K+ (1.5) > Na+ (1.0) > Li+ (0.7). Regarding divalent cations, a complex biphasic response to extracellular Na+ replacement by Ca2+ was observed, which suggests that the stimulated channels may have a small Ca2+ permeability but that exposure to high extracellular Ca2+ enhances recovery from MTX stimulation. No significant conductance for Mn2+ was observed. Application of 1 mM benzamil, 1 mM amiloride, or 100 microM 1-(beta-[3-(4-Methoxyphenyl)-propoxy]-4-methoxyphenethyl)-1H-imidazol e hydrochloride (SK&F 96365) reduced the MTX-stimulated inward current by 81%, 62%, or 65%, respectively. Gd3+ had an inhibitory effect of 29% and 38% at concentrations of 10 microM or 100 microM, respectively. Flufenamic acid, niflumic acid, (RS)-(3,4-dihydro-6, 7-dimethoxyisoquinoline-1-gamma1)-2-phenyl-N,N-di-[2-(2,3, 4-trimethoxyphenyl)-ethyl]-acetamide (LOE908), and 3', 5'-dichlorodiphenylamine-2-carboxylic acid (DCDPC), known blockers of other nonselective cation channels, had no significant effect. We conclude that MTX activates a nonselective cation conductance in Xenopus oocytes. The underlying channels may be involved in changes in Vm that occur during the early stages of fertilization.

Animals↗
PubMed1995

Purification of commercial gellan to monovalent cation salts results in acute modification of solution and gel-forming properties.

Lithium, sodium, potassium, and ammonium salts of the industrial polysaccharide gellan were prepared. The salts were freely soluble in water at room temperature (25 degrees C). The opinion had been generally held that heating to 100 degrees C was necessary for gellan to achieve complete solubility in the presence of mono- or multivalent cations. Then, upon cooling, the solutions would form gels. These conclusions were based on the properties imposed upon gellan samples by the presence of contaminating divalent cations. Commercial gellan samples contain calcium and magnesium at levels exceeding 0.9%, sufficient for counterion formation with over one-third of gellan's carboxyl groups. Purification was rapid and included sequential treatments with a cation-exchange (H+) resin, LiOH, NaOH, KOH, or NH4OH, and an anion-exchange (Cl-) resin. About 95% of the divalent cations and nearly 90% of the phosphate that contaminated commercial gellan were removed. The purified monovalent salts of gellan set in the presence of divalent cations and provide well-defined agents for gelling media used for propagation of microbes and plants. In a manner analogous to sodium alginate, solutions of lithium, sodium, potassium, or ammonium gellanate form beads when dropped into solutions of divalent cations. This property was exploited for entrapment of enzymes and cells in beads.

Anion Exchange Resins↗
PubMed2001

Simultaneous separation of common mono- and divalent cations on a zirconium-modified silica gel column by ion chromatography with non-suppressed conductimetric detection and tartaric acid-15-crown-5 as eluent.

The application of laboratory-made zirconium-modified silica gels (Zr-silicas) as cation-exchange stationary phases to ion chromatography with conductimetric detection (IC-CD) for common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) was carried out. Zr-silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide (Zr(OCH2CH2CH2CH3)4) in ethanol. Zr-silica adsorbed on 10 mg zirconium g(-1) silica gel was a suitable cation-exchange stationary phase in IC-CD for the separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection for these cations were achieved in 10 min by IC-CD using a Zr-silica column (150x4.6 mm I.D.) and 10 mM tartaric acid containing 10 mM 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) as the eluent. The proposed IC-CD method was successfully applied to the determination of major mono- and divalent cations in natural water samples.

Cations, Divalent↗
PubMedDate not supplied

TRPC4 and TRPC5: receptor-operated Ca2+-permeable nonselective cation channels.

The seven mammalian channels from the classical (TRPC) subfamily of transient receptor potential (TRP) channels are thought to be receptor-operated cation channels activated in a phospholipase C (PLC)-dependent manner. Based on sequence similarity, TRPC channels can be divided into four subgroups. Group 4 comprises TRPC4 and TRPC5, and is most closely related to group 1 (TRPC1). The functional properties observed following heterologous expression of TRPC4 or TRPC5 in mammalian cells are contradictory and, therefore, controversial. In our hands, and in several independent studies, both channels, probably as homotetramers, form receptor-operated, Ca2+-permeable, nonselective cation channels activated independently of inositol 1,4,5-trisphosphate (InsP(3)) receptor activation or Ca2+ store-depletion. As heteromultimers with TRPC1, TRPC4 and TRPC5 form receptor-operated, Ca2+-permeable, nonselective cation channels with biophysical properties distinct from homomeric TRPC4 or TRPC5. In other studies, TRPC4 and TRPC5 have been shown to be store-operated channels, with moderate to high Ca2+ permeabilities. At present there is no clear explanation for these major differences in functional properties. To date, little is known as to which native cation channels are formed by TRPC4 and TRPC5. Endothelial cells from TRPC4(-/-) mice lack a highly Ca2+-permeable, store-dependent current, and data support a role for TRPC4 in endothelium-mediated vasorelaxation. A similar current in adrenal cortical cells is reduced by TRPC4 antisense. From similarities in the properties of the currents and expression of appropriate isoforms in the tissues, it is likely that heteromultimers of TRPC1 and TRPC4 or TRPC5 form receptor-operated nonselective cation channels in central neurones, and that TRPC4 contributes to nonselective cation channels in intestinal smooth muscle.

Animals↗
PubMed1999

Relative role of anions and cations in the stabilization of halophilic malate dehydrogenase.

Halophilic malate dehydrogenase unfolds at low salt, and increasing the salt concentration stabilizes, first, the folded form and then, in some cases, destabilizes it. From inactivation and fluorescence measurements performed on the protein after its incubation in the presence of various salts in a large range of concentrations, the apparent effects of anions and cations were found to superimpose. A large range of ions was examined, including conditions that are in general not of physiological relevance, to explore the physical chemistry driving adaptation to extreme environments. The order of efficiency of cations and anions to maintain the folded form is, for the low-salt transition, Ca(2+) approximately Mg(2+) > Li(+) approximately NH(4)(+) approximately Na(+) > K(+) > Rb(+) > Cs(+), and SO(4)(2)(-) approximately OAc(-) approximately F(-) > Cl(-), and for the high-salt transition, NH(4)(+) approximately Na(+) approximately K(+) approximately Cs(+) > Li(+) > Mg(2+) > Ca(2+), and SO(4)(2)(-) approximately OAc(-) approximately F(-) > Cl(-) > Br(-) > I(-). If a cation or anion is very stabilizing, the effect of the salt ion of opposite charge is limited. Anions of high charge density are always the most efficient to stabilize the folded form, in accordance with the order found in the Hofmeister series, while cations of high charge density are the most efficient only at the lower salt concentrations and tend to denature the protein at higher salt concentrations. The stabilizing efficiency of cations and anions can be related in a minor way to their effect on the surface tension of the solution, but the interaction of ions with sites only present in the folded protein has also to be taken into account. Unfolding at high salt concentrations corresponds to interactions of anions of low charge density and cations of high charge density with the peptide bond, as found for nonhalophilic proteins.

Acetates↗
PubMed2001

Effect of monovalent-divalent cation exchange on the swelling of polyacrylate hydrogels in physiological salt solutions.

The volume transition induced by monovalent-divalent cation exchange of fully neutralized polyacrylate hydrogels was investigated in aqueous NaCl solutions. The variation of the osmotic swelling pressure, shear modulus, and mixing pressure was measured when Na(+) ions were substituted by divalent or trivalent cations. Alkali metal salts move freely throughout the entirely network, and alkaline earth metal salts (CaCl(2), SrCl(2)) promote aggregation of polyacrylate chains, but these aggregates are relatively weak. Transition metal salts (CoCl(2), NiCl(2)) form stronger interchain associates. Rare earth cations (La(3+) and Ce(3+)) bind practically irreversibly to the polymer. Experimental data indicate that transition metal cations modify both the elastic and mixing components of the free energy, while alkaline earth metal cations affect primarily the mixing term. The behavior of freely swollen gels was compared with similar gels subjected to uniaxial compression. In uniaxially compressed gels, volume transition occurs at lower cation concentrations than in the corresponding undeformed gels. The shift of the transition point increases with the deformation ratio and is larger for Co(2+) than for Ca(2+).

Acrylic Resins↗
PubMed1989

The interaction of cations with the dye arsenazo III.

1. The dye arsenazo III combines with a selection of cations to give an altered absorption spectrum. 2. Large metal cations such as Ca2+, La3+ and quadrivalent cations give a 1:1 complex with two new absorption peaks at about 610 nm and 655 nm and a KD of about 10(-6) M. 3. Aliphatic polyamines and complex cobalt ions give a 1:1 complex, with one absorption peak at about 610 nm and a KD from 10(-6) to 10(-3) M. 4. Small metal cations finally form a 2:1 complex and also have one absorption peak at about 610 nm, but with a KD of 10(-5)-10(-4) M. 5. The absorption peak at 610 nm is similar to that formed at high pH in the absence of bivalent cations and is due to ionization of phenolic groups with the dye molecule in an extended form. 6. The peak at 655 nm with 1:1 complex can be explained as a change in orientation of the diazo bonds caused by a conformational change of the molecule when it wraps around the single atom of Ca2+ or other large cation.

Arsenazo III↗
PubMed2003

Reduced tubular cation transport in diabetes: prevented by ACE inhibition.

BACKGROUND: The renal clearance of organic cations is important for the homeostasis of a number of exogenous and endogenous compounds. The organic cation transporters (OCTs) situated on the basolateral surface of proximal tubular cells mediate active cation excretion. Alterations of cation transport may occur in diabetes, although the role of the OCTs has not been previously assessed. METHODS: Experimental diabetes was induced in rats with streptozotocin (55 mg/kg) and animals were randomly assigned to receive ramipril (3 mg/mL) in drinking water for 24 weeks. In a second protocol, rats were infused with angiotensin II (Ang II) at a dose of 58.3 ng/kg/min for 2 weeks via an implanted osmotic pump. Expression of the OCTs and renal clearance of the endogenous cation N-methyl-nicotinamide (NMN) was assessed. RESULTS: Diabetes was associated with a reduction in gene and protein expression of both OCT-1 and OCT-2 and a reduction in NMN clearance. These effects were prevented by ramipril, associated with the prevention of albuminuria and tubular injury as demonstrated by the expression of osteopontin and glutathione peroxidase 3 (GPX-3). An infusion of Ang II also reduced NMN clearance but without altering the renal expression of OCTs. CONCLUSION: We hypothesize that reduced expression of OCTs in diabetes may be a marker of tubular injury. However, Ang II may also directly augment renal cation clearance independent of changes in transporter expression. Together these effects may provide additional mechanism to explain treatment-related improvements in creatinine clearance and renoprotection in diabetes following blockade of the renin-angiotensin system (RAS).

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Electrogenic properties and substrate specificity of the polyspecific rat cation transporter rOCT1.

The previously cloned rat cation transporter rOCT1 detected in renal proximal tubules and hepatocytes (Gründemann, D., Gorboulev, V., Gambaryan, S., Veyhl, M., and Koepsell, H. (1994) Nature 372, 549-552) was expressed in Xenopus oocytes, and transport properties were analyzed using tracer uptake studies and electrophysiological measurements. rOCT1 induced highly active transport of a variety of cations, including the classical substrates for cation transport, such as N-1-methylnicotinamide, 1-methyl-4-phenylpyridinium (MPP), and tetraethylammonium (TEA), but also the physiologically important choline. In oocytes rOCT1 also mediated efflux of MPP, which could be trans-stimulated by MPP and TEA. Cation transport via rOCT1 was electrogenic. In voltage-clamped oocytes, transport of TEA and choline via rOCT1 produced inwardly directed currents, which were independent of extracellular ion composition or pH. The choline- and TEA-induced currents were voltage-dependent at nonsaturating concentrations, and the apparent affinity of these cations was decreased at depolarized voltages. Other substrates transported by rOCT1 were the polyamines spermine and spermidine. Interestingly, the previously described potent inhibitors of rOCT1, cyanine 863, quinine, and D-tubocurarine were substrates themselves. The data indicate that rOCT1 is an effective transport system that is responsible for electrogenic uptake of a wide variety of organic cations into epithelial cells of renal proximal tubules and hepatocytes.

Animals↗
PubMed2000

Cation hexaammines are selective and potent inhibitors of the CorA magnesium transport system.

Cation hexaammines and related compounds are chemically stable analogs of the hydrated form of cations, particularly Mg(2+). We tested the ability of several of these compounds to inhibit transport by the CorA or MgtB Mg(2+) transport systems or the PhoQ receptor kinase for Mg(2+) in Salmonella typhimurium. Cobalt(III)-, ruthenium(II)-, and ruthenium(III)-hexaammines were potent inhibitors of CorA-mediated influx. Cobalt(III)- and ruthenium(III)chloropentaammines were slightly less potent inhibitors of CorA. The compounds inhibited uptake by the bacterial S. typhimurium CorA and by the archaeal Methanococcus jannaschii CorA, which bear only 12% identity in the extracellular periplasmic domain. Cation hexaammines also inhibited growth of S. typhimurium strains dependent on CorA for Mg(2+) uptake but not of isogenic strains carrying a second Mg(2+) uptake system. In contrast, hexacyano-cobaltate(III) and ruthenate(II)- and nickel(II)hexaammine had little effect on uptake. The inhibition by the cation hexaammines was selective for CorA because none of the compounds had any effect on transport by the MgtB P-type ATPase Mg(2+) transporter or the PhoQ Mg(2+) receptor kinase. These results demonstrate that cation hexaammines are potent and highly selective inhibitors of the CorA Mg(2+) transport system and further indicate that the initial interaction of the CorA transporter is with a fully hydrated Mg(2+) cation.

Amines↗