Presence Of LaCl3 Research Articles

Ring Expansion via One-Pot Conversion of Lactone Acetals to Cyclic Enones. Synthesis of (±)-1-epi-Xerantholide.

Baeyer-Villiger oxidation of α-alkoxy ketones 1 provides lactone acetals 2, which react with the lithium salts of dimethyl(alkyl) phosphonates in the presence of LaCl3·2LiCl to provide cyclic enones 3 in good to excellent yields after treatment with dilute aqueous potassium carbonate. Thus, five-, six-, and seven-membered lactones are converted to five-, six-, and seven-membered cyclic enones. The utility of this two-step ring expansion method is demonstrated in the synthesis of (±)-1-epi-xerantholide from 5-methyl-2-cyclohexen-1-one.

Effect of Metal Chloride Impurities on Equilibrium Potential of Fe/FeCl2 in Eutectic LiCl-KCl

Abstract In this study, interaction of dilute metal chloride solutes in molten eutectic LiCl-KCl was studied via equilibrium potential measurements. Open circuit potential (OCP) was measured between a pure iron rod and a Ag/AgCl reference electrode with concentration of FeCl2 varying from 0.2-1 mol% at 530oC. The Nernst equation was used to calculate activity coefficient of FeCl2 based on OCP. Measurements were made in LiCl-KCl-FeCl2 with and without additions of 0.5 mol% CsCl, NaCl, and LaCl3. The activity coefficient of FeCl2 was found to be unaffected by these small concentrations of CsCl, LaCl3, and NaCl. However, there was observed evidence that the activity coefficient of FeCl2, above 0.8 mol% Fe, may be affected by the presence of LaCl3 at higher concentrations beginning around 0.5 mol% La. Over the full range of conditions tested, the activity coefficient of FeCl2 in molten LiCl-KCl ranged from 2.95x10-5 to 1.01x10-4.

Biophysical interaction between lanthanum chloride and (CG)n or (GC)n repeats: A reversible B-to-Z DNA transition

The transition from right-handed to left-handed DNA is not only acts as the controlling factor for switching gene expression but also has equal importance in designing nanomechanical devices. The (CG)n and (GC)n repeat sequences are well known model molecules to study B-Z transition in the presence of higher concentration of monovalent cations. In this communication, we report a cyclic transition in (CG)6 DNA using millimolar concentration of trivalent lanthanide salt LaCl3. The controlled and reversible transition was seen in (CG)12, and (GC)12 DNA employing CD spectroscopy. While LaCl3 failed to induce B-Z transition in shorter oligonucleotides such as (CG)3 and (GC)3, a smooth B-Z transition was recorded for (CG)6, (CG)12 and (GC)12 sequences. Interestingly, the phenomenon was reversible (Z-B transition) with addition of EDTA. Particularly, two rounds of cyclic transition (B-Z-B-Z-B) have been noticed in (CG)6 DNA in presence of LaCl3 and EDTA which strongly suggest that B-Z transition is reversible in short repeat sequences. Thermal melting and annealing behaviour of B-DNA are reversible while the thermal melting of LaCl3-induced Z-DNA is irreversible which suggest a stronger binding of LaCl3 to the phosphate backbone of Z-DNA. This was further supported by isothermal titration calorimetric study. Molecular dynamics (MD) simulation indicates that the mode of binding of La3+ (of LaCl3) with d(CG)8.d(CG)8 is through the minor groove, wherein, 3 out of 11 La3+ bridge the anionic oxygens of the complementary strands. Such a tight coordination of La3+ with the anionic oxygens at the minor groove surface may be the reason for the experimentally observed irreversibility of LaCl3-induced Z-DNA seen in longer DNA fragments. Thus, these results indicate LaCl3 can easily be adopted as an inducer of left-handed DNA in other short oligonucleotides sequences to facilitate the understanding of the molecular mechanism of B-Z transition.

2‐ and 6‐Purinylmagnesium Halides in Dichloromethane: Scope and New Insights into the Solvent Influence on the C−Mg Bond

AbstractThe generation of positionally stable purin‐2‐ and 6‐yl magnesium halides is complicated by the often very rapid isomerization to give the 8‐yl Grignards. By conducting the reaction in dichloromethane (DCM), we demonstrated that the anion isomerization can be stopped and these stable purin‐2‐ and 6‐yl Grignards react directly with a broad scope of aldehydes in good yields. Furthermore, purine functionalization with ketones has been achieved for the first time in the presence of LaCl3 ⋅ 2LiCl. Density functional theory calculations offer a possible explanation of the special role played by solvent in this chemistry and show that in DCM the C−Mg bond has a less polar character, whereas in THF it is predominantly ionic and much more basic in nature.

OsANN4 modulates ROS production and mediates Ca2+ influx in response to ABA

BackgroundPlant annexins are calcium- and lipid-binding proteins that have multiple functions, and a significant amount of research on plant annexins has been reported in recent years. However, the functions of annexins in diverse biological processes in rice are largely unclear.ResultsHerein, we report that OsANN4, a calcium-binding rice annexin protein, was induced by abscisic acid (ABA). Under ABA treatment, the plants in which OsANN4 was knocked down by RNA interference showed some visible phenotypic changes compared to the wild type, such as a lower rooting rate and shorter shoot and root lengths. Moreover, the superoxide dismutase (SOD) and catalase (CAT) activities of the RNAi lines were significantly lower and further resulted in higher accumulation of O2.- and H2O2 than those of the wild-type. A Non-invasive Micro-test Technology (NMT) assay showed that ABA-induced net Ca2+ influx was inhibited in OsANN4 knockdown plants. Interestingly, the phenotypic differences caused by ABA were eliminated in the presence of LaCl3 (Ca2+ channel inhibitor). Apart from this, we demonstrated that OsCDPK24 interacted with and phosphorylated OsANN4. When the phosphorylated serine residue of OsANN4 was substituted by alanine, the interaction between OsANN4 and OsCDPK24 was still observed, however, both the conformation of OsANN4 and its binding activity with Ca2+ might be changed.ConclusionsOsANN4 plays a crucial role in the ABA response, partially by modulating ROS production, mediating Ca2+ influx or interacting with OsCDPK24.

Membrane fusion of phospholipid bilayers under high pressure: Spherical and irreversible growth of giant vesicles

Membrane fusion of giant vesicles (GVs) for binary bilayers of unsaturated phospholipids, dioleoylphosphatidyl-ethanolamine (DOPE) having an ability to promote membrane fusion, and its homolog dioleoylphosphatidylcholine (DOPC) having an ability to form GV, was investigated under atmospheric and high pressure. While DOPC formed GVs in the presence of inorganic salts with a multivalent metal ion under atmospheric pressure, an equimolar mixture of DOPE and DOPC formed GVs both in the absence and the presence of LaCl3. We examined the change in size and shape of the GVs of this binary mixture in the absence and presence of LaCl3 as a function of time under atmospheric and high pressure. The size and shape of the GVs in the absence of LaCl3 under atmospheric and high pressure and those in the presence of LaCl3 under atmospheric pressure hardly changed with time. By contrast, the GV in the presence of LaCl3 under high pressure gradually changed in the size and shape with time on a time scale of several hours. Namely, the GV became larger than the original GV due to accelerated membrane fusion and its shape became more spherical. This pressure-induced membrane fusion was completely irreversible, and the growth rate was correlated with the applied pressure. The reason for the GV growth by applying pressure was considered on the basis of thermodynamic phase diagrams. We concluded that the growth is attributable to a closer packing of lipid molecules in the bilayer resulting from their preference of smaller volumes under high pressure. Furthermore, the molecular mechanism of the pressure-induced membrane fusion was explored by observing the fusion of two GVs with almost the same size. From their morphological changes, we revealed that the fusion is caused by the actions of Laplace and osmotic pressure.

Design, synthesis and biological assessment of acridine derivatives containing 1,3,4-thiadiazole moiety as novel selective acetylcholinesterase inhibitors

A novel series of acridine derivatives containing substituted thiadiazol-2-amine moiety was synthesized via multi-component condensation reaction of dimedone, aromatic aldehyde and 5-aryl-1,3,4-thiadiazol-2-amines in the presence of LaCl3 as a catalyst under solvent-free conditions. Anticholinesterase (AChE and BuChE) activity evaluation of the derivatives showed that all the derivatives are capable of inhibiting both enzymes and are highly selective towards AChE. Among them, the ability of 4i and 4d with respective IC50 values of 0.002 and 0.006 µM to inhibit AChE was higher than the reference compound tacrine (IC50 = 0.016 µM). The kinetics studies demonstrated that 4i and 4d inhibit AChE through a competitive/non-competitive mixed mechanism. The HEPG2 cell viability assay evidenced that 4i and 4d significantly exhibit lower hepatotoxicity compared with tacrine. Blind docking experiments performed on TcAChE (PDB ID: 2ACE) indicated that an unknown site is preferred for binding by all the derivatives over classic binding site of the enzyme, site 1 (CAS/PAS). Identification of the residues by protein structure alignment confirmed that this site is site 2 which was recently recognized as a new allosteric site of hAChE. The binding modes of 4i and 4d were also investigated using local docking studies on site 1 and site 2.

Synergistic adsorption of lanthanum ions and fatty acids for efficient rare-earth phosphate recovery: Surface analysis and ab initio molecular dynamics studies

Rare earth elements (REE) are indispensable in our daily life but they naturally occur in minerals, which are generally difficult to concentrate by the froth flotation method. Considering the significant affinity of lanthanum ions for phosphate species as well as for carboxylate groups, the influence of a lanthanum salt (LaCl3) on the adsorption of carboxylate species on monazite surface [(La,Ce,Nd)PO4] was investigated by bubble/particle adhesion tests, X-ray photoelectron spectroscopy (XPS), and atomistic simulations based on density functional theory (DFT). Both theoretical and experimental results demonstrated that lanthanum ions adsorb on the phosphate groups of monazite surface under the LaClCO3 form with a significant adsorption energy. Also, the hydrophobization of the monazite surface with fatty acids is considerably improved in presence of LaCl3, which is in accordance with DFT calculations: the lanthanum ions pre-adsorbed on monazite surface act as highly attractive adsorption sites for carboxylate collectors. In particular, these bridging cations significantly increase the adsorption energy of carboxylate collectors, from 344 to 420 kJ·mol−1 in absolute value. This synergistic adsorption will allow developing new methods for efficient monazite recovery from complex ores, a promising step for the recovery of critical raw materials.

Foliar-applied lanthanum chloride increases growth and phosphorus acquisition in phosphorus-limited adzuki bean seedlings

Lanthanum, a rare earth element, is used in agriculture and forestry to promote plant growth and productivity. We aimed to investigate its role in altering the roots and alleviating P deficiency in the adzuki bean Vigna angularis. The adzuki bean variety “Jin No. 5” was pre-cultivated in sand. Fourteen-day-old seedlings were sprayed twice with 0.4 mM LaCl3 solution. Next, we treated the seedlings with half-strength Hoagland solution containing P reduced to 1% of its original concentration (P-deficient); P reduced to 5% of the original (P-marginal); and unadjusted solution (P-sufficient). We measured plant growth, root structure, root hydraulic conductivity, P content, gas exchange, and photosynthetic pigment levels in all groups. LaCl3 application significantly increased leaf P concentration, effectively improving the P uptake efficiency of roots, shoots, and leaves under severe P stress. Root morphology and acid phosphatase (APase) activity varied significantly in response to LaCl3 under low-P stress. A greater leaf area, gas exchange ability, chlorophyll content, and carotenoid content were observed in the presence of LaCl3 under P-marginal stress. The application of LaCl3 can promote growth and P acquisition in adzuki beans under P limitation by inducing changes in root morphology, APase activity, and hydraulic conductivity.

Sequence-specific B-to-Z transition in self-assembled DNA: A biophysical and thermodynamic study

The most remarkable conformational transition in nature is the B-to-Z transition of DNA which not only contributes for epigenetic regulation but also is exploited to create several advanced nanomaterials for sensing and nanomechanics. The present communication focuses on the intrinsic factors that control the La3+/Ce3+-induced B-to-Z transition in self-assembled branched DNA (bDNA) nanostructures. The transition is sensitive even to two nucleotide change in the loop length and overhang sequences. Predominantly, bDNA structures having 3 T loop length are more sensitive towards helical switching than the 5 T bearing structures. Particularly, bDNA US-17, US-19 and US-23 having 3 T in the loop are showing B-Z transition in presence of LaCl3. Interestingly, with ‘GATC’ overhangs both La3+/Ce3+-induced B-to-Z transition was noticed in bDNA structures US-21 and US-22 (having 3 T and 5 T in the loop, respectively). The lanthanide-induced B-Z transition in bDNA is reversed with treatment of EDTA. Isothermal titration calorimetry (ITC) experiments show that the binding mode of lanthanide salts to bDNA followed an entropically and enthalpically favorable process. Further, for the first time ITC data suggests the B-to-Z transition in bDNA is a cooperative shift from exothermic to endothermic.

Role of oxalate in fungal precipitation and biorecovery of lanthanum

Lanthanum is an important member of the rare earth elements (REE) that are a global strategic resource and have many technological applications ranging from microelectronics manufacturing to the production of clean and renewable energy. Aspergillus niger is widely used in industrial fermentations due to its production of multiple secondary metabolites including citric and oxalic acids. Since it is a ubiquitous soil inhabitant and produces geoactive agents, it can play a role in the biotransformation of metal-containing minerals. Previous studies found that A. niger is capable of mineral solubilization and secondary mineral formation, many metals being precipitated as oxalates. However, there is limited knowledge about the biotransformation of La mediated by fungi. The aim of this project was to explore the mechanisms and factors determining the interactions between A. niger and La. In this study, fungal growth on La-supplemented solid media was carried out and it was discovered that crystalline deposits were formed around fungal colonies in the presence of LaCl3. These biogenic crystals were recovered and subjected to examination for their elemental composition, morphological features and mineral phases using energy dispersive X-ray analysis (EDXA), scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. These confirmed the biotransformation of lanthanum and identified the products as lanthanum oxalate [La2(C2O4)3·10H2O], which was further transformed into La2O3 by thermogravimetric (TG) treatment. Geochemical modelling also supported these results. Our findings provide a new aspect for the bioprecipitation and biorecovery of REE from solution using fungal culture systems.

Effect of LaCl3 addition on the hydrogen storage properties of MgH2

In this study, the effect of LaCl3 on the hydrogen storage properties of MgH2 prepared by ball milling was investigated for the first time. It was found that the MgH2 + 10 wt.% LaCl3 sample started to decompose at around 300 °C, which was 50 °C lower than in as-milled MgH2. For desorption kinetics, the LaCl3-doped MgH2 composite sample released about 4.2 wt.% hydrogen at 320 °C after 5 min dehydrogenation, while the as-milled MgH2 only released about 0.2 wt.% hydrogen for the same temperature and time. Meanwhile, a hydrogen absorption capacity of 5.1 wt.% was reached at 300 °C in 2 min for the LaCl3-doped MgH2 sample. In contrast, the ball-milled MgH2 only absorbed 3.8 wt.% hydrogen at 300 °C in 2 min. The activation energy of dehydrogenation was 166.0 kJ/mol for the as-milled MgH2 and 143.0 kJ/mol for the 10 wt.% LaCl3-added MgH2, indicating that the LaCl3 additive decreased the activation energy for the hydrogen desorption of the MgH2. The improved hydrogen storage properties of the MgH2 in the presence of LaCl3 is believed to be due to the catalytic effects of the La–Mg alloy and MgCl2 that were formed in situ during the heating process.

Pharmacological dose of melatonin reduces cytosolic calcium load in response to cholecystokinin in mouse pancreatic acinar cells.

Intracellular Ca(2+) overload has been considered a common pathological precursor of pancreatic injury. In this study, the effects of melatonin on Ca(2+) mobilization induced by cholecystokinin octapeptide (CCK-8) in freshly isolated mouse pancreatic acinar cells have been examined. Changes in intracellular free Ca(2+) concentration were followed by single cell fluorimetry. For this purpose, cells were loaded with the Ca(2+)-sensitive fluorescent dye fura-2-acetoxymethyl ester. In order to evaluate the contribution of Ca(2+) transport at the plasma membrane, at the endoplasmic reticulum (ER) or at the mitochondria, cells were incubated with CCK-8 alone or in combination with LaCl3, thapsigargin (Tps), or FCCP to, respectively, uncouple Ca(2+) transport at these localizations. The experiments were performed in the absence or in the presence of melatonin in combination with the stimuli mentioned. Our results show that the total Ca(2+) mobilization evoked by CCK-8 was attenuated by a 30% in the presence of 100 µM melatonin compared with the responses induced by CCK-8 alone. Upon inhibition of Ca(2+) transport into the ER by Tps, Ca(2+) mobilization was also reduced in the presence of melatonin. In the presence of LaCl3 plus melatonin, the total Ca(2+) mobilization induced by CCK-8 was significantly decreased, compared with the response obtained without melatonin but in the presence of LaCl3. No major differences were found when the cells were incubated with CCK-8 or Tps alone or in combination with LaCl3 plus melatonin and FCCP, compared with the responses obtained in the absence of FCCP. The initial Ca(2+) release from intracellular stores evoked by CCK-8 or Tps was not significantly reduced in the presence of melatonin. The effect of melatonin could be explained on the basis of a stimulated Ca(2+) transport out of the cell through the plasma membrane and by a stimulation of Ca(2+) reuptake into the ER. Accumulation of Ca(2+) into mitochondria might not be a major mechanism stimulated by melatonin. We conclude that melatonin alleviates intracellular Ca(2+) accumulation, a situation potentially leading to cell damage in the exocrine pancreas.

Inhibition of thioredoxin reductase by lanthanum chloride

Lanthanum chloride (LaCl3) is a good inhibitor of both the cytosolic and mitochondrial thioredoxin reductase with IC50 values of 1.75 and 7.46μM, respectively. On the contrary, the related enzyme glutathione reductase is not inhibited by lanthanum ions even at relatively high concentrations. In the presence of LaCl3, steady-state kinetics shows a non-competitive type of inhibition with 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) as a substrate suggesting no interaction of this ion with the thiol/selenol active site of thioredoxin reductase. Comparison of the electrostatic surface potential of thioredoxin reductase shows that the presence of a trivalent cation such as La3+ decreases the negatively charged area of the enzyme surface particularly in the region closed to the NADPH binding site. Human ovarian carcinoma cells (A2780 cells) incubated with lanthanum ions show a noticeable inhibition of thioredoxin reductase activity indicating the ability of this ion to reach the active site of the enzyme even in a cellular setting. In addition, A2780 cells treated with LaCl3 show an increase in reactive oxygen species production in part dependent on thioredoxin reductase inhibition.

Effects of LaCl3 on the growth and photosynthetic characteristics of Fny-infected tobacco seedlings

Plant growth, gas exchange characteristics, chlorophyll fluorescence, disease index, and disease prevention efficiency of LaCl3 in tobacco (Nicotiana glutinosa) plants infected by Fny-CMV (fny stain of cucumber mosaic virus) strain were determined. Leaf area, chlorophyll and carotenoid contents, maximum photosynthesis rate, apparent quantum yield, and carboxylation efficiency dramatically decreased after 5 weeks post inoculation. The plants infected by Fny-CMV only presented much severer symptom than those infected in the presence of appropriate concentration of LaCl3. ETR (apparent rate of photosynthetic electron transport), NPQ (nonphotochemical quenching), qP (coefficient of photochemical quenching), and yield (II) in infected tobacco plants obviously reduced in higher light intensity after 5 weeks post inoculation. And these fluorescence parameters in Fny-infected plants obviously reduced compared with those in the plants infected by Fny in the presence of LaCl3. Together with the growth status and disease index, it revealed that exogenously appropriate concentration of LaCl3 could significantly alleviate the damage of tobacco seedlings caused by Fny-CMV.

The combination of lanthanum chloride and the calcimimetic calindol delays the progression of vascular smooth muscle cells calcification

Phosphate (Pi)-binders are commonly used in dialysis patients to control high Pi levels, that associated with vascular calcification (VC). The aim of this study was to investigate the effects of lanthanum chloride (LaCl3) on the progression of high Pi-induced VC, in rat vascular smooth muscle cells (VSMCs). Pi-induced Ca deposition was inhibited by LaCl3, with a maximal effect at 100μM (59.0±2.5% inhibition). Furthermore, we studied the effects on VC of calcium sensing receptor (CaSR) agonists. Gadolinium chloride, neomycin, spermine, and the calcimimetic calindol significantly inhibited Pi-induced VC (55.9±2.2%, 37.3±4.7%, 30.2±5.7%, and 63.8±5.7%, respectively). To investigate the hypothesis that LaCl3 reduces the progression of VC by interacting with the CaSR, we performed a concentration–response curve of LaCl3 in presence of a sub-effective concentration of calindol (10nM). Interestingly, this curve was shifted to the left (IC50 9.6±2.6μM), compared to the curve in the presence of LaCl3 alone (IC50 19.0±4.8μM). In conclusion, we demonstrated that lanthanum chloride effectively reduces the progression of high phosphate-induced vascular calcification. In addition, LaCl3 cooperates with the calcimimetic calindol in decreasing Ca deposition in this in vitro model. These results suggest the potential role of lanthanum in the treatment of VC induced by high Pi.

Microsurface Potential Measurements: Repulsive Forces between Polyelectrolyte Brushes in the Presence of Multivalent Counterions

We propose a new way to determine weak repulsive forces operative between colloidal particles by measuring the rate of slow coagulation. The rate of slow coagulation is directly related to the competition of the repulsion with thermal motion. Since the thermal forces are weak, measurements of the coagulation rate can lead to precise information on repulsive potentials having a magnitude of just a few kT. We demonstrate this novel way by studying colloidal spherical polyelectrolyte brush (SPB) particles in aqueous solution containing trivalent La3+ counterions. The particles consist of a monodisperse polystyrene core of 121 nm radius from which linear sodium poly(styrenesulfonate) (PSS) chains are densely grafted (contour length 48 nm). We determine the rate of coagulation by time-resolved simultaneous static and dynamic light scattering in the presence of LaCl3 (0.2 to 150 mM). Direct measurements of the repulsive force between macroscopic brush layers demonstrate that the potential is decaying exponentially with distance. This is in good agreement with a simple theoretical treatment that furthermore leads to the effective surface potential Psi0. The good agreement of data obtained by the novel microscopic method with direct macroscopic measurements underscores the general validity of our approach.

Pretreatment with muscarinic receptor agonist activates a calcium-inhibitable adenylate cyclase in GH3 pituitary cells

We have demonstrated previously that pretreatment of GH3 pituitary cells with muscarinic agonists may induce a higher cAMP formation in response to vasoactive intestinal peptide (VIP) or forskolin. In the present study, we further examined the adenylate cyclase (AC) that may be involved. We found that carbachol-pretreatment enhanced both VIP- and forskolin-activated AC activities. The addition of calcium ions to the incubation buffer diminished this enhancing effect. Carbachol was found to induce a decrease in intracellular calcium concentration [Ca2+]i by inhibiting calcium influx through L-type Ca2+ channels. However, the incubation of cells in Ca(2+)-free buffer or in the presence of L-type Ca2+ channel blockers had no influence on forskolin-stimulated cAMP formation, although both treatments induced decreases in [Ca2+]i as carbachol did. On the other hand, incubation in the presence of LaCl3 at a low concentration not being able to enter cells, forskolin-stimulated cAMP formation as well as the enhancing effect of carbachol-pretreatment on this response, were both suppressed. Similar phenomena were observed when membrane-bound AC activities were measured in the presence of LaCl3. Taken together, these results seem to suggest that pretreatment of GH3 cells with muscarinic receptor agonist may activate a Ca(2+)-inhibitable AC for a higher stimulated response. Low intracellular calcium concentrations are essential but not sufficient for this effect.

Copper-induced formation of reactive oxygen species causes cell death and disruption of calcium homeostasis in trout hepatocytes.

We have previously shown that copper is acutely toxic for trout hepatocytes, inducing enhanced influx of Ca(2+) and a loss of cell viability. The aim of the present study was to elucidate the pathways of Ca(2+) entry into the cells, the hypothetical role of reactive oxygen species (ROS) in copper toxicity, and the interaction of ROS formation and the disruption of Ca(2+) homeostasis. We found that, acutely, copper-induced cell death occurred independently from an increase of intracellular free Ca(2+) (Ca(2+)i), but could be prevented by addition of agents interfering with ROS production. Addition of the Ca(2+) channel blocker verapamil did not affect the Ca(2+)i increase evoked by copper, whereas in the presence of LaCl(3), an inhibitor of both Ca(2+) channels and Na(+)/Ca(2+)-exchange, this increase was significantly delayed. ROS formation, estimated by use of the fluorescence indicator 2',7'-dichlorofluorescin diacetate, was significantly enhanced by copper. Omission of extracellular Ca(2+) or addition of either verapamil or LaCl(3) did not diminish ROS formation induced by copper. In contrast, the hydroxyl radical scavenger dimethyl sulfoxide and the ferric ion chelator deferoxamine inhibited radical production. In addition, these agents either partially (dimethyl sulfoxide) or completely (deferoxamine) prevented an increase of Ca(2+)i. Altogether our results indicate that ROS formation is the crucial event leading to cell death during acute exposure to copper, whereas the increase of Ca(2+)i is a secondary, acutely less toxic, phenomenon. Furthermore, these findings suggest that Ca(2+) entry occurs via a LaCl(3)-sensitive pathway, presumably representing Na(+)/Ca(2+)-exchange, and non-specific membrane leaks induced by lipid peroxidation in the presence of copper.

Ion regulation in ion-poor acidic water by the blackskirt tetra (Gymnocorymbus ternetzi), a fish native to the Amazon River.

We examined the ionoregulatory capabilities of the blackskirt tetra (Gymnocorymbus ternetzi), which is native to ion-poor acidic waters of the Amazon River. Examination of Na+ uptake, which was only slightly sensitive to the uptake blocker amiloride, revealed several specializations for uptake in these waters. Kinetic analysis of Na+ uptake (at pH 6.5) revealed a high maximum rate of uptake and a low Michaelis-Menten constant, which allows the tetras to take up Na+ at high rates even at very low water levels. At pH 4.5, a pH where they experience sizable ion disturbances, they displayed several mechanisms to restore balance. Kinetic analysis at pH 4.5 revealed that the maximum uptake rate rose 67% while the Michaelis-Menten constant remained unchanged. Further tests showed that the upregulation of Na+ uptake occurred within 12 h in response to a doubling of Na+ efflux. Despite these specializations of the Na+ uptake mechanism, blackskirt tetras were not especially tolerant of low pH. Upon exposure to pH 4.0, they experienced a massive loss of Na+ due to a fourfold increase of Na+ efflux (relative to pH 5.0) and an 80% inhibition of uptake. Measurement of Na+ efflux in waters with different Ca2+ levels and in the presence of LaCl, a strong Ca2+ competitor, correlated the stimulation of Na+ efflux at low pH with a low branchial affinity for Ca2+. These tests indicate that blackskirt tetras possess abilities to resist the disruptive effects of moderately low pH but cannot survive in waters with a pH of 4.0 or less because of leaching of Ca2+ from branchial tight junctions, which stimulates ion losses.