Protection by metallothionein against cadmium toxicity

1. The protective effect against Cd toxicity of prior exposure to Cd or Zn solutions at low concentration was studied. 2. Carp were bred in tap water (A), 1 ppm Cd solution (B) and 5 ppm Zn solution (C) for 14 days and then transferred into 15 ppm Cd solution. The survival ratio of carp decreased in the order: (C):(B):(A). 3. Binding capacity of Cd to high molecular and metallothionein fractions in the cytoplasmic solutions of the hepato-pancreas was studied and the binding capacity to the metallothionein fraction was stronger than that to the high molecular fraction. The authors recognized that Zn in the metallothionein fraction is substituted by Cd.     

Effects of tricyclohexylhydroxytin on the kinetics of adenosine triphosphatase system and protection by thiol reagents

Tricyclohexylhydroxytin, commonly known as Plictran® inhibited Na⁺, K⁺ -ATPase activity of rat brain synaptosomes in a concentration-dependent manner with median inhibitory concentration (IC-50) of 2 μM. Both K⁺ -stimulated para-nitrophenylphosphatase and [3-H]-ouabain binding to synaptosomes were also inhibited by Plictran with IC-50 values of 11 and 30 μM, respectively. Altered pH and Na⁺, K⁺ -ATPase activity curves demonstrated comparable inhibition in buffered neutral and alkaline pH ranges, and no inhibition was observed in acidic pH. The inhibition of Na⁺, K⁺ -ATPase was independent of temperature. Kinetic studies of substrate (ATP) activation of Na⁺, K⁺ -ATPase indicated uncompetitive inhibition. Results also showed noncompetitive inhibition for p-nitrophenylphosphate and uncompetitive inhibition for K⁺ activations of p-nitrophenylphosphatase. Preincubation of synaptosomes with dithiothreitol, a sulfhydryl (SH) agent, resulted in the complete protection of Plictran inhibition of Na⁺, K⁺ -ATPase, K⁺ -para-nitrophenylphosphatase, and [3-H]-ouabain binding. The protection was specific and concentration dependent since cysteine and glutathione did not afford protection. These results indicate that Plictran inhibited Na⁺, K⁺ -ATPase by interacting with dephosphorylation of the enzyme-phosphoryl complex and exerted a similar effect to that of SH-blocking agents.     

Protection against cadmium toxicity in yeast by alcohol dehydrogenase.

A cDNA expression library from Schizosaccharomyces pombe was transformed into Saccharomyces cerevisiae to screen for genes capable of conferring cadmium resistance to S. cerevisiae cells. The cDNA library was cloned into the S. cerevisiae expression vector pDB20 which is designed to express cDNAs via the constitutively-expressed promoter of the gene for alcohol dehydrogenase I (ADH1). Terminator and polyadenylation signals are also provided by the ADH1 gene. Cadmium resistant colonies were shown to arise by a recombination event leading to the exchange of the S. pombe DNA with the chromosomal ADH1 gene and a consequent dramatic increase in the ADH1 gene expression due to the high copy number of the plasmid. The overexpression of ADH1 effectively buffered the cells for cadmium ions by formation of Cd-ADH.     

Temperature-specific inhibition of human red cell Na+/K+ ATPase by 2,450-MHz microwave radiation

The ATPase activity in human red blood cell membranes was investigated in vitro as a function of temperature and exposure to 2,450-MHz continuous wave microwave radiation to confirm and extend a report of Na+ transport inhibition under certain conditions of temperature and exposure. Assays were conducted spectrophotometrically during microwave exposure with a custom-made spectrophotometer-waveguide apparatus. Temperature profiles of total ATPase and Ca+2 ATPase (ouabain-inhibited) activity between 17 and 31 degrees C were graphed as an Arrhenius plot. Each data set was fitted to two straight lines which intersect between 23 and 24 degrees C. The difference between the total and Ca+2 ATPase activities, which represented the Na+/K+ ATPase activity, was also plotted and treated similarly to yield an intersection near 25 degrees C. Exposure of membrane suspensions to electromagnetic radiation, at a dose rate of 6 W/kg and at five temperatures between 23 and 27 degrees C, resulted in an activity change only for the Na+/K+ ATPase at 25 degrees C. The activity decreased by approximately 35% compared to sham-irradiated samples. A possible explanation for the unusual temperature/microwave interaction is proposed.     

Inhibition of Methanosarcina barkeri strain 227 by cadmium

Abstract The effect of cadmium (Cd) on methane formation from methanol and/or H₂–CO₂ by Methanosarcina barkeri was examined in a defined growth medium and in a simplified buffer system containing 50 mM Tes with or without 2 mM dithiothreitol (DTT). No inhibition of methanogenesis by high concentrations of cadmium was observed in growth medium. Similarly, little inhibition of methanogenesis by whole cells in the Tes buffer system was observed in the presence of 430 μM Cd or 370 μM mercury (Hg) with 2 mM DTT. When the concentration of DTT was reduced to 0.4 mM, almost complete inhibition of methanogenesis from H₂–CO₂ and methanol by 600 μM Cd was observed. In the absence of DTT, 150 μM Cd inhibited methanogenesis from H₂–CO₂ completely and from methanol by 97%. Methanogenesis from H₂–CO₂ was more sensitive to Cd than that from methanol.     

Mechanism of inhibition of rat brain (Na +-K +)-stimulated adenosine triphosphatase reaction by cadmium and methyl mercury

The mechanisms of inhibition of rat brain Na ⁺-K ⁺- ATPase by cadmium chloride (CdCl₂) and methylmercuric chloride (CH₃HgCl) were studied in vitro by assessing the effects of these heavy metals on this enzyme and associated component parameters. Both the heavy metals significantly inhibited the overall Na ⁺-K ⁺ -ATPase in a concentration-dependent manner with an estimated median inhibitory concentration (IC-50) of 3.2 × 10^?5M for CdCl₂ and 6 × 10^?6M for CH₃HgCl. Protection of enzyme against heavy metal inhibition by 5 × 10^?5M to 1 × 10^?4 M dithiothreitol (DTT) and glutathione (GSH) or cysteine (CST) indicates that both monothiols and dithiols have the same ability in regenerating sulfhydryl (–SH) groups or chelating the metals. Inhibition of K⁺-p-nitrophenyl phosphatase (K⁺-PNPPase), the component enzyme catalyzing the K⁺-dependent dephosphorylation in the overall Na ⁺-K ⁺ATPase reaction by these heavy metals, indicates that the mechanism of inhibition involves binding to this phosphatase. Reversal of K⁺-PNPPase inhibition by DTT, GSH, and CST suggests sulfhydryl groups as binding sites. Binding of ³H-oubain, a cardiac glycocide and inhibitor of both phosphorylation and dephosphorylation, to brain fraction was significantly decreased by CH₃HgCl, and this inhibition was reversed by the three thiol compounds, suggesting presence of –SH group(s) in the ouabain receptor site. Cadmium chloride failed to inhibit the binding of this receptor, indicating that the mechanics of inhibition of ATPase by CH₃HgCl and CdCl₂ are different from each other. The results suggest that the critical conformational property of enzyme common to both kinase (E₁) and phosphatase (E₂) is susceptible to CH₃HgCl whereas only phosphatase is sensitive to CdCl₂.     

Early life stage salinity tolerance of wild and hatchery-reared juvenile pink salmon Oncorhynchus gorbuscha

Salinity tolerance in wild (Glendale) and hatchery (Quinsam) pink salmon Oncorhynchus gorbuscha (average mass 0·2 g) was assessed by measuring whole body [Na⁺] and [Cl^?] after 24 or 72 h exposures to fresh water (FW) and 33, 66 or 100% sea water (SW). Gill Na⁺, K⁺‐ATPase activity was measured following exposure to FW and 100% SW and increased significantly in both populations after a 24 h exposure to 100% SW. Whole body [Na⁺] and whole body [Cl^?] increased significantly in both populations after 24 h in 33, 66 and 100% SW, where whole body [Cl^?] differed significantly between Quinsam and Glendale populations. Extending the seawater exposure to 72 h resulted in no further increases in whole body [Na⁺] and whole body [Cl^?] at any salinity, but there was more variability among the responses of the two populations. Per cent whole body water (c. 81%) was maintained in all groups of fish regardless of salinity exposure or population, indicating that the increase in whole body ion levels may have been related to maintaining water balance as no mortality was observed in this study. Thus, both wild and hatchery juvenile O. gorbuscha tolerated abrupt salinity changes, which triggered an increase in gill Na⁺, K⁺‐ATPase within 24 h. These results are discussed in terms of the preparedness of emerging O. gorbuscha for the marine phase of their life cycle.     

Lack of inhibition of vasopressin-stimulated NA+K+ATPase by atrial natriuretic factor in the rat renal medullary thick ascending limb of Henle's loop

The anti-diuretic hormone, arginine vasopressin (AVP) stimulates the activity of Na+K+ATPase in the rat renal medullary thick ascending limb of Henle's loop (mTAL). Atrial natriuretic factor (ANF) has been suggested to exert a tubular effect on the mammalian nephron, perhaps in part, by interacting with other hormones. In the present study, we investigated the effect of rat ANF with and without AVP upon mTAL Na+K+ATPase activity using cytochemical methods. ANF alone failed to inhibit or stimulate Na+K+ATPase activity in mTAL at any of the concentrations tested (10 nmol-0.1 pmol l-1). Unlike the rat hypothalamic digitalis-like factor, ANF (10 nmol-10 fmol l-1) did not inhibit Na+K+ATPase activity after stimulation with AVP (1 fmol l-1) for either 4 or 10 min. The results suggest that ANF does not exert an effect on mTAL, either alone or in conjunction with AVP.     

Characteristics of Ca2+-stimulated ATPase in rat heart sarcolemma in the presence of dithiothreitol and alamethicin

We have studied the activities of Ca²⁺-stimulated ATPase in rat heart sarcolemma upon modulating the redox state of membrane thiol groups with dithiothreitol (DTT). The suitability of alamethicin to unmask the latent activity of this enzyme was also investigated. The Ca²⁺-stimulated ATPase in sarcolemma exhibited two activation sites — one with low affinity (Km = 0.70 ± 0.2 mM; Vmax = 10.0 ± 2.2 mol Pi/mg/h) and the other with high affinity (Km = 0.16 ± 0.7 mM; Vmax = 4.6 ± 0.8 mol Pi/mg/h) for Mg²⁺ATP. Alamethicin at a ratio of 1:1 with the sarcolemmal protein caused a 3-fold activation of Ca²⁺-stimulated ATPase without affecting its sensitivity to Ca²⁺ or Mg²⁺ATP. Treatment of sarcolemma with deoxycholate or sodium dodecyl sulfate resulted in a total loss of the enzyme activity; high concentrations of alamethicin also showed a detergent-like action on the sarcolemmal vesicles. DTT at 5–10 mM concentrations caused a 4–5 fold activation of Ca²⁺-stimulated ATPase in sarcolemma and this effect was observed to be dependent on the concentration of Mg²⁺ATP. DTT increased the affinity of the enzyme to Mg²⁺ATP at the high affinity site and enhanced the Vmax at the low affinity site in addition to increasing the sensitivity of Ca²⁺-stimulated ATPase to Ca²⁺. DTT protected the Ca²⁺-stimulated ATPase against deterioration by detergents and restored the enzyme activity after treatment with N-ethylmaleimide. The mechanism of action of DTT on Ca²⁺-stimulated ATPase may involve the reduction of essential thiols at the active site of the enzyme or its interaction with specific DTT-dependent inhibitor protein. No changes in the sensitivity of sarcolemmal Ca²⁺-stimulated ATPase to orthovanadate was evident in the absence or presence of DTT and alamethicin. The results suggest the use of both DTT and alamethicin for the determination of Ca²⁺-stimulated ATPase activity in sarcolemmal preparations.     

Oligomycin inhibition of Na,K,ATPase

It is shown that the incomplete, uncompetitive inhibition pattern exhibited by oligomycin toward Na,K,ATPase cannot be explained by a single-cycle enzyme model. In contrast, the experimental data are easily explained in terms of a dimeric enzyme, only one subunit of which can bind oligomycin at a time, and that subunit is then rendered inactive. In a brief analysis of the model thus obtained by way of numerical examples it is shown that it may show activation at small concentrations of moderator, which disappears at higher concentrations, a property observed for the hydrolysis ofp-nitro-phenylphosphate, which is also catalyzed by Na,K,ATPase.     

Comparison of the effects of auxin and fusicoccin on phosphate absorption by aged potato tuber discs

Auxin (IAA, 5 × 10⁻⁵ M ) partially prevents the increase in the rate of phosphate uptake during ageing of potato tuber discs ( Solatium tuberosum L. cv. Bintje), whereas fusicoccin (FC, 10⁻⁵ M) stimulates it. After the development of enhanced phosphate transport capacity, the response to fusicoccin is greater than with fresh discs. Complementary experiments on K⁺ (⁸⁶Rb) absorption show that FC also slightly enhances the rate of K⁺ uptake, while IAA has no much effect. It is suggested that IAA acts specifically on the development of a mechanism which occurs during the ageing period, while FC action may be more directly linked to the system of phosphate transport itself.     

Methylmercury toxicity: amelioration by selenium and water‐soluble chelators as N‐acetyl cysteine and dithiothreitol

The protective potential of chelators, i.e. N‐acetyl cysteine (0.6 mg /kg, intraperitoneally) and dithiothreitol (15.4 mg kg^?1, intraperitoneally) with selenium (0.5 mg kg^?1, pre‐oral) were evaluated individually and in combination against methylmercury‐induced biochemical alterations and oxidative stress consequences. Forty‐two male Sprague–Dawley rats were exposed with methylmercury (1.5 mg kg^?1, pre‐oral) daily for 21 days followed by different treatments for five consecutive days. Administration of methylmercury caused significant enhancement in the release of transaminases, alkaline phosphatases and lactate dehydrogenases in serum. A significant increased was observed in lipid peroxidation level with a concomitant decreased in glutathione content after methylmercury exposure in liver, kidney and brain. Hepatic microsomal drug metabolizing enzymes (aniline hydroxylase and amidopyrine N‐demethylase) of cytochrome p4502E₁ showed sharp depletion after methylmercury exposure. Alterations in histological changes in liver, kidney and brain were also noted in methylmercury administered group. All treated groups showed recovery pattern, but the combined treatments with N‐acetyl cysteine and dithiothreitol in combination with selenium were more effective than that with either alone treatments in recovering blood biochemical changes after methylmercury toxicity. In conclusion, the results demonstrated that combination therapy may recover all blood biochemical alterations and offer maximum protection against methylmercury‐induced toxicity. Copyright © 2014 John Wiley & Sons, Ltd.     

Bioremediation of cadmium induced renal toxicity in Rattus norvegicus by medicinal plant Catharanthus roseus

Cadmium is the second most hazardous metals with bio-concentration factor (BCF)?>?100 Although WHO permitted cadmium concentration in drinking water is 0.005?mg/L, yet the reality is far above to this limit because of industrial utility of this metal. Oral exposure of cadmium to human results in dreadful symptoms of metabolic disorders especially in liver and kidneys. Endogenous protection could be supported by some exogenous herbal supplement (viz., Catharanthus roseus in this case) to overcome the toxic effects. Present Study has been designed to find out the functional renal changes under the effect of cadmium and Catharanthus roseus in the model organism albino rats. Cadmium significantly (p?>?0.01) increases the level of nitrogenous waste (Urea, BUN, Uric Acid and Creatinin), while decreases the serum protein profile in acute and sub-acute sets. Urea concentration of control ranged from 16.56 to 17.72?mg/dl while that of Group-B and D were 19.84 to 20.87?mg/dl and 17.56 to 17.59?mg/dl respectively. Similarly uric acid concentration ranged in control form 6.98 to 8.01?mg/dl in group-B from 7.58 to 10.25?mg/dl, in Group-D 8.02 to 8.59?mg/dl respectively. Creatinin concentration ranged in control 0.57 to 0.65?mg/dl, in group-B 0.97 to 1.02?mg/dl, in group-D – 0.95 to 0.98?mg/dl respectively.These results might be due to altered filtration rate of kidney because of protein disruption. The studies conclude the efficient nephro-protection offered by Catharanthus roseus extract against Cadmium toxicity.     

Protection against acute paraquat toxicity by ambroxol

An expression vector for G-CSF, pASLB3-3, was constructed and introduced into Namalwa KJM-1 cells (Hosoi et al., 1988), and cells resistant to 100 nM of methotrexate (MTX) were obtained. Among them, the highest producer, clone SC57, was selected and the productivity of this clone was further characterized. The maximal production of G-CSF was at the most 1.8 g/ml/day using a 25 cm² tissue culture flask, even though the cell number was above 7×10⁵ cells/ml. The limiting factors at high density were analyzed as the deficiency of nutrients, such as glucose, cysteine and serine, and pH control. The depression of specific G-CSF productivity per cell under the batch culture conditions was overcome by using a perfusion culture system, Biofermenter^TM (Sato, 1983) with modifications of nutrients supplementation by a dialysis membrane and/or dissolved oxygen (DO) supplementation by microsilicone fibers. ITPSGF medium was modified to elevate concentrations of amino acids and glucose by 2.0- and 2.5-times, respectively. Under the control of pH at 7.4 and DO at 3 ppm, the specific G-CSF productivity was not depressed even at high cell density (above 1×10⁷ cells/ml), and the amount of G-CSF reached 41 g/ml. These results indicated the possibility of finding the optimum culture conditions for the production of recombinant proteins by Namalwa KJM-1 cells.Abbreviations ABTS 2,2-Azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid - BSA Bovine Serum Albumin - BSA-PBS Phosphate-buffered Saline without Ca²⁺ and Mg²⁺ containing Bovine Serum Albumin - dhfr Dihydrofolate Reductase - DO Dissolved Oxygen - G-CSF Granulocyte Colony-stimulating Factor - HEPES 4-(2-Hydroxyethyl)-1-piperazineethansulfonic Acid - IFN Interferon - MTX Methotrexate - PBS(-) Phosphate-buffered saline without Ca²⁺ and Mg²⁺ - Tween-PBS Phosphate-buffered saline without Ca²⁺ and Mg²⁺ containing 0.05% of Tween 20     

Amomum tsaoko fruit extract exerts anticonvulsant effects through suppression of oxidative stress and neuroinflammation in a pentylenetetrazol kindling model of epilepsy in mice

BackgroundChronic epilepsy is a multifaceted common brain disorder with manifold underlying factors. Epilepsy affects around 70 million peoples worldwide. Amomum tsaoko is a perennial herbaceous plant that is extensively cultivated in many provinces of China reported to exert immense biological activities.ObjectiveThis research work was aimed to reveal the therapeutic actions of ethanolic extract of A.tsaoko fruits (EE-ATF) against the pentylenetetrazol (PTZ)-provoked convulsive seizures in the mice.MethodologyThe convulsive seizures were provoked to the animals via administering 70 mg/kg of PTZ through intraperitoneally to trigger the convulsive seizures then treated with the EE-ATF at 50, 75, and 100 mg/kg orally 30 min prior to PTZ challenge. After the 30 min of PTZ challenge, animals closely monitored for signs of convulsion, generalized clonic and tonic convulsion durations, and mortality. A sub-convulsive dose 35 mg/kg of PTZ was used to provoke the kindling and seizure stages were examined using standard method. The levels of dopamine, GABA, glutamate, and Na + K + ATPase and Ca + ATPase activities in the brain tissues were studied using marker specific assay kits. The oxidative stress and antioxidant markers studied using standard methods. The mRNA expressions of COX-2, TNF-α, NF-κB, TLR-4, and IL-1β in the brain tissues were studied using RT-PCR analysis. The brain tissues were examined histologically.ResultsEE-ATF treatment remarkably decreased the onset and duration of convulsion and suppressed the seizure severity and mortality in the PTZ animals. EE-ATF treatment appreciably ameliorated the PTZ triggered modifications in the GABA, glutamate, dopamine levels and Ca + 2ATPase and Na + K + ATPase activities in the brain tissues. EE-ATF suppressed the mRNA expressions of NF-κB, IL-1β, TLR-4, TNF-α, and COX-2. The status of antioxidants were elevated by the EE-ATF. Histological findings also demonstrated the curative actions of EE-ATF.ConclusionOur findings evidenced that the EE-ATF substantially ameliorated the PTZ-provoked convulsive seizures in the mice.     

Cd2+-induced damage to yeast plasma membrane and its alleviation by Zn2+: studies on Schizosaccharomyces pombe cells and reconstituted plasma membrane vesicles

In Schizosaccharomyces pombe, Cd²⁺ shares the same uphill uptake system with Zn²⁺. Both heavy metals inhibited growth, respiration, H⁺/glucose uptake, and glucose-induced proton extrusion, Cd²⁺ being a 10–15-fold stronger inhibitor. In contrast, both had a similar effect on the plasma membrane H⁺-ATPase, enhancing its affinity for ATP and reducing the rate of ATP splitting. Cd²⁺ caused protracted strong fluidization of the plasma membrane of energized cells, whereas deenergized cells, phosphatidylcholine liposomes, and plasma membrane fragments, either purified or incorporated into the liposomes, exhibited only a short initial fluidization. Zn²⁺, which caused only a marginal membrane fluidization, suppressed the fluidizing action of Cd²⁺. The fluidizing effect of both heavy metals on liposomes was reduced by the presence of plasma membrane fragments in the liposome membrane. At 50 μM, Cd²⁺ brought about loss K⁺ (18 K⁺/1 Cd²⁺) from energized, but not from deenergized cells since Cd²⁺ must first accumulate in the cells before causing a detectable effect. A simple membrane disruption by external Cd²⁺ is, therefore, unlikely to be the main mechanism of cadmium-induced potassium loss in intact cells. Zn²⁺ had virtually no effect below 1 mM concentration, and it again weakened the K⁺-releasing effect of Cd²⁺. Cd²⁺ caused a strong loss of K⁺ also from K⁺-containing liposomes, probably because of a direct interaction with liposome phospholipids. Incorporation of plasma membrane fragments into the liposomes reduced the K⁺ loss sixfold. Received: 13 November 1995 / Accepted: 31 January 1996     

The ubiquitous cofactor NADH protects against substrate-induced inhibition of a pyridoxal enzyme.

In the usual reaction catalyzed by D-amino acid transaminase, cleavage of the alpha-H bond is followed by the reversible transfer of the alpha-NH2 to a keto acid cosubstrate in a two-step reaction mediated by the two vitamin B6 forms pyridoxal 5'-phosphate (PLP) and pyridoxamine 5'-phosphate (PMP). We report here a reaction not on the main pathway, i.e., beta-decarboxylation of D-aspartate to D-alanine, which occurs at 0.01% the rate of the major transaminase reaction. In this reaction, beta-C-C bond cleavage of the single substrate D-aspartate occurs rather than the usual alpha-bond cleavage in the transaminase reaction. The D-alanine produced from D-aspartate slowly inhibits both transaminase and decarboxylase activities, but NADH or NADPH instantaneously prevent D-aspartate turnover and D-alanine formation, thereby protecting the enzyme against inhibition. NADH has no effect on the enzyme spectrum itself in the absence of substrates, but it acts on the enzyme.D-aspartate complex with an apparent dissociation constant of 16 microM. Equivalent concentrations of NAD or thiols have no such effect. The suppression of beta-decarboxylase activity by NADH occurs concomitant with a reduction in the 415-nm absorbance due to the PLP form of the enzyme and an increase at 330 nm due to the PMP form of the enzyme. alpha-Ketoglutarate reverses the spectral changes caused by NADH and regenerates the active PLP form of the enzyme from the PMP form with an equilibrium constant of 10 microM. In addition to its known role in shuttling electrons in oxidation-reduction reactions, the niacin derivative NADH may also function by preventing aberrant damaging reactions for some enzyme-substrate intermediates. The D-aspartate-induced effect of NADH may indicate a slow transition between protein conformational studies if the reaction catalyzed is also slow.     

Effect of hardness on bioavailability and toxicity of cadmium to rainbow trout

Abstract

Water quality characteristics affecting toxicity of metals to aquatic life include pH, inorganic and organic ligands (negatively charged ions and molecules), and water hardness. Ligands control the ability of natural waters to bind metals which could adversely affect aquatic life. Bioavailability of metals in natural waters is primarily controlled by alkalinity. Hardness does not affect metal complexation but can reduce acute toxicity through antagonistic mechanisms. In most natural waters, concentrations of alkalinity and hardness are similar, but they may be very different in some waters.

Most toxicity studies have not distinguished between reduced toxicity resulting from effects of hardness and that resulting from complexation of metals by ligands. A series of acute and long-term experiments were conducted to assess these relationships while exposing rainbow trout (Oncorhynchus mykiss) to cadmium (Cd) in waters of low alkalinity (30 mg L^?1) and hardnesses of 400, 200, and 50 mg L^?1 adjusted with magnesium sulfate (MgSO⁴). These tests did not show a strong antagonistic influence of Mg hardness on Cd toxicity. At Mg hardnesses of 50, 200, and 400 mg L^?1, 96-h LC50s were 3.02, 6.12, and 5.70 μg Cd L^?1, differing by a factor of only 1.8. Similarly, chronic values derived from 100-day experiments in waters with the same range of hardness were 1.47, 3.57, and 3.64 μg L^?1, respectively. With an eight-fold difference in Mg hardness, chronic values differed by a factor of only 2.5. Antagonistic properties of hardness are primarily controlled by Ca with Mg playing a minor role. The long-term role of Ca in reducing metal toxicity will require further investigation.     

Influence of vitamin C on cadmium absorption and distribution in rats

The purpose of the present study was to evaluate the effect of a dietary vitamin C supplement on cadmium absorption and distribution in an animal model. An aqueous solution of cadmium chloride (labelled with cadmium-109) was given by gavage to male Wistar rats for 28 days at a daily dose corresponding to 10 mg Cd/kg diet (1.0-1.2 mg Cd/kg b.w.). The animals assigned to groups 1 and 2 (45 animals per group) received a standard laboratory diet LSM, and tap water or tap water supplemented with ascorbic acid (1.5 mg/l), respectively. The radioactivity of the samples was measured using a liquid scintillation counter (tissue samples) and a gas-flow automatic counter (ashed carcasses). The fractional uptake of cadmium-109 in the carcass and organs was evaluated within 32 days after treatment by dividing the cadmium-109 activity in the whole sample by the total activity of cadmium-109 administered for 28 days. Results were compared using AUC (areas under the concentration time curve) values. The vitamin C supplement decreased the carcass cadmium burden and the cadmium content in the liver, kidneys, testicles and muscles; the highest decreases were found in the testicles, the lowest ones in the muscles. In addition, the rats supplemented with vitamin C revealed an improved body weight gain during the experimental period.     

Late migration and seawater entry is physiologically disadvantageous for American shad juveniles

Juvenile American shad Alosa sapidissima were subjected to isothermal transfers into sea water (salinity 24)‘early’(1 September; 24° C) and ‘late’(10 November; 10° C) in the autumn migratory season. Early acclimation resulted in a modest osmotic perturbation that recovered rapidly. Haematocrit declined by 14% at 24 h, recovering within 48 h. Plasma osmolality increased by 6% at 4 h, recovering within 8 h. Early acclimation caused a two‐fold increase in gill Na⁺, K⁺‐ATPase activity by 24 h and a four‐fold increase by 4 days. The number of chloride cells on the primary gill filament increased two‐fold by 4 days. Chloride cells on the secondary lamellae rapidly decreased from 22 cells mm^?1 to <2 cells mm^?1 within 4 days. Late acclimation resulted in a severe and protracted osmotic perturbation. Haematocrit levels declined by 23% at 4 days, recovering by 14 days. Plasma osmolality increased by 36% by 48 h, recovering by 4 days. Initial gill Na⁺, K⁺‐ATPase activity was two‐fold greater than in ‘early’ fish and did not change during acclimation. Initial numbers of chloride cells on the primary filament were two‐fold greater than ‘early’ fish and did not increase during acclimation. Initial number of chloride cells on the secondary lamellae was five‐fold greater than ‘early’ fish (116 v. 22 cells mm^?1) and declined to negligible numbers over 14 days. Differences between initial measures for ‘early’ and ‘late’ fish reflect previously described physiological changes associated with migration. These data indicate that late migrants face a greater physiological challenge during seawater acclimation than early migrants. Physiological performance apparently limits the observed duration of autumnal migration.