Cadmium Inhibition of the Erythrocyte Ca2+ Pump

Linking molecular targets of Cd in the bloodstream to organ-based adverse health effects

The chronic exposure of human populations to toxic metals remains a global public health concern. Although chronic Cd exposure is linked to kidney damage, osteoporosis and cancer, the underlying biomolecular mechanisms remain incompletely understood. Since other diseases could also be causally linked to chronic Cd exposure, a systems toxicology-based approach is needed to gain new insight into the underlying exposure-disease relationship. This approach requires one to integrate the cascade of dynamic bioinorganic chemistry events that unfold in the bloodstream after Cd enters with toxicological events that unfold in target organs over time. To this end, we have conducted a systematic literature search to identify all molecular targets of Cd in plasma and in red blood cells (RBCs). Based on this information it is impossible to describe the metabolism of Cd and the toxicological relevance of it binding to molecular targets in/on RBCs is elusive. Perhaps most importantly, the role that peptides, amino acids and inorganic ions, including HCO₃^-, Cl^- and HSeO₃^- play in terms of mediating the translocation of Cd to target organs and its detoxification is poorly understood. Causally linking human exposure to this metal with diseases requires a much better integration of the bioinorganic chemistry of Cd that unfolds in the bloodstream with target organs. This from a public health point of view important goal will require collaborations between scientists from different disciplines to untangle the complex mechanisms which causally link Cd exposure to disease.

CaMKⅡ mediates cadmium induced apoptosis in rat primary osteoblasts through MAPK activation and endoplasmic reticulum stress

Ca²⁺ is an important ion in various intracellular metabolic pathways. Endoplasmic reticulum (ER) is a major intracellular calcium store and ER calcium homeostasis plays a key part in the regulation of apoptosis. We have previously shown that Cadmium (Cd) induces apoptosis in osteoblasts (OBs), accompany by increased cytoplasmic calcium. As the role of calcium in OBs apoptosis induced by Cd has not been clarified we investigated the effects of Cd exposure in rat OBs on intracellular Ca²⁺, CaMKII phosphorylation, and the pathways implicated in inducing apoptosis. The results showed that cadmium(Cd) induced elevation of intracellular Ca²⁺ ([Ca²⁺]_i) in OBs by the release of Ca²⁺ from ER and the inflow of Ca²⁺ from the extracellular matrix. Cd induced [Ca²⁺]_i elevation and phosphorylation of CaMKII which might be involved in activation of MAPKs and participated in Cd-induced mitochondrial apoptosis through the alteration of the ratio of Bax/Bcl-2 expression. Meanwhile, CaMKII phosphorylation activated unfolded protein response (UPR) during cadmium treatment and could enable the ER apoptosis pathway through the activation of caspase-12. These results indicated that CaMKII plays an important role in Cd induced ER apoptosis and MAPK activation. Our data provide new insights into the mechanisms underlying apoptosis in OBs following Cd exposure. This provides a theoretical basis for future investigations into the clinical therapeutic application of CaMKⅡ inhibitors in osteoporosis induced by Cd exposure.

Effects of cadmium alone and in combination with low molecular weight chitosan on metallothionein, glutathione-S-transferase, acid phosphatase, and ATPase of freshwater crab Sinopotamon yangtsekiense

Cadmium (Cd) is an environmental contaminant showing a variety of deleterious effects, including the potential threat for the ecological environment and human health via food chains. Low molecular weight chitosan (LMWC) has been demonstrated to be an effective antioxidant. Metallothionein (MT) mRNA levels and activities of glutathione-S-transferase (GST), superoxide dismutase (SOD), acid phosphatase (ACP), Na(+),K(+)-ATPase, and Ca(2+)-ATPase as well as malondialdehyde (MDA) contents in the gills of the freshwater crab Sinopotamon yangtsekiense were analyzed in vivo in order to determine the injury of Cd exposure on the gill tissues as well as the protective effect of LMWC against this injury. The results showed that there was an apparent accumulation of Cd in the gills, which was lessened by the presence of LMWC. Moreover, Cd(2+) significantly increased the gill MT mRNA levels, ACP activity and MDA content while decreasing the activities of SOD, GST, Na(+),K(+)-ATPase, and Ca(2+)-ATPase in the crabs relative to the control. Cotreatment with LMWC reduced the levels of MT mRNA and ACP but raised the activities of GST, Na(+),K(+)-ATPase, and Ca(2+)-ATPase in gill tissues compared with the crabs exposed to Cd(2+) alone. These results suggest that LMWC may exert its protective effect through chelating Cd(2+) to form LMWC-Cd(2+) complex, elevating the antioxidative activities of GST, Na(+),K(+)-ATPase, and Ca(2+)-ATPase as well as alleviating the stress pressure on MT and ACP, consequently protecting the cell from the adverse effects of Cd.

Silver nanoparticles stimulate glycogenolysis in rainbow trout (Oncorhynchus mykiss) hepatocytes

Silver nanoparticles (AgNPs) are found in many consumer products yet their biological effects on non-target aquatic organisms are yet to be fully understood. This research aimed to investigate the effects of AgNPs on cell signaling in rainbow trout (Oncorhynchus mykiss) hepatocytes. We focused on the β-adrenoreceptor (AR), which mediates glycogenolysis, and the glucocorticoid receptor (GCR), which mediates gluconeogenesis. These two receptors have been extensively studied in trout hepatocytes due to their key roles during the stress response to increase glucose availability (among other things), allowing the organisms to cope with the stressor. We show for the first time that AgNPs at a concentration of 1 μg/mL did not interfere with the function of either the β-AR or the GCR systems in rainbow trout hepatocytes, but at the concentration of 10 μg/mL AgNPs stimulated glycogenolysis which was apparently receptor-independent. This study suggests that AgNPs could affect hormone-regulated cell signaling pathways at a concentration of 10 μg/mL.

A protective role of heme-regulated eIF2α kinase in cadmium-induced toxicity in erythroid cells

Although a number of studies have demonstrated that cadmium (Cd) can incur damage to mature red cells, the potential injuries of Cd to erythroid progenitor cells have not been investigated thus far. Heme-regulated eIF2α kinase (Hri) is essential for translational regulation and survival of erythroid precursors in the setting of iron deficiency. Hri has been demonstrated to activate Atf4 signaling in reducing oxidative stress and in promoting erythroid differentiation during stress erythropoiesis. Here, we demonstrated that Cd significantly provoked cell death and suppressed erythroid differentiation of erythroid progenitor cells. Importantly, our results established a crucial role of Hri in ameliorating Cd-induced impairment to erythropoiesis. Upon Cd treatment, Hri-eIF2αP-Atf4 signaling was activated to protect cells from cell death and differentiation attenuation in Wt fetal liver erythroblasts; in contrast, Hri(-/-) erythroblasts suffered from enhanced oxidative stress, as evidenced by increased levels of reactive oxygen species (ROS) and consequentially elevated apoptosis. As for Cd administration in vivo, impaired erythropoiesis in bone marrow and dramatic extramedullary erythropoiesis in spleen were observed in Hri(-/-) mice. Taken together, our combined data highlighted a crucial role of Hri in protecting survival and differentiation of erythroid progenitor cells upon Cd treatment.

Effects of cadmium on the actin cytoskeleton in renal mesangial cells

We provide an overview of our studies on cadmium and the actin cytoskeleton in mesangial cells, from earlier work on the effects of Cd2+ on actin polymerization in vivo and in vitro, to a role of disruption or stabilization of the cytoskeleton in apoptosis and apoptosis-like death. More recent studies implicate cadmium-dependent association of gelsolin and the Ca2+/calmodulin-dependent protein kinase II (CaMK-II) with actin filaments in cytoskeletal effects. We also present previously unpublished data concerning cadmium and the disruption of focal adhesions. The work encompasses studies on rat, mouse, and human mesangial cells. The major conclusions are that Cd2+ acts independently of direct effects on cellular Ca2+ levels to nevertheless activate Ca2+-dependent proteins that shift the actin polymerization–depolymerization in favour of depolymerization. Cadmium-dependent translocation of CaMK-IIδ, gelsolin, and a 50 kDa gelsolin cleavage fragment to the filamentous (F-)actin cytoskeleton appear to be involved. An intact filamentous actin cytoskeleton is required to initiate apoptotic and apoptotic-like death, but F-actin depolymerization is an eventual result.

Cellular transport and homeostasis of essential and nonessential metals

Metals can have a number of detrimental or beneficial effects in the cell, but first they must get in. Organisms have evolved transport mechanisms to get metals that are required, or essential into the cell. Nonessential metals often enter the cell through use of the machinery provided for essential metals. Much work has been done to advance our understanding of how these metals are transported across plasma and organelle membranes. This review provides an overview of essential and nonessential metal transport and homeostatic processes.

Low-molecular-weight-chitosan ameliorates cadmium-induced toxicity in the freshwater crab, Sinopotamon yangtsekiense

Cadmium (Cd) has been shown to induce oxidative stress. Low-molecular-weight-chitosan (LMWC) has been demonstrated to exhibit potent antioxidant effects. We investigated the regulation role in Cd²⁺-induced oxidative damage in the hepatopancreas of the freshwater crab Sinopotamon yangtsekiense and the protective effect of LMWC. The results showed that Cd²⁺ significantly increased the hepatopancreatic metallothionein (MT) mRNA levels and protein kinase C (PKC) activity while decreasing the activities of Na⁺,K⁺-ATPase and Ca²⁺-ATPase in crabs relative to the control group. Co-treatment with LMWC suppressed the levels of MT and PKC but raised the activities of Na⁺,K+-ATPase and Ca²⁺-ATPase in hepatopancreatic tissues compared with the crabs exposed to Cd²⁺ alone. We postulate that LMWC may exert its protective effect through regulating the expressions of MT, PKC, Na⁺,K⁺-ATPase and Ca²⁺-ATPase, thereby enhancing antioxidant defense. These observations suggest that LMWC may be beneficial because of its ability to alleviate the Cd²⁺-induced damages to the crabs.

Cd affects the translocation of some metals either Fe-like or Ca-like way in poplar

In plants, Cd causes perturbation of root metal uptake and is known to interfere with the metal translocation to the shoot. The most significant effect is the strongly reduced transport of Fe. Fe accumulation in roots under Cd stress revealed that it is not the Fe acquisition but the Fe loading to xylem elements that is blocked by Cd, which can be a result of competition between Fe and Cd for the transporters. However, in animal cells as well as in plant stomata guard cells, Cd was shown to move through Ca channels. To clarify whether the perturbation of metal translocation/xylem loading caused by Cd show any regularity, translocation ability was tested by the determination of the metal content in leaves of hydroponically cultured (¼ Hoagland nutrient solution, Fe source: 10 μM Fe((III))-citrate) poplar plants grown for three weeks with or without 10 μM Cd(NO₃)₂ treatment. Metals could be classified into two groups according to the behavior of their translocation under Cd treatment: alkaline earth metals (except Mg), Zn and Mn were influenced similarly to Ca, but other transition metals (together with alkali metals and Al) behaved like the Fe. Based on the translocation pattern, Cd seems to inhibit the transport of Ca-like metals competitively, but a different type of inhibition is exerted on the transition metal transport, with which Cd can share a common translocation system. The strongly decreased translocation of chelator-dependent transition metals may indicate Cd related disturbances in signalling pathways and gene expression of xylem transporters or chelators.

Evaluating the function of calcium antagonist on the Cd-induced stress in sperm of Russian sturgeon, Acipenser gueldenstaedtii

In the current study, the sperm of Russian sturgeon (Acipenser gueldenstaedtii) was used to evaluate the roles of Verapamil (VRP), a calcium channel blocker, against cadmium (Cd)-induced stress. Sturgeon sperm were exposed for 2h at 50μg/L VRP, 5.0μg/L Cd, the mixture of 50μg/L VRP+5.0μg/L Cd, 50μg/L Cd and the mixture of 50μg/L VRP+50μg/L Cd. After exposure, the sperm motility parameters (motility and velocity), oxidative stress levels (lipid peroxidation [LPO] and carbonyl protein [CP]) and antioxidant enzyme activities (superoxide dismutase [SOD], glutathione reductase [GR], glutathione peroxidase [GPx]) were measured in sturgeon sperm. Compared to the control, Cd-induced stress was apparent as reflected by depressed motility parameters, induced oxidative stress and inhibited antioxidant enzyme activities at both Cd concentrations. In the presence of VRP, Cd-induced stress was reduced in sturgeon sperm, especially all the measured parameters in the sperm exposed at 5.0μg/L Cd returned to control levels, expect for the sperm motility. The present results indicate that VRP can reduce the Cd-induced stress in sturgeon sperm and suggest that using of sperm in vitro assays may provide a novel and efficient means for evaluating the effects of residual metals in the aquatic environment of sturgeon.

Cadmium and transport of ions and substances across cell membranes and epithelia

Toxic metals such as cadmium (Cd(2+)) pose serious risks to human health. However, even though the importance of Cd(2+) as environmental health hazards is now widely appreciated, the specific mechanisms by which it produces its adverse effects have yet to be fully elucidated. Cd(2+) is known to enter cells, it binds and interacts with a multitude of molecules, it may indirectly induce oxidative stress and interfere with gene expression and repair of DNA. It also interacts with transport across cell membranes and epithelia and may therefore disturb the cell's homeostasis and function. Interaction with epithelial transport, especially in the kidney and the liver, may have serious consequences in general health. A lot of research still needs to be done to understand the exact way in which Cd(2+) interferes with these transport phenomena. It is not always clear whether Cd(2+) has primary or secondary effects on cell membrane transport. In the present review we try to summarize the work that has been done up to now and to critically discuss the relevance of the experimental work in vitro with respect to the in vivo situation.

Endoplasmic reticulum is a major target of cadmium toxicity in yeast

Cadmium (Cd(2+)) is a very toxic metal that causes DNA damage, oxidative stress and apoptosis. Despite many studies, the cellular and molecular mechanisms underlying its high toxicity are not clearly understood. We show here that very low doses of Cd(2+) cause ER stress in Saccharomyces cerevisiae as evidenced by the induction of the unfolded protein response (UPR) and the splicing of HAC1 mRNA. Furthermore, mutant strains (Delta ire1 and Delta hac1) unable to induce the UPR are hypersensitive to Cd(2+), but not to arsenite and mercury. The full functionality of the pathways involved in ER stress response is required for Cd(2+) tolerance. The data also suggest that Cd(2+)-induced ER stress and Cd(2+) toxicity are a direct consequence of Cd(2+) accumulation in the ER. Cd(2+) does not inhibit disulfide bond formation but perturbs calcium metabolism. In particular, Cd(2+) activates the calcium channel Cch1/Mid1, which also contributes to Cd(2+) entry into the cell. The results reinforce the interest of using yeast as a cellular model to study toxicity mechanisms in eukaryotic cells.

Inhibitory effect of Pb2+ on the transport cycle of the Na+,K+-ATPase

The effect of Pb(2+) on the transport cycle of the Na(+),K(+)-ATPase was characterized in detail at a molecular level by combining electrical and biochemical measurements. Electrical measurements were performed by adsorbing purified membrane fragments containing Na(+),K(+)-ATPase on a solid-supported membrane. Upon adsorption, the Na(+),K(+)-ATPase was activated by carrying out concentration jumps of different activating substrates, for example, Na(+) and ATP. Charge movements following Na(+),K(+)-ATPase activation were measured in the presence of various Pb(2+) concentrations to investigate the effect of Pb(2+) on different ion translocating steps of the pump cycle. These charge measurements were then compared to biochemical measurements of ATPase activity in the presence of increasing Pb(2+) concentration. Our results indicate that Pb(2+) inhibits cycling of the enzyme, but it does not affect cytoplasmic Na(+) binding and release of Na(+) ions at the extracellular side at concentrations below 10 muM. To explain the inhibitory effect of Pb(2+) on the Na(+),K(+)-ATPase, we propose that Pb(2+) may interfere with the hydrolytic cleavage of the phosphorylated intermediate E(2)P, which occurs in the K(+)-related branch of the pump cycle.

Cadmium interacts with the transport of essential micronutrients in the mammary gland - a study in rural Bangladeshi women

Although the concentrations of the toxic metal cadmium in breast milk are generally low (< 1 microg/L), experimental studies indicated neurobehavioral and endocrine effects in the suckling offspring. The aim of the present study was to elucidate how cadmium is transported to breast milk by assessing interactions with essential micronutrients. The study is nested into a food and micronutrient supplementation trial conducted among pregnant women in Matlab, a rural area in Bangladesh, where malnutrition is prevalent and the cadmium exposure is relatively high. We measured cadmium in breast milk (BM-Cd; median 0.14 microg/kg; range <0.050-1.0 microg/kg), in erythrocytes (Ery-Cd; median 1.5 microg/kg; range 0.46-4.8 microg/kg) and in urine (U-Cd; median 0.63 microg/L; range 0.050-4.5 microg/L), using inductively coupled plasma mass spectrometry (ICPMS). We found a significant positive association between Ery-Cd and BM-Cd and a breast milk-plasma ratio of approximately 3-4, indicating no barrier against cadmium transport from plasma to breast milk. BM-Cd was positively associated with manganese (r(s)=0.56; p<0.01) and iron (r(s)=0.55; p<0.01) in breast milk, but not with plasma ferritin. On the other hand, BM-Cd was negatively associated with BM-Ca (r(s)=-0.17; p=0.05), indicating that cadmium inhibits the transport of calcium to breast milk. In conclusion, the present study may indicate that cadmium shares common transporters with iron and manganese for transfer to breast milk, but inhibits secretion of calcium to breast milk.

Vanadium and cadmium in vivo effects in teleost cardiac muscle: metal accumulation and oxidative stress markers

Several biological studies associate vanadium and cadmium with the production of reactive oxygen species (ROS), leading to lipid peroxidation and antioxidant enzymes alterations. The present study aims to analyse and compare the oxidative stress responses induced by an acute intravenous exposure (1 and 7 days) to a sub-lethal concentration (5 mM) of two vanadium solutions, containing different vanadate n-oligomers (n=1-5 or n=10), and a cadmium solution on the cardiac muscle of the marine teleost Halobatrachus didactylus (Lusitanian toadfish). It was observed that vanadium is mainly accumulated in mitochondria (1.33+/-0.26 microM), primarily when this element was administrated as decameric vanadate, than when administrated as metavanadate (432+/-294 nM), while the highest content of cadmium was found in cytosol (365+/-231 nM). Indeed, decavanadate solution promotes stronger increases in mitochondrial antioxidant enzymes activities (catalase: +120%; superoxide dismutase: +140%) than metavanadate solution. On contrary, cadmium increases cytosolic catalase (+111%) and glutathione peroxidases (+50%) activities. It is also observed that vanadate oligomers induce in vitro prooxidant effects in toadfish heart, with stronger effects induced by metavanadate solution. In summary, vanadate and cadmium are differently accumulated in blood and cardiac subcellular fractions and induced different responses in enzymatic antioxidant defence mechanisms. In the present study, it is described for the first time the effects of equal doses of two different metals intravenously injected in the same fish species and upon the same exposure period allowing to understand the mechanisms of vanadate and cadmium toxicity in fish cardiac muscle.

Endoplasmic reticulum stress and alteration in calcium homeostasis are involved in cadmium-induced apoptosis

Cadmium, a toxic environmental contaminant, exerts adverse effects on different cellular pathways such as cell proliferation, DNA damage and apoptosis. In particular, the modulation of Ca(2+) homeostasis seems to have an important role during Cd(2+) injury, but the precise assessment of Ca(2+) signalling still remains poorly understood. We used aequorin-based probes specifically directed to intracellular organelles to study Ca(2+) changes during cadmium injury. We observed that cadmium decreased agonist-evoked endoplasmic reticulum (ER) Ca(2+) signals and caused a 40% inhibition of sarcoplasmic-ER calcium ATPases activity. Moreover, time course experiments correlate morphological alterations, processing of xbp-1 mRNA and caspase-12 activation during cadmium administration. Finally, the time response of ER to cadmium injury was compared with that of mitochondria. In conclusion, we highlighted a novel pathway of cadmium-induced cell death triggered by ER stress and involving caspase-12. Mitochondria and ER pathways seemed to share common time courses and a parallel activation of caspase-12 and caspase-9 seemed likely to be involved in acute cadmium toxicity.

Contrasting effects of heavy metals on sponge cell behavior

Mediterranean coastal areas are highly contaminated by heavy metals, which have been reported to produce harmful effects in marine organisms. Sponges are particularly vulnerable to waterborne metals because they are able to process large amounts of water. Dissociated sponge cells can move in response to external stimuli, and the cell body changes shape through production of pseudopodia and phylopodia. We studied for first time the effects of heavy metals (cadmium copper and mercury) on motility and aggregation of isolated sponge cells. Cell shape was assessed by using several shape indices. The three metals studied induced changes of different sign on cell shape. Mercury arrested movement of sponge cells, which tended to be rounded, without pseudopodia. In contrast, moderate concentrations of copper and cadmium enhanced pseudopodia formation and cell motility. On the other hand, the three metals enhanced cell aggregation at the concentrations assayed. Our results show that sponge cells respond to metal pollution in different ways and that these responses can be assessed by calculating several shape indices.

Role of calcium channels in cadmium-induced disruption of cortisol synthesis in rainbow trout (Oncorhynchus mykiss)

The mechanisms of toxicity of cadmium (Cd(2+)) in adrenal steroidogenesis were investigated in vitro in adrenocortical cells of rainbow trout (Oncorhynchus mykiss). Toxicity of Cd(2+) was increased in absence of extracellular Ca(2+), but was prevented in Ca(2+)-supplemented medium. Pretreatment of cells with BAY K8644 (BAY), an agonist of voltage-dependent calcium channels, increased the Cd(2+)-mediated inhibition of ACTH-stimulated secretion but not pregnenolone (PREG)-stimulated secretion. Nicardipine, an antagonist of voltage-dependent calcium channels, also increased the inhibition of adrenocorticotropic hormone (ACTH)-stimulated secretion by Cd(2+). These results suggest that opening of voltage-dependent calcium channels with BAY may allow Cd(2+) entry at the same time as calcium, thus increasing toxicity of Cd(2+), however voltage-dependent calcium channels may not be the only way of entry into adrenocortical cells. The influx of Cd(2+), measured as intracellular Cd(2+) using Fluo-3 in PREG-stimulated adrenocortical cells, was significantly enhanced by the stimulation. These results suggest that the deleterious effect of Cd(2+) on cortisol steroidogenesis may be enhanced when the endocrine stress response is triggered.

CadA, the Cd2+-ATPase from Listeria monocytogenes, can use Cd2+ as co-substrate

CadA is a membrane protein of the P-type ATPase family which is the major determinant of the resistance to Cd2+ in Listeria monocytogenes. During its catalytic cycle, CadA undergoes auto-phosphorylation from ATP at Asp398, which allows Cd2+ translocation across the membrane. In the reverse mode, Asp398 is phosphorylated from Pi. From the data obtained so far, the CadA catalytic mechanism is similar to that proposed for the sarcoplasmic reticulum Ca2+-ATPase, the model of the P-type ATPase family. We show here that CadA is sensitive to two different ranges of Cd2+ concentration. The 0.1-10 microM range of added CdCl2 corresponds to Cd2+ binding at the transport site of unphosphorylated CadA which induces the reaction of the enzyme with ATP and impairs its reaction with Pi. The 0.1-1 mM range of added CdCl2 could correspond to Cd2+ binding to the transport site accessible from the extracellular medium. In addition, although it is widely accepted that the actual substrate of P-type ATPases is the MgATP complex, we show here that CadA can also perform its cycle in the absence of Mg2+, using CdATP in the place of MgATP at the catalytic site.

Heavy metal interference with growth hormone signalling in trout hepatoma cells RTH-149

We have studied the effects of heavy metals (Hg2+, Cu2+, Cd2+) on growth hormone (GH) activation of tyrosine kinase and Ca2+ signaling in the trout (Oncorhynchus mykiss) hepatoma cell line RTH-149. Molecular cloning techniques using primer designed on Oncorhynchus spp. growth hormone receptor (GHR) genes allowed to isolate a highly homologous cDNA fragment from RTH-149 mRNA. Thereafter, cells were analysed by Western blotting or, alternatively, with Ca2+ imaging using fura-2/AM. Exposure of cells to ovine GH alone produced a stimulation of the JAK2/STAT5 pathway and intracellular free Ca2+ variations similar to what has been observed in mammalian models. Cell pre-exposure to Cu2+, Hg2+ or Cd2+ affected cell response to GH by enhancing (Cu2+) or inhibiting (Cd2+) the phosphorylation of JAK2 and STAT5. Heavy metals induced the activation of the MAP kinase p38, and pre-exposure to Hg2+ or Cu2+ followed by GH enhanced the effect of metal alone. Image analysis of fura2-loaded cells indicated that pre-treatment with Hg2+ prior to GH produced a considerable increase of the [Ca2+]i variation produced by either element, while using Cu2+ or Cd2+ the result was similar but much weaker. Data suggest that heavy metals interfere with GH as follows: Hg2+ is nearly ineffective on JAK/STAT and strongly synergistic on Ca2+ signaling; Cu2+ is activatory on JAK/STAT and slightly activatory on Ca2+; Cd2+ is strongly inhibitory on JAK/STAT and slightly activatory on Ca2+; heavy metals could partially activate STAT via p38 independently from GH interaction.

Identification and characterization of a family of Caenorhabditis elegans genes that is homologous to the cadmium-responsive gene cdr-1

Six Caenorhabditis elegans genes that are homologous to the novel, cadmium-responsive gene cdr-1 have been identified and characterized. Nucleotide and amino acid sequence comparisons among the CDR family, which includes cdr-1, cdr-2, cdr-3, cdr-4, cdr-5, cdr-6, and cdr-7, reveals a high degree of identity among the seven members in this family. There are high levels of amino acid and nucleotide sequence similarity in the lengths of the open reading frames, predicted sizes, and protein characteristics. The seven proteins are predicted to be extremely hydrophobic, and are classified as integral membrane proteins. Structural analysis of the predicted proteins suggests that they may have similar biological functions. In response to cadmium exposure, cdr-1, cdr-2, cdr-3, and cdr-4 transcription significantly increases. In contrast, the levels of cdr-5, cdr-6, and cdr-7 transcription are not significantly affected or inhibited by cadmium exposure. Further, in non-exposed C. elegans, cdr-2, cdr-4, cdr-6, and cdr-7 are constitutively expressed. When CDR-1 expression was inhibited using RNAi, numerous fluid droplets were observed throughout the nematode body cavity. This phenotype became more pronounced in the presence of hypotonic stress. This suggests that CDR-1 may function in osmoregulation to maintain salt balance in C. elegans.

Mercury- and copper-induced lysosomal membrane destabilisation depends on [Ca2+]i dependent phospholipase A2 activation

Heavy metals are environmental pollutants able to produce different cellular effects, such as an alteration of Ca2+ homeostasis and lysosomal membrane destabilisation. The latter is one of the most used stress indices in biomonitoring programs. Recently, it has been demonstrated that cytosolic calcium increase can modulate lysosomal membrane destabilisation via activation of Ca(2+)-dependent phospholipase A2 (cPLA2). The aim of this work was to investigate the possible involvement of Ca(2+)-activated PLA2 in lysosomal membrane destabilisation induced by heavy metals in mussel haemolymph cells. We have studied the effects of Hg2+ and Cu2+ on free cytosolic calcium using Fura2/AM-loaded cells and lysosomal membrane destabilisation using neutral red (NR) staining. Hg2+ induced a [Ca2+]i rise from 100 to 780 nM in 30 min, and a lysosome destaining of 70% after 60 min that indicates destabilisation of lysosomal membranes. Both effects were reduced in a Ca(2+)-free medium, suggesting a cause-effect relationship. Exposure to Cu2+ produced the same effects, but with an intensity of about 50% respect to Hg2+. Metal-induced lysosomal destabilisation was also reduced in cells pre-exposed to a specific Ca(2+)-dependent cPLA2 inhibitor (AACOCF3). Conversely, haemocyte pretreatment with a Ca(2+)-independent PLA2 inhibitor (bromoenol-lactone (BEL)) did not prevent the destabilizing effect of heavy metals on lysosomes. Exposure to heavy metals also produced an increase in lysosomal volume of 1.8-2-folds, that was prevented by pre-incubation with AACOCF3 but not with BEL. These data indicate an involvement of cPLA2 in lysosomal membrane destabilisation induced by heavy metals.

Regulation and modulation of pH in the brain

The regulation of pH is a vital homeostatic function shared by all tissues. Mechanisms that govern H+ in the intracellular and extracellular fluid are especially important in the brain, because electrical activity can elicit rapid pH changes in both compartments. These acid-base transients may in turn influence neural activity by affecting a variety of ion channels. The mechanisms responsible for the regulation of intracellular pH in brain are similar to those of other tissues and are comprised principally of forms of Na+/H+ exchange, Na+-driven Cl-/HCO3- exchange, Na+-HCO3- cotransport, and passive Cl-/HCO3- exchange. Differences in the expression or efficacy of these mechanisms have been noted among the functionally and morphologically diverse neurons and glial cells that have been studied. Molecular identification of transporter isoforms has revealed heterogeneity among brain regions and cell types. Neural activity gives rise to an assortment of extracellular and intracellular pH shifts that originate from a variety of mechanisms. Intracellular pH shifts in neurons and glia have been linked to Ca2+ transport, activation of acid extrusion systems, and the accumulation of metabolic products. Extracellular pH shifts can occur within milliseconds of neural activity, arise from an assortment of mechanisms, and are governed by the activity of extracellular carbonic anhydrase. The functional significance of these compartmental, activity-dependent pH shifts is discussed.

Comparative effects of cadmium, copper, paraquat and benzo[a]pyrene on the actin cytoskeleton and production of reactive oxygen species (ROS) in mussel haemocytes

The immune defence of mussels is comprised of cell-mediated and humoral mechanisms, in which haemocytes or blood cells play a key role. Environmental pollutants such as metallic and organic xenobiotics exert immunotoxical effects on aquatic organisms. Some of these xenobiotics are known to give rise to highly reactive oxygen species (ROS), thereby leading to oxidative damage to tissue macromolecules including DNA, proteins and lipids. Previously we have detected enhancement of ROS production together with severe alterations in the actin cytoskeleton after exposure of mussel haemocytes to the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene (b[a]p). In a similar way, cadmium is also known to cause disruption of the actin cytoskeleton in mussel haemocytes, however it is not known whether this effect occurs by direct action or through ROS production. The aim of the present study was to decipher whether cytoskeletal alterations caused by Cd in mussel haemocytes are linked to increased ROS production. ROS-producing model compounds copper (Cu), paraquat and b[a]p were used in parallel experiments for comparative purposes. In all contaminant exposure experiments actin cytoskeleton appeared damaged. On the other hand, ROS production was increased in paraquat and b[a]p exposure experiments but decreased in haemocytes exposed to Cu while no significant effects were detected in Cd exposure experiments. In conclusion, it appears that deleterious effects of Cu and Cd on the integrity of the actin cytoskeleton of haemocytes are not directly linked to ROS production, at least at the exposure conditions used in the present study.

Ionoregulatory disruption as the acute toxic mechanism for lead in the rainbow trout (Oncorhynchus mykiss)

The mechanism for acute toxicity of lead (Pb) in rainbow trout (Oncorhynchus mykiss) was investigated at Pb concentrations close to the 96 h LC50 of 1.0 mg dissolved Pb l(-1) (0.8-1.4, 95% C.I.) determined in dechlorinated Hamilton city tap water (from Lake Ontario, hardness=140 mg l(-1) CaCO(3)). Tissue Pb accumulation associated with death was highest in the gill, followed by kidney and liver. Significant ionoregulatory impacts were observed in adult rainbow trout (200-300 g) fitted with indwelling dorsal aortic catheters and exposed to 1.1+/-0.04 mg dissolved Pb l(-1). Decreased plasma [Ca(2+)], [Na(+)] and [Cl(-)] occurred after 48 h of exposure through to 120 h, with increases in plasma [Mg(2+)], ammonia, and cortisol. No marked changes in PaO(2), PaCO(2), pH, glucose, or hematological parameters were evident. Branchial Na(+)/K(+) ATPase activity in juvenile trout exposed to concentrations close to the 96 h LC50 was inhibited by approximately 40% after 48 h of Pb exposure. Calcium ion flux measurements using 45Ca as a radiotracer showed 65% inhibition of Ca(2+) influx after 0, 12, 24 or 48 h exposure to the 96 h LC50 concentration of Pb. There was also significant inhibition (40-50%) of both Na(+) and Cl(-) uptake, measured with 22Na and 36Cl simultaneously. We conclude that the mechanism of acute toxicity for Pb in rainbow trout occurs by ionoregulatory disruption rather than respiratory or acid/base distress at Pb concentrations close to the 96 h LC50 in moderately hard water.

Acute waterborne nickel toxicity in the rainbow trout (Oncorhynchus mykiss) occurs by a respiratory rather than ionoregulatory mechanism

The acute mechanism of toxicity of waterborne nickel (Ni) was investigated in the rainbow trout (Oncorhynchus mykiss) in moderately hard ( approximately 140 mg l(-1) as CaCO(3)) Lake Ontario water, where the 96-h LC(50) for juvenile trout (1.5-3.5 g) was 15.3 mg (12.7-19.0, 95% C.L.) dissolved Ni l(-1). No marked impact of Ni exposure on average unidirectional or net fluxes of Na(+), Cl(-), or Ca(2+) was observed in juvenile trout exposed for 48-60 h to 15.6 mg Ni l(-1) as NiSO(4). Furthermore, when adult rainbow trout (200-340 g) were fitted with indwelling dorsal aortic catheters and exposed for 117 h to 11.6 mg Ni l(-1) as NiSO(4), plasma ions (Na(+), Cl(-), Ca(2+), and Mg(2+)) were all well conserved. However, mean arterial oxygen tension dropped gradually to approximately 35% of control values. This drop in P(aO(2)) was accompanied by an acidosis primarily of respiratory origin. P(aCO(2)) rose to more than double control values with a concomitant drop in arterial pH of 0.15 units. Acute respiratory toxicity was further evidenced by a significant increase in hematocrit (Ht), and plasma lactate, and a significant decrease in spleen hemoglobin (Hb). Following 117 h of exposure to 11.6 mg Ni l(-1), the gill, intestine, plasma, kidney, stomach, and heart accumulated Ni significantly, with increases of 60, 34, 28, 11, 8, and 3-fold, respectively. Brain, white muscle, liver, and bile did not significantly accumulate Ni. Plasma Ni exhibited a remarkable linear increase with time to levels approximately 30-fold higher than controls. We conclude that in contrast to most other metals, Ni is primarily a respiratory, rather than an ionoregulatory, toxicant at exposure levels close to the 96-h LC(50). The implications of a waterborne metal as an acute respiratory toxicant (as opposed to ionoregulatory toxicants such as Cu, Ag, Cd, or Zn) with respect to toxicity modeling are discussed.

Cyclosporin A-sensitive permeability transition pore is involved in Cd(2+)-induced dysfunction of isolated rat liver mitochondria: doubts no more

There is dose-dependent Cd(2+)-evoked swelling of isolated rat liver mitochondria energized by complex I, II, or IV respiratory substrates in sucrose medium in the absence of added Ca(2+) and P(i), which is prevented by Sr(2+). Permeability transition effectors (ADP, CsA, EGTA, RR, DTT, ATR, P(i), and Ca(2+)) affect in a corresponding way Cd(2+)-promoted membrane permeabilization in NH(4)NO(3), KCl, and sucrose media. Maximal depression of Cd(2+)-induced swelling is achieved by simultaneous addition of ADP, Mg(2+), and CsA that produces either synergistic (NH(4)NO(3)) or additive (KCl and sucrose media) action. Sustained activation by low [Cd(2+)] of mitochondrial basal respiration in KCl medium is observed both in the absence and in the presence of rotenone and/or oligomycin but only in the latter case (rotenone+oligomycin) CsA inhibits completely Cd(2+) activation of St 4 respiration and partially reverses DNP-uncoupled respiration depressed by cadmium. Cd(2+) effects are discussed in terms of comparison with those of Zn(2+) and PhAsO.

Progressive inactivation of plasma membrane (Ca2++Mg2+)ATPase by Cd2+ in the absence of ATP and reversible inhibition during catalysis

The influence of Cd2+ ions on plasma membrane (Ca2++Mg2+)ATPase activity from red cells was investigated. When the membranes were preincubated with Cd2+ in the absence of ATP, basal (Ca2++Mg2+)ATPase activity (no calmodulin) was slowly and irreversibly inhibited (inactivated) following first-order kinetics (k/Ki = 0.0057 microM-1 min-1 at [Cd2+] = 0.25-1 microM). However, preincubation with Cd2+ did not affect the degree of stimulation by calmodulin added to the assay medium together with ATP. Inactivation was not released by prolonged exposure of membranes to EGTA prior to catalysis, but it was strongly attenuated when the pH in the preincubation medium was lowered from 7.2 to 6.4. When the reaction was started by supplying membranes simultaneously with Cd2+ and ATP (no preincubation), (Ca2++Mg2+)ATPase was inhibited by increasing concentrations of the CdATP complex ([CdATP]50 = 7.2 microM). In this condition, however, even total inhibition of the pump was almost completely released after addition of enough EGTA to decrease CdATP concentrations to the nanomolar range. These results, taken together, indicate that inactivation of the unphosphorylated enzyme by Cd2+ is influenced by dissociation of amino acid residues exhibiting pK between 6.0 and 7.0, and that recognition by the pump of the physiological modulator calmodulin is preserved in the preincubated pump molecules which did not undergo inactivation. In addition, they show that the catalytic site is a target for reversible inhibition of the pump by CdATP and that occupancy of the nucleotide binding site prevents inactivation.

Physiologically based models of metal kinetics

The issues confronting the modeler of metals kinetics are somewhat different from those with which the modeler of organic chemical behavior is faced. Particularly important features of metals kinetics include metal-protein binding and metal-metal interactions. Reduction, and for some metals oxidation, is frequently an intrinsic part of metal metabolism. Alkylation/dealkylation reactions may or may not render the metal less active, and the behavior of alkylated or dealkylated metabolites must often be included in a complete kinetic model. Despite these complexities, the kinetics of metals are as amenable to the techniques of physiologically based modeling as are the kinetics of organic chemicals. Like all models, those for metals kinetics have the potential to organize a variety of observations, sometimes including apparently inconsistent observations, into a coherent framework of behavior, to identify needs for more complete experimental information, and to assist the risk assessor in making judgments concerning dose-response relationships. Development of physiologically based models of the kinetic behavior of metals is in its very early stages. The kinetics of only four metals, arsenic, chromium, mercury, and lead, have been modeled with any degree of completeness. Of these, the lead model is the most fully realized at the present time. The chromium and mercury models are still in the process of development, and experimental data are being gathered to support further development and refinement of the arsenic model. We may expect to see continued progress made on these models and their practical applications, as well as the development of new models for other toxicologically significant metals such as cadmium, manganese, nickel, and aluminum.

Effect of calmodulin-inhibitors and verapamil on the nephrotoxicity of cadmium in rat

Recent reports indicate that calmodulin inhibitors (CIs) can modify cadmium (Cd) toxicity in rodents. Pretreatment with CIs prevents Cd-induced testicular damage in mice and reduces the severity of such damage in rats. On the other hand it has been suggested that the cellular transport of Cd can be partly inhibited by the calcium-channel inhibitor, verapamil. The aim of this study was to determine whether these inhibitors can prevent the toxic effects of Cd on the kidney which is the critical organ. For that purpose, we have examined the effects of two CIs (trifluoperazine and chlorpromazine) and of verapamil on the development of tubular damage in female Sprague-Dawley rats. The animals were injected subcutaneously 5 days a week for 8 weeks with cadmium chloride (1 mg Cd/kg), alone or in association with trifluoperazine (20 mg/kg), chlorpromazine (15 mg/kg) or verapamil (2 x 5 mg/kg). The development of renal dysfunction was followed by measuring the urinary excretion of the low molecular weight protein Clara cell protein (CC16). In Cd-treated rats, the urinary excretion of CC16 started to increase from week 6 to reach at the end of experiment values more than 100-times above normal. CIs or verapamil did not influence the rise of urinary CC16 induced by Cd. The three inhibitors, by contrast, enhanced the accumulation of Cd in the liver and, at the exception of chlorpromazine, in the kidneys of Cd-treated rats. Although interfering with the metabolism of Cd, CIs and verapamil do not prevent renal damage in rats chronically exposed to this heavy metal.

Cadmium disrupts the signal transduction pathway of both inhibitory and stimulatory receptors regulating chloride secretion in the shark rectal gland

The heavy metal cadmium causes nephrotoxicity and alters the transport function of epithelial cells. In the shark rectal gland, chloride secretion is regulated by secretagogues and inhibitors acting through receptors coupled to G proteins and the cyclic AMP-protein kinase A pathway. We examined the effects of cadmium on the response to the inhibitory peptide somatostatin (SRIF), and to the stimulatory secretagogues forskolin and vasoactive intestinal peptide (VIP). In control experiments, SRIF (100 nM) entirely inhibited the chloride secretory response to 10 microM forskolin (maximum chloride secretion with forskolin 1984 +/- 176 microEq/h/g; with forskolin + SRIF 466 +/- 93 microEq/h/g, P < 0.001). Cadmium (25 microM) entirely reversed the inhibitory response to SRIF (chloride secretion 2143 +/- 222 microEq/h/g) and caused an overshoot (2917 +/- 293 microEq/h/g) that exceeded the response to forskolin (P < 0.01). Cadmium also enhanced forskolin-stimulated chloride secretion (2628 +/- 418 vs. 1673 +/- 340 microEq/h/g, P < 0.02) and reversed the declining phase of the forskolin response. Cadmium had a concentration-dependent, biphasic effect on the response to VIP. Cd (10-100 microM) increased both chloride secretion and tissue cyclic AMP content, whereas higher concentrations (1 mM) inhibited chloride secretion and cyclic AMP accumulation. Our findings provide evidence that Cd disrupts the signal transduction pathways of both inhibitory receptors and secretagogues regulating cAMP mediated transport in an intact epithelia. The results are consistent with direct effects of cadmium on adenylate cyclase and/or phosphodiesterase activity in this marine epithelial model.

Inhibition of 8-hydroxyguanine repair in testes after administration of cadmium chloride to GSH-depleted rats

The main goal of this study is to investigate the mechanism of cadmium (Cd)-induced carcinogenesis by reactive oxygen species. Rats were divided into four groups and were treated with (i) saline (control), (ii) cadmium chloride (CdCl2), (iii) l-buthionine-[S, R]-sulfoximine (BSO, an inhibitor of GSH biosynthesis), and (iv) CdCl2 and BSO, respectively. They were euthanized at 0, 24, 48, and 72 hr after these treatments, and the lungs and testes were analyzed. After treatment with both CdCl2 and BSO, the testicular 8-OH-Gua level increased (48 hr), its repair activity decreased (48 and 72 hr), the GSH content was markedly suppressed (48 and 72 hr), the superoxide dismutase activities slightly (48 and 72 hr) decreased, and the lipid peroxidation level increased (24 and 72 hr) in the testes as compared to the control levels. These results suggest that under GSH-depleted conditions, CdCl2 inhibits 8-OH-Gua repair activity in the rat testis and 8-OH-Gua accumulates in the DNA, which may pertain to testicular carcinogenesis.

Cadmium perturbs calcium homeostasis in rat osteosarcoma (ROS 17/2.8) cells; a possible role for protein kinase C

The mechanism of the toxic effects of Cd2+ on bone cell function is not completely understood at this time. This study was designed to characterize the effect of Cd2+ on Ca2+ metabolism in ROS 17/2.8 cells. Cells were labeled with (45)Ca (1.87 mM Ca) for 20 h in the presence of 0.01, 0.1, or 1.0 microM Cd2+ and kinetic parameters were determined from (45)Ca efflux curves. Three kinetic compartments described the intracellular metabolism of (45)Ca. Cd2+ (0.01 microM) caused an approximate 9 x increase in Ca2+ flux across the plasma membrane and a decrease in the most rapidly exchanging intracellular Ca2+ compartment (S1). However, there was no change in total cell Ca2+, indicating an increased cycling of Ca2+ across the plasma membrane. Flux between S1 and the intermediate Ca2+ compartment (S2) was also increased and S2 increased significantly. All Cd2+ induced changes in Ca2+ homeostasis were obliterated by concurrent treatment with 0.1 microM calphostin C (CC), a potent protein kinase C (PKC) inhibitor. This data suggests that Cd2+ perturbs Ca2+ metabolism via a PKC dependent process.

The effect of cadmium on cytosolic free calcium, protein kinase C, and collagen synthesis in rat osteosarcoma (ROS 17/2.8) cells

Cadmium affects normal bone growth but the mechanisms of Cd2+ toxicity are not fully understood. Calcium is an integral component of bone growth and a second messenger necessary for the actions of calciotropic hormones. Ca2+ activates protein kinase C (PKC), and PKC is a mediator of [Ca2+]1 and mediator of collagen synthesis in osteoblastic cells. Therefore, PKC is a possible loci of Cd2+ effects on Ca2+ metabolism and Ca(2+)-regulated processes. This work was conducted to determine the effect of Cd2+ on cytosolic free Ca2+ ([Ca2+]i) levels, characterize the activation and/or inhibition of PKC by Cd2+ and Ca2+, and measure the effect of Cd2+ on collagen synthesis in ROS 17/2.8 cells. Cells were treated for 120 min with Cd2+ (0 to 30 microM) and [Ca2+]i was measured. Basal [Ca2+]i was 132 nM and the maximal increase to 268 nM occurred in the presence of 5 microM Cd2+. Treatment with 1 or 5 microM Cd2+ caused an increase in [Ca2+]i at 40 min with return to basal levels at 120 min of treatment. Pretreatment (24 hr) with 0.1 microM calphostin C (CC), a PKC inhibitor, produced no change in [Ca2+]i and prevented any rise in [Ca2+]i in response to Cd2+. Free Cd2+ activates PKC with an activation constant of 7.5 X 10(-11) M, while Ca2+ activates PKC with an activation constant of 3.6 X 10(-7) M. Cd2+ also caused a dose-dependent decrease in collagen synthesis, a PKC-mediated process. These data suggest that Cd2+ affects Ca2+ metabolism and Ca(2+)-mediated processes via unwarranted PKC activation as demonstrated by Cd2+ perturbation of collagen synthesis.

Kinetics of Cu2+ inhibition of Na+/K(+)-ATPase

The interaction of Cu2+ with enzymatic activity of rabbit kidney Na+/K(+)-ATPase was studied in media with buffered, defined free Cu2+ levels. The IC50-values are 0.1 mumol/l for Na+/K(+)-ATPase and 1 mumol/l for K(+)-pNPPase. Dithiothreitol (DTT) reverses the inhibitory effect of Cu2+ in vitro. Cu2+ exerts non-competitive effects on the enzyme with respect to Na+, K+, ATP or pNPP, but has a mixed-type inhibitory effect with respect to Mg2+. It is concluded that the appreciation of the inhibitory effect of Cu2+ on this enzyme requires carefully composed assay media that include a buffer for Cu2+, and that the IC50-values calculated according to this model indicate that Cu2+ may be more toxic than previously anticipated.

Sublethal effects of cadmium on arm regeneration in the burrowing brittlestar, Microphiopholis gracillima

: To assess the sublethal effects of sediment-bound cadmium on arm regeneration of Microphiopholis gracillima, a burrowing brittlestar, experiments were conducted to quantify the tissue and morphology of regenerating arms, the uptake of cadmium in various tissues and the effect M. gracillima had on the cadmium pools in muddy sediments. Regenerated arms of cadmium-exposed M. gracillima are thinner, with proportionally less soft and skeletal tissue and a greater number of developing ossicles than animals held in sediment without cadmium. Microphiopholis gracillima decreased pore water cadmium concentrations in muddy sediments. Uptake of cadmium in tissues dominated by the calcium carbonate endoskeleton was proportional to the measured sediment cadmium concentration, while concentrations in whole regenerating arms were more closely related to the pore water concentration. Both calcium and cadmium are accumulated in the early stages of arm regeneration with an apparent interaction which interferes with ossicle construction. Sediment-bound cadmium has a negative effect on the organism's recovery from sublethal tissue loss and, ultimately, its long-term survival.

Inhibitory effects of cadmium ion on extracellular Ca(2+)-independent contraction of rat aorta

In vitro effects of cadmium ion on vasoconstriction, particularly on vasoconstriction independent of extracellular Ca2+, were investigated using isolated rat aorta. Aorta incubation with CdCl2 (0.01, 0.1 mM) significantly attenuated contractile responses to KCl and phenylephrine in the medium containing normal Ca2+ (2.5 mM). The contractile response to phenylephrine in the presence of calcium channel antagonists, nifedipine (1 microM) or verapamil (1 microM), was markedly inhibited by CdCl2 (0.1 mM). In the medium without Ca2+, phenylephrine (10 microM) induced a phasic contraction, which was markedly inhibited by CdCl2 (0.1 mM). In the medium without Ca2+, phorbol 12-myristate 13-acetate (1 microM) and okadaic acid (10 microM) caused tonic contractile responses, which were strongly attenuated by CdCl2 (0.1 mM) pretreatment. Contractile response to sodium fluoride (5 approximately 15 mM) in the absence of extracellular Ca2+ was strongly attenuated by CdCl2 (0.1 mM) pretreatment. These results suggest that cadmium ion depresses an extracellular Ca(2+)-independent component of agonist-induced vasoconstriction by hindering an intracellular contractile mechanism(s).

Effects of heavy metals on the Ca(2+)-ATPase activity present in gill cell plasma-membrane of mussels (Mytilus galloprovincialis Lam.)

1. Heavy metals (Hg2+, Cu2+, Cd2+, Zn2+, Pb2+) at micromolar concentrations strongly inhibit the Ca(2+)-ATPase activity present in the plasma-membrane obtained from the gill cells of Mytilus galloprovincialis Lam. Heavy metals act through inhibition of the formation of the phosphorylated intermediate. 2. All the heavy metals tested inhibit the Ca(2+)-ATPase activity, the effect following the order: Hg2+ > Pb2+ > Cu2+ > Cd2+ > Zn2+; the simultaneous addition of different heavy metals causes a summatory inhibition of the enzyme activity; addition to the reaction mixture of GSH at a final concentration of 0.5 mM, reverses inhibitory effects of heavy metals. 3. The inhibitory effects of Cu2+ on Ca(2+)-ATPase are highly enhanced by addition of ascorbate to the reaction mixture. In the presence of ascorbate (100 microM), copper strongly stimulates the lipid peroxidation damage of the gill plasma-membranes, a result that may explain the high copper cytotoxicity.

The effect of Ca2+, Cd2+ and Ni2+ on detergent-permeabilized vascular smooth muscle from the shark, Squalus acanthias

We examined the effect of Ca2+, Cd2+, or Ni2+ on vascular smooth muscle intracellular proteins involved in contraction, using rings of detergent-permeabilized aortae from the spiny dogfish, Squalus acanthias. Addition of Ca2+ stimulated contraction of the vascular smooth muscle, and permeabilization by treatment with Triton X-100 increased the sensitivity to Ca2+ nearly 5 log units, demonstrating that this protocol left contractile and regulatory proteins intact. Addition of 1 microM calmodulin did not increase the sensitivity of the rings to Ca2+, suggesting that this preparation is not leaky to this regulatory protein. Neither Cd2+ nor Ni2+ stimulated contraction of permeabilized rings demonstrating that the previously-described contractile action of these heavy metals is not mediated by direct stimulation of intracellular proteins, rather by interaction with sarcolemmal proteins.

Cadmium ion is a non-competitive inhibitor of red cell Ca(2+)-ATPase activity

In the presence as well as in the absence of calmodulin, Cd2+ inhibits the human erythrocyte plasma membrane Ca(2+)-ATPase activity non-competitively with Ki = 2 nM, whereas ATP-dependent Ca(2+)-transport across the red cell membrane was found to be inhibited competitively by Cd2+ (Verbost, P.M., Flik, G., Pang, P.K.T., Lock, R.A.C. and Wendelaar Bonga, S.E. (1989) J. Biol. Chem. 264, 5613-5615). In this study it will be argued that Cd2+ also inhibits Ca(2+)-transport non-competitively, and that the discrepancy with previous conclusions most probably relies on use of an incorrect computer program that calculates the free concentrations of Ca2+ and Cd2+ at the experimental conditions applied for measurement of Ca2+ uptake.

Cadmium-induced changes of antioxidant and metabolic status in red blood cells of rats: in vivo effects

Chronic exposure of adult rats to dietary intake of cadmium (15 mg CdCl2/day/kg for 30 days) leads to development of anemia and thrombocytosis. Anemia is characterized by significant reticulocytosis (13.1 +/- 1.0%), anysocytosis, poikilocytosis, iron deficiency and marked alterations of antioxidant and metabolic status of red blood cells. Activities of SOD, catalase, GPx and GR were significantly increased in red blood cells of cadmium-treated rats. In treated animals cadmium induced an increase of red cell reduced and oxidized glutathione with no changes of GSSG/GSH ratio. However, significant reduction of lipid peroxidation was found. Plasma levels of tocopherol and ascorbate, as well as activity of glutathione-S-transferase, were all significantly increased in cadmium-treated rats. The energy metabolism of red blood cells was deeply altered in cadmium-treated rats. The levels of ATP, ADP, AMP and TAN were significantly increased while ATP/ADP ratio and adenylate energy charge (AEC) were significantly reduced. The level of 2,3-BPG was somewhat lower, but 2,3-BPG/Hb ratio was considerably higher, in red blood cells of cadmium-treated rats.