Possible involvement of the adenine nucleotide translocase in the activation of the permeability transition pore induced by cadmium

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Modulators of mitochondrial ATP-sensitive potassium channel affect cytotoxicity of heavy metals: Action on isolated rat liver mitochondria and AS-30D ascites hepatoma cells

Heavy metals are ubiquitous environmental pollutants that are extremely dangerous for public health, but the molecular mechanisms of their cytotoxic action are still not fully understood. In the present work, the possible contribution of the mitochondrial ATP-sensitive potassium channel (mK(ATP)), which is usually considered protective for the cell, to hepatotoxicity caused by heavy metals was investigated using polarography and swelling techniques as well as flow cytometry. Using isolated liver mitochondria from adult male Wistar rats and various potassium media containing or not containing penetrating anions (KNO₃, KSCN, KAcet, KCl), we studied the effect of mK(ATP) modulators, namely its blockers (5-hydroxydecanoate, glibenclamide, ATP, ADP) and activators (diazoxide, malonate), on respiration and/or membrane permeability in the presence of hepatotoxins such as Cd²⁺, Hg²⁺, and Cu²⁺. It has been shown for the first time that, contrary to Hg²⁺ and depending on media used, the mK(ATP) modulators affect Cd²⁺- and/or Cu²⁺-induced alterations in mitochondrial swelling and respiration rates, although differently, nevertheless, in the ways compatible with mK(ATP) participation in both these cases. On rat AS-30D ascites hepatoma cells, it was found that, unlike Cd²⁺, an increase in the production of reactive oxygen species was observed with the simultaneous use of Cu²⁺ and diazoxide; in addition, there was no protective effect of diazoxide against cell death, which also occurred in the presence of Cu²⁺. In conclusion, the relationships (functional, structural and/or regulatory) between mK(ATP), components of the mitochondrial electron transport chain (CI, CII-CIII and/or ATP synthase, CV) and mitochondrial permeability transition pores were discussed, as well as the role of these molecular structures in the mechanisms of the cytotoxic action of heavy metals.

Effects of Tl+ on the inner membrane thiol groups, respiration, and swelling in succinate-energized rat liver mitochondria were modified by thiol reagents

The effects of both Tl⁺ and thiol reagents were studied on the content of the inner membrane free SH-groups, detected with Ellman reagent, and the inner membrane potential as well as swelling and respiration of succinate-energized rat liver mitochondria in medium containing TlNO₃ and KNO₃. These effects resulted in a rise in swelling and a decrease in the content, the potential, and mitochondrial respiration in 3 and 2,4-dinitrophenol-uncoupled states. A maximal effect was seen when phenylarsine oxide reacting with thiol groups recessed into the hydrophobic regions of the membrane. Compared with phenylarsine oxide, the effective concentrations of other reagents were approximately one order of magnitude higher in experiments with mersalyl and 4,4'-diisothiocyanostilbene-2,2'-disulfonate, and two orders of magnitude higher in experiments with tert-butyl hydroperoxide and diamide. The above effects of Tl⁺ and the thiol reagents became even more pronounced with calcium overload of mitochondria. However, the effects were suppressed by inhibitors of the mitochondrial permeability transition pore (cyclosporine A, ADP, and n-ethylmaleimide). These findings suggest that opening of the pore induced by Tl⁺ in the inner membrane can be dependent on the conformation state of the adenine nucleotide translocase, which depends on the activity of its thiol groups.

Interaction of Agaric Acid with the Adenine Nucleotide Translocase Induces Mitochondrial Oxidative Stress

Mitochondrial permeability transition is characterized by the opening of a transmembranal pore that switches membrane permeability from specific to nonspecific. This structure allows the free traffic of ions, metabolites, and water across the mitochondrial inner membrane. The opening of the permeability transition pore is triggered by oxidative stress along with calcium overload. In this work, we explored if oxidative stress is a consequence, rather than an effector of the pore opening, by evaluating the interaction of agaric acid with the adenine nucleotide translocase, a structural component of the permeability transition pore. We found that agaric acid induces transition pore opening, increases the generation of oxygen-derived reactive species, augments the oxidation of unsaturated fatty acids in the membrane, and promotes the detachment of cytochrome c from the inner membrane. The effect of agaric acid was inhibited by the antioxidant tamoxifen in association with decreased binding of the thiol reagent eosin-3 maleimide to the adenine nucleotide translocase. We conclude that agaric acid promotes the opening of the pore, increasing ROS production that exerts oxidative modification of critical thiols in the adenine nucleotide translocase.

Mitigating effect of paxilline against injury produced by Cd2+ in rat pheochromocytoma PC12 and ascites hepatoma AS-30D cells

On two rat cell lines, pheochromocytoma PC12 and ascites hepatoma AS-30D, and on rat liver mitochondria we studied action of paxilline (lipophilic mycotoxin from fungus Penicillium paxilli which is blocker of large-conductance potassium channels) against harmful effects of Cd(II) - one of the most dangerous toxic metals and environmental pollutants. We investigated an influence of paxilline on cell viability and mitochondrial function in the presence and in the absence of Cd²⁺. As found, paxilline protected partially from the Cd²⁺-induced cytotoxicity, namely taken in concentration of 1 μM it decreased the Cd²⁺-induced cell necrosis in average by 10-14 or 13-23% for AS-30D and PC12 cells, respectively. Nevertheless, paxilline did not affect the Cd²⁺-induced apoptosis of AS-30D cells. The alleviating concentration of paxilline reduced an intracellular production of reactive oxygen species (ROS) in PC12 cells intoxicated by Cd²⁺ and enhanced the ROS production in control AS-30D cells; however, it weakly affected mitochondrial membrane potential of the cells in the absence and in the presence of Cd²⁺. The ameliorative concentration of paxilline decreased the maximal respiration rates of control cells of both types after short-term (3-5 h) treatment with it while the rates reached their control levels after long-term (24-48 h) incubation with the drug. Paxilline was not protective against the Cd²⁺-induced membrane permeability and respiration rate changes in isolated rat liver mitochondria. As result, the mitochondrial electron transport chain was concluded to contribute in the mitigating effect of paxilline against the Cd²⁺-produced cell injury.

Cell organelles as targets of mammalian cadmium toxicity

Ever increasing environmental presence of cadmium as a consequence of industrial activities is considered a health hazard and is closely linked to deteriorating global health status. General animal and human cadmium exposure ranges from ingestion of foodstuffs sourced from heavily polluted hotspots and cigarette smoke to widespread contamination of air and water, including cadmium-containing microplastics found in household water. Cadmium is promiscuous in its effects and exerts numerous cellular perturbations based on direct interactions with macromolecules and its capacity to mimic or displace essential physiological ions, such as iron and zinc. Cell organelles use lipid membranes to form complex tightly-regulated, compartmentalized networks with specialized functions, which are fundamental to life. Interorganellar communication is crucial for orchestrating correct cell behavior, such as adaptive stress responses, and can be mediated by the release of signaling molecules, exchange of organelle contents, mechanical force generated through organelle shape changes or direct membrane contact sites. In this review, cadmium effects on organellar structure and function will be critically discussed with particular consideration to disruption of organelle physiology in vertebrates.

On the oxidative damage by cadmium to kidney mitochondrial functions

In the kidney, the accumulation of heavy metals such as Cd2+ produces mitochondrial dysfunctions, i.e., uncoupling of the oxidative phosphorylation, inhibition of the electron transport through the respiratory chain, and collapse of the transmembrane electrical gradient. This derangement may be due to the fact that Cd2+ induces the transition of membrane permeability from selective to nonselective via the opening of a transmembrane pore. In fact, Cd2+ produces this injury through the stimulation of oxygen-derived radical generation, inducing oxidative stress. Several molecules have been used to avoid or even reverse Cd2+-induced mitochondrial injury, for instance, cyclosporin A, resveratrol, dithiocarbamates, and even EDTA. The aim of this study was to explore the possibility that the antioxidant tamoxifen could protect mitochondria from the deleterious effects of Cd2+. Our results indicate that the addition of 1 μmol/L Cd2+ to mitochondria collapsed the transmembrane electrical gradient, induced the release of cytochrome c, and increased both the generation of H2O2 and the oxidative damage to mitochondrial DNA (among other measured parameters). Of interest, these mitochondrial dysfunctions were ameliorated after the addition of tamoxifen.

Respiratory complex II in mitochondrial dysfunction-mediated cytotoxicity: Insight from cadmium

In the present work we studied action of several inhibitors of respiratory complex II (CII) of mitochondrial electron transport chain, namely malonate and thenoyltrifluoroacetone (TTFA) on Cd²⁺-induced toxicity and cell mortality, using two rat cell lines, pheochromocytoma PC12 and ascites hepatoma AS-30D and isolated rat liver mitochondria (RLM). It was shown that malonate, an endogenous competitive inhibitor of dicarboxylate-binding site of CII, restored in part RLM respiratory function disturbed by Cd²⁺. In particular, malonate increased both phosphorylating and maximally uncoupled respiration rates in KCl medium in the presence of CI substrates as well as palliated changes in basal and resting state respiration rates produced by the heavy metal on the mitochondria energized by CI or CII substrates. Notably, malonate enhanced Cd²⁺-induced swelling of the mitochondria energized by CI substrates in KCl and, in a much lesser extent and at higher [Cd²⁺], in sucrose media but did not influence on the Cd²⁺ effects in NaCl medium. Besides, malonate did not affect swelling in sucrose media of RLM energized by CIV substrates under using of Cd²⁺ or Ca²⁺ whereas it strongly increased the mitochondrial swelling produced by selenite. In addition, malonate produced some protection against Cd²⁺-promoted necrotic death of AS-30D and PC12 cells and reduced intracellular reactive oxygen species (ROS) formation evoked by Cd²⁺ in PC12 cells. Importantly, TTFA, an irreversible competitive inhibitor of Q-binding site of CII, per se induced apoptosis of AS-30D cells which was inhibited by co-treatment with Cd²⁺ as well as decreased the Cd²⁺-enhanced intracellular ROS formation. In turn, decylubiquinone (dUb) at low μM concentrations did not protect AS-30D cells against the Cd²⁺-induced necrosis and enhanced the Cd²⁺-induced apoptosis of the cells. High μM concentrations of dUb were highly toxic for the cells. As consequence, the findings give new evidence indicative of critical involvement of CII in mechanism(s) of Cd²⁺-produced cytotoxicity and support the notion on CII as a perspective pharmacological target in mitochondria dysfunction-mediated conditions and diseases.

To involvement the conformation of the adenine nucleotide translocase in opening the Tl(+)-induced permeability transition pore in Ca(2+)-loaded rat liver mitochondria

The conformation of adenine nucleotide translocase (ANT) has a profound impact in opening the mitochondrial permeability transition pore (MPTP) in the inner membrane. Fixing the ANT in 'c' conformation by phenylarsine oxide (PAO), tert-butylhydroperoxide (tBHP), and carboxyatractyloside as well as the interaction of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) with mitochondrial thiols markedly attenuated the ability of ADP to inhibit the MPTP opening. We earlier found (Korotkov and Saris, 2011) that calcium load of rat liver mitochondria in medium containing TlNO3 and KNO3 stimulated the Tl(+)-induced MPTP opening in the inner mitochondrial membrane. The MPTP opening as well as followed increase in swelling, a drop in membrane potential (ΔΨmito), and a decrease in state 3, state 4, and 2,4-dinitrophenol-uncoupled respiration were visibly enhanced in the presence of PAO, tBHP, DIDS, and carboxyatractyloside. However, these effects were markedly inhibited by ADP and membrane-penetrant hydrophobic thiol reagent, N-ethylmaleimide (NEM) which fix the ANT in 'm' conformation. Cyclosporine A additionally potentiated these effects of ADP and NEM. Our data suggest that conformational changes of the ANT may be directly involved in the opening of the Tl(+)-induced MPTP in the inner membrane of Ca(2+)-loaded rat liver mitochondria. Using the Tl(+)-induced MPTP model is discussed in terms finding new transition pore inhibitors and inducers among different chemical and natural compounds.

Influence of Tl(+) on mitochondrial permeability transition pore in Ca(2+)-loaded rat liver mitochondria

The Tl(+)-induced opening of the MPTP in Ca(2+)-loaded rat liver mitochondria energized by respiration on the substrates succinate or glutamate plus malate was recorded as increased swelling and dissipation of mitochondrial membrane potential as well as decreased state 4, or state 3, or 2,4-dinitrophenol-stimulated respiration. These effects of Tl(+) increased in nitrate media containing monovalent cations in the order of Li(+) < NH (4) (+) ≤ Na(+) < K(+). They were potentiated by inorganic phosphate and diminished by the MPTP inhibitors (ADP, CsA, Mg(2+), Li(+), rotenone, EGTA, and ruthenium red) both individually and more potently in their combinations. Maximal swelling of both non-energized and energized Ca(2+)-loaded mitochondria in rotenone-free media is an indication of Ca(2+) uptake driven by respiration on mitochondrial endogenous substrates. It is suggested that Tl(+) (distinct from Cd(2+), Hg(2+), and other heavy metals and regardless of the used respiratory substrates) can stimulate opening of the MPTP only in the presence of Ca(2+). We discuss the possible participation of Ca(2+)-binding sites, located near the respiratory complex I and the adenine nucleotide translocase, in inducing opening of the MPTP.

In vitro modulation of heavy metal-induced rat liver mitochondria dysfunction: a comparison of copper and mercury with cadmium

Cadmium (Cd), mercury (Hg) and copper (Cu) are very toxic environmental pollutants that exert their cytotoxic effects as cations by targeting mitochondria. To further underscore molecular mechanism(s) underlying the heavy metal-induced mitochondrial dysfunction we continued to compare the action of Cd, Hg and Cu using a simple and convenient in vitro model, namely isolated rat liver mitochondria incubated in assay media of different ionic contents and energized by respiratory substrates, glutamate plus malate for complex I, succinate plus rotenone for complex II, and ascorbate plus tetramethylphenylenediamine for complex IV. With the help of various selective electrodes, fluorescent probes, isotope and spectrophotofluorometric techniques, significant differences were found in the modulating action of various substances affecting the activity of these respiratory chain complexes and mitochondrial Ca²+ uniporter or permeability transition pore effectors on the mitochondrial function disturbed by the heavy metals, including clear-cut substrate specificity of many effects of these cations. Sequence of events manifested in the mitochondrial dysfunction produced by the metals under test was elucidated.

Reciprocal enhancement of uptake and toxicity of cadmium and calcium in rainbow trout (Oncorhynchus mykiss) liver mitochondria

The interactive effects of cadmium (Cd) and calcium (Ca) on energy metabolism in rainbow trout liver mitochondria were studied to test the prediction that Ca would protect against Cd-induced mitochondrial liability. Isolated rainbow trout liver mitochondria were energized with malate and glutamate and exposed to increasing concentrations (5-100 microM) of Cd and Ca singly and in combination at 15 degrees C. Accumulation of Cd and Ca in the mitochondria and mitochondrial respiration (oxygen consumption) rates were measured. Additionally, un-energized mitochondria were incubated with low doses (1 microM) of Cd and Ca singly and in combination, with time-course measurements of cation accumulation/binding and oxygen consumption rates. In energized actively phosphorylating mitochondria, the uptake rates of both Cd and Ca were dose-dependent and enhanced when administered concurrently. Upon low-dose incubation, Cd accumulation was rapid and peaked in 5 min, while no appreciable uptake of Ca occurred. Functionally, the resting (state 4, ADP-limited) respiration rate was not affected in the dose-response exposure, but it decreased remarkably on low-dose incubation. Adenosine diphosphate (ADP)-stimulated respiration (state 3) rate was impaired dose-dependently with maximal inhibitions (at the highest dose, 100 microM) of 32, 64 and 73% for Ca, Cd, and combined exposures, respectively. The combined effects of Ca and Cd suggested synergistic (more than additive) action and partial additivity of effects at low and higher doses of the two cations, respectively. Moreover, on a molar basis, Cd was twice as toxic as Ca to rainbow trout liver mitochondria and when combined, approximately 90% of the effects were attributable to Cd. The coupling efficiency, as measured by respiratory control ratio (RCR) and phosphorylation efficiency, measured as ADP/O ratio, both decreased as the exposure dosage and duration increased. In addition, Cd and Ca exposure decreased mitochondrial proton leak (state 4+ respiration) rates on prolonged exposure possibly by inhibiting processes that generate mitochondrial membrane potential, the force that drives proton leak. Overall these data suggest that the widely accepted theme that Ca and Cd are competitive antagonists does not hold for mitochondrial effects and that Cd and Ca cooperate to impair oxidative phosphorylation in rainbow trout liver mitochondria.

Cadmium and mitochondria

The heavy metal cadmium (Cd) a pollutant associated with several modern industrial processes, is absorbed in significant quantities from cigarette smoke, water, food and air contaminations. It is known to have numerous undesirable effects on health in both experimental animals and humans, targeting kidney, liver and vascular system. The molecular mechanism accounting for most of the biological effects of Cd are not well-understood and the toxicity targets are largely unidentified. The present review focuses on important recent advances about the effects of cadmium on mitochondria of mammalian cells. Mitochondria are the proverbial powerhouses of the cell, running the fundamental biochemical processes that produce energy from nutrients using oxygen. They are among the key intracellular targets for different stressors including Cd. This review provides new additional informations on the cellular and molecular aspects of the interaction between Cd and cells, emphasizing alterations of mitochondria as important events in Cd cytotoxicity, thus representing an important basis for understanding the mechanisms of cadmium effect on the cells.

Potential marker enzymes and metal-metal interactions in Helisoma duryi and Lymnaea natalensis exposed to cadmium

In this study, we investigate the effects of exposure to cadmium and copper on Lymnaea natalensis and Helisoma duryi. The snails were dosed with Cd2+ or Cu2+ for a period of 96h. Snails dosed with Cd accumulated the metal significantly (P<0.05) in tissues but not in shells. Mortality was observed at approximately 1mg Cd/l of culture water. In tissues and shells of snails dosed with Cd or Cu, synergistic and antagonistic metal-metal interactions involving Cd, Cu, Zn, and Pb were observed and these may affect metal toxicity. Glutamate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase were assayed in whole snail tissue sub-cellular fractions of Cd-dosed snails. Generally, enzyme activity significantly increased at lower concentrations of Cd but decreased at high concentrations of the metal. However, mitochondrial alanine aminotransferase activity progressively declined with increasing Cd concentration. The changes in some of the enzymes' activities suggest biomarker potential.

On the opening of an insensitive cyclosporin A non-specific pore by phenylarsine plus mersalyl

The purpose of this work was addressed to provide new information on the effect of thiol reagents on mitochondrial non-specific pore opening, and its response to cyclosporin A (CSA). To meet this proposal phenylarsine oxide (PHA) and mersalyl were employed as tools to induce permeability transition and CSA to inhibit it. PHA-induced mitochondrial dysfunction, characterized by Ca2+ efflux, swelling, and membrane de-energization, was inhibited by N-ethylmaleimide and CSA. Conversely, mersalyl failed to inhibit the inducing effect of phenylarsine oxide, it rather strengthened it. In addition, the effect of mersalyl was associated with cross-linking of membrane proteins. The content of membrane thiol groups accessible to react with PHA, mersalyl, and PHA plus mersalyl was determined. In all situations, permeability transition was accompanied by a significant decrease in the whole free membrane thiol content. Interestingly, it is also shown that mersalyl hinders the protective effect of cyclosporin A on PHA-induced matrix Ca2+ efflux.

On the role of the respiratory complex I on membrane permeability transition

In this work we studied permeability transition by incubating mitochondria in the presence of 50 muM Ca(2+) and malate/glutamate as substrates. This condition, besides inducing the release of pyridine nucleotides, promotes the generation of reactive oxygen-derived species by the complex I of the respiratory chain. The latter leads to the opening of the mitochondrial permeability transition pore. Ca(2+) release, mitochondrial swelling and collapse of the transmembrane electric potential, were analyzed to assess this process. We propose that the mechanism for pore opening, in addition to the oxidative stress, involves the uncoupling effect of fatty acids providing activation of phospholipase A2, lipid peroxidation, and the oxidation of membrane thiols. This proposal emerges from the data indicating the protective effect of bovine serum albumin and N-ethylmaleimide. The key role of reactive oxygen species was implied based on the fact that the scavenger alpha-phenyl-tert-butyl nitrone inhibited pore opening.

Cd2+ versus Ca2+-produced mitochondrial membrane permeabilization: a proposed direct participation of respiratory complexes I and III

A comparison of Cd2+ and Ca2+ effects on in vitro rat liver mitochondria function and a further study of their interaction were conducted. Similarity and distinction in action of rotenone, oligomycin, N-ethylmaleimide, dithiothreitol, catalase, dibucaine, ruthenium red, cyclosporin A (CsA), and ADP on Cd2+ and/or Ca2+-induced mitochondrial dysfunction were revealed. We found that rotenone exerted a strong protective action both against Ca2+ and Cd2+-produced mitochondrial membrane permeabilization (MMP). In contrast to Ca2+, catalase and dibucaine did not influence on main Cd2+ effects. In NH4NO3 medium N-ethylmaleimide (NEM) at low concentrations increased markedly Cd2+-produced swelling of non-energized mitochondria, whereas it exhibited a partial reversal effect following energization. In sucrose medium low [NEM] did not change Cd2+-produced mitochondrial swelling. High [NEM] promoted synergistic increase of the Cd2+-produced swelling in NH4NO3 medium; all above effects were reversed (and prevented) by dithiothreitol, DTT. We shown also that when exogenous Ca2+ and Pi were simultaneously present in NH4NO3 medium, DTT reversed only partially Cd2+-produced swelling of succinate plus rotenone-energized mitochondria, while DTT recovery action was complete when either Ca2+ or Pi were separately administered to the Cd2+-treated mitochondria. Besides, DTT added following a low Cd2+ pulse in KCl medium containing exogenous Ca2+ induced a substantial enhancing of sustained Cd2+ stimulation of mitochondrial basal respiration and the stimulation was CsA-sensitive, while the activation promoted by low [Cd2+] alone was totally eliminated by DTT supplement. We observed the similar respiratory activation earlier when high concentrations of Cd2+ in the absence of added Ca2+ were used but it was completely CsA-insensitive. A possible involvement of respiratory chain components, namely complex I (P-site) and complex III (S-site) in Cd2+ and/or Ca2+-produced MMP was discussed.

A proposed sequence of events for cadmium-induced mitochondrial impairment

Cadmium is a very important environmental toxicant, the cytotoxicity mechanism of which is likely to involve mitochondria as a target. In the present study we addressed the cause/effect relationship between the multiple cadmium-induced responses involving the mitochondrial energetic and oxidative status. Assays were performed with succinate-energized rat liver mitochondria incubated with 5 microM CdCl(2) for 0-25 min, in the absence or presence, respectively, of N-ethylmaleimide (NEM), butylhydroxytoluene (BHT), ruthenium red (RR), and cyclosporine A+ADP. A sequence of events accounting for cadmium-induced mitochondrial impairment is proposed, beginning with an apparent interaction of Cd(2+) with specific protein thiols in the mitochondrial membrane, which stimulates the cation's uptake via the Ca(2+) uniporter, and is followed by the onset of mitochondrial permeability transition (MPT); both effects dissipate the transmembrane electrical potential (Deltapsi), causing uncoupling, followed by an early depression of mitochondrial ATP levels. The respiratory chain subsequently undergoes inhibition, generating reactive oxygen species which together with iron mobilized by the cation, cause late, gradual mitochondrial membrane lipid peroxidation.

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.

Molecular chaperones in the kidney

The normal milieu of the kidney includes hypoxia, large osmotic fluxes, and an enormous amount of fluid/solute reabsorption. Renal adaptation to these conditions requires a host of molecular chaperones that stabilize protein conformation, target nascent proteins to their final intracellular destination, and prevent protein aggregation. Under physiologic or pharmacologic stress, inducible molecular chaperones provide additional mechanisms for repairing or degrading non-native proteins and for inhibiting stress-induced apoptosis. In contrast to intracellular chaperones, chaperones present on the cell surface regulate the immune system and have cytokine-like effects. A diverse range of chaperones and chaperone functions provide the renal cell with an armamentarium of responses to improve the chances of survival.