Sensitivity of the synaptic membrane Na+/Ca2+ exchanger and the expressed NCX1 isoform to reactive oxygen species

Association of Total Calcium With Serum Uric Acid Levels Among United States Adolescents Aged 12-19 Years: A Cross-Sectional Study

Aims

Evidence of a link between total calcium (CA) and serum uric acid (SUA) is absent in adolescents. Thus, this study aimed to determine the relationship between total CA levels and SUA levels in United States adolescents.

Methods

A cross-sectional study analyzed a sample composed of 8,309 United States adolescents aged 12–19 years from the National Health and Nutrition Examination Survey database (1999–2006 survey cycle). Multivariable linear regression analyses and multivariable logistic regression analyses were used to assess the correlation of total CA with SUA levels and hyperuricemia. Furthermore, the dose-response relationship of total CA and SUA levels was analyzed using smooth curve fitting (penalized spline method).

Results

According to multivariable linear regression analysis, every 1 mg/dL increase in total CA level is associated with a 0.33 mg/dL (β = 0.33, 95% CI: 0.27–0.40, p < 0.001) increase in SUA. Multivariable logistic regression analyses showed that every 0.1 mg/dL increase in total CA level is linked with an 8% increased risk of hyperuricemia (OR = 1.08, 95% CI: 1.06–1.10, p < 0.001). The analyses of smooth curve fitting revealed that total CA levels were linearly correlated with SUA levels (P_{non–linearity} = 0.152). The results were highly stable in all subgroups. The interaction analysis results presented that race/ethnicity had an interactive role in associating total CA with SUA levels.

Conclusions

In United States adolescents, total CA levels were linearly and positively correlated with SUA levels.

Redox regulation of store-operated Ca2+ entry

SIGNIFICANCE

Store-operated Ca2+ entry (SOCE) is a ubiquitous Ca2+ signaling mechanism triggered by Ca2+ depletion of the endoplasmic reticulum (ER) and by a variety of cellular stresses. Reactive oxygen species (ROS) are often concomitantly produced in response to these stresses, however, the relationship between redox signaling and SOCE is not completely understood. Various cardiovascular, neurological, and immune diseases are associated with alterations in both Ca2+ signaling and ROS production, and thus understanding this relationship has therapeutic implications.

RECENT ADVANCES

Several reactive cysteine modifications in stromal interaction molecule (STIM) and Orai proteins comprising the core SOCE machinery were recently shown to modulate SOCE in a redox-dependent manner. Moreover, STIM1 and Orai1 expression levels may reciprocally regulate and be affected by responses to oxidative stress. ER proteins involved in oxidative protein folding have gained increased recognition as important sources of ROS, and the recent discovery of their accumulation in contact sites between the ER and mitochondria provides a further link between ROS production and intracellular Ca2+ handling.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Future research should aim to establish the complete set of SOCE controlling molecules, to determine their redox-sensitive residues, and to understand how intracellular Ca2+ stores dynamically respond to different types of stress. Mapping the precise nature and functional consequence of key redox-sensitive components of the pre- and post-translational control of SOCE machinery and of proteins regulating ER calcium content will be pivotal in advancing our understanding of the complex cross-talk between redox and Ca2+ signaling.

Altered vascular smooth muscle function in the ApoE knockout mouse during the progression of atherosclerosis

Objectives

Relaxation of vascular smooth muscle (VSM) requires re-uptake of cytosolic Ca²⁺ into the sarcoplasmic reticulum (SR) via the Sarco/Endoplasmic Reticulum Ca²⁺ ATPase (SERCA), or extrusion via the Plasma Membrane Ca²⁺ ATPase (PMCA) or sodium Ca²⁺ exchanger (NCX). Peroxynitrite, a reactive species formed in vascular inflammatory diseases, upregulates SERCA activity to induce relaxation but, chronically, can contribute to atherogenesis and altered vascular function by escalating endoplasmic reticulum stress. Our objectives were to determine if peroxynitrite-induced relaxation and Ca²⁺ handling processes within vascular smooth muscle cells were altered as atherosclerosis develops.

Methods

Aortae from control and ApoE^−/− mice were studied histologically, functionally and for protein expression levels of SERCA and PMCA. Ca²⁺ responses were assessed in dissociated aortic smooth muscle cells in the presence and absence of extracellular Ca²⁺.

Results

Relaxation to peroxynitrite was concentration-dependent and endothelium-independent. The abilities of the SERCA blocker thapsigargin and the PMCA inhibitor carboxyeosin to block this relaxation were altered during fat feeding and plaque progression. SERCA levels were progressively reduced, while PMCA expression was upregulated. In ApoE^−/− VSM cells, increases in cytosolic Ca²⁺ [Ca²⁺]_c in response to SERCA blockade were reduced, while SERCA-independent Ca²⁺ clearance was faster compared to control.

Conclusion

As atherosclerosis develops in the ApoE^−/− mouse, expression and function of Ca²⁺ handling proteins are altered. Up-regulation of Ca²⁺ removal via PMCA may offer a potential compensatory mechanism to help normalise the dysfunctional relaxation observed during disease progression.

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Expression and function of SERCA and PMCA are temporally altered in ApoE^−/− VSM.

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TG-induced increases in [Ca²⁺]_c were reduced in ApoE^−/− aortic SM cells.

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Ca²⁺ extrusion is upregulated in isolated ApoE^−/− aortic SM cells.

Regulation of the Na+/Ca2+ exchanger by pyridine nucleotide redox potential in ventricular myocytes

The cardiac Na(+)/Ca(2+) exchanger (NCX) is the major Ca(2+) efflux pathway on the sarcolemma, counterbalancing Ca(2+) influx via L-type Ca(2+) current during excitation-contraction coupling. Altered NCX activity modulates the sarcoplastic reticulum Ca(2+) load and can contribute to abnormal Ca(2+) handling and arrhythmias. NADH/NAD(+) is the main redox couple controlling mitochondrial energy production, glycolysis, and other redox reactions. Here, we tested whether cytosolic NADH/NAD(+) redox potential regulates NCX activity in adult cardiomyocytes. NCX current (INCX), measured with whole cell patch clamp, was inhibited in response to cytosolic NADH loaded directly via pipette or increased by extracellular lactate perfusion, whereas an increase of mitochondrial NADH had no effect. Reactive oxygen species (ROS) accumulation was enhanced by increasing cytosolic NADH, and NADH-induced INCX inhibition was abolished by the H2O2 scavenger catalase. NADH-induced ROS accumulation was independent of mitochondrial respiration (rotenone-insensitive) but was inhibited by the flavoenzyme blocker diphenylene iodonium. NADPH oxidase was ruled out as the effector because INCX was insensitive to cytosolic NADPH, and NADH-induced ROS and INCX inhibition were not abrogated by the specific NADPH oxidase inhibitor gp91ds-tat. This study reveals a novel mechanism of NCX regulation by cytosolic NADH/NAD(+) redox potential through a ROS-generating NADH-driven flavoprotein oxidase. The mechanism is likely to play a key role in Ca(2+) homeostasis and the response to alterations in the cytosolic pyridine nucleotide redox state during ischemia-reperfusion or other cardiovascular diseases.

Serum calcium levels are associated with novel cardiometabolic risk factors in the population-based CoLaus study

BACKGROUND

Associations of serum calcium levels with the metabolic syndrome and other novel cardio-metabolic risk factors not classically included in the metabolic syndrome, such as those involved in oxidative stress, are largely unexplored. We analyzed the association of albumin-corrected serum calcium levels with conventional and non-conventional cardio-metabolic risk factors in a general adult population.

METHODOLOGY/PRINCIPAL FINDINGS

The CoLaus study is a population-based study including Caucasians from Lausanne, Switzerland. The metabolic syndrome was defined using the Adult Treatment Panel III criteria. Non-conventional cardio-metabolic risk factors considered included: fat mass, leptin, LDL particle size, apolipoprotein B, fasting insulin, adiponectin, ultrasensitive CRP, serum uric acid, homocysteine, and gamma-glutamyltransferase. We used adjusted standardized multivariable regression to compare the association of each cardio-metabolic risk factor with albumin-corrected serum calcium. We assessed associations of albumin-corrected serum calcium with the cumulative number of non-conventional cardio-metabolic risk factors. We analyzed 4,231 subjects aged 35 to 75 years. Corrected serum calcium increased with both the number of the metabolic syndrome components and the number of non-conventional cardio-metabolic risk factors, independently of the metabolic syndrome and BMI. Among conventional and non-conventional cardio-metabolic risk factors, the strongest positive associations were found for factors related to oxidative stress (uric acid, homocysteine and gamma-glutamyltransferase). Adiponectin had the strongest negative association with corrected serum calcium.

CONCLUSIONS/SIGNIFICANCE

Serum calcium was associated with the metabolic syndrome and with non-conventional cardio-metabolic risk factors independently of the metabolic syndrome. Associations with uric acid, homocysteine and gamma-glutamyltransferase were the strongest. These novel findings suggest that serum calcium levels may be associated with cardiovascular risk via oxidative stress.

Neurodegeneration in glaucoma: progression and calcium-dependent intracellular mechanisms

Glaucoma is an age-related optic neuropathy involving sensitivity to ocular pressure. The disease is now seen increasingly as one of the central nervous system, as powerful new approaches highlight an increasing number of similarities with other age-related neurodegenerations such as Alzheimer's and Parkinson's. While the etiologies of these diseases are diverse, they involve many important common elements including compartmentalized programs of degeneration targeting axons, dendrites and finally cell bodies. Most age-related degenerations display early functional deficits that precede actual loss of neuronal substrate. These are linked to several specific neurochemical cascades that can be linked back to dysregulation of Ca(2+)-dependent processes. We are now in the midst of identifying similar cascades in glaucoma. Here we review recent evidence on the pathological progression of neurodegeneration in glaucoma and some of the Ca(2+)-dependent mechanisms that could underlie these changes. These mechanisms present clear implications for efforts to develop interventions targeting neuronal loss directly and make glaucoma an attractive model for both interrogating and informing other neurodegenerative diseases.

Amiloride inhibits hydrogen peroxide-induced Ca2+ responses in human CNS pericytes

The aims of the present study were to investigate the mechanisms of Ca(2+) signaling caused by hydrogen peroxide in CNS pericytes. In cultured human brain microvascular pericytes, cytosolic Ca(2+) concentration was measured by means of fura-2 fluorescence. Reverse transcription and polymerase chain reaction was performed to examine the expression of mRNA. Knockdown of Na(+)/H(+) exchanger (NHE) was done by transfecting the cells with specific double-strand siRNAs for NHE. Externally applied hydrogen peroxide dose-dependently (100 microM-10 mM) increased cytosolic Ca(2+) in human CNS pericytes. Cytosolic Ca(2+) remained high after wash-out of hydrogen peroxide. However, the addition of dithiothreitol rapidly reversed cytosolic Ca(2+) to the resting level. The hydrogen peroxide-induced Ca(2+) increase was not inhibited by nicardipine, Gd(3+), La(3+), or omission of external Ca(2+). Neither thapsigargin nor carbonyl cyanide 4-trifluoromethoxyphenylhydrazone attenuated the hydrogen peroxide-induced Ca(2+) rise. Amiloride and its derivatives, benzamil and hexamethylene amiloride reversed the hydrogen peroxide-induced Ca(2+) increase. Human CNS pericytes expressed acid sensing ion channel (ASIC) 1a, Na(+)/Ca(2+) exchanger (NCX) 1, Na(+)/H(+) exchanger (NHE) 1, and NHE7. However, the removal of external Na(+), treatment with KB-R 7943 and mibefradil, or knockdown of NHE1 and NHE7 did not affect the hydrogen peroxide-induced Ca(2+) increase. Hydrogen peroxide releases Ca(2+) from intracellular Ca(2+) pool via an amiloride-sensitive protein, which is controlled by oxidation of thiol group in human CNS pericytes.

Crosstalk between calcium and redox signaling: from molecular mechanisms to health implications

Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

Gamma-secretase and metalloproteinase activity regulate the distribution of endoplasmic reticulum to hippocampal neuron dendritic spines

The neuronal endoplasmic reticulum (ER) contributes to many physiological and pathological processes in the brain. A subset of dendritic spines on hippocampal neurons contains ER that may contribute to synapse-specific intracellular signaling. Distribution of ER to spines is dynamic, but knowledge of the regulatory mechanisms is lacking. In live cell imaging experiments we now show that cultured hippocampal neurons rapidly lost ER from spines after phorbol ester treatment. ER loss was reduced by inhibiting gamma-secretase (DAPT at 2 microM) and metalloproteinase (TAPI-0 and GM6001 at 4 microM) activity. Inhibition of protein kinase C also diminished loss of ER by preventing exit of ER from spines. Furthermore, gamma-secretase and metalloproteinase inhibition, in the absence of phorbol ester, triggered a dramatic increase in spine ER content. Metalloproteinases and gamma-secretase cleave several transmembrane proteins. Many of these substrates are known to localize to adherens junctions, a structural specialization with which spine ER interacts. One interesting possibility is thus that ER content within spines may be regulated by proteolytic activity affecting adherens junctions. Our data demonstrate a hitherto unknown role for these two proteolytic activities in regulating dynamic aspects of cellular ultrastructure, which is potentially important for cellular calcium homeostasis and several intracellular signaling pathways.

Mitochondrial reactive oxygen species and Ca2+ signaling

Mitochondria are an important source of reactive oxygen species (ROS) formed as a side product of oxidative phosphorylation. The main sites of oxidant production are complex I and complex III, where electrons flowing from reduced substrates are occasionally transferred to oxygen to form superoxide anion and derived products. These highly reactive compounds have a well-known role in pathological states and in some cellular responses. However, although their link with Ca(2+) is well studied in cell death, it has been hardly investigated in normal cytosolic calcium concentration ([Ca(2+)](i)) signals. Several Ca(2+) transport systems are modulated by oxidation. Oxidation increases the activity of inositol 1,4,5-trisphosphate and ryanodine receptors, the main channels releasing Ca(2+) from intracellular stores in response to cellular stimulation. On the other hand, mitochondria are known to control [Ca(2+)](i) signals by Ca(2+) uptake and release during cytosolic calcium mobilization, specially in mitochondria situated close to Ca(2+) release channels. Mitochondrial inhibitors modify calcium signals in numerous cell types, including oscillations evoked by physiological stimulus. Although these inhibitors reduce mitochondrial Ca(2+) uptake, they also impair ROS production in several systems. In keeping with this effect, recent reports show that antioxidants or oxidant scavengers also inhibit physiological calcium signals. Furthermore, there is evidence that mitochondria generate ROS in response to cell stimulation, an effect suppressed by mitochondrial inhibitors that simultaneously block [Ca(2+)](i) signals. Together, the data reviewed here indicate that Ca(2+)-mobilizing stimulus generates mitochondrial ROS, which, in turn, facilitate [Ca(2+)](i) signals, a new aspect in the biology of mitochondria. Finally, the potential implications for biological modeling are discussed.

Association of hypoglutathionemia with reduced Na+/K+ ATPase activity in type 2 diabetes and microangiopathy

OBJECTIVE

Although recent studies link altered cellular redox state to protein dysfunction in various disease-states, such associations are least studied in clinical diabetes. Therefore, this study assessed the levels of reduced glutathione (GSH) and Na(+)/K(+) ATPase activities in type 2 diabetic patients with and without microangiopathy.

METHODS

The study group comprised of a total of 160 subjects, which included non-diabetic healthy controls (n = 40) and type 2 diabetic patients without (n = 60) and with microangiopathy (n = 60), defined as presence of retinopathy with or without nephropathy. Erythrocyte Na(+)/K(+) ATPase activity and GSH levels were estimated spectrophotometrically and fluorometry was used to determine the plasma thiobarbituric acid reactive substances (TBARS) and serum advanced glycation end products (AGEs).

RESULTS

GSH levels in diabetic subjects without (4.8+/- 0.15 mumol/g Hb) and with microangiopathy (5.2+/- 0.14 micromol/g Hb) were significantly lower (p < 0.001) compared to control subjects (6.3 +/- 0.14 mumol/g Hb). Erythrocyte Na(+)/K(+) ATPase activity was significantly reduced (p < 0.001) in diabetes subjects with (272 +/- 7 nmol Pi/mg protein/h) and without microangiopathy (304 +/- 8) compared to control (374 +/- 6) subjects. TBARS were significantly higher (p < 0.001) in diabetes subjects with (10.65 +/- 0.81 nM/ml) and without microangiopathy (9.90 +/- 0.5 nM/ml) compared to control subjects (5.18 +/- 0.18 nM/ml). Advanced glycation end product levels were also significantly (p < 0.001) elevated in diabetic subjects with microangiopathy (8.2+/- 1.8 AU) when compared to diabetes subjects without microangiopathy (7.0 +/- 2.0 AU) and control subjects (4.6 +/- 1.9 AU). On multivariate regression analysis, GSH levels showed a positive association with the Na(+)/K(+) ATPase activity and negative association with TBARS and AGE levels.

CONCLUSION

Hypoglutathionemia and increased oxidative stress appears to be early biochemical aberrations in diabetes, and through protein alterations, oxidative stress and redox modifications may contribute to pathogenesis of diabetic microangiopathy.

Cytotoxicity and the levels of oxidative stress parameters in WI38 cells following 2 macrocyclic crown ethers treatment

BACKGROUND

Crown ethers as macrocyclic polyethers possess a hydrophilic cavity surrounded by hydrophobic ring which enable them to diffuse cell membrane. We evaluated cytotoxicity effects of 15-crown-5 and 18-crown-6 and the role of oxidative stress in WI38 cells culture.

METHODS

The effect of these ethers in a range of doses (0.1 to 2 mmol/l) on the activity of antioxidant enzymes; superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), and on some macromolecules oxidative damages end products; malondialdehyde (MDA) and dityrosine were assessed by spectrometry and HPLC methods.

RESULTS

Both compounds markedly inhibited the viability of cells with respect to control particularly at doses >0.5 mmol/l after 24- or 48 h incubation. The survivals of cells were measured using MTT assay. They lowered cell's viability and significantly promoted ROS generation, increased enzyme activities and enhanced oxidative damages in which 18-crown-6 was more effective. Treating cells with 30 microm of alpha-tocopherol in addition to 2 mmol/l of crown ethers showed significant decrease on the levels of ROS, enzyme activities, MDA and dityrosine.

CONCLUSION

We document the oxidative radicals forming ability of the studied crown ethers and further strengthens the documentation of their cytotoxicity effects through lipid and proteins oxidation damages.

Cerebrospinal fluid from human immunodeficiency virus--infected individuals facilitates neurotoxicity by suppressing intracellular calcium recovery

Neurologic decline associated with penetration of human immunodeficiency virus type 1(HIV-1) into the central nervous system is thought to be due, in large part, to inflammation and local secretion of neurotoxic substances. To examine the cellular processes that mediate neurotoxicity in vivo, the authors valuated the ability of neurons to maintain intracellular calcium homeostasis in the presence of toxic cerebrospinal fluid (CSF) (CSF(tox)) collected from a subset of HIV-infected individuals. Exposure of rat neural cultures to CSF(tox) resulted in a gradual increase in intracellular calcium in neurons (+63%), microglia (+251%), and astrocytes (+52%). Pretreatment of neural cultures with CSF(tox) resulted in an exaggerated calcium response to a brief pulse of glutamate and a > 90% suppression of the rate of recovery of intracellular calcium. Attempts to model the deficit using inhibitors of calcium transport across endoplasmic reticulum, mitochondrial, or plasma membrane indicated that blockade of the plasma membrane sodium/calcium exchanger was best able to reproduce the deficits seen during exposure to CSF(tox). Because the inability of cells to maintain calcium homeostasis would lead to exaggerated responses from a wide variety of stimuli, therapeutics designed to facilitate calcium transport from the cell may provide more comprehensive and effective intervention than strategies targeted to specific receptor pathways.

Alteration of cytosolic free calcium homeostasis by SIN-1: high sensitivity of L-type Ca2+ channels to extracellular oxidative/nitrosative stress in cerebellar granule cells

Exposure of cerebellar granule neurones in 25 mm KCl HEPES-containing Locke's buffer (pH 7.4) to 50-100 microm SIN-1 during 2 h decreased the steady-state free cytosolic Ca2+ concentration ([Ca2+]i) from 168 +/- 33 nm to 60 +/- 10 nm, whereas exposure to > or = 0.3 mm SIN-1 produced biphasic kinetics: (i) decrease of [Ca2+]i during the first 30 min, reaching a limiting value of 75 +/- 10 nm (due to inactivation of L-type Ca2+ channels) and (ii) a delayed increase of [Ca2+]i at longer exposures, which correlated with SIN-1-induced necrotic cell death. Both effects of SIN-1 on [Ca2+]i are blocked by superoxide dismutase plus catalase and by Mn(III)tetrakis(4-benzoic acid)porphyrin chloride. Supplementation of Locke's buffer with catalase before addition of 0.5-1 mm SIN-1 had no effect on the decrease of [Ca2+]i but further delayed and attenuated the increase of [Ca2+]i observed after 60-120 min exposure to SIN-1 and also protected against SIN-1-induced necrotic cell death. alpha-Tocopherol, the potent NMDA receptor antagonist (+)-MK-801 and the N- and P-type Ca2+ channels blocker omega-conotoxin MVIIC had no effect on the alterations of [Ca2+]i upon exposure to SIN-1. However, inhibition of the plasma membrane Ca2+ ATPase can account for the increase of [Ca2+]i observed after 60-120 min exposure to 0.5-1 mm SIN-1. It is concluded that L-type Ca2+ channels are a primary target of SIN-1-induced extracellular nitrosative/oxidative stress, being inactivated by chronic exposure to fluxes of peroxynitrite of 0.5-1 microm/min, while higher concentrations of peroxynitrite and hydrogen peroxide are required for the inhibition of the plasma membrane Ca2+ ATPase and induction of necrotic cell death, respectively.

Oxygen free radicals and redox biology of organelles

The presence and supposed roles of reactive oxygen species (ROS) were reported in literature in a myriad of instances. However, the breadth and depth of their involvement in cellular physiology and pathology, as well as their relationship to the redox environment can only be guessed from specialized reports. Whatever their circumstances of formation or consequences, ROS seem to be conspicuous components of intracellular milieu. We sought to verify this assertion, by collecting the available evidence derived from the most recent publications in the biomedical field. Unlike other reviews with similar objectives, we centered our analysis on the subcellular compartments, namely on organelles, grouped according to their major functions. Thus, plasma membrane is a major source of ROS through NAD(P)H oxidases located on either side. Enzymes of the same class displaying low activity, as well as their components, are also present free in cytoplasm, regulating the actin cytoskeleton and cell motility. Mitochondria can be a major source of ROS, mainly in processes leading to apoptosis. The protein synthetic pathway (endoplasmic reticulum and Golgi apparatus), including the nucleus, as well as protein turnover, are all exquisitely sensitive to ROS-related redox conditions. The same applies to the degradation pathways represented by lysosomes and peroxisomes. Therefore, ROS cannot be perceived anymore as a mere harmful consequence of external factors, or byproducts of altered cellular metabolism. This may explain why the indiscriminate use of anti-oxidants did not produce the expected "beneficial" results in many medical applications attempted so far, underlying the need for a deeper apprehension of the biological roles of ROS, particularly in the context of the higher cellular order of organelles.

Cytochrome P450: major player in reperfusion injury

While attention has historically focused on mitochondria as the primary source of ROS in myocardial ischemia/reperfusion injury, recent evidence has implicated cytochrome P450 monooxygenases (CYPs) as a significant factor. CYPs represent a large family of enzymes that catalyze the oxidation of endogenous and exogenous compounds. They catalyze arachidonic acid oxidation to a variety of biologically active eicosanoids that regulate ion channels and protein kinases, with effects on vasomotor tone and cardiac inotropy. They also represent a significant source of reactive oxygen species that may target cellular homeostatic mechanisms and mitochondria. In this review, we will consider the contribution of cytochrome P450 enzymes to reperfusion injury and will speculate on whether the mechanism of injury is due to CYP-mediated ROS production or arachidonic acid metabolites.

Na+/Ca2+ exchanger: target for oxidative stress in salt-sensitive hypertension

The Na+/Ca2+ exchanger regulates intracellular calcium ([Ca2+]i), and attenuation of Na+/Ca2+ exchange by oxidative stress might lead to dysregulation of [Ca2+]i. We have shown that the Na+/Ca2+ exchanger differs functionally and at the amino acid level between salt-sensitive and salt-resistant rats. Therefore, the purpose of these studies was to determine how oxidative stress affects the activities of the 2 Na+/Ca2+ exchangers that we cloned from mesangial cells of salt-resistant (RNCX) and salt-sensitive (SNCX) Dahl/Rapp rats. The effects of oxidative stress on exchanger activity were examined in cells expressing RNCX or SNCX by assessing 45Ca2+ uptake (reverse mode) and [Ca2+]i elevation (forward mode) in the presence and absence of H2O2 and peroxynitrite. Our results showed that 45Ca2+ uptake in SNCX cells was attenuated at 500 and 750 micromol/L H2O2 (63+/-12% and 25+/-7%, respectively; n=16) and at 50 and 100 micromol/L peroxynitrite (47+/-9% and 22+/-9%, respectively; n=16). In RNCX cells, 45Ca2+ uptake was attenuated at only 750 and 100 micromol/L H2O2 and peroxynitrite (61+/-9% and 63+/-6%, respectively; n=16). In addition, the elevation in [Ca2+]i was greater in SNCX cells than in RNCX cells in response to 750 micromol/L H2O2 (58+/-5.5 vs 17+/-4.1 nmol/L; n=13) and 100 micromol/L peroxynitrite (33+/-5 vs 11+/-6 nmol/L; n=19). The enhanced impairment of SNCX activity by oxidative stress might contribute to the dysregulation of [Ca2+]i that is found in this model of salt-sensitive hypertension.

Antisense oligonucleotide suppression of Na(+)/Ca(2+) exchanger activity in primary neurons from rat brain

An antisense (AS) oligodeoxynucleotide based on a conserved sequence in the three isoforms of the Na(+)/Ca(2+) exchanger (NCX) was used to decrease expression of this Ca(2+) transporter in primary neuronal cultures. Two AS oligo applications decreased NCX activity by approximately 40% within 12-24 h, and neither sense (S) or missense (MS) oligos altered NCX activity. The reduced NCX expression was confirmed by immunoblots and enzyme-linked immunosorbent assays (ELISAs). Resting [Ca(2+)](i) levels were 20% higher in AS-treated neurons and showed a slower return to baseline levels following activation of Ca(2+) influx by N-methyl-D-aspartate (NMDA). These results suggest that NCX plays a significant role in maintaining neuronal Ca(2+) homeostasis and in restoring baseline Ca(2+) levels following depolarization.