Early exposure to Aroclor 1254 in vivo disrupts the functional synaptic development of newborn hippocampal granule cells.

Neurogenesis in the dentate gyrus is sensitive to endogenous and exogenous factors that influence hippocampal function. Ongoing neurogenesis and the integration of these new neurons throughout life thus may provide a sensitive indicator of environmental stress. We examined the effects of Aroclor 1254 (A1254), a mixture of polychlorinated biphenyls (PCBs), on the development and function of newly generated dentate granule cells. Early exposure to A1254 has been associated with learning impairment in children, suggesting potential impact on the development of hippocampus and/or cortical circuits. Oral A1254 (from the 6th day of gestation to postnatal day 21) produced the expected increase in PCB levels in brain at postnatal day 21, which persisted at lower levels into adulthood. A1254 did not affect the proliferation or survival of newborn neurons in immature animals nor did it cause overt changes in neuronal morphology. However, A1254 occluded the normal developmental increase in sEPSC frequency in the third post-mitotic week without altering the average sEPSC amplitude. Our results suggest that early exposure to PCBs can disrupt excitatory synaptic function during a period of active synaptogenesis, and thus could contribute to the cognitive effects noted in children exposed to PCBs.

Exposure to endocrine disrupting chemicals and neurodevelopmental alterations.

The developing brain is remarkably malleable as neural circuits are formed and these circuits are strongly dependent on hormones for their development. For those reasons, the brain is very vulnerable to the effects of endocrine-disrupting chemicals (EDCs) during critical periods of development. This review focuses on three ubiquitous endocrine disruptors that are known to disrupt the thyroid function and are associated with neurobehavioral deficits: polychlorinated biphenyls, polybrominated diphenyl ethers, and bisphenol A. The human and rodent data suggesting effects of those EDCs on memory, cognition, and social behavior are discussed. Their mechanisms of action go beyond relative hypothyroidism with effects on neurotransmitter release and calcium signaling.

[Endocrine disruption: a challenge in research, public health and clinical practice]. / La perturbation endocrinienne: entre enjeux de recherche, enjeux de santé publique et enjeux de pratique quotidienne.

Epidemiological and experimental data highlight the fetal and early postnatal life as critical periods for the effects of endocrine disrupting chemicals (EDCs), since exposure to EDCs during these periods can predispose to disease later in life. EDCs' effects include disorders of the reproductive system throughout life (abnormalities of sexual differentiation, infertility or subfertility and some neoplasia) and disorders of energy balance (obesity and metabolic syndrome). They could also influence the development of the cerebral cortex. However, the demonstration of the involvement of a single EDC remains difficult in human since we are virtually exposed to a mixture of several ubiquitous EDCs which are variably persistent in the environment and the body and have lifelong consequences. Moreover, since their dose-response relationship can be non-monotonic, setting a threshold dose for EDCs effects has become meaningless. Pregnant women, newborns and young children appear to be mostly at risk. However, the role of the physician remains difficult and raises several questions: how can we formulate justified, applicable and updated recommendations that are not counterproductive or alarmist...in a society that has to take the necessary steps to regulate production and protect the population?

Early neuroendocrine disruption in hypothalamus and hippocampus: developmental effects including female sexual maturation and implications for endocrine disrupting chemical screening.

The timing of puberty has been mainly studied in females for several reasons, including the possible evaluation of a precise timer (i.e. menarcheal age) and concerns with respect to the high prevalence of precocity in females as opposed to males. Human evidence of altered female pubertal timing after exposure to endocrine disrupting chemicals (EDCs) is equivocal. Among the limiting factors, most studies evaluate exposure to single EDCs at the time of puberty and hardly assess the impact of lifelong exposure to mixtures of EDCs. Some rodent and ovine studies indicate a possible role of foetal and neonatal exposure to EDCs, in accordance with the concept of an early origin of health and disease. Such effects possibly involve neuroendocrine mechanisms because the hypothalamus is a site where homeostasis of reproduction, as well as control of energy balance, is programmed and regulated. In our previous studies, pulsatile gonadotrophin-releasing hormone (GnRH) secretion control via oestrogen, glutamate and aryl hydrocarbon receptors was shown to be involved in the mechanism of sexual precocity after early postnatal exposure to the insecticide dichlorodiphenyltrichloroethane. Very recently, we have shown that neonatal exposure to the potent synthetic oestrogen diethylstilbestrol (DES) is followed by early or delayed puberty depending on the dose, with consistent changes in developmental increase of GnRH pulse frequency. Moreover, DES results in reduced leptin stimulation of GnRH secretion in vitro, an effect that is additive with prenatal food restriction. Thus, using puberty as an endpoint of the effects of EDC, it appears necessary to consider pre- and perinatal exposure to low doses and to pay attention to the other conditions of prenatal life, such as energy availability, keeping in mind the possibility that puberty could not only be advanced, but also delayed through neuroendocrine mechanisms.

Protection of thrombin receptor expression under hypoxia.

Thrombin receptor (ThR) plays a significant role in myocyte contractility and hypertrophy. Heart myocyte ischemic damage, caused by insufficient blood supply, is the leading cause of heart infarction. Here we demonstrate that when primary myocyte cultures are subjected to hypoxic stress, ThR mRNA levels are reduced markedly. This takes place also in vivo in a model of ischemic pig heart, exhibiting reduced levels of ThR compared with normal heart sections. Prior activation of ThR however, by either thrombin receptor-activating peptide (TRAP) or by alpha-thrombin resulted in full protection of ThR mRNA levels under hypoxia. The effect appeared specific to ThR because the addition of TRAP did not affect the hypoxic damage as shown by the levels of lactic dehydrogenase release and up-regulated GLUT-1, a glucose transporter gene. This protection effect took place not only in primary myocytes but also in NIH3T3 fibroblasts. ThR protection occurs via specific cell signaling events because activation of the receptor by TRAP, following interruption of the signaling cascade by calphostin C, a protein kinase C inhibitor, resulted in loss of ThR mRNA protection. Because Ras and Src are part of the ThR signaling cascade, the introduction of either dominant ras or src oncogenes to NIH3T3 murine fibroblasts gave rise to similar protection of ThR mRNA levels under hypoxic conditions without the exogenous addition of TRAP. Likewise, ThR mRNA protection was obtained after transfection with proto-oncogene vav. The 95-kDa protein Vav undergoes tyrosine phosphorylation after ThR activation, serving thus as part of the receptor machinery cascade. We therefore conclude that the initiation of the signaling cascades either exogenously by TRAP or within the cell via src or ras, as well as via vav oncogene interconnecting G-binding protein to the tyrosine kinase pathway, ultimately results in ThR protection under hypoxia. We present hereby, a novel concept of activated receptors, which under minimal oxygen tension protect their otherwise decaying mRNA. Maintaining the level of ThR that plays an active role in normal myocyte function may provide a significant repair mechanism in ischemic tissue, assisting in the regaining of normal myocyte functions.

Mitochondrial respiratory enzymes are a major target of iron toxicity in rat heart cells.

Our previous studies in iron-loaded rat heart cells showed that in vitro iron loading results in peroxidative injury, manifested in a marked decrease in rate and amplitude of heart cell contractility and rhythmicity, which is correctable by treatment with deferoxamine (DF). In the present studies we explored the role of mitochondrial damage in myocardial iron toxicity. Iron loading by 24-hour incubation with 0.36 mmol/L ferric ammonium citrate resulted in a decrease in the activity of nicotinamide adenine dinucleotide (NADH)-cytochrome c oxidoreductase (complex I+III) to 35.3%+/-11.2% of the value in untreated controls; of succinate-cytochrome c oxidoreductase (complex II+III) to 57.4%+/-3.1%; and of succinate dehydrogenase to 63.5%+/-12.6% (p < 0.001 in all cases). The decrease in activity of other mitochondrial enzymes, including NADH-ferricyanide reductase, succinate ubiquinone oxidoreductase (complex II), cytochrome c oxidase (complex IV), and ubiquinol cytochrome c oxidoreductase (complex III), was less impressive and ranged from 71.5%+/-15.8% to 91.5%+/-14.6% of controls. That the observed loss of respiratory enzyme activity was a specific effect of iron toxicity was clearly demonstrated by the complete restoration of enzyme activities by in vitro iron chelation therapy. Sequential treatment with iron and doxorubicin caused a loss of complex I+III and complex II+III activity that was greater than that seen with either agent alone but was only partially correctable by DF treatment. Alterations in cellular adenosine triphosphate measurements paralleled very closely the changes observed in respiratory complex activity. These findings demonstrate for the first time the impairment of cardiac mitochondrial respiratory enzyme activity caused by iron loading at conditions formerly shown to produce severe abnormalities in contractility and rhythmicity.

Both hydroxylamine and nitroxide protect cardiomyocytes from oxidative stress.

The unique anti-oxidative activity of nitroxide radicals protecting against reactive oxygen-derived species (ROS) has been recently demonstrated in several model systems. The present study focuses on the activity of nitroxide and of its reduced form in cultured rat ventricular cardiomyocytes exposed to O2.- and H2O2 generated by hypoxanthine (HX) and xanthine oxidase (XO). To evaluate cell injury, spontaneous beating, leakage of lactate dehydrogenase (LDH), and depletion of cellular ATP were determined. The protective effect of 4-OH-2,2,6,6-tetramethyl-piperidine-N-oxyl (TPL) was compared with that of 4-OH-2,2,6,6-tetramethyl-1-hydroxypiperidine (TPL-H) and of several common anti-oxidants. A rapid exchange between TPL and TPL-H, is mediated by cellular metabolism and through reactions with ROS. In particular, TPL under O2.- flux is oxidized to oxo-ammonium cation (TPL+) which comproportionates with TPL-H yielding two nitroxide radicals. Because this exchange limits the distinction between the biological activities of TPL and TPL-H, NADH which can reduce TPL+ was included in order to maintain the nitroxide in its reduced form. The results demonstrate that both TPL and TPL-H protect cardiomyocytes against beating loss and LDH leakage. Conversely, cellular ATP depletion induced by HX/XO is inhibited by TPL-H, though not by TPL, suggesting that different mechanisms underlie their protective activities. Through a flip-flop between the two forms, which coexist in the system, the levels of TPL-H and TPL are continuously replenished. The conversion, upon reaction, of each antioxidant into the other one enables them, contrary to common antioxidants which operate in a stoichiometric mode, to act catalytically.

Pneumococcal sacroiliitis.

We report an unusual case of Streptococcus pneumoniae sacroiliitis in a previously healthy 31-year-old woman. Six cases of pneumococcal sacroiliitis have been reported; the only two cases in adults occurred in young women in the preantibiotic era. Our patient had fever and a depressed level of consciousness, with subsequent right buttock and thigh pain. Blood cultures revealed S pneumoniae, and a bone scan showed increased tracer activity in the right sacroiliac joint. Although the cerebrospinal fluid white blood cell count was only 3/microL, culture of cerebrospinal fluid grew S pneumoniae. Our patient was successfully treated with a 6-week course of intravenous antibiotics (penicillin G after an initial week of ceftriaxone), followed by 2 weeks of oral penicillin therapy.

Fever in the clinical diagnosis of acute pyelonephritis.

Acute pyelonephritis is a clinical syndrome that can be confused with other conditions. To investigate this problem, a retrospective cohort study was conducted using two mutually exclusive sets of clinical criteria for acute pyelonephritis in women 15 years of age or older who presented to the emergency department of a university hospital. All patients had pyuria, and one group had documented fever (temperature of > or = 37.8 degrees C) while the other group had a temperature of < 37.8 degrees C but had other evidence of possible upper tract infection. The study cohort was comprised of 103 febrile and 201 afebrile patients. Afebrile hospitalized patients were ultimately found to have another diagnosis more often than were the febrile hospitalized patients (35% v 7%; P = .02), and the afebrile nonhospitalized patients were more likely to have another diagnosis than were the febrile nonhospitalized patients (13% v 0%; P = .004). Other diagnoses included cholecystitis, pelvic inflammatory disease, and diverticulitis. The positive predictive value of the definition of pyelonephritis in the febrile group was 0.98, and it was 0.84 for the afebrile group. Physicians examining patients with clinical evidence of acute pyelonephritis but without objective fever should be alert for alternative diagnoses.

Bacteremia in young urban women admitted with pyelonephritis.

The objective of this study was to determine the rate of bacteremia in young women admitted to the hospital with presumed pyelonephritis and compare it with other published rates. The study design was a retrospective, structured chart review and a review of published reports of bacteremic pyelonephritis. An urban county teaching hospital provided the setting for the study. The patients were nonpregnant women (n = 98) 44 years of age or younger who were without bladder dysfunction and who had not been admitted to an intensive care unit. Further criteria for participation included discharge with the diagnosis of acute pyelonephritis. Blood cultures were ordered for 69 women; the results of 64 were noted in the chart. Twenty-three women (35.9% of those cultured; 23.4% of all patients) were diagnosed with bacteremia. In patients for whom blood culture results were obtained, trends developed between those patients with bacteremia and those with complicated pyelonephritis, defined as a known or newly discovered genitourinary abnormality or a risk factor (P = 0.044), those who were black (P = .044), those with higher pulses on admission (P = .050), those with more white blood cells per high-powered field after urinalysis (P = 0.007), and those whose fever lasted longer (P = 0.033). Blood culture results were positive in two patients whose urine cultures were negative. This comparatively high bacteremia rate supports routine ordering of blood cultures for urban women suspected of having pyelonephritis.

Glucose is essential for the initiation of fatty acid oxidation in ATP-depleted cultured ventricular myocytes.

Cultured cardiac myocytes were depleted of ATP by incubation with oligomycin (1 mg/ml). Then the ability of the cells to oxidize various substrates and to restore ATP levels was studied. Following ATP depletion, the cells were found to be able to oxidize glucose given alone, but not palmitate. However, with both substrates, palmitate was oxidized in the presence of glucose and ATP recovery was enhanced. Pyruvate had a minor effect on palmitate oxidation, while acetate given alone was oxidized, but did not enhance cellular ATP content. These results show that glucose is essential for restoration of mitochondrial function and the coupling between oxidation and ATP synthesis.

Effect of TaiCatoxin (TCX) on the electrophysiological, mechanical and biochemical characteristics of spontaneously beating ventricular cardiomyocytes.

TaiCatoxin (TCX), a complex toxin isolated from Taipan snake venom, is believed to have a specific blocking activity on voltage-dependent cardiac calcium channels. The aim of this study was to investigate the effects of TCX on a broad range of heart muscle cell functions, i.e. electrophysiology, contractility, automaticity and the related biochemical modifications. Myocyte-enriched cultures were prepared from newborn rat heart ventricles. The transmembrane potentials were recorded with glass microelectrodes. The contractions were monitored photometrically. TCX decreased the action potential amplitudes, mainly by lowering the plateau. The action potential duration and the contraction parameters were decreased. Although TCX has a minor overall negative chronotropic effect, it evoked transient but severe arrhythmias and prolonged changes in the intercellular electrical coupling. Moreover, the action of TCX appeared to be dose-dependent. These effects are consistent with a specific blockade of the L-type, voltage-dependent calcium channels, but effects of other components of the toxin complex cannot be excluded. TCX also exhibits phospholipase A2 activity leading to the release of Iysophospholipids and FFA (acyl CoA and acyl carnitine), which have detrimental effects on cellular integrity and function.

Reversible and irreversible damage in reoxygenated 'ischemic' ventricular myocytes in culture.

The LDH release pattern from cardiomyocytes under 'ischemia-like' conditions shows two phases. In the initial slow phase, reoxygenation immediately stops further enzyme release. Accelerated LDH release, which occurs concomitantly with Iysosomal enzyme release, characterizes the second phase of 'ischemia.' Reoxygenation at this stage does not put a stop to further enzyme release. Reoxygenation during the first phase of 'ischemia' rapidly restored ATP level, while in the second phase, ATP levels remained low even after 6 h of reoxygenation. This study as well as previous data seem to suggest that irreversible cellular damage leading to cell death, occurs by synergistic action of many effectors, each of which does not necessarily cause irreversible damage.

Oxygen deprivation and reoxygenation augment prostacyclin synthesis in cultured ventricular myocytes.

Prostacyclin production in cultured cardiomyocytes is not induced by cellular ATP depletion per se, suggesting that the mechanism of ischemic injury is more complex. In the present study we subjected cultured ventricular myocytes to 'simulated ischemia' followed by reoxygenation. A slight increase in 6-keto-PGF(1 alpha) (the stable metabolite of PGI(2)) was found during 'ischemia', which continued to increase markedly during reoxygenation. PGE(2) levels were pronouncedly enhanced during ischemia but decreased during reoxygenation, and TXB(2) levels remained undetectable throughout. These findings reflect a cardiomyocyte response to anoxic injury, suggesting that they act to protect against cardiac injury by producing the potent vasodilators PGI(2) and PGE(2) during ischemia and reoxygenation.

Role of iron in the potentiation of anthracycline cardiotoxicity: identification of heart cell mitochondria as a major site of iron-anthracycline interaction.

The role of iron in anthracycline toxicity was studied in rats in vivo in intact animals and in vitro in heart cell cultures. In animals treated with 8 mg/kg doxorubicin, iron loading resulted in severe weight loss and a twofold increase in rate of mortality. Studies in cultured heart cells aimed at defining the subcellular target of interaction between iron and anthracycline toxicity showed no evidence of anthracycline-induced damage to sarcolemmal thiolic enzymes represented by 5'-nucleotidase and only a limited increase in lysosomal fragility as monitored by an increase in beta-hexosaminidase activity in cell homogenates and its release into the culture medium. By contrast, doxorubicin treatment resulted in a marked inhibition of mitochondrial function as monitored by a decrease in carbon 14-labeled palmitate utilization, to 33% +/- 4% of controls, and prior iron loading resulted in a further decrease in palmitate utilization, to 18% +/- 3% of controls. Conversely, iron-chelation treatment by either deferoxamine or deferiprone (L1) eliminated the harmful effects of iron loading and resulted in a partial inhibition of doxorubicin toxicity in both normal and iron-loaded cells. Our studies represent the first demonstration in intact animals of the potentiation of anthracycline toxicity by iron overload. They also indicate that mitochondria represent an important target of combined iron-anthracycline toxicity. These observations provide new insights into the mechanism of anthracycline cardiotoxicity and may be useful in developing better strategies for tumor therapy.

Prevention of anthracycline cardiotoxicity by iron chelation.

The use of anthracycline antineoplastic drugs is limited by a cumulative, dose-dependent toxicity to the heart. Of the cellular organelles proposed as possible primary sites of anthracycline toxicity, the mitochondrial membrane appears to be most likely target. Cardiolipin, a major phospholipid component of the inner mitochondrial membrane is rich in polyunsaturated fatty acids and is particularly susceptible to peroxidative injury by harmful radicals produced by redox cycling of anthracyclines. This, in turn, leads to the inactivation of key enzymes in the mitochondrial respiratory chain. Since the formation of free radicals is catalyzed by iron through the Haber-Weiss reaction, it was hypothesized that iron depletion by deferoxamine (DFO) may limit anthracycline cardiotoxicity. Recent studies indicate that iron-loading aggravates doxorubicin cardiotoxicity by enhancing mitochondrial damage, and this can be prevented by prior DFO treatment. Although these observations are intriguing, further studies are required to show that the cardioprotective effects of DFO do not interfere with the therapeutic, antitumoral action of anthracyclines.

Do nitroxides protect cardiomyocytes from hydrogen peroxide or superoxide?

The aim of the research was to study the role played by extracellular O2-radicals, which are implicated in cardiac cell damage and the protective effect by cell-permeable, nitroxide, superoxide dismutase-mimics. Cardiomyocytes cultures from 1-day-old rats served as the test-system. Experiments were performed since 5th day in culture when > 80% of the cells were beating myocardial cells. Oxidative damage was induced by 0.5 mM hypoxanthine and 0.06 U/ml xanthine oxidase or by 10 mM glucose and 0.15 U/ml glucose oxidase. The parameters used to evaluate damages were spontaneous beating, lactate dehydrogenase release and ATP level. The rhythmic pulsation was followed microscopically. To determine the kinetics of cytosolic enzyme release from the cells, media samples were collected at various points of time and assayed for enzyme activity. To determine the cellular ATP, cells were washed with sodium phosphate buffer, scraped off and boiled for 3 min with sodium phosphate buffer. Following centrifugation the supernatant was collected and ATP was determined by the chemiluminogenic assay using firefly tails. The present results indicate that nitroxide stable free radicals in the millimolar concentration range, provide full protection without toxic side-effect. Unlike exogenously added SOD that failed to protect, exogenous catalase provided almost full protection. In addition, the metal-chelating agent dipyridyl, but not diethylene-triamine-pentaacetate or desferrioxamine, protected the cultured cells. The present results suggest that H2O2 is the predominant toxic species mediating the oxidative damage whereas extracellular superoxide radical does not contribute to cultured cardiomyocyte damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Upregulation of vascular endothelial growth factor expression induced by myocardial ischaemia: implications for coronary angiogenesis.

OBJECTIVE: The process of coronary collateral development is poorly understood. It is assumed that particular angiogenic factors are upregulated during episodes of myocardial ischaemia and act as a trigger for neovascularisation. However, the identity of these factors is unknown. The angiogenic factor vascular endothelial growth factor (VEGF) has been shown to be hypoxia inducible, so this factor may mediate ischaemia induced angiogenesis in the heart. The aim of this study was to examine hypoxia inducibility of VEGF in cultured myocardial cells as well as in normally perfused and ischaemic porcine myocardium. METHODS: (1) In vitro experiment: cultured rat myocardial cells were subjected to hypoxia, and steady state levels of VEGF mRNA were measured after 2 and 4 h of hypoxia. (2) In vivo experiment: myocardial ischaemia in pigs hearts was induced by repeated 2-10 min left anterior descending coronary artery occlusions, separated by 20 min of reperfusion. Hearts were retrieved after 6 h of intermittent ischaemia. Total RNA was extracted from normal and ischaemic zones of the heart and processed for RNA blot hybridisation analysis. RESULTS: In vitro experiment: as soon as 2-4 h after exposure of cultures to hypoxia, VEGF mRNA levels were significantly raised (6-10-fold). In vivo experiment: VEGF expression was significantly augmented in the ischaemic territory of the myocardium (three- to fivefold induction). Furthermore, polymerase chain reaction amplification of the reverse transcribed mRNA showed increased production of multiple forms of differentially spliced VEGF mRNA in the ischaemic myocardium. CONCLUSIONS: VEGF production in the myocardium is significantly upregulated by hypoxia in vitro and by ischaemia in vivo. These results suggest that VEGF is a likely mediator in the natural process of ischaemia induced myocardial neovascularisation.

ED management of acute pyelonephritis in women: a cohort study.

Various treatment strategies are currently used in the management of acute pyelonephritis, with some patients being treated as inpatients and others as outpatients. To better describe the clinical course of patients with this condition and the management strategies of physicians treating these patients, a retrospective cohort study of febrile nonpregnant women presenting to the emergency department with clinical evidence of acute pyelonephritis was conducted. Acute pyelonephritis was defined as infected urine (> or = 7 white blood cells/high-power field and/or urine culture with > or = 10(4) colony-forming units [CFU]/mL) and fewer (> or = 37.8 degrees C) without other source. Between October 1990 and September 1991, 28 hospitalized and 83 nonhospitalized patients satisfied these criteria. Data were abstracted from hospital charts, and clinical outcomes were determined from chart reviews and telephone or mailed questionnaires. The hospitalized patients were significantly older (odds ratio [OR] = 1.07), had higher temperatures (OR = 6.12), and were more likely to have diabetes (OR = 10.57), genitourinary tract abnormalities (OR = 10.53), and vomiting (OR = 12.17) than the nonhospitalized patients. Sixty-six (80%) of the nonhospitalized patients were treated with a single dose of parenteral antibiotic (usually gentamicin or ceftriaxone) before discharge on oral antibiotics. Seventy-one (86%) were treated with oral trimethoprim-sulfamethoxazole. Follow-up was obtained for 75 (90%) of the nonhospitalized patients. Nine (12%) of the 75 returned because of symptoms of acute pyelonephritis, with 8 returning within 1 day of the initial visit. Seven of those returning were admitted. All responded to additional antibiotic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Ability of the orally effective iron chelators dimethyl- and diethyl-hydroxypyrid-4-one and of deferoxamine to restore sarcolemmal thiolic enzyme activity in iron-loaded heart cells.

In view of the profound functional and structural abnormalities shown in our previous studies in cultured, iron-loaded rat heart cells, we have examined the ability of the orally effective iron chelators dimethyl-3-hydroxypyrid-4-one (DMHP or L1) and diethyl-3-hydroxy-pyrid-4-one (DEHP or CP94) and of deferoxamine (DF) to reverse the damage caused by iron loading to heart cell organelles. At a concentration of 1.0 mmol/L, all three iron chelators were equally efficient in removing iron and restoring the activity of the thiolic sarcolemmal enzymes 5'-nucleotidase and Na,K,ATPase. However, at 0.1 mmol/L DMHP and DEHP were less effective than DF both in their iron-mobilizing effect and in promoting thiolic enzyme recovery. The superior efficiency of DF at low concentrations illustrates the advantage of the hexadentate chelating action of DF as compared with bidentate chelators such as DMHP and DEHP requiring a 3 to 1 molar ratio to iron for optimal effect. In contrast to its beneficial effect on sarcolemmal enzyme activity, iron chelation was unable to reverse the increase in beta-hexosaminidase activity caused by abnormal lysosomal fragility. Our study demonstrates for the first time that iron-induced peroxidative damage to the myocardial cell is associated with a marked loss of Na,K,ATPase activity, an enzyme with a major role in the maintenance of cellular resting potential. The timing of this damage and the restoration of Na,K,ATPase function by iron-chelating treatment suggest a cause-and-effect relationship between the observed injury to the sarcolemmal enzyme and the reversible electrophysiologic abnormalities observed in the same heart culture system in our previous studies.