Effects of low-molecular-weight aluminum complexes on brain tissue calcium homeostasis

The in vitro effects of low-molecular-weight aluminum complexes (citrate, lactate, and ATP complex) on the Ca²⁺ uptake and aluminum-induced lipid peroxidation of brain tissue show that the modification of the calcium homeostasis is determined by the nature of the ligand and that there is no correlation between the aluminum-induced lipid peroxidation and the Ca²⁺ uptake. The same characteristics have been shown by a similar study performed with Ehrlich carcinoma cells. The electrophoretic analyses of the aluminum lactate-albumin and aluminum lactate-ATP interactions indicate an aluminum transfer from the lactate to the albumin and ATP ligands. The increased Ca²⁺ uptake when ATP is present in the incubation medium with aluminum citrate and aluminum lactate corroborates the suggested mediator role of ATP in cellular calcium homeostasis modification induced by iron.     

Glutathione depleting agents and lipid peroxidation

The mechanisms by which glutathione (GSH) depleting agents produce cellular injury, particularly liver cell injury have been reviewed. Among the model molecules most thoroughly investigated are bromobenzene and acetaminophen. The metabolism of these compounds leads to the formation of electrophilic reactants that easily conjugate with GSH. After substantial depletion of GSH, covalent binding of reactive metabolites to cellular macromolecules occurs. When the hepatic GSH depletion reaches a threshold level, lipid peroxidation develops and severe cellular damage is produced. According to experimental evidence, the cell death seems to be more strictly related to lipid peroxidation rather than to covalent binding. Loss of protein sulfhydryl groups may be an important factor in the disturbance of calcium homeostasis which, according to several authors, leads to irreversible cell injury. In the bromobenzene-induced liver injury loss of protein thiols as well as impairment of mitochondrial and microsomal Ca2+ sequestration activities are related to lipid peroxidation. However, some redox active compounds such as menadione and t-butylhydroperoxide produce direct oxidation of protein thiols.     

Malondialdehyde epitopes as mediators of sterile inflammation

Enhanced lipid peroxidation occurs during oxidative stress and results in the generation of lipid peroxidation end products such as malondialdehyde (MDA), which can attach to autologous biomolecules, thereby generating neo-self epitopes capable of inducing potentially undesired biological responses. Therefore, the immune system has developed mechanisms to protect from MDA epitopes by binding and neutralizing them through both cellular and soluble effectors. Here, we briefly discuss innate immune responses targeting MDA epitopes and their pro-inflammatory properties, followed by a review of physiological carriers of MDA epitopes that are relevant in homeostasis and disease. Then we discuss in detail the evidence for cellular responses towards MDA epitopes mainly in lung, liver and the circulation as well as signal transduction mechanisms and receptors implicated in the response to MDA epitopes. Last, we hypothesize on the role of MDA epitopes as mediators of inflammation in diseases and speculate on their contribution to disease pathogenesis. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.     

Protection against cell damage due to hypoxia and reoxygenation: The role of taurine and the involved mechanisms

Summary The effect of taurine on cell viability and metabolism of human colon and porcine renal cells was investigated during and after hypoxia. Taurine administered during hypoxia markedly reduced cellular deterioration due to hypoxia and reoxygenation and led to a significantly greater recovery of cellular function following the hypoxic insult. The responsible mechanisms for the beneficial effects were an improvement in osmotic status and calcium homeostasis and an induction in cellular growth despite oxygen deficiency and reoxygenation. Free oxygen radical generation and lipid membrane peroxidation were not reduced by taurine. Taurine acted as a potent endogenous agent with multifactorial effects against cellular damage due to hypoxia and reoxygenation.     

The role of ATP as a mediator in the action of iron complexes on cellular calcium homeostasis

The effects of the interaction between low molecular weight iron complexes (citrate, lactate, and ATP complexes) with ATP and proteins, on the modification of Ehrlich carcinoma cell calcium homeostasis have been studied. In that modification the ferric-ATP complex shows much higher activity than the others. Sodium ATP, by iron translocation from citrate and lactate, increases their activity. This phenomenon implicates ATP as a mediator on the cellular activity of the complexes. Proteins, particularly ferritin, appear to moderately reduce their activity, whereas glutathione and ascorbic acid, acting as lipid peroxidation-inhibitors, show only a slight reduction of the iron complex’s effects on cellular calcium uptake.     

Neuronal and glial calcium signaling in Alzheimer's disease

Cognitive impairment and emotional disturbances in Alzheimer's disease (AD) result from the degeneration of synapses and death of neurons in the limbic system and associated regions of the cerebral cortex. An alteration in the proteolytic processing of the amyloid precursor protein (APP) results in increased production and accumulation of amyloid beta-peptide (Abeta) in the brain. Abeta has been shown to cause synaptic dysfunction and can render neurons vulnerable to excitotoxicity and apoptosis by a mechanism involving disruption of cellular calcium homeostasis. By inducing membrane lipid peroxidation and generation of the aldehyde 4-hydroxynonenal, Abeta impairs the function of membrane ion-motive ATPases and glucose and glutamate transporters, and can enhance calcium influx through voltage-dependent and ligand-gated calcium channels. Reduced levels of a secreted form of APP which normally regulates synaptic plasticity and cell survival may also promote disruption of synaptic calcium homeostasis in AD. Some cases of inherited AD are caused by mutations in presenilins 1 and 2 which perturb endoplasmic reticulum (ER) calcium homeostasis such that greater amounts of calcium are released upon stimulation, possibly as the result of alterations in IP(3) and ryanodine receptor channels, Ca(2+)-ATPases and the ER stress protein Herp. Abnormalities in calcium regulation in astrocytes, oligodendrocytes, and microglia have also been documented in studies of experimental models of AD, suggesting contributions of these alterations to neuronal dysfunction and cell death in AD. Collectively, the available data show that perturbed cellular calcium homeostasis plays a prominent role in the pathogenesis of AD, suggesting potential benefits of preventative and therapeutic strategies that stabilize cellular calcium homeostasis.     

Lipid peroxidation triggers neurodegeneration: A redox proteomics view into the Alzheimer disease brain

Lipid peroxidation involves a cascade of reactions in which production of free radicals occurs selectively in the lipid components of cellular membranes. Polyunsaturated fatty acids easily undergo lipid peroxidation chain reactions, which, in turn, lead to the formation of highly reactive electrophilic aldehydes. Among these, the most abundant aldehydes are 4-hydroxy-2-nonenal (HNE) and malondialdehyde, while acrolein is the most reactive. Proteins are susceptible to posttranslational modifications caused by aldehydes binding covalently to specific amino acid residues, in a process called Michael adduction, and these types of protein adducts, if not efficiently removed, may be, and generally are, dangerous for cellular homeostasis. In the present review, we focused the discussion on the selective proteins that are identified, by redox proteomics, as selective targets of HNE modification during the progression and pathogenesis of Alzheimer disease (AD). By comparing results obtained at different stages of the AD, it may be possible to identify key biochemical pathways involved and ideally identify therapeutic targets to prevent, delay, or treat AD.     

Reactions of 4-hydroxynonenal with proteins and cellular targets

Peroxidative degradation of lipids yields the aldehyde 4-hydroxy-2-nonenal (4HNE) as a major product. The lipid aldehyde is an electrophile, and reactivity of 4HNE toward protein nucleophiles (i.e., Cys, His, and Lys) has been characterized. Through the use of purified enzymes and isolated cells, various pathways for biotransformation of the lipid aldehyde have been identified and include enzyme-mediated oxidation, reduction, and glutathione conjugation. Uncontrolled oxidative stress can yield excessive lipid peroxidation and 4HNE generation, however, and overwhelm these cellular defenses. Indeed, in vitro and in vivo production of 4HNE in response to pro-oxidant exposure has been demonstrated using antibodies to protein adducts of the lipid aldehyde. Recent evidence suggests a role for protein modification by 4HNE in the pathogenesis of several diseases (e.g., alcohol-induced liver disease); however, the precise mechanism(s) is currently unknown but likely results from adduction of proteins involved in cellular homeostasis or biological signaling.     

Growth modulation of human cells in vitro by mild oxidative stress and 1,4-dihydropyridine derivative antioxidants

Reactive oxygen species and lipid peroxidation products are not only cytotoxic but may also modulate signal transduction in cells. Accordingly, antioxidants may be considered as modifiers of cellular redox signaling. Therefore, the effects of two novel synthetic antioxidants, analogues of 1,4-dihydropyridine derivatives, cerebrocrast and Z41-74 were analysed in vitro on human osteosarcoma cell line HOS, the growth of which can be modulated by lipid peroxidation. The cells were pretreated with either cerebrocrast or Z41-74 and afterwards exposed to mild, copper induced lipid peroxidation or to 4-hydroxynonenal (HNE), the end product of lipid peroxidation. The results obtained have shown that both antioxidants exert growth modulating effects interfering with the lipid peroxidation. Namely, cells treated with antioxidants showed increased metabolic rate and cell growth, thereby attenuating the effects of lipid peroxidation. Such biomodulating effects of cerebrocrast and Z41-74 resembled growth modulating effects of HNE, suggesting that the antioxidants could eventually promote cellular adaptation to oxidative stress interacting with redox signaling and hydroxynonenal HNE-signal transduction pathways. This may be of particular relevance for better understanding the beneficial role of hydroxynonenal HNE in cell growth control. Therefore, cerebrocrast and Z41-74 could be convenient to study further oxidative homeostasis involving lipid peroxidation.     

Perturbed Synaptosomal Calcium Homeostasis and Behavioral Deficits Following Carbofuran Exposure: Neuroprotection by <Emphasis Type="Italic">N</Emphasis>-Acetylcysteine

The protective effects of N-acetylcysteine (NAC) on carbofuran-induced alterations in calcium homeostasis and neurobehavioral functions were investigated in rats. Rats were exposed to carbofuran at a dose of 1 mg/kg body weight, orally for a period of 28 days. A significant decrease in Ca²⁺ATPase activity was observed following carbofuran exposure with a concomitant increase in K⁺-induced ⁴⁵Ca²⁺ uptake through voltage operated calcium channels. This was accompanied with a marked accumulation of intracellular free calcium in synaptosomes. The increase in intracellular calcium levels were associated with an increased lipid peroxidation and decreased glutathione content in carbofuran exposed animals. NAC administration (200 mg/kg body weight, orally) to the carbofuran exposed animals had a beneficial effect on carbofuran-induced alterations in calcium homeostasis and resulted in repletion in glutathione levels and resulted in lowering the extent of lipid peroxidation. Marked impairment in the motor functions were seen following carbofuran exposure, which were evident by the significant decrease in the locomotor activity and reduction in the retention time of the rats on rotating rods. Cognitive deficits were also seen as indicated by the significant decrease in active and passive avoidance response. NAC treatment, on the other hand, protected the animals against carbofuran-induced neurobehavioral deficits. The results support the hypothesis that carbofuran exerts its toxic effects by disrupting calcium homeostasis, which may have serious consequences on neuronal functioning, and clearly show the potential beneficial effects of N-acetylcysteine on carbofuran induced alterations in synaptosomal calcium homeostasis.     

In vivo treatment with stobadine prevents lipid peroxidation,protein glycation and calcium overload but does not ameliorate Ca2+ -ATPase activity in heart and liver of streptozotocin-diabetic rats: comparison with vitamin E

Hyperglycemia leads to excess production of reactive oxygen species (ROS), lipid peroxidation and protein glycation that may impair cellular calcium homeostasis and results in calcium sequestration and dysfunction in diabetic tissues. Stobadine (ST) is a pyridoindole antioxidant has been postulated as a new cardio- and neuroprotectant. This study was undertaken to test the hypothesis that the treatment with ST inhibits calcium accumulation, reduces lipid peroxidation and protein glycation and can change Ca2+,Mg2+-ATPase activity in diabetic animals. The effects of vitamin E treatment were also evaluated and compared with the effects of combined treatment with ST. Diabetes was induced by streptozotocin (STZ, 55 mg/kg i.p.). Some of diabetic rats and their age-matched controls were treated orally with a low dose of ST (24.7 mg/kg/day), vitamin E (400-500 IU/kg/day) or ST plus vitamin E for 10 weeks. ST and vitamin E separately produced, in a similar degree, reduction in diabetes-induced hyperglycemia. Each antioxidant alone significantly lowered the levels of plasma lipid peroxidation, cardiac and hepatic protein glycation in diabetic rats but vitamin E treatment was found to be more effective than ST treatment alone. Diabetes-induced increase in plasma triacylglycerol levels was not significantly altered by vitamin E treatment but markedly reduced by ST alone. The treatment with each antioxidant completely prevented calcium accumulation in diabetic heart and liver. Microsomal Ca2+,Mg2+-ATPase activity significantly decreased in both tissues of untreated diabetic rats. ST alone significantly increased microsomal Ca2+,Mg2+-ATPase activity in the heart of normal rats. However, neither treatment with ST nor vitamin E alone, nor their combination did change cardiac Ca2+,Mg2+-ATPase activity in diabetic heart. In normal rats, neither antioxidant had a significant effect on hepatic Ca2+,Mg2+-ATPase activity. Hepatic Ca2+,Mg2+-ATPase activity of diabetic rats was not changed by single treatment with ST, while vitamin E alone completely prevented diabetes-induced inhibition in microsomal Ca2+,Mg2+-ATPase activity in liver. Combined treatment with ST and vitamin E provided more benefits in the reduction of hyperglycemia and lipid peroxidation in diabetic animals. This study describes potential mechanisms on cellular effects of ST in the presence of diabetes-induced hyperglycemia that may delay or inhibit the development of diabetic complications. The use of ST together with vitamin E can better control hyperglycemia-induced oxidative stress.     

Glutathione depletion and the production of reactive oxygen species in isolated hepatocyte suspensions

Diethyl maleate (DEM) (5 mM) and ethyl methanesulfonate (EMS) (35 mM) treatments rapidly depleted cellular reduced glutathione (GSH) below detectable levels (1 nmol/10(6) cells), and induced lipid peroxidation and necrotic cell death in freshly isolated rat hepatocytes. In hepatocytes incubated with 2.5 mM DEM and 10 mM EMS, however, the complete depletion of cellular GSH observed was not sufficient to induce lipid peroxidation or cell death. Instead, DEM- and EMS-induced lipid peroxidation and cell death were dependent on increased reactive oxygen species (ROS) production as measured by increases in dichlorofluorescein fluorescence. The addition of antioxidants (vitamin E succinate and deferoxamine) prevented lipid peroxidation and cell death, suggesting that lipid peroxidation is involved in the sequence of events leading to necrotic cell death induced by DEM and EMS. To investigate the subcellular site of ROS generation, the cytochrome P450 inhibitor, SKF525A, was found to reduce EMS-induced lipid peroxidation but did not protect against the loss of cell viability, suggesting a mitochondrial origin for the toxic lipid peroxidation event. In agreement with this conclusion, mitochondrial electron transport inhibitors (rotenone, thenoyltrifluoroacetone and antimycin A) increased EMS-induced lipid peroxidation and cell death, while the mitochondrial uncoupler, carbonyl cyanide m-chlorophenylhydrazone, blocked EMS- and DEM-mediated ROS production and lipid peroxidation. Furthermore, EMS treatment resulted in the significant loss of mitochondrial alpha-tocopherol shortly after its addition, and this loss preceded losses in cellular alpha-tocopherol levels. Treatment of hepatocytes with cyclosporin A, a mitochondrial permeability transition inhibitor, oxypurinol, a xanthine oxidase inhibitor, or BAPTA-AM, a calcium chelator, provided no protection against EMS-induced cell death or lipid peroxidation. Our results indicate that DEM and EMS induce cell death by a similar mechanism, which is dependent on the induction of ROS production and lipid peroxidation, and mitochondria are the major source for this toxic ROS generation. Cellular GSH depletion in itself does not appear to be responsible for the large increases in ROS production and lipid peroxidation observed.     

Three models of free radical-induced cell injury

Three models of free radical-induced cell injury are presented in this review. Each model is described by the mechanism of action of few prototype toxic molecules. Carbon tetrachloride and monobromotrichloromethane were selected as model molecules for alkylating agents that do not induce GSH depletion. Bromobenzene and allyl alcohol were selected as prototypes of GSH depleting agents. Paraquat and menadione were presented as prototypes of redox cycling compounds. All these groups of toxins are converted, during their intracellular metabolism, to active species which can be radical species or electrophilic intermediates. In most cases the activation is catalyzed by the microsomal mixed function oxidase system, while in other cases (e.g. allyl alcohol) cytosolic enzymes are responsible for the activation. Radical species can bind covalently to cellular macromolecules and can promote lipid peroxidation in cellular membranes. Of course both phenomena produce cell damage as in the case of CCl4 or BrCCl3 intoxication. However, the covalent binding is likely to produce damage at the molecular site where it occurs; lipid peroxidation, on the other hand, besides causing loss of membrane structure, also gives rise to toxic products such as 4-hydroxyalkenals and other aldehydes which in principle can move from the site of origin and produce effects at distant sites. Electrophilic intermediates readily reacts with cellular nucleophiles, primarily with GSH. The result is a severe GSH depletion as in the case of bromobenzene or allyl alcohol intoxication. When the depletion reaches some threshold values lipid peroxidation develops abruptly and in an extensive way. This event is accompanied by cellular death. The reason for which lipid peroxidation develops in a cell severely depleted of GSH remains to be clarified. Probably the loss of the defense systems against a constitutive oxidative stress is not compatible with cellular life. Some free radicals generated by one-electron reduction can react with oxygen to give superoxide anions which can be converted to other more dangerous reactive oxygen species. This is the case of paraquat and menadione. Damage to cellular macromolecules is due to the direct action of these oxygen radicals and, at least in the menadione-induced cytotoxicity, lipid peroxidation is not involved. All these initial events affect the protein sulfhydryl groups in the membranes. Since some protein thiols are essential components of the molecular arrangement responsible for the Ca2+ transport across cellular membranes, loss of such thiols can affect the calcium sequestration activity of subcellular compartments, that is the capacity of mitochondria and microsomes to regulate the cytosolic calcium level.(ABSTRACT TRUNCATED AT 400 WORDS)     

Heightened susceptibility of fish oil polyunsaturate-enriched neoplastic cells to ethane generation during lipid peroxidation

We have studied the generation of volatile hydrocarbons by fatty acid-modified L1210 leukemia cells in tissue culture as a measure of lipid peroxidation. There was considerable generation of ethane, and this was dependent on cell number and Fe2+ concentration; it was eliminated by antioxidants and augmented by ascorbic acid. The assay was sensitive and reproducible; ethane was detected when as little as 0.03% of the cellular n-3 (omega-3) fatty acids were peroxidized. To gain further understanding we used a lipid modification model that allows study of cells enriched with fatty acids of different degrees of unsaturation. The quantity of ethane generated was greatest by cells modified with fatty acids of the n-3 family, and there was a high direct correlation of percentage of n-3 fatty acids contained in cellular lipids with peroxidation as measured by ethane generation. Ethane generation was more sensitive in detecting peroxidation than loss of polyunsaturated fatty acids. We conclude that lipid-supplemented leukemic cells produce ethane, and that the rate of generation is a sensitive, quantitative, and highly useful measure of lipid peroxidation when small amounts of iron are present.     

Contracture and cell damage in calcium paradox is not caused by lipid peroxidation

The role of oxygen radicals and lipid peroxidation in calcium-paradox injury in isolated perfused rat hearts was studied by examining the effects of mannitol and (or) allopurinol on this phenomenon. Myocardial changes due to calcium paradox were characterized by contractile failure, a rise in resting tension, and cell damage. These changes were also accompanied by increased lipid peroxidation, as indicated by an increase in malondialdehyde content. Mannitol (an effective quencher of hydroxyl radicals) treatment resulted in a dose-dependent decrease in lipid peroxidation but did not affect other changes due to calcium paradox. Allopurinol (an inhibitor of xanthine oxidase) neither affected lipid peroxidation nor modified any of the structure-function changes due to calcium paradox. These data demonstrate the occurrence of lipid peroxidation which, however, may not be involved in the observed structure-function changes due to calcium paradox. It is also suggested that in this experimental model, xanthine oxidase may not be the inducer of oxygen radicals or of lipid peroxidation.     

The effect of calcium on phospholipid peroxidation

The effect of calcium ions on the peroxidation of ox-brain phospholipid liposomes in different free-radical catalysing systems has been assessed. Using thiobarbituric acid-reactivity (TBA) as a measure of lipid peroxidation, calcium ions both inhibited and enhanced peroxidation in the different systems.Changing the composition of the ox-brain phospholipid liposome with synthetic non TBA-reactive phosphatidylcholine, significantly altered its susceptibility to peroxidation both in the presence and absence of calcium ions.The results are discussed with reference to the possibility that calcium ions induce conformational changes in membrane phospholipids. Susceptibility to peroxidation is then influenced by a complex interrelationship between the qualitative lipid composition of the membrane, the pro-oxidant catalyst and the presence of calcium or other active ions.     

Iron toxicity in neurodegeneration

Iron is an essential element for life on earth, participating in a plethora of cellular processes where one-electron transfer reactions are required. Its essentiality, coupled to its scarcity in aqueous oxidative environments, has compelled living organisms to develop mechanisms that ensure an adequate iron supply, at times with disregard to long-term deleterious effects derived from iron accumulation. However, iron is an intrinsic producer of reactive oxygen species, and increased levels of iron promote neurotoxicity because of hydroxyl radical formation, which results in glutathione consumption, protein aggregation, lipid peroxidation and nucleic acid modification. Neurons from brain areas sensitive to degeneration accumulate iron with age and thus are subjected to an ever increasing oxidative stress with the accompanying cellular damage. The ability of these neurons to survive depends on the adaptive mechanisms developed to cope with the increasing oxidative load. Here, we describe the chemical and thermodynamic peculiarities of iron chemistry in living matter, review the components of iron homeostasis in neurons and elaborate on the mechanisms by which iron homeostasis is lost in Parkinson's disease, Alzheimer's disease and other diseases in which iron accumulation has been demonstrated.     

Posttranslational modification and regulation of glutamate-cysteine ligase by the α,β-unsaturated aldehyde 4-hydroxy-2-nonenal

4-Hydroxy-2-nonenal (4-HNE) is a lipid peroxidation product formed during oxidative stress that can alter protein function via adduction of nucleophilic amino acid residues. 4-HNE detoxification occurs mainly via glutathione (GSH) conjugation and transporter-mediated efflux. This results in a net loss of cellular GSH, and restoration of GSH homeostasis requires de novo GSH biosynthesis. The rate-limiting step in GSH biosynthesis is catalyzed by glutamate-cysteine ligase (GCL), a heterodimeric holoenzyme composed of a catalytic (GCLC) and a modulatory (GCLM) subunit. The relative levels of the GCL subunits are a major determinant of cellular GSH biosynthetic capacity and 4-HNE induces the expression of both GCL subunits. In this study, we demonstrate that 4-HNE can alter GCL holoenzyme formation and activity via direct posttranslational modification of the GCL subunits in vitro. 4-HNE directly modified Cys553 of GCLC and Cys35 of GCLM in vitro, which significantly increased monomeric GCLC enzymatic activity, but reduced GCL holoenzyme activity and formation of the GCL holoenzyme complex. In silico molecular modeling studies also indicate these residues are likely to be functionally relevant. Within a cellular context, this novel posttranslational regulation of GCL activity could significantly affect cellular GSH homeostasis and GSH-dependent detoxification during periods of oxidative stress.     

Regional alterations in calcium homeostasis in the primate brain following chronic aluminium exposure

The present study investigates the possible effects of chronic aluminium exposure on the various aspects of calcium homeostasis in the primate central nervous system. Aluminium administration caused a marked decline in the activity of Ca2+ ATPase in the monkey brain. The total calcium content was also significantly raised following aluminium exposure. Concomittant to the increase in the calcium content, the levels of lipid peroxidation were also augmented in the aluminium treated animals, thereby further accentuating the aluminium induced neuronal damage. In addition, aluminium had an inhibitory effect on the depolarization induced 45Ca2+ uptake via the voltage operated channels. The results presented herein, indicate that the toxic effects of aluminium could be mediated through modifications in the intracellular calcium homeostasis with resultant altered neuronal function.     

Carbon tetrachloride-induced liver cell injury in the Mongolian gerbil (Meriones unguiculatus)

1. Male Mongolian gerbils (Meriones unguiculatus) liver activates CCl4 to free radicals that bind covalently to cellular components (CB) and stimulate a lipid peroxidation (LP) process to a larger extent than the rat liver. 2. CCl4 administration results in a less intense necrogenic effect in gerbils than in rats and does not cause fatty liver. 3. CCl4 causes less intense effects on liver ultrastructure or calcium metabolism but more marked depression of glucose 6 phosphatase activity (G6P-ase) in gerbils than in rats. 4. Results suggest that a better ability of gerbil liver to keep calcium homeostasis than rat liver might be the cause of their relative resistance to necrosis. Higher intensity of CB and LP in gerbils than in rats might explain more intense effects on G6P-ase.