Effect of hypoxic acclimation on anoxia tolerance in Vitis roots: response of metabolic activity and K+ fluxes

The effect of a hypoxic pre-treatment (HPT) on improving tolerance to prolonged anoxia conditions in two contrasting Vitis species (V. riparia, anoxia tolerant; V. rupestris, anoxia sensitive) was evaluated. The energy economy of root cells was studied by measuring heat production, the activity of pyruvate decarboxylase (PDC) and alcohol dehdrogenase (ADH), ethanol and ATP production, and K(+) fluxes. The results showed that HPT is an effective tool in order to maintain a sustainable metabolic performance in both the species under anoxia conditions, especially in sensitive species such as V. rupestris. Our results showed that the improved tolerance was mainly driven by: (i) an enhanced activity of key enzymes in alcohol fermentation (ADC and PDC); (ii) the capability to maintain a higher level of respiration, evidenced by a lesser decrease in heat development and ATP production; and (iii) the maintenance of a better ion homeostasis (highlighted by measurement of K(+) fluxes) and K(+) channel functionality.     

Evidence of anoxia-induced channel arrest in the brain of the goldfish (Carassius auratus)

The common goldfish (Carassius auratus) is extremely anoxia tolerant and here we provide evidence that "channel arrest" in the brain of these fish contributes to ATP conservation during periods of anoxia. Whole-cell patch-clamp recordings of slices taken from the telencephalon indicated that the N-methyl-d-aspartate (NMDA) receptor, an ionotropic glutamate receptor and Ca(2+)-channel, underwent a 40-50% reduction in activity during 40 min of acute anoxia. This is the first direct evidence of channel arrest in an anoxia-tolerant fish. Because goldfish produce ethanol as a byproduct of anaerobic metabolism we then conducted experiments to determine if the observed reduction in NMDA receptor current amplitude was due to inhibition by ethanol. NMDA receptor currents were not inhibited by ethanol (10 mmol L(-1)), suggesting that channel arrest of the receptor involved other mechanisms. Longer-term (48 h) in vivo exposure of goldfish to anoxic conditions (less than 1% dissolved O(2)) provided indirect evidence that a reduction in Na(+)/K(+)-ATPase activity also contributed to ATP conservation in the brain but not the gills. Anoxia under these conditions was characterized by a decrease in brain Na(+)/K(+)-ATPase activity of 30-40% by 24 h. Despite 90% reductions in the rates of ventilation, no change was observed in gill Na(+)/K(+)-ATPase activity during the 48-h anoxia exposure, suggesting that branchial ion permeability was unaffected. We conclude that rapid "channel arrest" of NMDA receptors likely prevents excitotoxicity in the brain of the goldfish, and that a more slowly developing decrease in Na(+)/K(+)-ATPase activity also contributes to the profound metabolic depression seen in these animals during oxygen starvation.     

Manipulation of ethanol production in anoxic rice coleoptiles by exogenous glucose determines rates of ion fluxes and provides estimates of energy requirements for cell maintenance during anoxia

Ethanol production by anoxic, excised, 7-10 mm tips of rice coleoptiles was manipulated using a range of exogenous glucose concentrations. Such a dose-response curve enabled good estimates at which level of ethanol production (and hence by inference ATP production), injury commenced and also allowed assessments of energy requirements for maintenance in anoxia. Rates of net uptake or loss of K+ and P by these excised coleoptile tips were related to rates of ethanol production (r2 of 0.59 and 0.68, respectively). At 72 h anoxia, ATP levels in excised tips were similar at 0, 2.5, and 50 mol m(-3) exogenous glucose, despite large differences in the inferred rates of ATP production. At 96 h anoxia, tips without exogenous glucose had low ATP concentrations; these may be the cause or the consequence of cell injury. In tips without glucose, injury was indicated by losses of K+ and Cl- between 72-96 h anoxia, and during the first hour after re-aeration, while later than 1 h after re-aeration, rates of net uptake were substantially lower than for re-aerated tips previously in anoxia with exogenous glucose. Between 96 h and 124 h anoxia, ion losses from tips without exogenous glucose increased while recovery of net uptake after re-aeration was very sluggish and incomplete. The energy requirement for maintenance of health and survival of anoxic coleoptile tips, expressed on a fresh weight basis, was lower than for three other anoxia-tolerant plant tissues/cells, studied previously. However, the energy requirement on a protein basis was assessed at 1.4 micromol ATP mg(-1) protein h(-1) and this value is 2.6-5.4-fold higher than for the other plant tissues/cells. Yet, this requirement was still only 58-88% of the published values for aerated tissues. The reason for this relatively high ATP requirement per unit protein in anoxic rice coleoptiles remains to be elucidated.     

Short- and long-term enzymatic regulation secondary to metabolic insult in the rat retina

Changes in oxygen and/or glucose availability may result in altered levels of ATP production and amino acid levels, and alteration in lactic acid production. However, under certain metabolic insults, the retina demonstrates considerable resilience and maintains ATP production, and/or retinal function. We wanted to investigate whether this resilience would be reflected in alterations in the activity of key enzymes of retinal metabolism, or enzymes associated with amino acid production that may supply their carbon skeleton for energy production. Enzymatic assays were conducted to determine the activity of key retinal metabolic enzymes total ATPase and Na(+)/K(+)-ATPase, aspartate aminotransferase and lactate dehydrogenase. In vitro anoxia led to an increase in retinal lactate dehydrogenase activity and to a decrease in retinal aspartate aminotransferase activity, without significant changes in Na(+)/K(+)-ATPase activity. In vivo inhibition of glutamine synthetase resulted in a short-term significant decrease in retinal aspartate aminotransferase activity. An increase in retinal aspartate aminotransferase and lactate dehydrogenase activities was accompanied by altered levels of amino acids in neurons and glia after partial inhibition of glial metabolism, implying that short- and long-term up- and down-regulation of key metabolic enzymes occurs to supply carbon skeletons for retinal metabolism. ATPase activity does not appear to fluctuate under the metabolic stresses employed in our experimental procedures.     

A Basic Peroxidase Isoenzyme, Marker of Resistance Against Plasmopara viticola in Grapevines, is Induced by an Elicitor from Trichoderma viride in Susceptible Grapevines

The constitutive expression of basic peroxidase isoenzymes in the Plasmopara viticola -resistant ( Vitis vinifera × Vitis rupestris) × Vitis riparia crossing and in the P. viticola -susceptible V. vinifera parent species was studied. The results illustrate that both leaves and stems of the ( V. vinifera × V. rupestris) × V. riparia crossing showed the differential expression of a basic peroxidase isoenzyme B₃ (pl = 8.9), this being almost completely absent from the P. viticola -susceptible V. vinifera parent species. To test whether the basic peroxidase isoenzyme B₃ may be considered as a molecular marker of disease resistance in Vitis spp., suspension cell cultures derived from the P. viticola -susceptible V. vinifera parent species were treated with an elicitor (cellulase Onoztika R-10) from the soil fungus Trichoderma viride , a specific and well-known elicitor of disease resistance reactions in grapevines. The results showed that treatment with the elicitor induces, simultaneously with the activation of the disease resistance mechanism, the appearance of B₃ in the cell cultures. These results suggest that the basic peroxidase isoenzyme B₃ may be considered as a marker of disease resistance in Vitis species since it is present in the P. viticola -resistant ( V. vinifera × V. rupestris) × V. riparia hybrid and is induced by the elicitor Onozuka R-10 in cell cultures of the P. viticola -susceptible Vitis vinifera parent species. This conclusion is supported by the presence of this isoenzyme in other resistant and its absence in other susceptible Vitis spp.     

Stress preconditioning of spreading depression in the locust CNS

Cortical spreading depression (CSD) is closely associated with important pathologies including stroke, seizures and migraine. The mechanisms underlying SD in its various forms are still incompletely understood. Here we describe SD-like events in an invertebrate model, the ventilatory central pattern generator (CPG) of locusts. Using K(+) -sensitive microelectrodes, we measured extracellular K(+) concentration ([K(+)](o)) in the metathoracic neuropile of the CPG while monitoring CPG output electromyographically from muscle 161 in the second abdominal segment to investigate the role K(+) in failure of neural circuit operation induced by various stressors. Failure of ventilation in response to different stressors (hyperthermia, anoxia, ATP depletion, Na(+)/K(+) ATPase impairment, K(+) injection) was associated with a disturbance of CNS ion homeostasis that shares the characteristics of CSD and SD-like events in vertebrates. Hyperthermic failure was preconditioned by prior heat shock (3 h, 45 degrees C) and induced-thermotolerance was associated with an increase in the rate of clearance of extracellular K(+) that was not linked to changes in ATP levels or total Na(+)/K(+) ATPase activity. Our findings suggest that SD-like events in locusts are adaptive to terminate neural network operation and conserve energy during stress and that they can be preconditioned by experience. We propose that they share mechanisms with CSD in mammals suggesting a common evolutionary origin.     

Selective ion changes during spontaneous mitochondrial transients in intact astrocytes

The bioenergetic status of cells is tightly regulated by the activity of cytosolic enzymes and mitochondrial ATP production. To adapt their metabolism to cellular energy needs, mitochondria have been shown to exhibit changes in their ionic composition as the result of changes in cytosolic ion concentrations. Individual mitochondria also exhibit spontaneous changes in their electrical potential without altering those of neighboring mitochondria. We recently reported that individual mitochondria of intact astrocytes exhibit spontaneous transient increases in their Na(+) concentration. Here, we investigated whether the concentration of other ionic species were involved during mitochondrial transients. By combining fluorescence imaging methods, we performed a multiparameter study of spontaneous mitochondrial transients in intact resting astrocytes. We show that mitochondria exhibit coincident changes in their Na(+) concentration, electrical potential, matrix pH and mitochondrial reactive oxygen species production during a mitochondrial transient without involving detectable changes in their Ca(2+) concentration. Using widefield and total internal reflection fluorescence imaging, we found evidence for localized transient decreases in the free Mg(2+) concentration accompanying mitochondrial Na(+) spikes that could indicate an associated local and transient enrichment in the ATP concentration. Therefore, we propose a sequential model for mitochondrial transients involving a localized ATP microdomain that triggers a Na(+)-mediated mitochondrial depolarization, transiently enhancing the activity of the mitochondrial respiratory chain. Our work provides a model describing ionic changes that could support a bidirectional cytosol-to-mitochondria ionic communication.     

Characterisation of the oxygen fluxes in the division, elongation and mature zones of Vitis roots: influence of oxygen availability

Oxygen fluxes into and from root cells of Vitis rupestris (flooding sensitive), V. riparia (flooding tolerant) and V. vinifera (medium tolerance to flooding) were measured under different levels of O2 availability using a recently developed polarographic O2-selective, vibrating-microelectrode system. The system enables fluxes to be measured with a spatial resolution of 2-3 microm and a temporal resolution of 10 s. No difference in root porosity was found among the genotypes when grown for 30 days in an aerated solution. Under normoxic conditions, O2 influx was characterised by two distinct peaks, one in the division zone and the other in the elongation zone of the roots. This pattern was found in all three species studied, although the fluxes showed a different magnitude. The peak in the elongation zone coincided with maximum relative elemental growth rates. When the energetics of the cell was disturbed by cyanide, both growth and oxygen O2 influxes ceased at the same time. Under hypoxic conditions, V. riparia plants showed a precise strategy directed toward the maintenance of enough O2 for the respiratory needs of mitosis in the apical meristem of the roots. Thus, whereas in the division zone of V. rupestris and V. vinifera, at bulk O2 concentrations of 0.094 mol x m(-3), the O2 influx was reduced by 70.5 and 38.5%, respectively, for V. riparia no variation in the O2 influx was detected down to bulk O2 concentrations of 0.078 mol x m(-3). Moreover, in accordance with the different tolerances of the plants, the Vitis genotypes were found to differ in their radial O2 loss from the adventitious roots when in an O2-free environment. The results are discussed in terms of possible mechanisms of response to anoxia in Vitis species with different tolerances to flooding.     

Quantifying ATP turnover in anoxic coleoptiles of rice (Oryza sativa) demonstrates preferential allocation of energy to protein synthesis

Oxygen deprivation limits the energy available for cellular processes and yet no comprehensive ATP budget has been reported for any plant species under O(2) deprivation, including Oryza sativa. Using 3-d-old coleoptiles of a cultivar of O. sativa tolerant to flooding at germination, (i) rates of ATP regeneration in coleoptiles grown under normoxia (aerated solution), hypoxia (3% O(2)), and anoxia (N(2)) and (ii) rates of synthesis of proteins, lipids, nucleic acids, and cell walls, as well as K(+) transport, were determined. Based on published bioenergetics data, the cost of synthesizing each class of polymer and the proportion of available ATP allocated to each process were then compared. Protein synthesis consumed the largest proportion of ATP synthesized under all three oxygen regimes, with the proportion of ATP allocated to protein synthesis in anoxia (52%) more than double that in normoxic coleoptiles (19%). Energy allocation to cell wall synthesis was undiminished in hypoxia, consistent with preferential elongation typical of submerged coleoptiles. Lipid synthesis was also conserved strongly in O(2) deficits, suggesting that membrane integrity was maintained under anoxia, thus allowing K(+) to be retained within coleoptile cells. Rates of protein synthesis in coleoptiles from rice cultivars with contrasting tolerance to oxygen deficits (including mutants deficient in fermentative enzymes) confirmed that synthesis and turnover of proteins always accounted for most of the ATP consumed under anoxia. It is concluded that successful establishment of rice seedlings under water is largely due to the capacity of coleoptiles to allocate energy to vital processes, particularly protein synthesis.     

Importance of glycolysis for the energetics of anoxia-tolerant and anoxia-intolerant teleost hepatocytes

The importance of glycolysis, as an ATP-producing and substrate-providing pathway, was studied in anoxia-tolerant (goldfish) and anoxia-intolerant (trout) hepatocytes. Inhibition of glycolysis with iodoacetic acid (IAA) left aerobic ATP production largely unaffected in hepatocytes from both species but caused a significant decrease of ATP contents in the goldfish cells. Ouabain-sensitive oxygen consumption (osVo2), an estimate of mitochondrial ATP production coupled to ATP consumption by the Na(+) pump, was significantly reduced in IAA-treated goldfish hepatocytes, whereas it was unaltered in trout hepatocytes. Partial reduction of mitochondrial respiration, achieved by titration with cyanide (CN), strongly stimulated glycolytic flux but did not affect ATP contents of hepatocytes from both species. Under these conditions, osVo2 became undetectable. Rb(+)-uptake rates, providing a direct estimate of Na(+)-pump activity, were in good agreement with estimates derived from osVo2 in IAA-treated cells, showing a decrease in goldfish and no change in trout. However, they indicated persistent Na(+)-pump activity despite the lack of osVo2 in CN-treated cells. Overall, these data indicate that in goldfish hepatocytes Na(+)-pump activity is more dependent on glycolytic ATP production as compared to trout hepatocytes. Protein synthesis of goldfish hepatocytes was inhibited in IAA- and CN-treated cells, possibly reflecting the hierarchical organization of energy metabolism. In trout hepatocytes, protein synthesis could be sustained at control levels, given that energetic substrate provision was not limited.     

Na+-K+-ATPase in rat skeletal muscle: muscle fiber-specific differences in exercise-induced changes in ion affinity and maximal activity

It is unclear whether muscle activity reduces or increases Na(+)-K(+)-ATPase maximal in vitro activity in rat skeletal muscle, and it is not known whether muscle activity changes the Na(+)-K(+)-ATPase ion affinity. The present study uses quantification of ATP hydrolysis to characterize muscle fiber type-specific changes in Na(+)-K(+)-ATPase activity in sarcolemmal membranes and in total membranes obtained from control rats and after 30 min of treadmill running. ATPase activity was measured at Na(+) concentrations of 0-80 mM and K(+) concentrations of 0-10 mM. K(m) and V(max) values were obtained from a Hill plot. K(m) for Na(+) was higher (lower affinity) in total membranes of glycolytic muscle (extensor digitorum longus and white vastus lateralis), when compared with oxidative muscle (red gastrocnemius and soleus). Treadmill running induced a significant decrease in K(m) for Na(+) in total membranes of glycolytic muscle, which abolished the fiber-type difference in Na(+) affinity. K(m) for K(+) (in the presence of Na(+)) was not influenced by running. Running only increased the maximal in vitro activity (V(max)) in total membranes from soleus, whereas V(max) remained constant in the three other muscles tested. In conclusion, muscle activity induces fiber type-specific changes both in Na(+) affinity and maximal in vitro activity of the Na(+)-K(+)-ATPase. The underlying mechanisms may involve translocation of subunits and increased association between PLM units and the alphabeta complex. The changes in Na(+)-K(+)-ATPase ion affinity are expected to influence muscle ion balance during muscle contraction.     

Operation of the F(0) motor of the ATP synthase

ATP, the universal carrier of cell energy is manufactured from ADP and phosphate by the enzyme ATP synthase using the energy stored in a transmembrane ion gradient. The two components of the ion gradient (DeltapH or DeltapNa(+)) and the electrical potential difference Deltapsi are thermodynamically but not kinetically equivalent. In contrast to accepted wisdom, the electrical component is kinetically indispensable not only for bacterial ATP synthases but also for that from chloroplasts. Recent biochemical studies with the Na(+)-translocating ATP synthase of Propionigenium modestum have given a good idea of the ion translocation pathway in the F(0) motor. Taken together with biophysical data, the operating principles of the motor have been delineated.     

Balancing of mitochondrial and glycolytic ATP production and of the ATP-consuming processes of Ehrlich mouse ascites tumour cells in a high phosphate medium

A balance of energy budgeting of Ehrlich mouse ascites tumour cells including mitochondrial and glycolytic ATP production and about 80% of ATP consumption in a high phosphate medium is presented. In the share of glycolysis was about one-third of the total ATP production, more than twice that found in a low phosphate medium. The extent of a single energy reaction was assessed from the decrease of coupled oxygen consumption and lactate formation following the specific inhibition of this process. The inhibitory effects on coupled respiration and glycolysis were identical for the energy consuming processes measured: protein turnover, Na+/K(+)-ATPase, Ca2(+)-transport and RNA synthesis.     

The role of glucose in the survival and `recovery'' of the anoxic isolated perfused rat heart

Studies with the isolated perfused working rat heart were carried out to investigate factors that may enable the heart to recover after periods of anoxia. It was found that the presence of glucose in the perfusion fluid during anoxia was essential for complete post-anoxic recovery and the presence of a high concentration of K(+) increased not only the rate of recovery but also the final extent of recovery. In an attempt to clarify the roles played by glucose and K(+) in aiding the survival and recovery of the anoxic myocardium the concentrations of parameters associated with energy liberation and anaerobic glycolysis (ATP, ADP, AMP, P(i), creatine phosphate, glycogen and lactate) were measured in the presence and absence of glucose during the anoxic phase. Determinations of these parameters were carried out during the working aerobic control period, the anoxic period (K(+) arrest) and the recovery period. The results demonstrated that glucose acted as an energy source during anoxia and thus maintained myocardial concentrations of high-energy phosphates, particularly ATP. These studies have also shown a direct relationship between the ability of the heart to recover and the concentration of myocardial ATP at the time of reoxygenation.     

The existence of the K(+) channel in plant mitochondria.

In this study, evidence is given that a number of isolated coupled plant mitochondria (from durum wheat, bread wheat, spelt, rye, barley, potato, and spinach) can take up externally added K(+) ions. This was observed by following mitochondrial swelling in isotonic KCl solutions and was confirmed by a novel method in which the membrane potential decrease due to externally added K(+) is measured fluorimetrically by using safranine. A detailed investigation of K(+) uptake by durum wheat mitochondria shows hyperbolic dependence on the ion concentration and specificity. K(+) uptake electrogenicity and the non-competitive inhibition due to either ATP or NADH are also shown. In the whole, the experimental findings reported in this paper demonstrate the existence of the mitochondrial K(+)(ATP) channel in plants (PmitoK(ATP)). Interestingly, Mg(2+) and glyburide, which can inhibit mammalian K(+) channel, have no effect on PmitoK(ATP). In the presence of the superoxide anion producing system (xanthine plus xanthine oxidase), PmitoK(ATP) activation was found. Moreover, an inverse relationship was found between channel activity and mitochondrial superoxide anion formation, as measured via epinephrine photometric assay. These findings strongly suggest that mitochondrial K(+) uptake could be involved in plant defense mechanism against oxidative stress due to reactive oxygen species generation.     

Adenosine as a signal for ion channel arrest in anoxia-tolerant organisms

Certain freshwater turtles and fish are extremely anoxia-tolerant, capable of surviving hours of anoxia at high temperatures and weeks to months at low temperatures. There is great interest in understanding the cellular mechanisms underlying anoxia-tolerance in these groups because they are anoxia-tolerant vertebrates and because of the far-reaching medical benefits that would be gained. It has become clear that a pre-condition of prolonged anoxic survival must involve the matching of ATP production with ATP utilization to maintain stable ATP levels during anoxia. In most vertebrates, anoxia leads to a severe decrease in ATP production without a concomitant reduction in utilization, which inevitably leads to the catastrophic events associated with cell death or necrosis. Anoxia-tolerant organisms do not increase ATP production when faced with anoxia, but rather decrease utilization to a level that can be met by anaerobic glycolysis alone. Protein synthesis and ion movement across the plasma membrane are the two main targets of regulatory processes that reduce ATP utilization and promote anoxic survival. However, the oxygen sensing and biochemical signaling mechanisms that achieve a coordinated reduction in ATP production and utilization remain unclear. One candidate-signaling compound whose extracellular concentration increases in concert with decreasing oxygen availability is adenosine. Adenosine is known to have profound effects on various aspects of tissue metabolism, including protein synthesis, ion pumping and permeability of ion channels. In this review, I will investigate the role of adenosine in the naturally anoxia-tolerant freshwater turtle and goldfish and give an overview of pathways by which adenosine concentrations are regulated.     

Plasma membrane depolarization reduces nitric oxide (NO) production in P388D.1 macrophage-like cells during Leishmania major infection

In the present study, we compare changes in host cell plasma membrane potential (V(m)), K(+) fluxes, and NO production during K(+) channel blockade with those changes that occur during infection with Leishmania major. Infection of P388D.1 cells with L. major promastigotes or treatment with K(+) channel blockers (either 1mM 4-AP, 10mM TEA, or 200 microM quinine) suppressed NO production. Inhibition of NO production correlated with depolarization of the P388D.1 cell V(m). Infection of P388D.1 cells with L. major increased the unidirectional influx of rubidium (86Rb), a tracer for K(+) flux, that was comparable to that induced by K(+) channel blockade by 1mM 4-AP. The similar effects of K(+) channel blockers and L. major on NO production, K(+) influx, and V(m) suggest that K(+) channel activity and the maintenance of V(m) is important for NO production in these cells. We suggest that intracellular parasites employ a strategy to inhibit NO production by disrupting V(m) during the invasion/infection process by altering host cell K(+) channel activity.     

Effect of lead on Na+, K(+)-ATPase activity in Penaeus indicus postlarvae

In vivo effect of lead on Na, K(+)-ATPase was studied in plasma membrane/mitochondrial fraction of P. indicus post-larvae (PL), exposed to 30 days to a sublethal concentration (1.44 ppm) of lead. A significant (P < 0.05) decrease in the enzyme activity was observed for exposed PL with respect to their controls at different intervals except 24hr. Further the substrate (ATP) and ion (Na+ and K+)-dependent kinetics of Na+, K(+)-ATPase was studied with the plasma membrane/mitochondrial fractions of control and 30 days exposed PL. The apparent KM and V(max). values were calculated to determine the nature of inhibition. Both the control and exposed PL showed almost the same apparent KM values in the presence of different substrate or ion concentrations indicating that lead interacts with the enzyme at a different binding site.     

Effects of sodium nitroprusside and nitrite on ouabaine-sensitive Na+, K(+)-ATPase activity of myometrium smooth muscle

Effective inhibiting effect of sodium nitroprusside and nitrite on Na+, K(+)-ATPase enzymatic activity of miometrium sarcolemma fraction was shown. Seeming Ki was of micromolar and submicromolar magnitudes. Investigations with sodium nitroprusside demonstrated an uncompetitive inhibition for ATP (growth of affinity for ATP and decrease of maximal velocity) and mixed inhibition for cations (decrease of maximal velocity and activation of constant for K+). Inhibitory effect of ouabain was reduced in the presence of sodium nitroprusside; ditiothreitol prevented enzyme inactivation by sodium nitroprusside. Kinetic analysis of experimental results using ouabain and ditiothreitol suggests chemical modification of enzyme sulfhydryl groups. Resistant component of Na+, K(+)-ATPase activity, which is sensitive to the action of detergent digitonine, was observed. In comparative investigations with postnucleus fraction stimulating actions of sodium nitroprusside, sodium nitrite, cGMP (more enhance) were shown. Methylene blue (soluble guanilate-cyclase inhibitor) prevented the activation of Na+, K(+)-ATPase activity by sodium nitrite. We suppose that the way of enzyme activation is prevalent in the condition of the moderate formation of nitric oxide and in the absence of hyper(over)production of reactive oxygen species.