The role of ATPase in glycolysis of Ehrlich ascites tumor cells

The Anti-Cancer Effect of Quercetin: Molecular Implications in Cancer Metabolism

Cancer is a problem with worldwide importance and is the second leading cause of death globally. Cancer cells reprogram their metabolism to support their uncontrolled expansion by increasing biomass (anabolic metabolism-glycolysis) at the expense of their energy (bioenergetics- mitochondrial function) requirements. In this aspect, metabolic reprogramming stands out as a key biological process in understanding the conversion of a normal cell into a neoplastic precursor. Quercetin is the major representative of the flavonoid subclass of flavonols. Quercetin is ubiquitously present in fruits and vegetables, being one of the most common dietary flavonols in the western diet. The anti-cancer effects of quercetin include its ability to promote the loss of cell viability, apoptosis and autophagy through the modulation of PI3K/Akt/mTOR, Wnt/-catenin, and MAPK/ERK1/2 pathways. In this review, we discuss the role of quercetin in cancer metabolism, addressing specifically its ability to target molecular pathways involved in glucose metabolism and mitochondrial function.

Metabolic reprogramming and dysregulated metabolism: cause, consequence and/or enabler of environmental carcinogenesis?

Environmental contributions to cancer development are widely accepted, but only a fraction of all pertinent exposures have probably been identified. Traditional toxicological approaches to the problem have largely focused on the effects of individual agents at singular endpoints. As such, they have incompletely addressed both the pro-carcinogenic contributions of environmentally relevant low-dose chemical mixtures and the fact that exposures can influence multiple cancer-associated endpoints over varying timescales. Of these endpoints, dysregulated metabolism is one of the most common and recognizable features of cancer, but its specific roles in exposure-associated cancer development remain poorly understood. Most studies have focused on discrete aspects of cancer metabolism and have incompletely considered both its dynamic integrated nature and the complex controlling influences of substrate availability, external trophic signals and environmental conditions. Emerging high throughput approaches to environmental risk assessment also do not directly address the metabolic causes or consequences of changes in gene expression. As such, there is a compelling need to establish common or complementary frameworks for further exploration that experimentally and conceptually consider the gestalt of cancer metabolism and its causal relationships to both carcinogenesis and the development of other cancer hallmarks. A literature review to identify environmentally relevant exposures unambiguously linked to both cancer development and dysregulated metabolism suggests major gaps in our understanding of exposure-associated carcinogenesis and metabolic reprogramming. Although limited evidence exists to support primary causal roles for metabolism in carcinogenesis, the universality of altered cancer metabolism underscores its fundamental biological importance, and multiple pleiomorphic, even dichotomous, roles for metabolism in promoting, antagonizing or otherwise enabling the development and selection of cancer are suggested.

Effect of traumatic brain injury and nitrone radical scavengers on relative changes in regional cerebral blood flow and glucose uptake in rats

Changes in regional cerebral blood flow (rCBF) and glucose metabolism are commonly associated with traumatic brain injury (TBI). Reactive oxygen species (ROS) have been implicated as key contributors to the secondary injury process after TBI. Here, pretreatment with the nitrone radical scavengers (alpha-phenyl-N-tert-butyl nitrone (PBN) or its sulfonated analogue sodium 2-sulfophenyl-N-tert-butyl nitrone (S-PBN) were used as tools to study the effects of ROS on rCBF and glucose metabolism after moderate (2.4-2.6 atm) lateral fluid percussion injury (FPI) in rats. S-PBN has a half-life in plasma of 9 min and does not penetrate the blood-brain barrier (BBB). In contrast, PBN has a half-life of 3 h and readily penetrates the BBB. Regional cerebral blood flow (rCBF) and glucose metabolism was estimated by using (99m)Tc-HMPAO and [(18)F]Fluoro-2-deoxyglucose (FDG) autoradiography, respectively, at 42 min (n = 37) and 12 h (n = 34) after the injury. Regions of interest were the parietal cortex and hippocampus bilaterally. As expected, FPI produced an early (42-min) hypoperfusion in ipsilateral cortex and an increase in glucose metabolism in both cortex and hippocampus, giving way to a state of hypoperfusion and decreased glucose metabolism at 12 h postinjury. On the contralateral side, a hypoperfusion in the cortex and hippocampus was seen at 12 h only, but no significant changes in glucose metabolism. Both S-PBN and PBN attenuated the trauma-induced changes in rCBF and glucose metabolism. Thus, the early improvement in rCBF and glucose metabolism correlates with and may partly mediate the improved functional and morphological outcome after TBI in nitrone-treated rats.

Sorting of metabolic pathway flux by the plasma membrane in cerebrovascular smooth muscle cells

We used beta-escin-permeabilized pig cerebral microvessels (PCMV) to study the organization of carbohydrate metabolism in the cytoplasm of vascular smooth muscle (VSM) cells. We have previously demonstrated (Lloyd PG and Hardin CD. Am J Physiol Cell Physiol 277: C1250-C1262, 1999) that intact PCMV metabolize the glycolytic intermediate [1-(13)C]fructose 1,6-bisphosphate (FBP) to [1-(13)C]glucose with negligible production of [3-(13)C]lactate, while simultaneously metabolizing [2-(13)C]glucose to [2-(13)C]lactate. Thus gluconeogenic and glycolytic intermediates do not mix freely in intact VSM cells (compartmentation). Permeabilized PCMV retained the ability to metabolize [2-(13)C]glucose to [2-(13)C]lactate and to metabolize [1-(13)C]FBP to [1-(13)C]glucose. The continued existence of glycolytic and gluconeogenic activity in permeabilized cells suggests that the intermediates of these pathways are channeled (directly transferred) between enzymes. Both glycolytic and gluconeogenic flux in permeabilized PCMV were sensitive to the presence of exogenous ATP and NAD. It was most interesting that a major product of [1-(13)C]FBP metabolism in permeabilized PCMV was [3-(13)C]lactate, in direct contrast to our previous findings in intact PCMV. Thus disruption of the plasma membrane altered the distribution of substrates between the glycolytic and gluconeogenic pathways. These data suggest that organization of the plasma membrane into distinct microdomains plays an important role in sorting intermediates between the glycolytic and gluconeogenic pathways in intact cells.

Internal regulation of ATP turnover, glycolysis and oxidative phosphorylation in rat hepatocytes

Previously [Ainscow, E.K. & Brand, M.D. (1999) Eur. J. Biochem. 263, 671-685], top-down control analysis was used to describe the control pattern of energy metabolism in rat hepatocytes. The system was divided into nine reaction blocks (glycogen breakdown, glucose release, glycolysis, lactate production, NADH oxidation, pyruvate oxidation, mitochondrial proton leak, mitochondrial phosphorylation and ATP consumption) linked by five intermediates (intracellular glucose 6-phosphate, pyruvate and ATP levels, cytoplasmic NADH/NAD ratio and mitochondrial membrane potential). The kinetic responses (elasticities) of reaction blocks to intermediates were determined and used to calculate control coefficients. In the present paper, these elasticities and control coefficients are used to quantify the internal regulatory pathways within the cell. Flux control coefficients were partitioned to give partial flux control coefficients. These describe how strongly one block of reactions controls the flux through another via its effects on the concentration of a particular intermediate. Most flux control coefficients were the sum of positive and negative partial effects acting through different intermediates; these partial effects could be large compared to the final control strength. An important result was the breakdown of the way ATP consumption controlled respiration: changes in ATP level were more important than changes in mitochondrial membrane potential in stimulating oxygen consumption when ATP consumption increased. The partial internal response coefficients to changes in each intermediate were also calculated; they describe how steady state concentrations of intermediates are maintained. Increases in mitochondrial membrane potential were opposed mostly by decreased supply, whereas increases in glucose-6-phosphate, NADH/NAD and pyruvate were opposed mostly by increased consumption. Increases in ATP were opposed significantly by both decreased supply and increased consumption.

Top-down control analysis of ATP turnover, glycolysis and oxidative phosphorylation in rat hepatocytes

Control analysis was used to analyse the internal control of rat hepatocyte metabolism. The reactions of the cell were grouped into nine metabolic blocks linked by five key intermediates. The blocks were glycogen breakdown, glucose release, glycolysis, lactate production, NADH oxidation, pyruvate oxidation, mitochondrial proton leak, mitochondrial phosphorylation and ATP consumption. The linking intermediates were intracellular glucose-6-phosphate, pyruvate and ATP levels, cytoplasmic NADH/NAD ratio and mitochondrial membrane potential. The steady-state fluxes through the blocks and the levels of the intermediates were measured in the absence and presence of specific effectors of hepatocyte metabolism. Application of the multiple modulation approach gave the kinetic responses of each block to each intermediate (the elasticities). These were then used to calculate all of the control coefficients, which describe the degree of control each block had over the level of each intermediate, and over the rate of each process. Within this full description of control, many different interactions could be identified. One key finding was that the processes that consumed ATP had only 35% of the control over the rate of ATP consumption. Instead, the reactions that produced ATP exerted the most control over ATP consumption rate; particularly important were mitochondrial phosphorylation (30% of control) and glycolysis (19%). The rate of glycolysis was positively controlled by the glycolytic enzymes themselves (66% of control) and by ATP consumption (47%). Mitochondrial production of ATP, including oxidative, proton leak and phosphorylation processes, had negative control over glycolysis (-26%; the Pasteur effect). In contrast, glycolysis had little control over the rate of ATP production by the mitochondria (-10%; the Crabtree effect). Control over the flux through the mitochondrial phosphorylation block was shared between pyruvate oxidation (23%), ATP consumption (28%) and the mitochondrial phosphorylation block itself (64%).

The effects of phosphate- and substrate-free incubation conditions on glycolysis in Ehrlich ascites tumour cells

The influence of phosphate-free medium buffered with synthetic organic buffers, and of a preliminary incubation of cells in medium lacking added substrate ('pre-incubation') was investigated with mouse-cultured Ehrlich ascites tumour cells. In comparison to phosphate-containing bicarbonate-buffered balanced-salts medium, organic-buffered medium, without a preliminary substrate-free pre-incubation, was associated with 20-30% reduction in the rate of glycolysis, the 3- to 4-fold accumulation of fructose 1,6-bisphosphate and the halving of both ATP and total adenine nucleotide levels. These perturbations were reversed by the inclusion of 5 mM sodium phosphate in the organic-buffered medium. Pre-incubation for up to 90 min, before inclusion of glucose, resulted in greater depression of the glycolytic rate and concentrations of adenine nucleotides. This occurred in both the balanced-salts medium and the organic-buffered medium. During pre-incubation cells were lysed, releasing lactate dehydrogenase, when physically agitated too vigorously. It was concluded that the use of phosphate-free medium and pre-incubation are not advisable procedures for routine metabolic investigations with this cell line.

Effects of quercetin on rat testis aerobic glycolysis

Lactate production by testicular fragments and isolated germinal cells at various stages of spermatogenesis was studied in aerobic and anerobic conditions. Several ATPase inhibitors were used to determine the role of ATPase activities in the control of aerobic lactate production. Aerobic glycolysis reached a high level in spermatogonia plus Sertoli cell and in primary spermatocyte populations. The activity was twice that found in early spermatids. Neither Na+-K+ ATPase nor mitochondrial F1 ATPase seemed to participate directly in the control of aerobic glycolysis. The uncoupling of oxidative phosphorylation revealed the potential role of F1 ATPase in providing ADP and P(i) for the glycolytic pathway. Lactate production was inhibited by quercetin in all the experimental conditions tested. Quercetin (100 microM) halted lactate production by the Sertoli cell plus spermatogonia population and by isolated primary spermatocytes. In spermatids, quercetin inhibited aerobic glycolysis only by 40%, even at higher concentrations. Only during the first meiotic prophase did quercetin inhibit the activity of a cytosolic Ca(2+)-Mg2+ ATPase. This ATPase was also inhibited by erythro-9-[3-3(hydroxynonyl)]adenine (EHNA), suggesting that a cytoplasmic dynein could be involved in the control of glycolysis in Sertoli cells, spermatogonia, and early primary spermatocytes.

Adenylate kinase-catalyzed phosphoryl transfer couples ATP utilization with its generation by glycolysis in intact muscle

We previously suggested that an importance of adenylate kinase (AdK) in skeletal muscle is to function as a high energy phosphoryl transfer system regulating ATP generation in correspondence with its consumption by specific cellular processes. The present experiments are intended to define the ATP-generating system coupled to and regulated by AdK-catalyzed phosphotransfer in skeletal muscle and also to examine the relationship between AdK- and creatine kinase (CK)-catalyzed phosphotransfer. Rates of phosphoryl transfer catalyzed by AdK were assessed in intact, isolated rat diaphragm by determining rates of AMP phosphorylation with endogenously generated [gamma-18O]ATP under conditions of altered anaerobic and aerobic ATP production. AdK-catalyzed phosphoryl transfer rates accelerated incrementally up to 12-fold in direct proportion to stimulated contractile frequency in parallel with equivalent increases in rates of ATP generation by lactate producing glycolysis. Stoichiometric equivalent increases of AdK-catalyzed phosphotransfer and anaerobic ATP production also occurred up to more than 20-fold when oxidative phosphorylation was impaired by either O2 deprivation or treatment with KCN or p-(trifluoromethoxy)-phenylhydrazone. These enhanced rates of AMP phosphorylation were balanced by virtually identically increased rates of AdK-catalyzed generation of AMP. This AMP was traced to arise from AdK-catalyzed phosphotransfer involving ADP generated by a muscle ATPase. Increased AdK-catalyzed phosphotransfer paired with the apparent compensatory increase in ATP generation by anaerobic glycolysis in oxygen-deprived muscle occurred coincident with diminished rates of CK-catalyzed phosphoryl transfer indicative of a pairing between oxidatively produced ATP and CK-catalyzed phosphotransfer. A metabolic model consistent with these results and conforming to the Mitchell general principle of vectorial ligand conduction is suggested.

Nutritional and physiological consequences of tumour glycolysis

A frequent characteristic of many malignant tumours is an increase in anaerobic glycolysis, that is the conversion of glucose to lactate, when compared to normal tissues. The causes of this intensification involve changes in enzyme and glucose transporter levels, shifts of the isoenzyme patterns in the cancer cells to those similar to foetal tissues and a breakdown in the normal control mechanisms, most notably the Pasteur effect. The host must adapt, with a corresponding increase in gluconeogenesis. This change, along with other adaptations made by the host, eventually results in the syndrome known as cancer cachexia, which is characterized by anorexia and depletion and redistribution of the host energy stores. In some ways many malignant tumours behave much like parasites, drawing upon the host for nutrients such as glucose and returning waste products such as lactate to the host for recycling or disposal. This cycling of glucose and lactate between host and tumour has been the target for a number of proposed and tested treatments, with regard to the possible inhibition of tumour growth and/or possible prevention of some or all of the cachectic effects. Some of these suggested treatments have reached the point of clinical testing and show promise for continued research.

Glucose decreases respiratory control ratio in EL-4 tumor cells

EL-4 ascites thymoma cells are shown to have high aerobic glycolysis and decreased Pasteur effect. At the same time, glucose produces a much smaller inhibitory effect on cell respiration (Crabtree effect) than in Ehrlich ascites carcinoma (EAC) cells. In intact EL-4 cells, the respiratory control ratio (RCR) was found to be 6.2 with endogenous substrates and 8.0 with glutamine. Glucose decreased the RCR to 3.2, by stimulating the state 4 respiration. In rat thymocytes and EAC cells, such an effect of glucose was absent (RCR of 7.0 and 7.2, respectively). It is suggested that in EL-4 tumor cells, the high aerobic glycolysis and small Crabtree effect may be due to glucose-induced 'uncoupling' of oxidation and phosphorylation.

Balancing of energy-consuming processes of K 562 cells

A balance of ATP-consuming processes in human erythroleukemia (K 562) cells by use of the decreased 14CO2 formation from [1-14C]-glutamate following inhibition of energy-requiring processes is presented. This method was tested on Ehrlich mouse ascites tumour cells and was used in suspensions of K 562 cells with a low cell content. More than 90 percent of the ATP produced by oxidative phosphorylation could be accounted for in K 562 cells. Protein synthesis consumed about 35 percent, Na+/K(+)-ATPase about 20 percent and transcription processes 5-10 percent of the total ATP. The share of the Ca(2+)-dependent reactions was notably high at 25 percent in comparison with Ehrlich mouse ascites tumour cells, reticulocytes or hepatocytes. ATP consumption by DNA synthesis was assessed at 5-10 percent. Only less than 10 percent of the consumption of ATP produced oxidatively remained for other cellular reactions. The degree of coupling of K 562 cells was high in comparison with that of other eukaryotic cell types.

Identification of regulatory properties of metabolic networks by graph theoretical modeling

An earlier graph theoretical model of metabolic and gene-expression networks has been modified and extended to include the effect of electrical potentials on binding constants, representation of uncatalyzed processes, and treatment of parallel reactions catalyzed by a single enzyme. Formal operations on the graph, which are facilitated by a set of standardized guidelines, identify the feedback signals in the network and rank them according to their influence. The technique was applied to a model of glycolysis in ascites tumor cells in the absence and presence of 12.5 mM exogenous glucose. Feedback regulation was widely distributed and mostly due to binding of adenine nucleotide cofactors to the enzymes of the network. The major changes in feedback regulation on adding glucose is the relief of inhibition of hexokinase and phosphofructokinase and the activation of pyruvate kinase. We conclude that regulation of tumor cell glycolysis is not restricted to hexokinase or to (Na+,K+)-ATPase as was previously suggested by others.

ATP-producing and consuming processes of Ehrlich mouse ascites tumor cells in proliferating and resting phases

The extents of ATP-yielding and consuming processes in Ehrlich mouse ascites tumor cells during the proliferating and resting growth phase were compared. In the resting phase the total ATP production was decreased by one-third. The ATP supply by oxidative phosphorylation was drastically reduced, whereas the rate of glycolysis stayed nearly constant. All ATP-consuming processes investigated, i.e., protein turnover, Na+/K(+)-ATPase, Ca2(+)-ATPase, and RNA synthesis, were decreased proportionally with the total ATP consumption.

Balancing of energy-consuming processes of rat hepatocytes

A method for the quantification of energy consuming processes described by Siems et al. for reticulocytes and by Müller et al. for ascites tumour cells was applied to balance the ATP-consumption of isolated rat hepatocytes. On the basis of decreased coupled respiration rates following the specific inhibition of energy-requiring reactions, the energy demands of protein turnover, nucleic acid synthesis, Na+/K(+)-ATPase and Ca2(+)-transport of hepatocytes in different incubation media were assessed. These processes together with urea synthesis account for about 60 per cent of the total energy consumption in a glucose and amino acid-enriched Eagle/Borsook medium. The metabolic flux rates of total ATP-consumption and ATP-consumption of single energy-requiring processes in hepatocytes are compared with those in reticulocytes and different tumour cell types.

Subcellular distribution of adenine nucleotides in two Ehrlich cell lines metabolizing glucose

Adenine nucleotide compartmentation and cytochrome redox state were studied in two Ehrlich ascites tumor cell lines incubated in the presence of 5mM glucose to show differences between their energy metabolisms. Changes in the subcellular distribution of adenine nucleotides were very different in both cell lines. Glucose seemed to energize the less malignant cell line, as shown by the asymmetry of the ATP/ADP ratios between cytosolic and mitochondrial compartments, but this was not the case for the more malignant cell line. The cytochrome contents were similar in both cell lines, but the degree of cytochrome oxidation was higher in the less malignant cell line; this result is in agreement with a higher oxygen consumption in the less malignant cell line.

Modulation of mammalian sperm motility by quercetin

The flavonoid quercetin inhibits collective motility of ejaculated ram spermatozoa in the first 2 hr of incubation; during the next 3-4 hr motility is stimulated. To explain this interesting effect, we followed the influence of quercetin on sperm glycolysis, extracellular pH, ATP content, mitochondrial respiration, and lipid peroxidation. The collective motility of untreated cells is decreased to about 40% of the original motility during two hours of incubation. During this time, the rate of glycolysis is constant, respiration rate is increasing, there is no change in ATP content, the rate of lipid peroxidation is very slow, and the extracellular pH became very acidic (pH 5.5). It is concluded that motility is decreased due to this acidification. This acidification is prevented to some extent by quercetin, which indirectly inhibits glycolysis. Quercetin inhibits motility due to the inhibition of the plasma membrane calcium pump, as we showed previously (Breitbart et al., J Biol Chem 260:11548-11553, 1985). The motility of untreated cells is arrested after 3.5 hr of incubation, whereas quercetin-treated cells show high motility, which continues for additional 2-3 hr. After 3.5 hr, the control cells show no glycolytic activity, ATP content and respiration rates are decreased, and rate of lipid peroxidation is highly increased. At this time, quercetin-treated cells show no glycolytic activity, only a small decrease in ATP content and respiratory rate, and a very low rate of lipid peroxidation. Based on these data it is concluded that sperm motility after 3.5 hr of incubation is dependent mainly on mitochondrial respiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of phosphofructokinase during trout haemopoiesis: physiological regulation of glycolysis

1. The regulatory properties of phosphofructokinase (PFK) has been investigated in two cellular population representatives of trout haemopoiesis; haemopoietic cells (capable of replication and differentiation) and erythrocytes (highly specialized cells). 2. The intracellular levels of substrates and effectors have been quantified and their effect on PFK activity determined. 3. Fructose 1,6-bisphosphate anc cyclic AMP show a higher activation of the PFK from haemopoietic cells than the enzyme from erythrocytes. 4. AMP and phosphoenolpyruvate act as activators of the haemopoietic cell PFK while for erythrocytes PFK, AMP is an inhibitor and phosphoenolpyruvate does not display any effect. 5. Citrate inhibits PFK activity from haemopoietic cells but was not assayed in erythrocytes since it was not detected in these cells. 6. The differences in PFK regulation in both cellular populations may be attributed to the intracellular levels of the effectors and/or different isoenzymatic patterns. 7. The different regulation of PFK together with the higher enzymatic activity of PFK and pyruvate kinase from haemopoietic cells are related to the higher glycolytic flux that exhibits the haemopoietic cells. 8. The results shown in this investigation allow us to conclude that PFK has a specific role depending on the energetic requirements of the cellular population in which the enzyme is present. 9. The requirements are related to the physiological function of each type of cell.

Glycolysis-induced discordance between glucose metabolic rates measured with radiolabeled fluorodeoxyglucose and glucose

We have developed an autoradiographic method for estimating the oxidative and glycolytic components of local CMRglc (LCMRglc), using sequentially administered [18F]fluorodeoxyglucose (FDG) and [14C]-6-glucose (GLC). FDG-6-phosphate accumulation is proportional to the rate of glucose phosphorylation, which occurs before the divergence of glycolytic (GMg) and oxidative (GMo) glucose metabolism and is therefore related to total cerebral glucose metabolism GMt: GMg + GMo = GMt. With oxidative metabolism, the 14C label of GLC is temporarily retained in Krebs cycle-related substrate pools. We hypothesize that with glycolytic metabolism, however, a significant fraction of the 14C label is lost from the brain via lactate production and efflux from the brain. Thus, cerebral GLC metabolite concentration may be more closely related to GMo than to GMt. If true, the glycolytic metabolic rate will be related to the difference between FDG- and GLC-derived LCMRglc. Thus far, we have studied normal awake rats, rats with limbic activation induced by kainic acid (KA), and rats visually stimulated with 16-Hz flashes. In KA-treated rats, significant discordance between FDG and GLC accumulation, which we attribute to glycolysis, occurred only in activated limbic structures. In visually stimulated rats, significant discordance occurred only in the optic tectum.

The contribution of ATP turnover by the Na+/K+-ATPase to the rate of respiration of hepatocytes. Effects of thyroid status and fatty acids

In less than 1 min ouabain maximally inhibits oxygen consumption due to gramicidin-induced ATP turnover by the Na+/K+-ATPase in hepatocytes. Ouabain rapidly inhibits respiration on palmitate or glucose by only 6-10% indicating that the Na+/K+-ATPase plays a minor role in cell ATP turnover. 29% of the extra oxygen consumption of hepatocytes isolated from hyperthyroid rats was inhibited by ouabain showing that the Na+/K+-ATPase is responsible for some but not the majority of the stimulation of respiration induced by thyroid hormone.

Motility, heat, and lactate production in ejaculated bovine sperm

Effects of various inhibitors on motility, heat, and lactate production of ejaculated bovine sperm were determined in the presence of antimycin A and rotenone. erythro-9-[3-(2-Hydroxynonyl)]adenine (EHNA) and polyvinylpyrrolidone (PVP-360) stopped motility and reduced heat or lactate production by 30-50%. Carbodiimides resulted in loss of motility and a reduction of metabolism by 60-75%. Quercetin treatment, which enhanced rather than inhibited motility, depressed heat and lactate production by 50-60%. Since mechanical immobilization reduced heat production by only 30%, the question arises as to what other cellular processes are major contributors to the energy budget. Inhibitors of ion flux had little-to-no effect on heat or lactate production, suggesting that neither mitochondrial nor Na+/K+ ATPases were major ATP-requiring processes. Calcium flux at the plasma membrane also was minimal and previous reports eliminated glycolytic substrate cycling as major consuming processes for ATP. Although quercetin inhibited lactate production in intact cells, no effect of quercetin on cell-free glycolysis and the ATPase activities of isolated dynein was detected. Quercetin did, however, inhibit ATPase activity of plasma membrane, suggesting that this unidentified ATPase may contribute to the formation of ADP and Pi required for lactate production by the intact cell. We propose (a) that the bioenergetic costs of motility are divided between regulatory events and dynein-microtubule interaction (dynein ATPase), (b) that some of the membrane-related processes may be "inefficient," and (c) that quercetin may render these steps more "efficient," in a manner analogous to its action on the Na+/K+ pump of Ehrlich ascites tumor cells.

Ouabain sensitizes tumor cells but not normal cells to radiation

Ouabain is a cardiac glycoside that blocks the sodium, potassium-pump (Na,K-Pump). When A549 human lung adenocarcinoma cells were treated with 10(-6) M ouabain for 4 hr starting 1 hr before irradiation, they were sensitized (enhancement ratio at 1% survival 1.46 +/- .07, N = 5). Ouabain affected radiation repair because it decreased the shoulder of the cell survival curve and it sensitized cells when added after radiation. CCL-210 normal human lung fibroblasts were not radiosensitized by ouabain concentrations from 10(-8) M to 10(-5) M. These results suggest that it may be possible to exploit differences in the Na,K-pumps of normal cells and tumor cells to improve the therapeutic index of radiation.

Quantification of ATP-producing and consuming processes of Ehrlich ascites tumour cells

ATP production of Ehrlich ascites tumour cells was estimated on the basis of their coupled respiration and lactate formation. ATP-consuming processes were assessed from the effects of selective inhibitors of RNA synthesis, protein synthesis and proteolysis, Na+/K+-ATPase on respiration. The extent of protein synthesis and proteolysis were also determined directly. From these values and those of the inhibition of respiration by selective inhibitors, a P/O ratio of 2.2 was calculated. About 75% of the total ATP consumption could be assigned to specific processes. The major ATP-consuming processes of tumour cells in an amino-acid-enriched medium, in which they are in an approximate steady state, are protein synthesis with about 30% of total ATP consumption, and Na+/K+-ATPase with about 20%, while RNA synthesis, ATP-dependent proteolysis and Ca2+-ATPase contribute about 10% each. In an amino-acid-free glucose medium, protein synthesis is reduced to a third, with a corresponding decrease of respiration, whereas the rate of the other ATP-consuming processes is unchanged.

Influence of medium amino acids on the ouabain sensitive and insensitive 86Rb+-fluxes in HeLa cells

Components of the 86Rb+-influx in HeLa cells were investigated in Joklik minimal essential medium, or in Earle's balanced salt solution with and without medium amino acids. The presence of amino acids led to the stimulation of the ouabain sensitive 86Rb+-uptake and inhibition of the diuretic-sensitive and residual 86Rb+-fluxes. These results show that the presence of amino acids is an important regulator of the K+/Rb+-fluxes under normal conditions in growth medium.

On the mechanism of glycolysis stimulation by neutral detergents in 3T3 and Ehrlich ascites tumor cells

Glycolysis of 3T3 and Ehrlich ascites tumor cells was greatly enhanced by Nonidet P-40 or Triton X-100 at about 100 micrograms/mg cell protein. This enhanced glycolysis was partly sensitive to rutamycin and partly sensitive to ouabain, suggesting that the detergent released the control of the ATPase of the mitochondria and of the plasma membrane Na+K+-ATPase. Nonidet P-40 had no effect on glycolysis in cell-free extracts from Ehrlich ascites tumor cells to which soluble mitochondrial ATPase was added. Measuring ouabain-sensitive 22Na efflux and using ouabain-sensitive lactate production as a measure of ATP hydrolysis by the Na+K+ pump, it was shown that Nonidet P-40 greatly decreased the efficiency of the Na+K+ pump. Quercetin increased the efficiency of pumping in EAT cells both in the absence and presence of the detergent.

Studies of insulin action on the amphibian oocyte plasma membrane using NMR, electrophysiological and ion flux techniques

Insulin (0.1-10 microM) reinitiates the meiotic divisions in Rana oocytes and produces a 14-20 mV negative-going hyperpolarization of the plasma membrane as well as a 0.25 unit increase in intracellular pH during the first 90 min. During hyperpolarization, the Na+ conductance of the membrane decreases by 40-50% with a concomitant increase in 22Na+ uptake from the medium. The increased uptake of Na+ during a period of decreasing Na+ conductance is apparently due to an increase in fluid phase turnover associated with insulin-mediated endocytosis. Both membrane hyperpolarization and increase in pHi are Na+-dependent and are blocked by the serine proteinase inhibitor, phenylmethylsulfonyl fluoride. The membrane potential of the prophase oocyte has a significant electrogenic component with potential but not conductance sensitive to glycosides and substitution of Li+ for Na+. Insulin hyperpolarizes Li+ or glycoside-treated oocytes whereas glycosides do not affect insulin-hyperpolarized oocytes. [3H]Ouabain binding by the plasma membrane of the untreated oocyte shows at least two K+-sensitive components (Kd = 42 and 2000 nM) linked to inhibition of the Na+ pump. Insulin-treated oocytes show a single class of intermediate-affinity ouabain sites (Kd = 490 nM) which appear to result from insulin-induced internalization of membrane-bound ouabain. [125I]Insulin binding to the plasma membrane shows a class of high-affinity sites (Kd = 87 nM) with 40-50 pump sites per insulin-binding site. Our results suggest that insulin-induced mediator peptides stimulate Na+-H+ exchange resulting in an increase in intracellular pH and Na+ uptake concomitant with an increase in receptor-mediated endocytosis and a decrease in Na+ conductance and associated membrane hyperpolarization. The net result appears to be a down-regulation of the Na+ pump which together with a decrease in Na+ conductance may divert high-energy phosphate compounds from cation regulation to anabolic processes of meiosis.

Gluconeogenesis predominates in periportal regions of the liver lobule

Rates of gluconeogenesis from lactate were calculated in periportal and pericentral regions of the liver lobule in perfused rat livers from increases in O2 uptake due to lactate. When lactate (0.1-2.0 mM) was infused into livers from fasted rats perfused in either anterograde or the retrograde direction, a good correlation (r = 0.97) between rates of glucose production and extra O2 uptake by the liver was observed as expected. Rates of oxygen uptake were determined subsequently in periportal and pericentral regions of the liver lobule by placing miniature oxygen electrodes on the liver surface and measuring the local change in oxygen concentration when the flow was stopped. Basal rates of oxygen uptake of 142 +/- 11 and 60 +/- 4 mumol X g-1 X h-1 were calculated for periportal and pericentral regions, respectively. Infusion of 2 mM lactate increased oxygen uptake by 71 mumol X g-1 X h-1 in periportal regions and by 29 mumol X g-1 X h-1 in pericentral areas of the liver lobule. Since the stoichiometry between glucose production and extra oxygen uptake is well-established, rates of glucose production in periportal and pericentral regions of the liver lobule were calculated from local changes in rates of oxygen uptake for the first time. Maximal rates of glucose production from lactate (2 mM) were 60 +/- 7 and 25 +/- 4 mumol X g-1 X h-1 in periportal and pericentral zones of the liver lobule, respectively. The lactate concentrations required for half-maximal glucose synthesis were similar (0.4-0.5 mM) in both regions of the liver lobule in the presence or absence of epinephrine (0.1 microM). In the presence of epinephrine, maximal rates of glucose production from lactate were 79 +/- 5 and 59 +/- 3 mumol X g-1 X h-1 in periportal and pericentral regions, respectively. Thus, gluconeogenesis from lactate predominates in periportal areas of the liver lobule during perfusion in the anterograde direction; however, the stimulation by added epinephrine was greatest in pericentral areas. Differences in local rates of glucose synthesis may be due to ATP availability, as a good correlation between basal rates of O2 uptake and rates of gluconeogenesis were observed in both regions of the liver lobule in the presence and absence of epinephrine. In marked contrast, when livers were perfused in the retrograde direction, glucose production was 28 +/- 5 mumol X g-1 X h-1 in periportal areas and 74 +/- 6 mumol X g-1 X h-1 in pericentral regions.(ABSTRACT TRUNCATED AT 400 WORDS)

A reduction in the activity of the Na+, K+-pump in dimethylsulfoxide-treated Friend erythroleukemia cells is not due to partial inactivation of the Na+, K+-ATPase

Treatment of Friend-erythroleukemia cells with 1.5% dimethylsulfoxide (DMSO) caused a decrease in ouabain sensitive 86Rb+-uptake beginning six to seven hours after DMSO addition indicating a reduced function of the Na+, K+-pump. However, analysis of the ouabain sensitive 86Rb+-uptake after Na+-preloading of the cells as well as measurements on the Na+, K+-ATPase activity in isolated membrane fragments revealed that no inhibition of the Na+, K+-ATPase occurred during the first 12 hours. On the contrary the Na+, K+-ATPase activity was initially enhanced and then returned to control levels during the early phase of induction by DMSO. On the other hand, 22Na+-transport into DMSO-treated cells was reduced similar to the ouabain sensitive 86Rb+ uptake in cells without Na+ preloading. The piretanide sensitive 86Rb+-uptake, due to the Na+, K+, 2Cl - cotransport system was inhibited after seven hours exposure to DMSO. Some three hours after DMSO addition the incorporation of 35S-methionine into proteins began to decrease, which was accompanied with or followed by a reduction in the methionine uptake of DMSO treated cells. Membrane-potential-dependent tetraphenylphosphonium cation uptake was not altered relative to the controls in the first 12 hours following DMSO addition. These results suggest that the reduced activity of the Na+, K+-pump in Friend cells after DMSO exposure is not due to inhibition of the Na+, K+-ATPase, but most probably due to a smaller Na+-influx, which results from inhibition of Na+-cotransport processes (amino acid uptake, Na+, K+, 2Cl - cotransport system).

Characteristics of adenine nucleotide fluxes and transport in human tumor mitochondria

The efflux of adenine nucleotides from three human tumor mitochondria has been investigated with mitochondria prelabeled with radioactive ATP. Uncouplers induce a large efflux of adenine nucleotides from mitochondria from human hepatoma and oat cell carcinoma while efflux from astrocytoma mitochondria is less. This efflux does not require exchangeable anions, i.e., adenine nucleotides or pyrophosphate, in the extramitochondrial medium, and is not sensitive to atractyloside. The efflux is more extensive with dinitrophenol and CCCP than with valinomycin-K+, and may account for the differential effects of the two types of uncouplers on uncoupler-stimulated ATPase of tumor mitochondria previously reported by us. Dinitrophenol and CCCP do not elicit any efflux of adenine nucleotides from normal liver mitochondria. Efflux of orthophosphate from tumor mitochondria is also greater with dinitrophenol and CCCP; however, the more interesting finding is that the concentration of orthophosphate in these mitochondria is unusually high, i.e., 10-40-times greater than the intramitochondrial phosphate concentration of liver mitochondria. Atractyloside sensitive transport of ATP and ADP in human tumor mitochondria has also been determined. Vmax values for both ADP and ATP transport are lower than those obtained with liver mitochondria, especially with ADP transport. ATP transport in tumor mitochondria is not affected by CCCP in contrast to the 4-5-fold stimulation observed in liver mitochondria.