Effect of acute starvation on monoamine oxidase and Na+, K+-ATPase activity in rat brain

The activities of monoamine oxidase (MAO), responsible for oxidative deamination of many biogenic amines, and Na⁺, K⁺-ATPase, which plays a crucial role in the release mechanism of neurotransmitters, were determined in rat brain after acute starvation. They were assayed biochemically from four different regions of the brain in two subcellular fractions. Acute starvation decreased the activity of MAO, whereas the Na⁺, K⁺-ATPase activity was increased. An effect of starvation was also seen on the blood glucose level, body wt, and the protein content of different brain regions. Starvation or normal dietary fluctuations of certain nutrients that exert precursor influence over neurotransmitter synthesis are important to the brain, and contribute to its regulation of both neuroendocrine response and behavior. A rise in the substrate level, i.e., ATP, as a result of increased utilization of ketone bodies and low level of monoamines in the brain after acute starvation, may be the underlying factor for increasing the activity of Na⁺, K⁺-ATPase in rat brain. These results suggest that, probably, certain adaptive mechanisms become operative in the brain under disturbed physiological conditions.     

Methylmalonate administration decreases Na+,K+-ATPase activity in cerebral cortex of rats

Buffered methylmalonate (MMA) was injected s.c. into rats twice a day at 8 h intervals from 5 to 25 days of age (chronic treatment), or into 10-day-old rats three times a day at 1 h intervals (acute treatment). Control rats received saline in the same volumes. Na+,K+-ATPase and Mg2+-ATPase activities were determined in the synaptic plasma membranes from cerebral cortex of rats. Na+,K+-ATPase activity was reduced by 30-40% in MMA-treated rats, whereas Mg2+-ATPase activity was not. In contrast, MMA at final concentrations ranging from 0.1 to 2.0 mM had no in vitro effect on these enzyme activities. However, when brain homogenates were incubated with 2 mM MMA before membrane preparation, Na+,K+-ATPase activity was decreased by 44%. Furthermore, this reduction was totally prevented by the simultaneous addition of glutathione and MMA, suggesting that oxidation of thiol groups or other oxidative damage to the enzyme could be responsible for this effect.     

Effect of organic and inorganic mercuric salts on Na+K+ATPase in different cerebral fractions in control and intrauterine growth-retarded rats: alterations induced by serotonin

An intrauterine growth-retarded (IUGR) model based on restriction of blood supply to the rat fetus at the 17th day of pregnancy was studied. We investigated in vitro the effects of thimerosal and mercuric chloride on Na+K+ATPase activity in total brain homogenate, synaptosomes and myelin at weaning. In addition, we evaluated the reversal effect of serotonin on mercury-inhibited Na+K+ATPase activity. The toxicity, in terms of inhibition of Na+K+ATPase activity was greater with mercuric chloride than with thimerosal. Synaptosomes and principally myelin were more sensitive to the metal salts than total homogenate. Serotonin stimulated the Na+K+ATPase activity in total brain homogenate and synaptosomes but inhibited the enzyme in the myelin fraction. This effect was more marked in the IUGR group than in the control group. Serotonin (1 mM) added to total homogenate pretreated with the mercury salts produced variable reversal effects. In the synaptosomal fraction reverse effect was noted with serotonin. In myelin fraction, added serotonin increased inhibition caused by thimerosal.     

Na+, K+ ATPase activity is markedly reduced by cis-4-decenoic acid in synaptic plasma membranes from cerebral cortex of rats

We have previously demonstrated that octanoic (OA) and decanoic acids (DA) inhibit Na+, K+ ATPase activity in synaptic plasma membranes from rat brain. The objective of the present study was to investigate the in vitro effects of the other metabolites that accumulate in tissues of medium-chain acyl-CoA dehydrogenase (MCAD)-deficient patients, namely cis-4-decenoic acid (cDA), octanoylcarnitine (OC), hexanoylcarnitine (HC), hexanoylglycine (HG), phenylpropionylglycine (PPG) and suberoylglycine (SG), on Na+, K+ ATPase activity in synaptic plasma membrane from cerebral cortex of 30-day-old rats. cDA, the pathognomonic compound found in this disorder, provoked the strongest inhibition on this enzyme activity at concentrations as low as 0.25 mM, whereas OC inhibited this activity at 1.0 mM and higher concentrations in a dose-dependent manner. In contrast, HC, HG, PPG and SG did not affect Na+, K+ ATPase activity. Furthermore, pre-treatment of cortical homogenates with the antioxidant enzymes catalase plus superoxide dismutase totally prevented cDA-induced Na+, K+ ATPase inhibition. We also provided evidence that cDA, as well as OA and DA, caused lipid peroxidation, which may explain, at least in part, the inhibitory properties of these compounds towards Na+, K+ ATPase. Considering that Na+, K+ ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings, especially those regarding to the marked inhibitory effect of cDA, may be involved in the pathophysiology of the neurological dysfunction of MCAD-deficient patients.     

Effect of neonatal hypothyroidism on the kinetic properties of Na+, K+ -ATPase from rat brain microsomes

The effects of neonatal hypothyroidism on the kinetic properties of Na+, K+ -ATPase from rat brain microsomes were examined. Neonatal hypothyroidism resulted in decreased Na+, K+ -ATPase activity compared to control samples (7.4 +/- 1.48 and 29.8 +/- 2.30 micromol Pi/h/mg protein, respectively, P < 0.001). Substrate kinetics studies with ATP, Na+ and K+ revealed that there were generalised decreases in Vmax. For ATP, Na+ and K+, activities resolved into two kinetic components in the control group. In hypothyroid animals, the low-affinity component for ATP was absent. The opposite pattern (i.e. an absence of the high-affinity component) was noted for Na+. For K+, although both kinetic components were discernible in neonatal hypothyroid brain microsomes, the Km of the high-affinity component was significantly higher (P < 0.001) compared to control samples. In the control group, the enzyme displayed allosteric behaviour at high concentrations of Mg2+; in hypothyroid animals, the pattern was completely allosteric. The Na+, K+ -ATPase enzyme from the hypothyroid brain microsomes bound two molecules of ATP rather than one, unlike in the control animals. Our results thus indicate that neonatal hypothyroidism results in an impairment of microsomal Na+, K+ -ATPase activity in the rat brain, together with subtle alterations in the kinetic properties of the enzyme.     

Functional activity of Na+, K+-pump in normal and pathological tissues

Na⁺,K⁺-ATPase, supporting the ionic homeostasis of the cell, is under control of Na⁺, K⁺, Mg²⁺, and ATP. The regulating effect of Mg²⁺ is rather unclear, whereas the Na⁺/K⁺ ratio in the cytoplasm is a potent regulatory factor, especially for osmotic balance in excitable cells. We have demonstrated two possibilities for regulation of ion pumping activity: First, via the number of Na⁺,K⁺-ATPase molecules under operation, and second, via changes in the turnover rate of the active molecules. In the presence of low ATP concentration, which is typical for cells with membrane damage (ischemic cardiac myocytes, tumor cells, fatigued muscles) Na⁺,K⁺-ATPase is transformed to a regime of the decreased efficiency. Radiation inactivation study demonstrates the weakening of the interprotein interactions in the enzyme complexes during ATP deficiency. Thus, measurements of ATPase activity of the purified enzyme under optimal conditions in vitro may be useless for the discrimination of pathological from normal tissues. In such a case, the estimation of lipid composition and microviscosity of the membranes under study could be important. This review briefly discusses several basic mechanisms of the regulation of Na⁺,K⁺-ATPase—an integral protein of the outer cell membranes.     

Stimulation by noradrenaline of Na+K+ ATPase in different fractions of rat brain cortex

Summary Distribution of Na⁺K⁺-ATPase (EC. 3.6.1.3) and its susceptibility to noradrenaline (NA) were studied on electronmicroscopically characterized subcellular fractions of rat brain cortex. The highest specific activity of Na⁺K⁺-ATPase was present in synaptosomal fraction disrupted in distilled water (29.52±5.53moles phosphate/mg protein/hour). In the presence of 1 mM EGTA significantly higher specific activity was determined in all fractions studied, except homogenate and synaptosome. The effect of NA was studied in concentration range from 10^–6-10^–3M. 10^–4M of NA produced the highest activation of the enzyme in different fractions. Also in the presence of EGTA NA was able to increase the enzyme activity. The effect of NA was much more marked on disrupted synaptosomal fraction. No qualitative differences have been found between the Na⁺K⁺-ATPase activities exhibited by the synaptosomal fraction and by other subcellular fractions with respect to susceptibility to NA. Therefore, it seems very probable that NA might modulate neurochemical transmission not only via an effect on nerve terminals but also via stimulating other part of the neuron.     

一氧化碳对局灶性脑缺血脂质过氧化物及Na+-K+ ATP酶的影响

目的　研究一氧化碳对局灶性脑缺血脑组织脂质过氧化物及Na K ATP酶的影响 ,试图从亚细胞水平阐明CO对脑组织保护作用的机理。方法　将SD大鼠随机分为三组 (n =6 ) ,使用HO诱导剂、HO抑制剂腹腔注射为实验组 ,等量生理盐水作为对照组腹腔注射 ,12h后制成MCAO模型。栓塞后 2 4h检测CO浓度、脂质过氧化及Na K ATP酶活性。结果　与对照组相比 ,HO诱导剂组CO浓度明显升高 ,MDA减少 ,SOD及Na K ATP酶增高 (各为P <0 .0 1、P <0 .0 1、P <0 .0 5、P <0 .0 5 ) ,而HO抑制剂组CO浓度明显降低 ,MDA增加 ,SOD及Na K ATP酶活性降低 (各为P <0 .0 0 1、P <0 .0 5、P <0 .0 5、P <0 .0 5 )。HO诱导剂、HO抑制剂对非栓塞侧脑组织脂质过氧化物及Na K ATP酶的活性没有影响 (P >0 .0 5 )。结论　CO是一种信使分子 ,通过减少自由基、增加SOD及Na K ATP酶活性对局灶性缺血的脑组织起保护作用     

Human epileptic brain Na, K ATPase activity and phenytoin concentrations.

An abnormal flux of monovalent cations may be related to the epileptogenic process in man. One possible mechanism for deranged electrolyte metabolism in epileptic brain is an abnormality in sodium, potassium-dependent adenosine triphosphatase (Na, K ATPase). We found the activity of Na, K ATPase to be significantly less in epileptic human corfex than in nonepileptic cortex. Histological changes have been simultaneously evaluated in epileptic brain. A second membrane-bound enzyme, acetylcholinesterase (AChE), was also assayed as a marker for neuronal membranes and found not to correlate with the epileptogenicity of human brain. In addition, the concentrations of the anticonvulsant compound phenytoin have been determined in the serum and cerebral cortex of epileptic and nonepileptic patients. The ratio of phenytoin in cortex to serum concentration is significantly lower in epileptic patients than in nonepileptic controls.     

MAgnetic stimulation of the brain increase Na+, K+-ATPase activity decreased by injection of AlCl3 into nucleus basalis magnocellularis of rats

This article reports here on the influence of the static magnetic fields (MFs), locally applied to the brain area, on Na, K-ATPase activity in the rat with lesioned nucleus basalis magnocellularis (NBM) by intracerebral injection of 5 microl, 1% AlCl3 into the nucleus. Two AKMA micromagnets (M) flux density of 60 miliTesla, 5 mm in diameter, were bilaterally implanted with "N" polarity facing down to the cranial bones in the vicinity of the pineal gland (PG), immediately after the lesioning of NBM, during the same operation procedure. Ten days after the lesions of NBM, Na, K-ATPase activity on the erythrocyte membranes in the peripheral blood, measured spectrophotometrically, was completely inhibited. Magnetic stimulation (60 mT) of the brain during the 10 days significantly increased Na, K-ATPase activity on the erythrocyte membranes of rats with lesioned NBM. This results suggests that altered by lesions Na, K-ATPase activity in an experimental model of Alzheimer's disease might be ameliorated by magnetic stimulation of the brain.     

Effect of hypoxanthine on Na+,K+-ATPase activity and some parameters of oxidative stress in rat striatum

The main objective of this study was to investigate the effects of preincubation of rat striatum homogenate in the presence of hypoxanthine, a metabolite accumulated in Lesch-Nyhan disease, on Na+,K+-ATPase activity and on some parameters of oxidative stress namely thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant parameter (TRAP) and membrane protein thiol content. Results showed that hypoxanthine significantly increased TBA-RS and reduced Na+,K+-ATPase activity, TRAP and membrane protein thiol content. In addition, we also evaluated the effect of glutathione, trolox, allopurinol and Nvarpi-nitro-L-arginine methyl ester (L-NAME) on the inhibitory effect of hypoxanthine on Na+,K+-ATPase activity in the same rat cerebral structure. All tested compounds per se did not alter Na+,K+-ATPase activity, but only glutathione and trolox prevented the effect of hypoxanthine on the enzyme activity. The effect of glutathione and trolox on hypoxanthine-induced increase of TBA-RS levels was also investigated. These antioxidants alone or combined with hypoxanthine reduced TBA-RS levels. Our present findings show that hypoxanthine induces oxidative stress in rat striatum and that the inhibition of Na+,K+-ATPase activity caused by this oxypurine was probably mediated by reactive oxygen species. It is presumed that these results might be associated with the neuronal dysfunction of patients affected by Lesch-Nyhan disease.     

The role of Na+‐K+‐ATPase in the epileptic brain

Na+‐K+‐ATPase, a P‐type ATP‐powered ion transporter on cell membrane, plays a vital role in cellular excitability. Cellular hyperexcitability, accompanied by hypersynchronous firing, is an important basis for seizures/epilepsy. An increasing number of studies point to a significant contribution of Na+‐K+‐ATPase to epilepsy, although discordant results exist. In this review, we comprehensively summarize the structure and physiological function of Na+‐K+‐ATPase in the central nervous system and critically evaluate the role of Na+‐K+‐ATPase in the epileptic brain. Importantly, we further provide perspectives on some possible research directions and discuss its potential as a therapeutic target for the treatment of epilepsy.     

Brain Na+,K+-ATPase isozyme activity and protein expression in ouabain-induced hypertension

In normotensive rats, chronic infusion of exogenous ouabain causes hypertension involving central mechanisms. To determine whether ouabain-induced hypertension is associated with specific changes in brain Na+,K+-ATPase activity and expression, we assessed brain Na+,K+-ATPase isozyme activity and protein expression in rats treated with ouabain (50 microg/day s.c. or 10 microg/day i.c.v. for 14 days). Resting mean arterial pressure (MAP) was higher in s.c.- and i.c.v.-ouabain-treated animals vs. control (124+/-2 vs. 105+/-2 and 130+/-2 vs. 109+/-2, respectively, p<0.01). Ouabain infused s.c. or i.c.v. for 14 days had no effect on Na+,K+-ATPase isozyme activity in hypothalamic, pontine/medullary or cortical microsomes. However, the percent increase in total Na+,K+-ATPase activity produced in vitro by antibody Fab fragments that bind ouabain with high affinity (Digibind) was two-fold greater in s.c.- and i.c.v.-ouabain-treated rats vs. control, but only in hypothalamic microsomes. Thus, ouabain infused s.c. or i.c.v. does appear to directly inhibit Na+,K+-ATPase activity in the hypothalamus. On the other hand, in the hypothalamus, s.c.- and i.c.v.-ouabain infusions tended to increase alpha3 (by 30-44%), but had no effect on alpha1 or alpha2 Na+,K+-ATPase isozyme protein expression. In addition, ouabain was found to partially dissociate from the Na+,K+-ATPase enzyme following sample processing. Thus, the inability to detect a decrease in enzyme activity in the hypothalamus in response to ouabain may be due, in part, to an increase in enzyme expression and the dissociation of ouabain during sample processing.     

A serotonin agonist-antagonist reversible effect on Na+-K+-ATPase activity in the developing rat brain

In brain of adult and developing rats the Na+-K+-adenosine triphosphatase (Na+-K+-ATPase) system seems to react to serotonin (5-HT) changes induced pharmacologically. A 5-HT agonist (quipazine) elicits a response of the enzyme activity in the cerebral cortex in vivo, which is neutralized with a 5-HT antagonist (methysergide). This effect was observed from day 21 to adulthood. Also in a state of 5-HT receptor hypersensitivity (rats treated early with 5,6-dihydroxytryptamine), the response of Na+-K+-ATPase to the 5-HT agonist was higher than without neurotoxic lesion of 5-HT paths. These data suggest an involvement of the Na+-K+-ATPase system in 5-HT receptor sensitivity in the rat brain.     

MK-801 alters Na+, K+-ATPase activity and oxidative status in zebrafish brain: reversal by antipsychotic drugs

Schizophrenia is a debilitating mental disorder with a global prevalence of 1% and its etiology remains poorly understood. In the current study we investigated the influence of antipsychotic drugs on the effects of MK-801 administration, which is a drug that mimics biochemical changes observed in schizophrenia, on Na(+), K(+)-ATPase activity and some parameters of oxidative stress in zebrafish brain. Our results showed that MK-801 treatment significantly decreased Na(+), K(+)-ATPase activity, and all antipsychotics tested prevented such effects. Acute MK-801 treatment did not alter reactive oxygen/nitrogen species by 2'7'-dichlorofluorscein (H2DCF) oxidation assay, but increased the levels of thiobarbituric acid reactive substances (TBARS), when compared with controls. Some antipsychotics such as sulpiride, olanzapine, and haloperidol prevented the increase of TBARS caused by MK-801. These findings indicate oxidative damage might be a mechanism involved in the decrease of Na(+), K(+)-ATPase activity induced by MK-801. The parameters evaluated in this study had not yet been tested in this animal model using the MK-801, suggesting that zebrafish is an animal model that can contribute for providing information on potential treatments and disease characteristics.     

Effect of noradrenaline and vanadium on Na+K+-activated ATPase in rat cerebral cortex synaptosomal preparation

Summary The effect of l-noradrenaline and vanadate on the activity of Na⁺K⁺-activated ATPase was studied on synaptosomal brain cortex preparation. Using neutron activation analysis it was found that the rat cerebral cortex synaptosomal preparation contains 0.16M. vanadium. The concentration of vanadium needed to reduce enzyme activity by 50% proved to be 2×10^–6 M. Evidence has been provided that the increase by noradrenaline of enzyme activity in synaptosomal preparation depends on the presence of an inhibitory contaminant in commercial ATP preparations. In homogenate, however, noradrenaline was able to enhance enzyme activity even when vanadium-free ATP was used. This fact indicates that noradrenaline removes the inhibitory effect of cytoplasmic factor thereby stimulating enzyme activity.