Changes in Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Activity and Alpha 3 Subunit Expression in CNS After Administration of Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Inhibitors

The expression of Na⁺, K⁺-ATPase α3 subunit and synaptosomal membrane Na⁺, K⁺-ATPase activity were analyzed after administration of ouabain and endobain E, respectively commercial and endogenous Na⁺, K⁺-ATPase inhibitors. Wistar rats received intracerebroventricularly ouabain or endobain E dissolved in saline solution or Tris–HCl, respectively or the vehicles (controls). Two days later, animals were decapitated, cerebral cortex and hippocampus removed and crude and synaptosomal membrane fractions were isolated. Western blot analysis showed that Na⁺, K⁺-ATPase α3 subunit expression increased roughly 40% after administration of 10 or 100 nmoles ouabain in cerebral cortex but remained unaltered in hippocampus. After administration of 10 μl endobain E (1 μl = 28 mg tissue) Na⁺, K⁺-ATPase α3 subunit enhanced 130% in cerebral cortex and 103% in hippocampus. The activity of Na⁺, K⁺-ATPase in cortical synaptosomal membranes diminished or increased after administration of ouabain or endobain E, respectively. It is concluded that Na⁺, K⁺-ATPase inhibitors modify differentially the expression of Na⁺, K⁺-ATPase α3 subunit and enzyme activity, most likely involving compensatory mechanisms.     

Role of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase in natriuretic effect of prolactin in a model of cholestasis of pregnancy

Participation of Na⁺/K⁺-ATPase in the natriuretic effect of prolactin in a cholestasis of pregnancy model was investigated. The Na⁺/K⁺-ATPase activity in rat kidney medulla, where active sodium reabsorption occurs, decreased in the model of cholestasis of pregnancy and other hyperprolactinemia types compared with intact animals. This effect was not connected with the protein level of α1- and β-subunits of Na⁺/K⁺-ATPase measured by Western blotting in the kidney medulla. Decrease in Na⁺/K⁺-ATPase activity in the kidney cortex was not significant, as well as decrease in the quantity of mRNA and proteins of the α1- and β-subunits of Na⁺/K⁺-ATPase. There were no correlations between the Na⁺/K⁺-ATPase activity and sodium clearance, although sodium clearance increased significantly in the model of cholestasis of pregnancy and other hyperprolactinemia groups under conditions of stable glomerular filtration rate measured by creatinine clearance. We conclude that the Na⁺/K⁺-ATPase is not the only mediator of the natriuretic effect of prolactin in the model of cholesta- sis of pregnancy.     

A possible mechanism for low affinity of silkworm Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase for K<Superscript>+</Superscript>

The affinity for K⁺ of silkworm nerve Na⁺/K⁺-ATPase is markedly lower than that of mammalian Na⁺/K⁺-ATPase (Homareda 2010). In order to obtain clues on the molecular basis of the difference in K⁺ affinities, we cloned cDNAs of silkworm (Bombyx mori) nerve Na⁺/K⁺-ATPase α and β subunits, and analyzed the deduced amino acid sequences. The molecular masses of the α and β subunits were presumed to be 111.5 kDa with ten transmembrane segments and 37.7 kDa with a single transmembrane segment, respectively. The α subunit showed 75% identity and 93% homology with the pig Na⁺/K⁺-ATPase α1 subunit. On the other hand, the amino acid identity of the β subunit with mammalian counterparts was as low as 30%. Cloned α and β cDNAs were co-expressed in cultured silkworm ovary-derived cells, BM-N cells, which lack endogenous Na⁺/K⁺-ATPase. Na⁺/K⁺-ATPase expressed in the cultured cells showed a low affinity for K⁺ and a high affinity for Na⁺, characteristic of the silkworm nerve Na⁺/K⁺-ATPase. These results suggest that the β subunit is responsible for the affinity for K⁺ of Na⁺/K⁺-ATPase.     

The Study of Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Activity of Rat Brain during Crush Syndrome

Crush syndrome (CS) results from severe traumatic damage to the organism that is characterized by stress, acute homeostatic failure of the tissues, and myoglobinuria with severe intoxication. This leads to an acute impairment of kidneys and heart. The peripheral and central nervous systems are also the subject of significant changes in CS. Na⁺, K⁺-ATPase is a critical enzyme in neuron that is essential for the regulation of neuronal membrane potential, cell volume as well as transmembrane fluxes of Ca⁺⁺ and Excitatory Amino Acids. In the present study, Na⁺, K⁺-ATPase activity of rat brain regions [Olfactory lobes (OL), Cerebral cortex (CC), Cerebellum (CL), and Medulla oblongata (MO)] during CS was investigated. Experimental model of CS in albino rats was induced by 2-h of compression followed by 2, 24, and 48-h of decompression of femoral muscle tissue. In this study, we have observed elevation in Na⁺, K⁺-ATPase activity above normal/control levels in all parts of brain (OL: 34.4%; CC: 1.0%; CL: 3.3% and MO: 45%) during 2-h compression in comparison to controls.     

Clozapine Administration Modifies Neurotensin Effect on Synaptosomal Membrane Na<Superscript>+</Superscript>, K<Superscript>+</Superscript> -ATPase Activity

Na⁺, K⁺-ATPase is inhibited by neurotensin, an effect which involves the peptide high affinity receptor (NTS1). Neurotensin effect on cerebral cortex synaptosomal membrane Na⁺, K⁺-ATPase activity of rats injected i.p. with antipsychotic clozapine was studied. Whereas 3.5 × 10⁻⁶ M neurotensin decreased 44% Na⁺, K⁺-ATPase activity in the controls, the peptide failed to modify enzyme activity 30 min after a single 3.0, 10.0 and 30.0 mg/kg clozapine dose. Neurotensin decreased Na⁺, K⁺-ATPase activity 40 or 20% 18 h after 3.0 or 5.6 mg/kg clozapine administration, respectively, and lacked inhibitory effect 18 h after 17.8 and 30.0 mg/kg clozapine doses. Results indicated that the clozapine treatment differentially modifies the further effect of neurotensin on synaptosomal membrane Na⁺, K⁺-ATPase activity according to time and dose conditions employed. Taken into account that clozapine blocks the dopaminergic D2 receptor, findings obtained favor the view of an interplay among neurotensinergic receptor, dopaminergic D2 receptor and Na⁺, K⁺-ATPase at synaptic membranes.     

Effects of ouabain on proliferation of human endothelial cells correlate with Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase activity and intracellular ratio of Na<Superscript>+</Superscript> and K<Superscript>+</Superscript>

Side-by-side with inhibition of the Na⁺,K⁺-ATPase ouabain and other cardiotonic steroids (CTS) can affect cell functions by mechanisms other than regulation of the intracellular Na⁺ and K⁺ ratio ([Na⁺]_i/[K⁺]_i). Thus, we compared the doseand time-dependences of the effect of ouabain on intracellular [Na⁺]_i/[K⁺]_i ratio, Na⁺,K⁺-ATPase activity, and proliferation of human umbilical vein endothelial cells (HUVEC). Treatment of the cells with 1-3 nM ouabain for 24-72 h decreased the [Na⁺]_i/[K⁺]_i ratio and increased cell proliferation by 20-50%. We discovered that the same ouabain concentrations increased Na⁺,K⁺-ATPase activity by 25-30%, as measured by the rate of ⁸⁶Rb⁺ influx. Higher ouabain concentrations inhibited Na⁺,K⁺-ATPase, increased [Na⁺]_i/[K⁺]_i ratio, suppressed cell growth, and caused cell death. When cells were treated with low ouabain concentrations for 48 or 72 h, a negative correlation between [Na⁺]_i/[K⁺]_i ratio and cell growth activation was observed. In cells treated with high ouabain concentrations for 24 h, the [Na⁺]_i/[K⁺]_i ratio correlated positively with proliferation inhibition. These data demonstrate that inhibition of HUVEC proliferation at high CTS concentrations correlates with dissipation of the Na⁺ and K⁺ concentration gradients, whereas cell growth stimulation by low CTS doses results from activation of Na⁺,K⁺-ATPase and decrease in the [Na⁺]_i/[K⁺]_i ratio.     

Neurochemical Evidence that Pristanic Acid Impairs Energy Production and Inhibits Synaptic Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Activity in Brain of Young Rats

Pristanic acid (Prist) accumulates in some peroxisomal disorders characterized by neurologic dysfunction and brain abnormalities. The present work investigated the in vitro effects of Prist on important parameters of energy metabolism in brain cortex of young rats. CO₂ production from labeled acetate and the activities of the respiratory chain complexes I–IV, creatine kinase and synaptic Na⁺, K⁺-ATPase were measured. Prist decreased CO₂ production and the activities of complexes I, II and II–III. Prist also reduced Na⁺, K⁺-ATPase activity, but did not affect the activity of creatine kinase. Considering the importance of the citric acid cycle and the electron flow through the respiratory chain for brain energy production and of Na⁺, K⁺-ATPase for the maintenance of membrane potential, the present data indicate that Prist compromises brain bioenergetics and neurotransmission. It is presumed that these pathomechanisms may be involved in the neurological damage found in patients affected by disorders in which Prist accumulates.     

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase stabilization by Hsp70 in the outer stripe of the outer medulla in rats during recovery from a low-protein diet

A low-protein (LP) diet induces injury from energy depletion in renal epithelial cells. Overexpression of heat-shock proteins has been implicated in the restoration of the cytoskeletal anchorage of Na⁺/K⁺-ATPase. We tested if Hsp70 stabilizes renal Na⁺/K⁺-ATPase attachment to the cytoskeleton from the cortex and the outer stripe of the outer medulla (OSOM) in rats during recovery from a LP diet. Rats were fed with a LP diet (8% protein) for 14 days, and then the rats were recovered with a 24% protein (RP) diet. The control group received a 24% protein (NP) diet. Increased Na⁺/K⁺-ATPase dissociation was demonstrated in soluble fraction from OSOM with lower ATP content as a result of LP diet vs NP. Meanwhile, decreased Hsp70 levels in the same fraction were shown. Translocation of Hsp70 to the cytoskeletal injured fraction associated with stabilization of Na⁺/K⁺-ATPase was shown in OSOM from LP after in vitro co-incubation of the cytoskeletal fraction of LP and non-cytoskeletal fraction of RP. These effects were abolished by the addition of the anti-Hsp70 antibody. Absence of Na⁺/K⁺-ATPase detachment from its cytoskeletal anchorage was demonstrated in proximal duct segments from cortex in LP. Co-immunoprecipitation showed that the amount of Na⁺/K⁺-ATPase co-precipitating with Hsp70 increased in the OSOM as a result of the LP diet. In the cortex tissues from rats fed the LP and the RP diet, the interaction of both proteins were similar to the control groups. Our results indicate that Hsp70 has a critical role in protecting the integrity of the cytoskeletal anchorage of Na⁺/K⁺-ATPase during recovery from ATP-depleted injury resulting from LP in OSOM. Portions of this study were presented in abstract form at the World Congress of Nephrology in Rio de Janeiro, Brasil. April 21–25, 2007.     

Neurochemical Evidence that Lysine Inhibits Synaptic Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase Activity and Provokes Oxidative Damage in Striatum of Young Rats In vivo

Lysine (Lys) accumulation in tissues and biological fluids is the biochemical hallmark of patients affected by familial hyperlysinemia (FH) and other inherited metabolic disorders. In the present study we investigated the effects of acute administration of Lys on relevant parameters of energy metabolism and oxidative stress in striatum of young rats. We verified that Lys in vivo intrastriatal injection did not change the citric acid cycle function and creatine kinase activity, but, in contrast, significantly inhibited synaptic Na⁺,K⁺-ATPase activity in striatum prepared 2 and 12 h after injection. Moreover, Lys induced lipid peroxidation and diminished the concentrations of glutathione 2 h after injection. These effects were prevented by the antioxidant scavengers melatonin and the combination of α-tocopherol and ascorbic acid. Lys also inhibited glutathione peroxidase activity 12 h after injection. Therefore it is assumed that inhibition of synaptic Na⁺,K⁺-ATPase and oxidative damage caused by brain Lys accumulation may possibly contribute to the neurological manifestations of FH and other neurometabolic conditions with high concentrations of this amino acid.     

The Administration of Levocabastine,a NTS2 Receptor Antagonist,Modifies Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Properties

Neurotensin behaves as a neuromodulator or as a neurotransmitter interacting with NTS1 and NTS2 receptors. Neurotensin in vitro inhibits synaptosomal membrane Na⁺, K⁺-ATPase activity. This effect is prevented by administration of SR 48692 (antagonist for NTS1 receptor). The administration of levocabastine (antagonist for NTS2 receptor) does not prevent Na⁺, K⁺-ATPase inhibition by neurotensin when the enzyme is assayed with ATP as substrate. Herein levocabastine effect on Na⁺, K⁺-ATPase K⁺ site was explored. For this purpose, levocabastine was administered to rats and K⁺-p-nitrophenylphosphatase (K⁺-p-NPPase) activity in synaptosomal membranes and [³H]-ouabain binding to cerebral cortex membranes were assayed in the absence (basal) and in the presence of neurotensin. Male Wistar rats were administered with levocabastine (50 μg/kg, i.p., 30 min) or the vehicle (saline solution). Synaptosomal membranes were obtained from cerebral cortex by differential and gradient centrifugation. The activity of K⁺-p-NPPase was determined in media laking or containing ATP plus NaCl. In such phosphorylating condition enzyme behaviour resembles that observed when ATP hydrolyses is recorded. In the absence of ATP plus NaCl, K⁺-p-NPPase activity was similar for levocabastine or vehicle injected (roughly 11 μmole hydrolyzed substrate per mg protein per hour). Such value remained unaltered by the presence of 3.5 × 10^?6 M neurotensin. In the phosphorylating medium, neurotensin decreased (32 %) the enzyme activity in membranes obtained from rats injected with the vehicle but failed to alter those obtained from rats injected with levocabastine. Levocabastine administration enhanced (50 %) basal [³H]-ouabain binding to cerebral cortex membranes but failed to modify neurotensin inhibitory effect on this ligand binding. It is concluded that NTS2 receptor blockade modifies the properties of neuronal Na⁺, K⁺-ATPase and that neurotensin effect on Na⁺, K⁺-ATPase involves NTS1 receptor and -at least partially- NTS2 receptor.     

DDT inhibits Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, Mg<Superscript>2+</Superscript>-ATPase in the Intestinal Mucosae and Gills of Marine Teleosts

SODIUM-potassium-activated, magnesium-dependent, adenosine triphosphatase (Na⁺, K⁺, Mg²⁺-ATPase) is widely accepted as an essential factor in sodium transport¹ and observations on fish substantiate this view. There are concurrent increases, for example, of both Na⁺, K⁺, Mg²⁺-ATPase activity and osmoregulatory sodium transport², in the intestinal mucosae^3,4 and the gills^3,5 of euryhaline teleosts during adaptation to seawater. Furthermore, the gills of stenohaline seawater teleosts, which actively secrete sodium, exhibit higher Na⁺, K⁺, Mg²⁺-ATPase activity than the gills of stenohaline freshwater teleosts, which do not actively secrete sodium^3,5. Na⁺, K⁺, Mg²⁺-ATPase therefore seems to be important in maintaining tissue osmolarity well below that of seawater. It is disquieting to report therefore that Na⁺, K⁺, Mg²⁺-ATPase activity in the intestinal mucosae and gills of marine teleosts is inhibited by the organochlorine insecticide DDT. This observation may help to clarify the unexplained sensitivity of teleosts to DDT⁶.     

The Expression of NMDA Receptor Subunits in Cerebral Cortex and Hippocampus is Differentially Increased by Administration of Endobain E,a Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Inhibitor

Previous studies showed that endobain E, an endogenous Na⁺, K⁺-ATPase inhibitor, decreases dizocilpine binding to NMDA receptor in isolated membranes. The effect of endobain E on expression of NMDA receptor subunits in membranes of rat cerebral cortex and hippocampus was analyzed by Western blot. Two days after administration of 10 μl endobain E (1 μl = 29 mg fresh tissue) NR1 subunit expression enhanced 5-fold and 2.5-fold in cerebral cortex and hippocampus, respectively. NR2A subunit expression increased 2-fold in cerebral cortex and 1.5-fold in hippocampus. The level of NR2B subunit raised 3-fold in cerebral cortex but remained unaltered in hippocampus. NR2C subunit expression was unaffected in either area. NR2D subunit enhanced 1.6 and 2.1-fold for cerebral cortex and hippocampus, respectively. Results indicate that endogenous Na⁺, K⁺-ATPase inhibitor endobain E differentially modifies the expression of NMDA receptor subunits.     

The Na<Superscript>+</Superscript> pump and intracellular signaling mechanisms

The main properties of Na⁺/K⁺-ATPase as a natural receptor for cardiotonic steroids are considered. Primary attention is focused on structural and functional differences between the α-subunit isoforms of Na⁺/K⁺-ATPase in different tissues. General information on the role of the Na⁺ pump in signaling cascades in kidney epithelial cells, cardiomyocytes and neurons is presented. The data obtained indicate that, in neurons, several α-isoforms of Na⁺/K⁺-ATPase possessing different sensitivity to ouabain may have different signaling functions.     

Different domain organization of two main conformational states of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase

The Na⁺/K⁺-ATPase generates an electrochemical gradient of Na⁺ and K⁺, which is necessary for the functioning of animal cells. During the catalytic act, the enzyme passes through two principal conformational states, E₁ and E₂. To assess the domain organization of the protein in these conformations, thermal denaturation of Na⁺/K⁺-ATPases from duck salt gland and from rabbit kidney has been studied in the absence and in the presence of Na⁺ or K⁺, which induce the transition to E₁ or E₂. The melting curves for the ion-free forms of the two ATPases have different shapes: the rabbit protein shows one transition at 56.1°C, whereas the duck protein shows two transitions, at 49.8 and 56.9°C. Addition of Na⁺ or K⁺ ions abolishes the difference in thermal behavior between these enzymes, but through opposite effects. The melting curves for the E₂ conformation (K⁺ bound) in both cases exhibit a single peak of heat absorption at ∼63°C. For the E₁ conformation (Na⁺ bound), each melting curve has three peaks, indicating denaturation of three domains. The difference in the domain organization of Na⁺/K⁺-ATPase in the E1 and E2 states may account for the different sensitivity to temperature, proteolysis, and oxidative stress observed for the two enzyme conformations.     

Isovaleric Acid Reduces Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Activity in Synaptic Membranes from Cerebral Cortex of Young Rats

1. Patients affected by isovaleric acidemia (IVAcidemia) suffer from acute episodes of encephalopathy. However, the mechanisms underlying the neuropathology of this disease are poorly known. The objective of the present study was to investigate the in vitro effects of the metabolites that predominantly accumulate in IVAcidemia, namely isovaleric acid (IVA), 3-hydroxyisovaleric acid (3-OHIVA) and isovalerylglycine (IVG), on important parameters of energy metabolism, such as ¹⁴CO₂ production from acetate and the activities of the respiratory chain complexes I–IV, creatine kinase and Na⁺, K⁺-ATPase in synaptic plasma membranes from cerebral cortex homogenates of 30-day-old rats. 2. We observed that 3-OHIVA acid and IVG did not affect all the parameters analyzed. Similarly, ¹⁴CO₂ production from acetate (Krebs cycle activity), the activities of creatine kinase, and of the respiratory chain complexes was not modified by IVA. In contrast, IVA exposition to cortical homogenates provoked a marked inhibition of Na⁺, K⁺-ATPase activity. However, this activity was not changed when IVA was directly exposed to purified synaptic plasma membranes, suggesting an indirect effect of this organic acid on the enzyme. Furthermore, pretreatment of cortical homogenates with α-tocopherol and creatine totally prevented IVA-induced inhibition on Na⁺, K⁺-ATPase activity from synaptic plasma membranes, whereas glutathione (GSH) and the NO synthase inhibitor N^ω-nitro-l-arginine methyl ester (L-NAME) did not alter this inhibition. 3. These data indicate that peroxide radicals were probably involved in this inhibitory effect. Since Na⁺, K⁺-ATPase is a critical enzyme for normal brain development and functioning and necessary to maintain neuronal excitability, it is presumed that the inhibitory effect of IVA on this activity may be involved in the pathophysiology of the neurological dysfunction of isovaleric acidemic patients.     

Rottlerin Inhibits (Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>)-ATPase Activity in Brain Tissue and Alters <Emphasis Type="SmallCaps">d</Emphasis>-Aspartate Dependent Redistribution of Glutamate Transporter GLAST in Cultured Astrocytes

The naturally occurring toxin rottlerin has been used by other laboratories as a specific inhibitor of protein kinase C-delta (PKC-δ) to obtain evidence that the activity-dependent distribution of glutamate transporter GLAST is regulated by PKC-δ mediated phosphorylation. Using immunofluorescence labelling for GLAST and deconvolution microscopy we have observed that d-aspartate-induced redistribution of GLAST towards the plasma membranes of cultured astrocytes was abolished by rottlerin. In brain tissue in vitro, rottlerin reduced apparent activity of (Na⁺, K⁺)-dependent ATPase (Na⁺, K⁺-ATPase) and increased oxygen consumption in accordance with its known activity as an uncoupler of oxidative phosphorylation (“metabolic poison”). Rottlerin also inhibited Na⁺, K⁺-ATPase in cultured astrocytes. As the glutamate transport critically depends on energy metabolism and on the activity of Na⁺, K⁺-ATPase in particular, we suggest that the metabolic toxicity of rottlerin and/or the decreased activity of the Na⁺, K⁺-ATPase could explain both the glutamate transport inhibition and altered GLAST distribution caused by rottlerin even without any involvement of PKC-δ-catalysed phosphorylation in the process.     

Involvement of protons in the ion transport cycle of Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase

The effect of pH on electrogenic sodium transport by the Na⁺,K⁺-ATPase has been studied. Experiments were carried out by admittance recording in a model system consisting of a bilayer lipid membrane with adsorbed membrane fragments containing purified Na⁺,K⁺-ATPase. Changes in the membrane admittance (capacitance and conductance increments in response to photo-induced release of ATP from caged ATP) were measured as function of AC voltage frequency, sodium ion concentration, and pH. In solutions containing 150 mM Na⁺, the frequency dependence of capacitance increments was not significantly dependent on pH in the range between 6 and 8. At a low NaCl concentration (3 mM), the capacitance increments at low frequencies decreased with the increasing pH. In the absence of NaCl, the frequency-dependent capacitance increment at low frequencies was similar to that measured in the presence of 3 mM NaCl. These results may be explained by involvement of protons in the Na⁺,K⁺-ATPase pump cycle, i.e., electroneutral exchange of sodium ions for protons under physiological conditions, electrogenic transport of sodium ions at high pH, and electrogenic transport of protons at low concentrations (and in the absence) of sodium ions.     

Effect of Toluene and Nutritional Status on Serotonin,Lipid Peroxidation Levels and NA<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase in Adult Rat Brain

The aim was to evaluate the effect of toluene and nutritional status on levels of serotonin (5-HT), 5-hydroxytryptophan (5-HTP), Na⁺/K⁺-ATPase, total ATPase and lipid peroxidation (TBARS) in rat brain. Study was conducted with malnourished (MN), well-nourished (WN) and normal Wistar rats. Three groups were formed for each nutritional status: control group I received 0.9% NaCl; toluene (1 g/kg) was administered to group II, and 1.5 g/kg to group III. Levels of 5-HT decreased (P < 0.05) in WN toluene groups, and 5-HTP decreased (P < 0.05) in the WN 1 g toluene and MN 1.5 g toluene groups. TBARS decreased (P < 0.05) in WN toluene groups. A trend to increase in Na⁺/K⁺-ATPase was found in WN and MN toluene groups, while total ATPase increased (P < 0.05) in the WN 1.5 g toluene group. The results suggest that high concentrations of toluene in single doses induce significant changes in the serotonergic system and alter membrane fluidity more perceptibly in the brain of adult animals with regular diet than in malnourished animals.     

Glutamatergic hypothesis of schizophrenia: involvement of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-dependent glutamate transport

Summary Hypothetical model based on deficient glutamatergic neurotransmission caused by hyperactive glutamate transport in astrocytes surrounding excitatory synapses in the prefrontal cortex is examined in relation to the aetiology of schizophrenia. The model is consistent with actions of neuroleptics, such as clozapine, in animal experiments and it is strongly supported by recent findings of increased expression of glutamate transporter GLT in prefrontal cortex of patients with schizophrenia. It is proposed that mechanisms regulating glutamate transport be investigated as potential targets for novel classes of neuroactive compounds with neuroleptic characteristics. Development of new efficient techniques designed specifically for the purpose of studying rapid activity-dependent translocation of glutamate transporters and associated molecules such as Na⁺, K⁺-ATPase is essential and should be encouraged.