SODIUM-STIMULATED ADENOSINE TRIPHOSPHATASE ACTIVITY OF RAT BRAIN MITOCHONDRIA

Abstract The endogenous ATPase activity of rat brain mitochondria was stimulated 30-50 per cent by 15-50 m m concentrations of NaCl or Na acetate. The Na stimulation was completely abolished by small amounts of oligomycin but unaffected by ouabain. The differential effects of these inhibitors indicated that the Na-induced ATPase activity did not result from microsomal or synaptosomal contamination of mitochrondria. Sodium salts decreased the stimulatory effects of DNP, gramicidin, or Ca, but not that of Mg on the endogenous ATPase activity. These interactions were specific for Na⁺ as the corresponding salts of K⁺ did not affect the endogenous ATPase or inhibit the DNP-stimulated ATPase activity except at high concentrations. The Na-induced increases in ATPase activity and respiration were more sensitive to aging of the mitochondria than were ADP/O and respiratory control ratios, or the DNP-induced ATPase activity. These results suggest that Na⁺ may interact in brain mitochondria with the same high-energy intermediate of oxidative phosphorylation proposed for DNP and Ca.     

Subcellular Site of Action of Imipramine in Rodent Brain

To determine the site of action of imipramine, the subcellular distribution of [3H]imipramine in rodents was followed after both in vivo administration and in vitro incubation with tissue slices under "physiological" conditions. Total [3H]imipramine (10-1,000 nM) binding was associated with all primary fractions, but in particular with the nuclear (P1) and mitochondrial (P2) pellets and the synaptosomal (P2B) and myelin (P2A) fractions. Using an excess of imipramine to define any nonspecific interactions, a specific association was observed mainly in those fractions containing isolated nerve terminals and to a lesser extent with the purified myelin fraction. Preparation of subsynaptosomal fractions by osmotic lysis indicated that [3H]imipramine was associated with the synaptic vesicle and microsomal fractions and also with synaptosomal membranes. The degree of binding to the vesicular and microsomal fractions was increased with the length of preparation time, whereas there was an inverse relationship between the length of preparation and the amount bound to the synaptosomal membrane fraction. There was no evidence of an intrasynaptosomal accumulation of [3H]imipramine at concentrations up to 1,000 nM. [3H]2-Nitroimipramine, a slowly dissociating imipramine derivative, was exclusively located in synaptic membrane fractions. Prior treatment of rats with a combination of 5,7-dihydroxytryptamine and desipramine reduced 5-hydroxytryptamine levels and the levels of [3H]imipramine associated with the synaptosomal fractions to the same extent. It is concluded that imipramine is associated with a binding site localised on 5-hydroxytryptaminergic nerve terminals and that there is a redistribution to other sites (vesicular and microsomal) during the isolation procedure.     

Plasmalemma from the roots of cucumber: Isolation by two-phase partitioning and characterization

Plasmalemma was isolated from the roots of 2-week-old cucumber plants ( Cucumis sativus L. cv. Rhensk druv) by utilizing an aqueous polymer two-phase system with 6.5%:6.5% (w/w) Dextran T500 and polyethylene glycol (PEG) 3350 at pH 7.8. The plasmalemma fraction comprised ca 6% of the membrane proteins contained in the microsomal fraction. The specific activity of the plasma membrane marker enzyme (K⁺, Mg²⁺-ATPase) was 14- to 17-times higher in the upper (PEG-rich) than in the lower (Dextran-rich) phase, and the reverse was true for marker enzymes (cytochrome c oxidase, EC 1.9.3.1, and antimycin A-resistant NADPH cytochrome c reductase) of intracellular membranes. The ATPase was highly stimulated by the addition of detergent (Triton X-100), so that the isolated plasmalemma vesicles appear tightly sealed and in a right-side-out orientation. Further characterization of the ATPase activities showed a pH optimum at 6.0 in the presence of Mg²⁺. This optimum was shifted to pH 5.8 after addition of K⁺. K⁺ stimulated the ATPase activity below pH 6 and inhibited above pH 6. The ATPase activity was specific for ATP and sensitive to N,N-dicyclohexylcarbodiimide and sodium vanadate, with K⁺ enhancing the vanadate inhibition. The enzyme was insensitive to sodium molybdate, NO⁻₃, azide and oligomycin. No Ca²⁺-ATPase was detected, and even as little as 0.05 m M Ca²⁺ inhibited the Mg²⁺-ATPase activity.     

CATION MODULATION OF SYNAPTOSOMAL RESPIRATION

Abstract— Synaptosomes were prepared from the cerebral cortex of the adult rat by a rapid technique, involving the use of centrifugation in a Ficoll-sucrose discontinuous gradient. Adequate respiratory control ratios were obtained with glutamate and succinate plus rotenone. The addition of Na⁺ to the incubation medium stimulated synaptosomal, State-4 respiration, with a half-maximal response at 15 mM Na⁺. The stimulation by Na⁺ was inhibited by atractylate, oligomycin, ouabain or EDTA. A cooperative interaction between Na⁺ and low concentrations of Mg²⁺ was observed. A significant proportion (39 per cent) of the total Na-K ATPase (EC 3.6.1.4) activity in the discontinuous gradient was localized in the synaptosomal fraction. In the absence of exogenous Mg²⁺, Na⁺ induced a 64 per cent stimulation of the synaptosomal ATPase activity which was sensitive to ouabain. Such stimulation of ATP hydrolysis would account for the formation of increased amounts of ADP, with consequent recycling to ATP through adequately controlled oxidative phosphorylation. These observations demonstrate a significant role for transmembrane cationic gradients in the control of synaptosomal respiration and mitochondrial oxidative phosphorylation. The preparation exhibits moderate respiratory control and should prove useful in studies of integrated mitochondrial oxidative metabolism and neuronal membrane function.     

Protein Phosphorylation and Calcium Uptake into Rat Forebrain Synaptosomes: Modulation by the σ Ligand, 1,3-Ditolylguanidine

Abstract: The σ ligand 1,3-di- O -tolylguanidine (DTG) increased basal dynamin and decreased depolarization-stimulated phosphorylation of the synaptosomal protein synapsin Ib without having direct effects on protein kinases or protein phosphatases. DTG dose-dependently decreased the basal cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) and blocked the depolarization-dependent increases in [Ca²⁺]_i. These effects were inhibited by the σ antagonists rimcazole and BMY14802. The nitric oxide donors sodium nitroprusside (SNP) and 8-( p -chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate decreased basal [Ca²⁺]_i and the KCl-evoked rise in [Ca²⁺]_i to an extent similar to DTG. SNP, but not DTG, produced a rise in cyclic GMP levels, suggesting that the effect of DTG on [Ca²⁺]_i was not mediated via downstream regulation of cyclic GMP levels. DTG increased ⁴⁵Ca²⁺ uptake and efflux under basal conditions and inhibited the ⁴⁵Ca²⁺ uptake induced by depolarization with KCl. The KCl-evoked rise in [Ca²⁺]_i was inhibited by ω-conotoxin (ω-CgTx)-GVIA and -MVIIC but not nifedipine and ω-agatoxin-IVA. The effect of DTG on decreasing the KCl-evoked rise in [Ca²⁺]_i was additive with ω-CgTx-MVIIC but not with ω-CgTx-GVIA. These data suggest that DTG was producing some of its effects on synapsin I and dynamin phosphorylation and intrasynaptosomal Ca²⁺ levels via inhibition of N-type Ca²⁺ channels.     

THE EFFECTS OF LITHIUM ON ATPase ACTIVITY IN SUBCELLULAR FRACTIONS FROM RAT BRAIN

Abstract— The effects of lithium chloride in vitro and in vivo were investigated on Na-K ATPase and Mg ATPase activities in synaptic plasma membrane, mitochondrial and synaptic vesicle fractions prepared from rat brain. In vitro , lithium chloride (10⁻³-10⁻⁸ m ) had no effect on ATPase activity in any of the fractions studied. Lithium chloride given chronically by i.p. injection (30 mg/rat/day) for 9 days had little effect on synaptic plasma membrane ATPases. Dietary administration of lithium chloride (60 mmol/kg food) produced a small but significant increase in synaptic plasma membrane Mg ATPase activity after 3 weeks administration and mitochondrial Mg ATPase activity after 1 week. There was no effect on synaptic plasma membrane Na-K ATPase activity. Salt supplementation reduced the toxic effects of lithium administration and it is suggested that toxicity may account for some of the previously reported changes in synaptic membrane ATPases produced by lithium.     

ACTOMYOSIN-LIKE PROTEIN IN BRAIN: SUBCELLULAR DISTRIBUTION

Abstract— An actomyosin-like protein (neurostenin) has been isolated from the synaptosomal fraction of bovine and rat brains. A similar protein could not be obtained from the mitochondrial, microsomal, myelin or supernatant fractions. The synaptosomal protein is a Mg²⁺ -Ca²⁺ -stimulated ATPase which exhibited the phenomenon of superprecipitation and viscosimetric sensitivity to ATP characteristic of actomyosins. It constituted 8–10 per cent of the total synaptosomal proteins. The protein could be dissociated into actin-like (neurin) and myosin-like (stenin) proteins by ultracentrifugation in sucrose gradients containing KI and ATP. The neurin, as well as muscle actin, stimulated the Mg²⁺ -ATPase activity of stenin and muscle myosin; the relative viscosities of the mixtures were increased and became sensitive to added ATP. The neurin contained 0.9 mol of 3-methylhistidine per 50,000 g of protein. The presence of these proteins in the synaptosomes suggests the possibility that they participate in nerve-ending functions, e.g. release of transmitter materials.     

Sucrose and ouabain effects on the kinetic properties of a membrane-bound (Na++ K++ Mg2+) ATPase in sugar beet roots

Kinetic studies of a microsomal (Na⁺+ K⁺+ Mg²⁺)ATPase from sugar beet roots ( Beta vulgaris L. cv. Monohill) show that sucrose influences the MgATPase in different ways depending on the presence of K⁺ and/or Na⁺ 1) In the presence of the substrate MgATP and Na⁺ the effect of sucrose follows simple Michaelis-Menten kinetics. 2) In the presence of substrate together with K⁺ or (K⁺+ Na⁺), sucrose has little effect on the ATPase activity. 3) In the presence of Na⁺, onabain acts as an uncompetitive inhibitor with respect to MgATP. 4) In the presence of K⁺ or (K⁺+ Na⁺), the inhibition by ouabain is somewhat depressed and shows non-linearity when 1/v is plotted versus 1/MgATP. 5) Sucrose and Na⁺ activate in a competitive way, so that a successive increase of the Na⁺ level decreases the activation by sucrose. Both K_m and V-values are thereby changed. 6) The sucrose activation in the presence of Na⁺ is also influenced by ouabain. It is, therefore, suggested that Na⁺ may regulate the interference between the Na⁺/K⁺ pump and a sucrose sensitive system.     

Picomolar concentrations of tentoxin affect Mg2+- and Ca2+-ATPase activities of plasma membrane vesicles from roots of winter wheat seedlings

Purified plasmalemma vesicles were isolated in the presence of 250 m M sucrose from roots of 14-day-old seedlings of winter wheat ( Triticum aestivum L. Martonvásári-8) by phase partitioning of salt-washed microsomal fractions in a Dextran-polyethylene glycol two-phase system, and both Mg²⁺- and Ca²⁺-ATPase activities were detected. Orthovanadate-sensitive Mg²⁺-ATPase activity associated with the inside of right side-out plasmalemma (PM) vesicles (latency 98%) was inhibited 76% by 0.3 m M Ca²⁺, Ca²⁺-dependent ATPase activity located partly on the inside and partly on the outside of plasmalemma vesicles (latency 47%) was not affected by Mg²⁺.
Mg²⁺-ATPase activity was inhibited by 68% and inhibition of Mg²⁺ activation by 0.3 m M Ca²⁺ partly disappeared in the presence of 10 p M tentoxin, a fungal phytotoxin. Mg²⁺-ATPase activity remained inhibited up to 10 n M tentoxin while at 1 μ M tentoxin Mg²⁺ activation was as high as without tentoxin. K⁺-stimulation and vanadate inhibition was increased and decreased, respectively, by 100 p M -10 n M tentoxin. Ca²⁺-dependent ATPase activity was continuously increased by 1 p M -10 n M tentoxin, but at 1 μ M tentoxin the stimulation disappeared. The effects of p M tentoxin on plasma-lemma Mg²⁺-ATPase are discussed in relation to its influence on K⁺ transport in wheat seedlings.     

Effects of Ca2+ and polyamines on Na+ and Rb+ influx in excised maize roots

When 1 m M spermidine or spermine was included in an absorption solution which contained 20 m M Na⁺ and 1 m M Rb⁺, Na⁺ influx into excised maize roots ( Zea mays L. cv. Golden Cross Bantam) was reduced. Rb⁺ influx was reduced in the presence of spermidine and uneffected in the presence of spermine when compared with control solutions. When 1 m M Ca²⁺ replaced the polyamines, Na⁺ influx was strongly reduced and Rb⁺ influx was promoted. Rb⁺ influx from 1 m M Rb⁺ solutions which did not contain Na⁺ was also promoted by 1 m M Ca²⁺, but was inhibited by 1 m M spermidine. This Ca²⁺ promotion of Rb⁺ influx could be reversed by 10 times greater concentration of spermidine in the absorption solution. H⁺ efflux from excised roots was inhibited by spermidine when compared with Ca²⁺ or control solutions, however, the plasma membrane ATPase was not inhibited by spermidine. It is concluded that external Ca²⁺ plays two separate roles in membrane function, only one of which can be substituted for by polyamines. The first role, maintenance of membrane integrity, can be substituted for by spermidine or spermine. The second function, maintenance of the Rb⁺ transport mechanism, is Ca²⁺ specific and cannot be substituted for by spermidine or spermine. The results of this study are discussed in terms of electrostatic interactions between the plasma membrane and the Ca²⁺ or polyamines.     

Calcium-Dependent and -Independent Acetylcholine Release from Electric Organ Synaptosomes by Pardaxin: Evidence of a Biphasic Action of an Excitatory Neurotoxin

Abstract: The effect of pardaxin, a new excitatory neurotoxin, on neurotransmitter release was tested using purely cholinergic synaptosomes of Torpedo marmorata electric organ. Pardaxin elicited the release of acetylcholine with a biphasic dose dependency. At low concentrations (up to 3 × 10⁻⁷ M ), the release was calcium-dependent and synaptosomal structure was well preserved as revealed by electron microscopy and measurements of occluded lactate dehydrogenase activity. At concentrations from 3 × 10⁻⁷ M to 10⁻⁵ M , the pardaxin-induced release of acetylcholine was independent of extracellular calcium, and occluded synaptosomal lactate dehydrogenase activity was lowered, indicating a synaptosomal membrane perturbation. Electron microscopy of 10⁻⁶ M pardaxin-treated synaptosomes revealed nerve terminals depleted of synaptic vesicles and containing cisternae. At higher toxin concentrations ( 10⁻⁵ M ), there were striking effects on synaptosomal morphology and occluded lactate dehydrogenase activity, suggesting a membrane lytic effect. We conclude that, at low concentrations, this neurotoxin is a promising tool to investigate calcium-dependent mechanisms of neurotransmitter release in the nervous system.     

Effects of phloridzin, metavanadate and oligomycin on membrane bound (Na++ K++ Mg2+)ATPase activity in sugar beet roots

To clarify the reaction mechanism of a (Na⁺+ K⁺+ Mg²⁺)ATPase activity in sugar beet roots ( Beta vulgaris L. cv. Monohill) phloridzin, oligomycin (inhibitors of animal ATPases) and metavanadate (NH₄VO₃) have been used. Kinetic studies showed that: 1) Phloridzin inhibition is uncompetitive with respect to MgATP and not influenced by Na⁺ or K⁺. 2) This inhibition is only found in preparations made in the absence of sucrose. 3) Oligomycin and vanadate inhibit the ATPase in different ways. Omission of sucrose from the preparation medium favours vanadate inhibition but suppresses oligomycin inhibition. 4) The kinetic pattern of the Na⁺ activation of the ATPase differs in preparations made in the absence and presence of sucrose, but that of K⁺ activation is the same. – These results indicate that inclusion as against omission of sucrose from the preparation medium causes a conformational change of the membrane fragments/vesicles, which then expose different surfaces to the surrounding medium.     

Transport of Mg2+ and Ca2+, and Mg2+-stimulated adenosine triphosphatase activity in oat roots as affected by mineral nutrition

Mg²⁺- and Ca²⁺-uptake was measured in dark-grown oat seedlings ( Avena sativa L. cv. Brighton) cultivated at two levels of mineral nutrition. In addition the stimulation of the ATPase activity of the microsomal fraction of the roots by Mg²⁺ was measured. Ca²⁺-uptake by the roots was mainly passive. Mg²⁺-uptake mainly active; the passive component of Mg²⁺-uptake was accompanied by Ca²⁺-efflux up to 60% of the Ca²⁺ present in the roots.
In general Mg²⁺ -uptake of oat roots was biphasic. The affinity of the second phase correspond well with that of the Mg²⁺-stimulation of the ATPase activity, in low-salt roots as well as in high-salt roots and in roots of plants switched to the other nutritional condition. Linear relationships were observed when [phase 2] Mg²⁺-uptake was plotted against Mg²⁺-stimulation of the ATPase activity of the microsomal fraction of the roots. In 5 days old high-salt plants 1 ATP (hydrolysed in the presence of Mg²⁺ J corresponded with active uptake of a single Mg²⁺ ion, but in older high-salt roots and in low-salt roots more ATP was hydrolysed per net uptake of a Mg²⁺ ion. The results are discussed against the background of regulation of the Mg²⁺-level of the cytoplasm of root cells by transport of Mg²⁺ by a Mg²⁺-ATPase to the vacuole, to the xylem vessels, and possibly outwards.     

ATPase activity of isolated plasma membrane vesicles of leaves of Elodea as affected by thiol reagents and NADH/NAD+ ratio

The goal of this study was to test the hypothesis that the plasma membrane-bound ATPase activity is influenced by the redox poise of the cytoplasm. Purified plasma membrane vesicles from leaves of Elodea canadensis Michx. and E. nuttallii (Planch.) St. John were isolated using an aqueous polymer two-phase batch procedure. The distribution of marker enzyme activities confirmed the plasma membrane origin of the vesicles. The vesicles exhibited NADH-ferricyanide reductase activity, indicating the presence of a redox chain in the plasma membrane. The K⁺, Mg²⁺-ATPase activity associated with these vesicles was inhibited by the sulfhydryl reagents N-ethylmaleimide and glutathione (GSSG). Furthermore the activity was inhibited by NAD⁺. This inhibition by NAD⁺ was relieved by increasing the NADH/NAD⁺ ratio. The possibility that the ATPase activity is regulated by the cytoplasmic NAD(P)H/ NAD(P)⁺ ratio is discussed, as well as the role of a plasma membrane-bound redox chain.     

ADP-Ribosylation of Membrane Proteins in Cholinergic Nerve Terminals

Abstract: Lysed Torpedo synaptosomes or washed synaptosomal membranes were incubated with [³²P]NAD⁺ and subjected to electrophoresis on SDS-polyacrylamide gels. More than eight membrane proteins were ADP-ribosylated. The most intensely labeled proteins were those of M_r= 62,000 and 82,000. Radiolabeling was more intense in synaptosomes than in other subcel-lular fractions. Cholera toxin caused ribosylation of additional synaptosomal proteins with M_r= 42,000 and (in some preparations) 49,000. Neither endogenous nor cholera toxin-catalyzed ADP-ribosylation required added guanyl nu-cleotides. Cholera toxin increased the adenylate cyclase activity of synaptosomal membranes, suggesting that the cholera toxin substrates are regulatory components of adenylate cyclase in these synaptosomes.     

V- AND P-TYPE Ca2+-STIMULATED ATPases IN A CALCIFYING STRAIN OF PLEUROCHRYSIS SP. (HAPTOPHYCEAE)

Coccolithophorids are marine unicellular algae characterized by their ability to carry out controlled, subcellular calcification. The biochemical and kinetic features of membrane-bound Ca²⁺-stimulated ATPases have been examined. Membranes and organelles from axenic cultures of Pleurochrysis sp. (CCMP299) were isolated by means of sucrose density centrifugation. High levels of Ca²⁺-stimulated ATPase were detected in chloroplasts, Golgi apparatus, plasma membrane, and coccolith vesicles. The sensitivity of the enzyme activity in the organelles and membranes was assessed with pharmacologic agents that are known to be specific for the several isoforms of Ca²⁺-stimulated ATPase. The Ca²⁺-stimulated ATPase activity in the Golgi and coccolith vesicle preparations was sensitive to nitrate, thiocyanate, and sodium azide and insensitive to vanadate, cyclopiazonic acid, and thapsigargin. ATP-dependent H⁺ movement, but not ⁴⁵Ca²⁺ transport, across the coccolith vesicle was demonstrated. The Ca²⁺-stimulated ATPase in the plasma membrane preparation was sensitive to vanadate. ATP-dependent, vanadate-sensitive efflux of ⁴⁵Ca²⁺ was demonstrated for microsomal material derived from gradient-isolated plasma membrane. Polypeptides from isolated Golgi and coccolith vesicle preparations cross-reacted to an antibody raised against a subunit of the oat root proton pump, whereas polypeptides from the chloroplast preparations did not cross-react. These findings show that a V-type Ca²⁺-stimulated ATPase is located on the coccolith vesicle membrane and a P-type Ca²⁺-stimulated ATPase is located on the plasma membrane.     

Binding of phytochrome to plasma membranes in vivo

A microsomal fraction was prepared by differential centrifugation from the homogenate of dark grown shoots of oats ( Avena sativa L. cv. Sol II). Plasma membranes were prepared from the microsomal fraction by means of an aqueous polymer two phase partition method. The content of phytochrome in the microsomal fraction and the plasma membrane fraction, respectively, were studied after different irradiation treatments of the intact shoots. Red irradiation increased the content of phytochrome in both the microsomal and plasma membrane fraction, especially in the presence of Mg²⁺. The increase induced by red light was fully reversible by far-red light for the plasma membrane fraction both in the presence and absence of Mg²⁺, in contrast to the microsomal fraction where Mg²⁺ had to be omitted. KI treatment of the membranes destroyed the binding of phytochrome whereas agents such as KCI, EDTA, CaCl₂ and Triton X-100, did not have this effect, indicating that the phytochrome attachment to the membrane is hydrophobic. This in vivo binding resembles to a large extent the one obtained in vitro by Sundqvist and Widell (Physiol. Plant. 59: 35–41, 1983) even though some differences between the phytochrome species and the membrane side exposed probably occur; so that the present interaction between phytochrome and the plasma membrane does not necessarily reflect the interaction that leads to physiological responses, and there could be more than one type of interaction.     

Effect of nigericin on the H+-translocating adenosine triphosphatase from tonoplast of Hevea latex

Nigericin stimulated the ATPase activity of tightly-sealed membrane vesicles prepared from Hevea brasiliensis Müll.-Arg. lutoïds in the presence of K⁺. This stimulation required a functioning membrane since it was membrane-bound and since it was not observed for the ATPase activity solubilized from the tonoplast by dichloromethane. The extent of nigericin-induced stimulation of tonoplast ATPase was proportional to the ΔpH collapsed by the ionophore in the presence of K⁺.     

Enhancement of Tryptophan Uptake by Divalent Cations in the Absence of Sodium Ions

Abstract: Nations were found to inhibit the uptake of L-tryptophan into synaptosomes with a shallow dose-response curve. Almost maximal inhibition was obtained with 10 mM-Na⁺. The divalent cations Ca²⁺ and Mg²⁺ were shown to be responsible for the increased uptake of L-tryptophan in the absence of Na⁺ ions. Other divalent cations also promoted tryptophan uptake under this condition (Ca²⁺ < Mg²⁺ < Mn²⁺ < Fe²⁺ < Zn²⁺ < Cu²⁺). It was concluded that monovalent chelate complexes were responsible for this enhancing effect. The measured L-tryptophan uptake was the net product of membrane bound and unbound tryptophan. Both bound and unbound tryptophan were increased in the presence of divalent cations. If no divalent cations were added to the incubation medium, Na⁺ ions decreased the unbound tryptophan but were without effect on bound tryptophan. Under these circumstances D-tryptophan had no effect on binding of the L-isomer and affected the transport of 1.-tryptophan only at very high does (100 x conc. L-tryptophan). These results suggest that I -tryptophan binds to a stereospecific transport carrier located in the synaptosomal membrane and that Na⁺ ions prevent the translocation of this carrier amino acid complex from the outer to the inner site of the neuronal membrane.     

THE EFFECTS OF OUABAIN AND THE ACTIVATION OF NEURAL MEMBRANE ATPase BY BIOGENIC AMINES

Abstract— The effects of 10⁻⁵ m -noradrenaline (NA), 5-hydroxytryptamine (5-HT) and dopamine (DA) on the activities of Na⁺-K⁺ ATPase (EC 3.6.1.3) were studied in synaptic membranes from 6 regions of the rabbit brain. NA and 5-HT stimulated the synaptic membrane Na⁺-K⁺ ATPase from the cerebrum, but none of the amines influenced the activity of this enzyme in the other brain regions. The Na⁺-K⁺ ATPase activity of the cerebral synaptic membrane isolated at the 0.8/0.9 m & 0.9/1.0 m interphase of a sucrose density gradient was increased two-fold by 10⁻⁵ m -NA and 5-HT. The Na⁺-K ⁺ ATPase recovered at the 1.0/1.2 m interphase was not influenced by NA, DA or 5-HT. NA, DA and 5-HT did not activate the Mg ATPase of synaptic membranes from any of the 6 brain regions or whole brain synaptic vesicles. The cortex synaptic membrane (Na⁺-K⁺) ATPase is postulated to have a direct role in the uptake of the biogenic amines. An indirect role is proposed for this enzyme in amine uptake into brain stem.