Effect of transitional metal ions on (Na+ + K+) ATPase activity and the uptake of norepinephrine and choline by brain synaptosomes

Behavior and brain enzymatic changes after long-term intoxication with cadmium salt or contaminated potatoes

This study investigated the cadmium (Cd) intoxication on cognitive, motor and anxiety performance of rats subjected to long-term exposure to diet with Cd salt or with Cd from contaminated potato tubers. Potato plantlets were micropropagated in MS medium and transplanted to plastic trays containing sand. Tubers were collected, planted in sand boxes and cultivated with 0 or 10 μM Cd and, after were oven-dried, powder processed and used for diet. Rats were divided into six groups and fed different diets for 5 months: control, potato, potato+Cd, 1, 5 or 25 mg/kg CdCl2. Cd exposure increased Cd concentration in brain regions. There was a significant decrease in the step-down latency in Cd-intoxicated rats and, elevated plus maze task revealed an anxiolytic effect in rats fed potato diet per se, and an anxiogenic effect in rats fed 25 mg/kg Cd. The brain structures of rats exposed to Cd salt or Cd from tubers showed an increased AChE activity, but Na+,K+-ATPase decreased in cortex, hypothalamus, and cerebellum. Therefore, we suggest an association between the long-term diet of potato tuber and a clear anxiolytic effect. Moreover, we observed an impaired cognition and enhanced anxiety-like behavior displayed by Cd-intoxicated rats coupled with a marked increase of brain Cd concentration, and increase and decrease of AChE and Na+,K+-ATPase activities, respectively.

Inhibition of Na+/K+-ATPase and Mg2+-ATPase by metal ions and prevention and recovery of inhibited activities by chelators

Kinetics and inhibition of Na(+)/K(+)-ATPase and Mg(2+)-ATPase activity from rat synaptic plasma membrane (SPM), by separate and simultaneous exposure to transition (Cu(2+), Zn(2+), Fe(2+) and Co(2+)) and heavy metals (Hg(2+) and Pb(2+)) ions were studied. All investigated metals produced a larger maximum inhibition of Na(+)/K(+)-ATPase than Mg(2+)-ATPase activity. The free concentrations of the key species (inhibitor, MgATP(2-), MeATP(2-)) in the medium assay were calculated and discussed. Simultaneous exposure to the combinations Cu(2+)/Fe(2+) or Hg(2+)/Pb(2+) caused additive inhibition, while Cu(2+)/Zn(2+) or Fe(2+)/Zn(2+) inhibited Na(+)/K(+)-ATPase activity synergistically (i.e., greater than the sum metal-induced inhibition assayed separately). Simultaneous exposure to Cu(2+)/Fe(2+) or Cu(2+)/Zn(2+) inhibited Mg(2+)-ATPase activity synergistically, while Hg(2+)/Pb(2+) or Fe(2+)/Zn(2+) induced antagonistic inhibition of this enzyme. Kinetic analysis showed that all investigated metals inhibited Na(+)/K(+)-ATPase activity by reducing the maximum velocities (V(max)) rather than the apparent affinity (Km) for substrate MgATP(2-), implying the noncompetitive nature of the inhibition. The incomplete inhibition of Mg(2+)-ATPase activity by Zn(2+), Fe(2+) and Co(2+) as well as kinetic analysis indicated two distinct Mg(2+)-ATPase subtypes activated in the presence of low and high MgATP(2-) concentration. EDTA, L-cysteine and gluthathione (GSH) prevented metal ion-induced inhibition of Na(+)/K(+)-ATPase with various potencies. Furthermore, these ligands also reversed Na(+)/K(+)-ATPase activity inhibited by transition metals in a concentration-dependent manner, but a recovery effect by any ligand on Hg(2+)-induced inhibition was not obtained.

Influence of transition and heavy metal ions on ATP-ases activity in rat synaptic plasma membranes

The influence of transition metal (Cu2+, Zn2+, Fe2+ and Co2+) and heavy metal ions (Hg2+, Pb2+ and Cd2+) on the activities of Na+/K+-ATPase and Mg2+-ATPase isolated from rat synaptic plasma membranes (SPM) was investigated. The aim of the study was to elucidate the inhibition of both ATPase activities by exposure to the considered metal ions as a function of their affinity to bind to the ?SH containing ligand L-cysteine, as a model system. The half-maximum inhibitory activities (IC 50) of the enzymes were determined as parameters of rectangular hyperbolas and correlated with the stability constant (K s) of the respectivemetal- ion-L-cysteine complex. The linear Dixon plots indicate equilibrium binding of the investigated ions to both enzymes.

Prevention and recovery of CuSO4-induced inhibition of Na+/K+ -ATPase and Mg2+ -ATPase in rat brain synaptosomes by EDTA

Enzymatic activities of Na+/K+-ATPase and Mg2+ -ATPase from rat brain synaptic plasma membrane were studied in the absence and presence of EDTA. The aim of the study was to examine the ability of this strong chelator to prevent and recover the CuSO4-induced inhibition. The influence of experimentally added CuSO4 and EDTA on MgATP2- complex and 'free' Cu2+ concentrations in the reaction mixture was calculated and discussed. CuSO4 induced dose-dependent inhibition of both enzymes in the absence and presence of 1 mM EDTA. In the absence of EDTA, the IC50 values of Cu2+, as calculated from the experimental curves, were 5.9x10(-7) M for Na+/K+ -ATPase and 3.6x10(-6) M for Mg2+ -ATPase. One millimolar EDTA prevented the enzyme inhibition induced by CuSO4, but also reversed the inhibited activity, in a concentration-dependent manner, following exposure of the enzymes to the metal ion, by lowering 'free' Cu2+ concentration. Kinetic analysis showed that CuSO4 inhibits both the Na+/K+ -ATPase and Mg2+ -ATPase, by reducing their maximum enzymatic velocities (Vmax), rather than apparent affinity for substrate MgATP2- (K0.5), implying the noncompetitive nature of enzyme inhibition induced by the metal. The kinetic analysis also confirmed two distinct Mg2+ -ATPase subtypes activated in the presence of low and high MgATP2- concentrations. K0.5 and Vmax were calculated using a computer-based program. The results of calculation showed that MgATP2- concentration in the kinetic experiments exceeded three times the apparent K0.5 value for the enzyme activation.

Protection against amyloid beta peptide toxicity by zinc

Zinc (Zn) is an essential element in normal development and biology, although it is toxic at high concentrations. Recent studies show that Zn at high concentrations accelerates aggregation of amyloid beta peptide (Abeta), the major component of senile plaques in Alzheimer's disease (AD). This study reports the effect of varying Zn concentrations on Abeta toxicity and the mechanism by which low concentrations function in a protective role. At Abeta/Zn molar ratios of 1:0.1 and 1:0.01, Zn produces significant protection against Abeta toxicity in cultured primary hippocampal neurons. At higher concentrations (1:1 molar ratio), Zn offers no protection or enhances Abeta toxicity. The protective effect of Zn against Abeta toxicity is due in part to the enhancement of Na+/K+ ATPase activity which prevents the disruption of calcium homeostasis and cell death associated with Abeta toxicity. Analysis of Na+/K+ ATPase activity in cultured rat cortical cells indicated that Zn exposure alone afforded a 20% increase in enzyme activity, although the differences were statistically insignificant. However, in cortical cultures exposed to a toxic dose of Abeta (50 microM), Zn at concentrations of 5 and 0.5 microM led to significant increases in Na+/K+ ATPase activity compared with levels in cells treated with Abeta alone. Zn at a 1:1 molar ratio (50 microM) led to a significant decrease in enzyme activity. Together, these data suggest that Zn functions as a double-edged sword, affording protection against Abeta at low concentrations and enhancing toxicity at high concentrations.

Oral aluminum administration and oxidative injury

For a long time, aluminium (Al) has been considered an indifferent element from a toxicological point of view. In recent years, however, Al has been implicated in the pathogenesis of several clinical disorders, such as dialysis dementia, the fulminant neurological disorder that can develop in patients on renal dialysis. In the present study, the effect of chronic oral administration of Al on certain biochemical parameters of brain homogenate has been investigated. The feeding of test diet for 6 wk resulted in a decrease of thiols, glutathione reductase (GR), and adenosine Triphosphatase (ATPase). A nonsignificant decrease in peroxidation and glutathione-S-transferase (GST) was also detected in the Al-treated rats. From this study, it can be concluded that oxidative stress is produced by the metal.

Inhibition of ATPase activity in rat synaptic plasma membranes by simultaneous exposure to metals

Inhibition of Na+/K+-ATPase and Mg2+-ATPase activities by in vitro exposure to Cd2+, Pb2+ and Mn2+ was investigated in rat brain synaptic plasma membranes (SPMs). Cd2+ and Pb2+ produced a larger maximal inhibition of Na+/K+-ATPase than of Mg2+-ATPase activity. Metal concentrations causing 50% inhibition of Na+/K+-ATPase activity (IC50 values) were Cd2+ (0.6 microM) < Pb2+ (2.1 microM) < Mn2+ (approximately 3 mM), and the former two metals were substantially more potent in inhibiting SPM versus synaptosomal Na+/K+-ATPase. Dixon plots of SPM data indicated that equilibrium binding of metals occurs at sites causing enzyme inhibition. In addition, IC50 values for SPM K+-dependent p-nitrophenylphosphatase inhibition followed the same order and were Cd2+ (0.4 microM) < Pb2+ (1.2 microM) < Mn2+ (300 microM). Simultaneous exposure to the combinations Cd2+/Mn2+ or Pb2+/Mn2+ inhibited SPM Na+/K+-ATPase activity synergistically (i.e., greater than the sum of the metal-induced inhibitions assayed separately), while Cd2+/Pb2+ caused additive inhibition. Simultaneous exposure to Cd2+/Pb2+ antagonistically inhibited Mg2+-ATPase activity while Cd2+/Mn2+ or Pb2+/Mn2+ additively inhibited Mg2+-ATPase activity at low Mn2+ concentrations, but inhibited antagonistically at higher concentrations. The similar IC50 values for Cd2+ and Pb2+ versus Mn2+ inhibition of Na+/K+-ATPase and the pattern of inhibition/activation upon exposure to two metals simultaneously support similar modes of interaction of Cd2+ and Pb2+ with this enzyme, in agreement with their chemical reactivities.

Sensitivity of adenosine triphosphatases in different brain regions to polychlorinated biphenyl congeners

Polychlorinated biphenyl (PCBs) mixtures contain a number of different congeners, some of which have been proposed to be neuroactive. Recent studies have suggested that ortho-substituted PCBs may be neuroactive, while 'dioxin-like' non-ortho-substituted congeners are not. This study compared the in vitro effects of a putative neuroactive ortho-biphenyl (2,2'-dichlorobiphenyl; DCBP) with that of a putative non-neuroactive congener lacking ortho-chlorine substitutions (3,3',4,4',5-pentachlorobiphenyl; PCBP) on Mg(2+)-ATPase activity in mitochondrial and synaptosomal preparations from striatum, hypothalamus, cerebellum and hippocampus. In these studies, DCBP significantly inhibited oligomycin-sensitive (OS) Mg(2+)-ATPase activity in all four brain regions in a concentration-dependent manner; PCBP, on the other hand, had no effect on OS Mg(2+)-ATPase activity in any brain region examined at concentrations up to 100 microM. The striatum, a dopamine-rich region, was not preferentially sensitive to the effects of DCBP. Furthermore, DCBP did not inhibit synaptosomal Na+/K(+)-ATPase activity, suggesting a specificity of action on OS Mg(2+)-ATPase. These data support previous structure-activity relationships, suggesting that ortho-substituted PCB congeners are neuroactive while non-ortho-substituted congeners are not. Disruption of mitochondrial oxidative energy production may play a role in the neuroactivity of ortho-chlorinated PCBs.

Effect of CH3HgCl and several transition metals on the dopamine neuronal carrier; peculiar behaviour of Zn2+

CH3Hg+ and metal ions inhibited the specific binding of (1-[2-(diphenylmethoxy)ethyl]-4-(3-phenyl-2-[1-3H]propenyl) piperazine) ([3H]GBR 12783) to the dopamine neuronal carrier present in membranes from rat striatum with a general rank order of potency CH3Hg+ > Cu2+ > Cd2+ > Zn2+ > Ni2+ = Mn2+ = Co2+, suggesting that -SH groups are chiefly involved in this inhibition. Five millimolar dithiothreitol reversed the rather stable block of the specific binding produced by Cd2+ or Zn2+. An increase in the concentration of Na+, or addition of either K+ or Ca2+ reduced the inhibitory effects of metal cations, except Cu2+. Zn2+ (3 microM) reduced the inhibitory potency of Cd2+ on the binding but was ineffective against CH3Hg+ and Cu2+. Zn2+ at 0.3 to 10 microM significantly enhanced the specific binding of [3H]GBR 12783 and [3H]cocaine by 42 to 146%. Zn2+ (3 microM) increased the affinity of all pure uptake inhibitors tested and of the majority of the substrates for the [3H]GBR 12783 binding site. Dissociation experiments revealed that Zn2+ both inhibited and enhanced the [3H]GBR 12783 binding by recognizing amino acids located close to or in the radioligand binding site. Micromolar concentrations of Zn2+ noncompetitively blocked the [3H]dopamine uptake but they did not modify the block of the transport provoked by pure uptake inhibitors. These findings suggest that Na+, K+, Ca2+ and metal ions could recognize some -SH groups located in the [3H]GBR 12783 binding site; low concentrations of Zn2+ could allow a protection of these -SH groups.

In vitro interaction of heavy metals with ouabain receptors in rat brain microsomes

This study investigates the influence of heavy metals on ouabain-binding in presence of thiol (sulfhydryl) compounds. The data on in vitro effects of mercury (Hg), lead (Pb) and cadmium (Cd) showed significant inhibition of 3H-ouabain binding to microsomal membrane in a concentration-dependent manner. Maximum inhibition of 3H-ouabain binding was observed at 1 microM for Hg and 100 microM each for Pb and Cd. Preincubation with monothiol (L-cysteine or glutathione) or dithiol (dithiothreitol) protected inhibition of 3H-ouabain binding to the membranes by Hg or Pb. Dithiol but not monothiols partially protected Cd-inhibition. The present data confirm that the heavy metals interact with ouabain receptors in a manner similar to SH-blocking agents and protection of metal-inhibited 3H-ouabain binding by thiol compounds is metal specific.

Effects of cadmium and mercury on Na(+)-K+, ATPase and uptake of 3H-dopamine in rat brain synaptosomes

Effects in vivo of cadmium (Cd), mercury (Hg) and methylmercury (CH3Hg) on Na(+)-K+ ATPase and uptake of 3H-dopamine (DA) in rat brain synaptosomes were studied. These heavy metals significantly inhibited the Na(+)-K+ ATPase activity in a dose-dependent manner. Similarly, inhibition of DA uptake by synaptosomes was also observed in rats treated with these metals. Intraperitoneal route of metal administration was found to be more effective than per os treatment. Mercuric compounds compared to Cd elicited a higher inhibition of Na(+)-K+ ATPase and DA uptake in rat brain synaptosomes.

Effects of mercuric chloride on [3H]dopamine release from rat brain striatal synaptosomes

Electrophysiological studies employing amphibian neuromuscular preparations have shown that mercuric chloride (HgCl2) in vitro increases both spontaneous and evoked neurotransmitter release. The present study examines the effect of HgCl2 on the release of [3H]dopamine from synaptosomes prepared from mammalian brain tissue. Mercuric chloride (3-10 microM) produces a concentration-dependent increase in spontaneous [3H]dopamine release from "purified" rat striatal synaptosomes, in both the presence and absence of extra-synaptosomal calcium. The effects of HgCl2 on transmitter release from amphibian neuromuscular junction preparations resemble those produced by the Na+, K+-ATPase inhibitor ouabain. Experiments were performed to determine whether the HgCl2 effects on mammalian synaptosomal dopamine release are a consequence of Na+, K+-ATPase inhibition. Na+, K+-ATPase activity in lysed synaptosomal membranes is inhibited by HgCl2 (IC50 = 160 nM). However, mercuric chloride in the presence of 1 mM ouabain still increased [3H]dopamine release. The specific inhibitor of Na+-dependent, high-affinity dopamine transport, RMI81,182 inhibited ouabain-induced [3H]dopamine release whereas it had no effect on HgCl2-induced [3H]dopamine release. These data suggest that augmentation of spontaneous [3H]dopamine release by HgCl2 probably is not mediated by an inhibition of Na+, K+-ATPase and HgCl2 does not act directly on the dopamine transporter.

Possible role of regional superoxide dismutase activity and lipid peroxide levels in cadmium neurotoxicity: in vivo and in vitro studies in growing rats

Cd2+ (0.4 mg/kg) administration to growing rats (45 +/- 5 g) intraperitoneally, daily for 30 days was found to decrease the activity of superoxide dismutase (SOD) in all the brain regions, except hippocampus. The concentrations of lipid peroxides were significantly elevated in the cerebellum, cerebral cortex, corpus striatum and midbrain. A 100% inhibition in SOD activity was observed by 14 microM and 50 microM of Cd2+ in bovine blood and rat brain preparations, respectively. Cadmium-induced strong inhibitory effect on brain and purified bovine blood SOD suggested a direct effect of the metal on enzyme molecule. Furthermore, in vitro addition of a wide range of Cd2+ (1-100 microM) increased the rate of lipid peroxidation (LPO) reaction in fresh brain homogenate, however, did not affect boiled homogenate. The studies on LPO in reconstituted homogenate resulting from mixing of fresh and/or heated different subcellular fractions indicated the presence of some heat-labile Cd2+ -sensitive factor in 15000 x g pellet fraction. It is suggested that Cd2+ directly and indirectly through inhibition of SOD, increases the LPO of cell membranes and thus produces damage to the associated physiological functions leading to central nervous dysfunctions.

Effect of lead on Na+,K+ATPase activity in the developing brain of intra-uterine growth-retarded rats

Lead (Pb) intoxication in developing mammals, including humans, produces serious brain damage. In addition, it is known that nutritional status influences the susceptibility to Pb toxicity. We developed an in utero undernutrition model based on restriction of blood supply to fetuses on d 17 of pregnancy (IUGR rats). The aim of this study was to investigate in vitro the possible effect of Pb on Na+, K+ATPase activity in the brain of developing IUGR and control rats from 6 to 60 d after birth. In addition, we measured the stimulation of Na+, K+ATPase by the monoamines noradrenaline and serotonin. Our results show that: The neurotoxic effect of Pb is an age-related phenomenon. Both IUGR and control rats were more sensitive to Pb in the first week of life. In adults, Pb had a weak inhibitory potency; the delayed matured brain in IUGR animals seemed less sensitive to Pb when compared to age-paired control rats; in the IUGR group, at 15 and 22 d, low doses of Pb had a stimulatory effect on Na+, K+ATPase instead of an inhibitory effect; noradrenaline and serotonin stimulated Na+, K+ATPase activity to an equivalent extent, but this was greater in IUGR than control rats; and at low Pb concentrations, the studied monoamines reversed Pb-induced inhibition.

Effects of copper on dopaminergic function in the rat corpus striatum

Copper-loading was produced in rats by administration of 0.125% CuSO4 in the drinking water for a period of 11 months from weaning. At conclusion of the treatment the animals had significant increases in liver (552%) and brain (26%) copper content relative to age-matched controls. Whereas the concentration of dopamine was unaffected, the concentration of 3,4-dihydroxyphenylacetic acid in the corpus striatum was found to be lower (25% decrease) in the copper-treated group. Saturation studies of the striatal D-2 dopamine receptors using [3H]spiperone indicated that in copper-loaded animals the affinity was significantly increased threefold, whereas there was a trend for the number of receptors to decrease. When included in the radioligand binding assay, copper salts (Cu2+) inhibited specific [3H]spiperone binding to untreated corpora striata. The inhibition produced by copper was competitive with a significant decrease in affinity, the 50% effective concentration of Cu2+ was 21 to 24 microM, and the potency of dopamine agonists was also decreased. These results are discussed in relation to the mechanism by which copper affects dopaminergic function and to the use of copper-loaded rats as a model of Wilson's disease.

Influence of mercury on uptake of [3H]dopamine and [3H]norepinephrine by rat brain synaptosomes

Mercuric compounds have been shown to alter several membrane-bound enzymes and associated receptor activities. The present studies were initiated to investigate the in vitro effects of mercuric chloride (HgCl2) and methylmercury chloride (CH3HgCl) on the uptake of [3H]dopamine (3HDA), [3H]norepinephrine (3HNE), and Na+, K+-ATPase in rat brain synaptosomes. Brain synaptosomes were prepared by the ficoll-sucrose gradient method from normal, adult male Sprague-Dawley rats, weighing approx. 200 g. The effect of mercury on Na+, K+-ATPase was determined by using a coupled enzymatic method. Uptake of DA and NE by brain synaptosomes was determined by filtration in the presence and absence of 0-30 microM HgCl2 and 0-100 microM CH3HgCl. A parallel inhibition in the synaptosomal uptake of 3HDA and 3HNE, and the activity of the synaptosomal membrane Na+, K+-ATPase, was observed in both mercuric chloride and methylmercury treatments. The mercury compounds also significantly inhibited the mitochondrial ATPase (Mg2+-oligomycin-sensitive ATPase). The inhibitory influences of the toxins were concentration-dependent. The results suggest that the mercury compound mediated decrease in DA and NE uptake in brain synaptosomes may be related to the inhibition of Na+, K+-ATPase by the same toxins.

Inhibition of gamma-[3H]aminobutyric acid uptake by organotin compounds in vitro

Trimethyltin, its tetra-, di-, and monomethyl analogs, inorganic tin (Sn II and Sn IV), triethyltin, tripropyltin, tributyltin, and triphenyltin were tested for their ability in inhibiting the uptake of gamma-[3H]aminobutyric acid (GABA) into mouse forebrain synaptosomes in vitro. All organotins containing three carbon-tin bonds were potent inhibitors of [3H]GABA uptake with IC50 values ranging from 10(-4) to 10(-6) M. Various thiol and sulfur compounds, particularly sodium sulfide, were capable of antagonizing the inhibitory effect of triphenyltin and, to a minor extent, of other organotins. All triorganotins also inhibited Na+,K+-ATPase, measured by binding of [3H]ouabain and by hydrolysis of ATP. Although a correlation between inhibition of ouabain binding and GABA uptake by organotins could be found, inhibition of [3H]GABA uptake by the specific inhibitors ouabain and strophantidin was qualitatively and quantitatively different from organotins. These results suggest that all triorganotins are capable of inhibiting synaptosomal [3H]GABA uptake in vitro by a mechanism involving, but not exclusively, inhibition of Na+,K+-ATPase. The role of [3H]GABA uptake inhibition in the neurotoxicity of organotins remains to be determined.

Elevated copper and lowered zinc in the placentae of pre-eclamptics

Selected cations (Ca, Co, Cu, Mg, Zn, Si, and K) were determined in the placentae of 18 women. Between pre-eclamptic and normal subjects there were significant (p less than 0.05) differences in copper and zinc concentrations and borderline significant differences in cobalt concentration. In the placentae of the ten women with a normal pregnancy, the average concentrations of copper and zinc were 53 and 192 micrograms atoms/kg placenta, respectively. In the placentae of 8 women with pre-eclampsia, the concentrations were 124 and 134 micrograms atoms/kg placenta for copper and zinc, respectively. Elevation of copper and decrease in zinc may be an exaggeration of normal pregnancy physiology that occurs in pre-eclampsia.

Neurotoxic effects of copper: inhibition of glycolysis and glycolytic enzymes

The effects of Cu2+ on glycolysis and several glycolytic enzymes were studied in rat brain extracts in vitro. At concentrations reportedly found in Wilson's disease, Cu2+ significantly inhibited lactate production from glucose or glucose-6-phosphate in rat brain postnuclear supernatant with an IC50 of about 3 microM. Cu2+ also inhibited several glycolytic enzymes. Amongst the latter, Cu2+ was most effective in inhibiting hexokinase (IC50 for Cu2+ = 7 microM), moderately effective in inhibiting pyruvate kinase (IC50 for Cu2+ = 56 microM), but least effective in inhibiting lactate dehydrogenase (IC50 for Cu2+ = 300 microM). These results suggest that inhibition of brain glycolysis may have pathophysiological importance in copper poisoning and in Wilson's disease.

Effect of interaction of heavy metals on (Na+ -K+) ATPase and the uptake of 3H-DA and 3H-NA in rat brain synaptosomes

The effect of interaction of Mn2+, Pb2+ and Cd2+ on (Na+ -K+) ATPase and uptake of labelled dopamine (3H-DA) and labelled noradrenaline (3H-NA) were studied in vitro in rat brain synaptosomes. The inhibition of (Na+ -K+) ATPase by Pb2+ and Cd2+ alone was concentration dependent, however, Mn2+ had almost no effect on the activity of this enzyme. Interaction of Cd2+ with either Pb2+ or Mn2+ was most powerful in inhibiting the activity of synaptosomal transport ATPase. Lower concentrations of Pb2+ increased while higher concentrations inhibited synaptosomal uptake of 3H-DA and 3H-NA. Lower concentrations of Cd2+ increased the uptake of 3H-DA while at concentrations of 100 microM, the uptake was inhibited, this metal had strong inhibitory effect on the uptake of 3H-NA. Mn2+ had inhibited the uptake of labelled amines. Interaction of Mn2+ with Pb2+ or Cd2+ produced inhibition on the uptake of 3H-DA and 3H-NA. The results of the uptake of biogenic amines in the presence of metal ions apparently had no correlation with the activity of (Na+ -K+) ATPase which is involved in the active transport of cations across cell membranes.

Effects of certain mono-, di- and trivalent metal cations on the K+-stimulated p-Nitrophenyl phosphatase in rat brain

The effects of certain monovalent (Ag+1 and Li+1), divalent (Hg+2, Cu+2, Zn+2, Co+2, Fe+2, Pb+2, Mn+2, Sn+2, Ni+2, and Se+2) and trivalent (Fe+3, As+3, and Al+3) metals on a mitochondrial preparation of K+-stimulated-p-nitrophenyl phosphatase (K+-PNPPase) from rat brain were studied. Except for salts of Ni+2, Se+2 and Li+1, which irrespective of concentration failed to produce 50% inhibition, all of the metals examined were found to be potent inhibitors of the enzyme with 150 values of 0.24 microM for Ag+1 among the monovalent, 0.70, 30, 37, 38, 47, 60, 62, 490 and 850 microM for Hg+2, Cu+2, Cd+2, Zn+2, Co+2, Fe+2, Pb+2, Mn+2 and Sn+2, respectively, among the divalents and 100, 550 and 870 microM for Fe+3, As+3, and AL+3 respectively, among the trivalents. Salts of silver and mercury were the most toxic for this enzyme. All metals showed concentration dependent inhibition except lithium. The order of their potency was Ag+1 greater than Hg+2 greater than Cu+2 greater than Cd+2 greater than Zn+2 greater than Co+2 greater than Fe+2 greater than Pb+2 greater than Fe+3 greater than Mn+2 greater than As+3 greater than Sn+2 greater than Al+3 greater than Ni+2 greater than Se+2 greater than Li+1.

Effects of manganese on rat brain microsomal Mg2+-Na+-K+-ATPase: in vivo and in vitro studies

The effect of manganese on brain microsomal Mg2+-Na+K+-ATPase was examined both in vitro and in vivo. Daily intraperitoneal administration of MnCl2 . 4H2O (Mn2+, 6 mg/kg) to the rats for a period of 90 days produced 10% (P less than 0.05) inhibition in the activity of Mg2+-ATPase, and 72 and 63% increases in the contents of manganese and copper, respectively, in the microsomal fraction of brain. In in vitro studies, lower concentrations of Mn2+ activated while higher concentrations inhibited the activity of brain microsomal ATPase. Addition of equal concentrations of Mn2+ + Cu2+ (8 mM) in vitro produced 8% inhibition in the activity of Mg2+-ATPase and 83% inhibition in Na+-K+-ATPase. Free Cu2+ ions were able to antagonize the effect of Mn2+ on ATPase in vitro and inhibited the activity of Mg2+-Na+-K+-ATPase with more pronounced effect of Na+-K+-ATPase. The lack of change in the activity of Na+-K+-ATPase in the brain microsomes of rats administered manganese, in spite of a significant increase in copper, could not be explained. It is, however, evident that a manganese-induced elevation in brain copper was not responsible for initiating biochemical changes in manganese neurotoxicity.

Effect of metavanadate on the uptake and release of noradrenaline in rat brain cerebral cortex slices

The effect of vanadium (as VO3-) on the uptake and release of tritiated noradrenaline ([3H]NA) was studied in vitro in rat cerebral cortex slices. Vanadate inhibited [3H]NA uptake and the inhibition was dependent upon concentration and on incubation time. The IC50 value (20 min incubation) was 8 X 10(-5) M of vanadate. Inhibition of Na+, K+ -ATPase activity by VO3-, chelation of noradrenaline or autooxidation of catecholamine by this oxyanion might contribute to the decrease of [3H]NA uptake. Vanadate inhibited also the release of [3H]NA in a time- and concentration-dependent fashion.

Effects of Cd2+, Mn2+, and Al3+ on rat brain synaptosomal uptake of noradrenaline and serotonin

Cd2+, Mn2+, and Al3+ inhibited synaptosomal amine uptake in a concentration-dependent and time-dependent manner. In the absence of Ca2+, the rank order of inhibition of noradrenaline uptake was: Cd2+ (IC50 = 250 microM) greater than Al3+ (IC50 = 430 microM) greater than Mn2+ (IC50 = 1.50 mM), the IC50 being the concentration of metal ions that gave rise to 50% inhibition of uptake. In the presence of 1 mM Ca2+, the rank order of inhibition of uptake was: Al3+ (IC50 = 330 microM) greater than Cd2+ (IC50 = 540 microM) greater than (IC50 = 1.5 mM). The rank order of inhibition of serotonin uptake without Ca2+ was: Al3+ (IC50 = 370 microM) greater than Cd2+ (IC50 = 610 microM) greater than Mn2+ (IC50 = 3.4 mM) and the rank order in the presence of 1 mM Ca2+ was: Al3+ (IC50 = 290 microM) greater than Cd2+ (IC50 = 1.5 mM) greater than Mn2+ (IC50 = 4.0 mM). Ca2+, at 1 mM, definitely antagonized the inhibitory actions of Cd2+ on noradrenaline and serotonin uptake. Al3+ stimulated noradrenaline uptake at concentrations around 20-250 microM but inhibited this uptake at concentrations exceeding 300 microM in a dose-related fashion. Ca2+, at 1 mM, enhanced both the stimulatory and inhibitory effects of Al3+. Ca2+ also enhanced the inhibitory actions of Al3+ on serotonin uptake. These results, in conjunction with those we have previously published, suggest that Cd2+, Mn2+, and Al3+ exert differential and selective effects on the structure and function of synaptosomal membranes.

Selective inhibition of L-glutamate and gammaaminobutyrate transport in nerve ending particles by aluminium, manganese, and cadmium chloride

AlCl3, MnCl2, and CdCl2 inhibited the rates of accumulation of [14C] L-glutamate and [3H] gammaaminobutyrate (GABA) in purified rat forebrain nerve-ending particles in a dose-dependent fashion. The concentrations that would give 50% inhibition (IC50) of GABA transport were 316 muM, 7.4 mM, and 1.4 mM, respectively. Ca2+ (1 mM) enhanced the inhibitory effect of Al3+ (IC50 decreased to 149 muM) but antagonized that of Mn2+ (IC50 = 10 mM) and Cd2+ (IC50 = 2.1 mM). For glutamate transport 1 mM Ca2+ changed the IC50 values from 299 to 224 micron for Al3+, 7.1 to 10 mM for Mn2+, and 2 to 3 mM for Cd2+. In contrast, the rates of accumulation of [14C] 2-deoxy-glucose and [3H] L-phenylalanine were mostly unaffected by these metal ions. The results indicate that Al3+, Mn2+, and Cd2+ exerted selective and differential effects on the transport systems of neurotransmitter substances in the synaptosomal membrane.

Growth inhibition of cultured fibroblasts by cobalt and nickel

It is known that tissues surrounding the site of an implanted prosthetic alloy are exposed to increased concentrations of the metals comprising the alloy. However, the exact identity and concentration of such metallic products are usually unknown, thus limiting the possibilities for quantifying any observed toxicological response to the metals. This report describes some of the effects of increased concentrations (7.5-30 microgram/ml; 1-5 x 10(-4)M) Of cobalt (as CoCl2.6H2O) and of nickel (NiCl2.6H2O) on the growth and morphology of cultured mouse fibroblasts. Ultrafiltration experiments indicated that much of the total Co or Ni present in cell culture medium could become bound to macromolecular serum components of the medium. Morphological changes and depressions in the cell growth rate were found to result from high concentrations (15-30 microgram/ml) of either Co or Ni. However, lower concentrations of nickel may have produced some stimulation of cell growth, whereas all concentrations of Co studied were found to depress the rate of cell growth. The growth rate of actively proliferating fibroblasts was quite sensitive to variations in the concentration of either cobalt or nickel. Increased concentrations of cobalt or nickel, therefore, might also affect the normal reconstructive activity of fibroblasts in vivo.

Subcellular mechanisms of lead neurotoxicity

The neurotoxic effects of inorganic lead (Pb) involve inhibition of calcium-dependent acetylcholine release and increases in calcium-dependent dopamine release. These apparently differential effects of Pb are associated with differing Pb-calcium (Ca) interactions: Pb blocks 45Ca binding to peripheral cholinergic ganglia and increases 45Ca binding to synaptosomes prepared from caudate nucleus (CN). Pb-induced increases in CN 45Ca binding did not result from nonspecific disruption of selective ion permeability of the membrane. Also, the Na-K ATPase-linked Ca extrusion system of synpatosomes was not affected by Pb. A Pb-sodium (Na) interaction was found such that elevation of intrasynaptosomal Na reversed effects of Pb on 45Ca binding. The intracellular localization of this effect appeared to be primarily at the mitochondrial level. Pb inhibited Na-induced release of 45Ca from preloaded mitochondria. This action may be translated into increased transmembrane flux of exogenous Ca, and thence into increased exocytotic events at the synapse. The apparently neurotransmitter-specific effects of Pb, cholinergic inhibition and dopaminergic augmentation, are hypothesized to result from different Pb-Ca interactions which are determined by the specific localization of Pb within nerve endings.

The role of cyclic nucleotides in the CNS

On the basis of the information presented in this review, it is difficult to reach any firm decision regarding the role of cyclic AMP (or cyclic GMP) in synaptic transmission in the brain. While it is clear that cyclic nucleotide levels can be altered by the exposure of neural tissues to various neurotransmitters, it would be premature to claim that these nucleotides are, or are not, essential to the transmission process in the pre-or post-synaptic components of the synapse. In future experiments with cyclic AMP it will be necessary to consider more critically whether the extracellularly applied nucleotide merely provides a source of adenosine and is thus activating an extracellularly located adenosine receptor, or whether it is actually reaching the hypothetical sites at which it might act as a second messenger. The application of cyclic AMP by intrcellular injection techniques should minimize this particular problem, although possibly at the expense of new diffulties. Prio blockade of the adenosine receptor with agents such as theophylline or adenine xylofuranoside may also assist in the categorization of responses to extracellularly applied cyclic AMP as being a result either of activation of the adenosine receptor or of some other mechanism. Utimately, the developement of highly specific inhibitor for adenylate cyclase should provide a firm basis from which to draw conclusions about the role of cyclic AMP in synaptic transmission. Similar considerations apply to the action of cyclic GMP and the role of its synthesizing enzyme, guanylate cyclase. The use of phosphodiesterase inhibitors in studies on cyclic nucleotides must also be approached with caution. The diverse actions of many of these compounds, which include calcium mobilization and block of adenosine uptake, could account for many of the results that have been reported in the literature.