Calcium-dependent cytosolic phospholipase A2 activation is implicated in neuroinflammation and oxidative stress associated with ApoE4

BACKGROUND

Apolipoprotein E4 (APOE4) is associated with a greater response to neuroinflammation and the risk of developing late-onset Alzheimer's disease (AD), but the mechanisms for this association are not clear. The activation of calcium-dependent cytosolic phospholipase A2 (cPLA2) is involved in inflammatory signaling and is elevated within the plaques of AD brains. The relation between APOE4 genotype and cPLA2 activity is not known.

METHODS

Mouse primary astrocytes, mouse and human brain samples differing by APOE genotypes were collected for measuring cPLA2 expression, phosphorylation, and activity in relation to measures of inflammation and oxidative stress.

RESULTS

Greater cPLA2 phosphorylation, cPLA2 activity and leukotriene B4 (LTB4) levels were identified in ApoE4 compared to ApoE3 in primary astrocytes, brains of ApoE-targeted replacement (ApoE-TR) mice, and in human brain homogenates from the inferior frontal cortex of patients with AD carrying APOE3/E4 compared to APOE3/E3. Greater cPLA2 phosphorylation was also observed in human postmortem frontal cortical synaptosomes and primary astrocytes after treatment with recombinant ApoE4 ex vivo. In ApoE4 astrocytes, the greater levels of LTB4, reactive oxygen species (ROS), and inducible nitric oxide synthase (iNOS) were reduced after cPLA2 inhibition.

CONCLUSIONS

Our findings implicate greater activation of cPLA2 signaling system with APOE4, which could represent a potential drug target for mitigating the increased neuroinflammation with APOE4 and AD.

Curcumin attenuates memory deficits and the impairment of cholinergic and purinergic signaling in rats chronically exposed to cadmium

This study investigated the protective effect of curcumin on memory loss and on the alteration of acetylcholinesterase and ectonucleotidases activities in rats exposed chronically to cadmium (Cd). Rats received Cd (1 mg/kg) and curcumin (30, 60, or 90 mg/kg) by oral gavage 5 days a week for 3 months. The animals were divided into eight groups: vehicle (saline/oil), saline/curcumin 30 mg/kg, saline/curcumin 60 mg/kg, saline/curcumin 90 mg/kg, Cd/oil, Cd/curcumin 30 mg/kg, Cd/curcumin 60 mg/kg, and Cd/curcumin 90 mg/kg. Curcumin prevented the decrease in the step-down latency induced by Cd. In cerebral cortex synaptosomes, Cd-exposed rats showed an increase in acetylcholinesterase and NTPDase (ATP and ADP as substrates) activities and a decrease in the 5'-nucleotidase activity. Curcumin was not able to prevent the effect of Cd on acetylcholinesterase activity, but it prevented the effects caused by Cd on NTPDase (ATP and ADP as substrate) and 5'-nucleotidase activities. Increased acetylcholinesterase activity was observed in different brain structures, whole blood and lymphocytes of the Cd-treated group. In addition, Cd increased lipid peroxidation in different brain structures. Higher doses of curcumin were more effective in preventing these effects. These findings show that curcumin prevented the Cd-mediated memory impairment, demonstrating that this compound has a neuroprotective role and is capable of modulating acetylcholinesterase, NTPDase, and 5'-nucleotidase activities. Finally, it highlights the possibility of using curcumin as an adjuvant against toxicological conditions involving Cd exposure. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 70-83, 2017.

Piracetam prevents scopolamine-induced memory impairment and decrease of NTPDase, 5'-nucleotidase and adenosine deaminase activities

Piracetam improves cognitive function in animals and in human beings, but its mechanism of action is still not completely known. In the present study, we investigated whether enzymes involved in extracellular adenine nucleotide metabolism, adenosine triphosphate diphosphohydrolase (NTPDase), 5'-nucleotidase and adenosine deaminase (ADA) are affected by piracetam in the hippocampus and cerebral cortex of animals subjected to scopolamine-induced memory impairment. Piracetam (0.02 μmol/5 μL, intracerebroventricular, 60 min pre-training) prevented memory impairment induced by scopolamine (1 mg/kg, intraperitoneal, immediately post-training) in the inhibitory avoidance learning and in the object recognition task. Scopolamine reduced the activity of NTPDase in hippocampus (53 % for ATP and 53 % for ADP hydrolysis) and cerebral cortex (28 % for ATP hydrolysis). Scopolamine also decreased the activity of 5'-nucleotidase (43 %) and ADA (91 %) in hippocampus. The same effect was observed in the cerebral cortex for 5'-nucleotidase (38 %) and ADA (68 %) activities. Piracetam fully prevented scopolamine-induced memory impairment and decrease of NTPDase, 5'-nucleotidase and adenosine deaminase activities in synaptosomes from cerebral cortex and hippocampus. In vitro experiments show that piracetam and scopolamine did not alter enzymatic activity in cerebral cortex synaptosomes. Moreover, piracetam prevented scopolamine-induced increase of TBARS levels in hippocampus and cerebral cortex. These results suggest that piracetam-induced improvement of memory is associated with protection against oxidative stress and maintenance of NTPDase, 5'-nucleotidase and ADA activities, and suggest the purinergic system as a putative target of piracetam.

Aging modifies the enzymatic activities involved in 2-arachidonoylglycerol metabolism

One of the principal monoacylglycerol (MAG) species in animal tissues is 2-arachidonoylglycerol (2-AG), and the diacylglycerol lipase (DAGL) pathway is the most important 2-AG biosynthetic pathway proposed to date. Lysophosphatidate phosphatase (LPAase) activity is part of another 2-AG-forming pathway in which monoacylglycerol lipase (MAGL) is the major degrading enzyme. The purpose of this study was to analyze the manner in which DAGL, LPAase, and MAGL enzymes are modified in the central nervous system (CNS) during aging. To this end, diacylglycerols (DAGs) and MAGs of different composition were used as substrates of DAGL and MAGL, respectively. All enzymatic activities were evaluated in membrane and soluble fractions as well as in synaptic terminals from the cerebral cortex (CC) of adult and aged rats. Results related to 2-AG metabolism show that aging: (a) decreases DAGL-α expression in the membrane fraction whereas in synaptosomes it increases DAGL-β and decreases MAGL expression; (b) decreases LPAase activity in both membrane and soluble fractions; (c) decreases DAGL and stimulates LPAase activities in CC synaptic terminals; (d) stimulates membrane-associated MAGL-coupled DAGL activity; and (e) stimulates MAGL activity in CC synaptosomes. Our results also reveal that during aging the net balance between the enzymatic activities involved in 2-AG synthesis and breakdown is low availability of 2-AG in CC membrane fractions and synaptic terminals. Taken together, our results lead us to conclude that these enzymes play crucial roles in the regulation of 2-AG tissue levels during aging.

Glucocorticoid receptors are localized to dendritic spines and influence local actin signaling

Glucocorticoids affect learning and memory but the cellular mechanisms involved are poorly understood. The present studies tested if the stress-responsive glucocorticoid receptor (GR) is present and regulated within dendritic spines, and influences local signaling to the actin cytoskeleton. In hippocampal field CA1, 13 % of synapses contained GR-immunoreactivity. Three-dimensional reconstructions of CA1 dendrites showed that GR aggregates are present in both spine heads and necks. Consonant with evidence that GRα mRNA associates with the translation regulator Fragile X Mental Retardation Protein (FMRP), spine GR levels were rapidly increased by group 1 mGluR activation and reduced in mice lacking FMRP. Treatment of cultured hippocampal slices with the GR agonist dexamethasone rapidly (15-30 min) increased total levels of phosphorylated (p) Cofilin and extracellular signal-regulated kinase (ERK) 1/2, proteins that regulate actin polymerization and stability. Dexamethasone treatment of adult hippocampal slices also increased numbers of PSD95+ spines containing pERK1/2, but reduced numbers of pCofilin-immunoreactive spines. Dexamethasone-induced increases in synaptic pERK1/2 were blocked by the GR antagonist RU-486. These results demonstrate that GRs are present in hippocampal spines where they mediate acute glucocorticoid effects on local spine signaling. Through effects on these actin regulatory pathways, GRs are positioned to exert acute effects on synaptic plasticity.

Acute and specific modulation of presynaptic aromatization in the vertebrate brain

Estrogens affect a diversity of peripheral and central physiological endpoints. Traditionally, estrogens were thought to be peripherally derived transcription regulators (i.e. slow acting). More recently, we have learned that estrogens are also synthesized in neuronal cell bodies and synaptic terminals and have potent membrane effects, which modulate brain function. However, the mechanisms that control local steroid concentrations in a temporal and spatial resolution compatible with their acute actions are poorly understood. Here, using differential centrifugation followed by enzymatic assay, we provide evidence that estrogen synthesis within synaptosomes can be modulated more dramatically by phosphorylating conditions, relative to microsomes. This is the first demonstration of a rapid mechanism that may alter steroid concentrations within the synapse and may represent a potential mechanism for the acute control of neurophysiology and behavior.

The effect of curcumin in the ectonucleotidases and acetylcholinesterase activities in synaptosomes from the cerebral cortex of cigarette smoke-exposed rats

With the evidence that curcumin may be a potent neuroprotective agent and that cigarette smoke is associated with a decline in the cognitive performance as our bases, we investigated the activities of Ecto-Nucleoside Triphosphate Diphosphohydrolase (NTPDase), 5'-nucleotidase and acetylcholinesterase (AChE) in cerebral cortex synaptosomes from cigarette smoke-exposed rats treated with curcumin (Cur). The experimental procedures entailed two sets of experiments. In the first set, the groups were vehicle, Cur 12·5, 25 and 50 mg·kg(-1) ; those in the second set were vehicle, smoke, smoke and Cur 12·5, 25 and 50 mg·kg(-1) . Curcumin prevented the increased NTPDase, 5'-nucleotidase and AChE activities caused by smoke exposure. We suggest that treatment with Cur was protective because the decrease of ATP and acetylcholine (ACh) concentrations is responsible for cognitive impairment, and both ATP and ACh have key roles in neurotransmission.

Astaxanthin inhibits glutamate release in rat cerebral cortex nerve terminals via suppression of voltage-dependent Ca(2+) entry and mitogen-activated protein kinase signaling pathway

The purpose of this study was to examine the effect and mechanism of astaxanthin, a natural carotenoid, on endogenous glutamate release in nerve terminals of rat cerebral cortex (synaptosomes). Results showed that astaxanthin exhibited a dose-dependent inhibition of 4-aminopyridine (4-AP)-evoked release of glutamate. The effect of astaxanthin on the evoked glutamate release was prevented by chelating the intrasynaptosomal Ca(2+) ions and by the vesicular transporter inhibitor, but was insensitive to the glutamate transporter inhibitor. Astaxanthin decreased depolarization-induced increase in [Ca(2+)](C), whereas it did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization. The effect of astaxanthin on evoked glutamate release was abolished by the N-, P- and Q-type Ca(2+) channel blockers, but not by the ryanodine receptor blocker or the mitochondrial Na(+)/Ca(2+) exchanger blocker. In addition, the inhibitory effect of astaxanthin on evoked glutamate release was prevented by the mitogen-activated protein kinase (MAPK) inhibitors PD98059 and U0126. Western blot analyses showed that astaxanthin significantly decreased the 4-AP-induced phosphorylation of MAPK, and this effect was blocked by PD98059. On the basis of these results, it was concluded that astaxanthin inhibits glutamate release from rat cortical synaptosomes through the suppression of presynaptic voltage-dependent Ca(2+) entry and MAPK signaling cascade.

PRMT3 is essential for dendritic spine maturation in rat hippocampal neurons

Protein arginine N-methyltransferase 3 (PRMT3) is a cytoplasmic enzyme that utilizes S-adenosyl-L-methionine (AdoMet) to methylate specific proteins, most of which contain GAR (glycine-arginine rich) motifs. PRMT3 has been shown to play a role in the proper maturation of the 80S ribosome by binding to and catalyzing the methylation of rpS2, a component of the 40S ribosomal subunit. However, the other roles of PRMT3 are fairly unclear, particularly in the brain, which is abundant in methylated proteins. In this study, we perturbed PRMT3 expression in cultured rat hippocampal neurons by transiently introducing siRNA oligonucleotides that were designed to hybridize with PRMT3 mRNA and then we examined the morphological and functional effects of neuronal PRMT3 depletion. PRMT3-defective neurons showed deformed spines without any change in spine number; less BDNF-induced protein translation of alphaCaMKII; and diminished rpS2 protein stability. Furthermore, overexpression of a methylation-resistant rpS2, whose methylated arginine residues were deleted, produced phenotypes that were similar to those associated with PRMT3 downregulation. These findings demonstrated that PRMT3 possibly plays a pivotal role in neuronal translation by interaction with rpS2 and that it contributes to activity-dependent changes in the dendritic spines.

Effect of lead on oxidative stress, Na+K+ATPase activity and mitochondrial electron transport chain activity of the brain of Clarias batrachus L

The present invivo study was designed to elucidate the toxic effect of lead on oxidative stress, Na(+)K(+)ATPase and mitochondrial electron transport chain activity of the brain of Clarias batrachus. The fish were exposed to 10 and 20% of the derived 96 h LC(50) value, 37.8 and 75.6 mg L(-1), respectively, and sampled on 20, 40 and 60 days. Exposure of fish brain to lead demonstrated an increased production of reactive oxygen species, increased lipid peroxidation, loss of protein thiol groups in synaptosomal fraction with the decreased activity of Na(+)K(+)ATPase, partial inactivation of mitochondrial electron transport chain activity and energy depletion. However, no change in protein carbonyl content in synaptosomal fraction was observed due to lead exposure. Concluding the results of our investigation we suggest that lead exposure induces oxidative stress in the brain of Clarias batrachus and the decline in Na(+)K(+)ATPase activity was presumeably mediated by the combined action of lipid peroxidation and deficient mitochondrial electron transport chain activity.

Transglutaminase participates in the blockade of neurotransmitter release by tetanus toxin: evidence for a novel biological function

Inhibition of neuroexocytosis by tetanus neurotoxin (TeNT) involves VAMP-2/synaptobrevin-2 cleavage. However, deletion of the TeNT activity does not completely abolish its inhibitory action. TeNT is a potent activator of the cross-linking enzyme transglutaminase 2 (TGase 2) in vitro. The role of the latter mechanism in TeNT poisoning was investigated in isolated nerve terminals and intact neurons. TeNT-induced inhibition of glutamate release from rat cortical synaptosomes was associated with a simultaneous activation of neuronal transglutaminase (TGase) activity. The TeNT-induced blockade of neuroexocytosis was strongly attenuated by pretreatment of either live Aplysia neurons or isolated nerve terminals with specific TGase inhibitors or neutralizing antibodies. The same treatments completely abolished the residual blockade of neuroexocytosis of a non-proteolytic mutant of TeNT light chain. Electrophysiological studies indicated that TGase activation occurs at an early step of TeNT poisoning and contributes to the inhibition of transmitter release. Bioinformatics and biochemical analyses identified synapsin I and SNAP-25 as potential presynaptic TGase substrates in isolated nerve terminals, which are potentially involved in the inhibitory action of TeNT. The results suggest that neuronal TGase activity plays an important role in the regulation of neuroexocytosis and is one of the intracellular targets of TeNT in neurons.

Resveratrol activation of nitric oxide synthase in rabbit brain synaptosomes: singlet oxygen (1O2) formation as a causative factor of neurotoxicity

In the present study it was shown that resveratrol (3,4,5-trihydroxystilbene), an efficient light-absorbing molecule, during its transition from trans to cis configuration under UV light, transfers its energy of excitation to triplet oxygen to produce singlet oxygen ((1)O(2)). This transition is prevented by Trolox, a quencher of singlet oxygen. In the presence of a stable amount of nitrosoglutathione, UV-irradiated resveratrol reacts with nitric oxide (NO) originating from the nitrosoglutathione to produce peroxynitrite (ONOO(-)). Beta-carotene, acting as a quencher of (1)O(2), prevents the transition of resveratrol from trans to cis. Beta-carotene also prevents DNA damage induced by the (1)O(2). NO synthase (NOS) activity in synaptosomes isolated from rabbit brain increased approximately three-fold by resveratrol and the NO released was converted to ONOO(-). Resveratrol increased the lipid fluidity of synaptosomal plasma membranes. These changes suggest that the incorporation of resveratrol into synaptosomal plasma membranes causes an up-regulation of NO synthase. On the other hand, the simultaneous ONOO(-) and (1)O(2) formation may cause disturbances in transmembrane signal transduction leading to neurotoxicity. The present study concerning the behavior of resveratrol with respect to its structure and potential prooxidant-antioxidant function provides important new clues as to the role of this fascinating molecule in pathophysiology.

Hyperglycemia-induced alterations in synaptosomal membrane fluidity and activity of membrane bound enzymes: beneficial effect of N-acetylcysteine supplementation

Diabetic encephalopathy is characterized by impaired cognitive functions that appear to underlie neuronal damage triggered by glucose driven oxidative stress. Hyperglycemia-induced oxidative stress in diabetic brain may initiate structural and functional changes in synaptosomal membranes. The objective of the present study was to examine the neuroprotective role of N-acetylcysteine (NAC) in hyperglycemia-induced alterations in lipid composition and activity of membrane bound enzymes (Na(+),K(+)-ATPase and Ca(2+)-ATPase) in the rodent model of type 1 diabetes. Male Wistar rats weighing between 180 and 200 g were rendered diabetic by a single injection of streptozotocin (50 mg/kg body weight, i.p.). The diabetic animals were administered NAC (1.4-1.5 g/kg body weight) for eight weeks and lipid composition along with membrane fluidity were determined. A significant increase in lipid peroxidation was observed in cerebral cortex of diabetic rats. NAC administration on the other hand lowered the hyperglycemia-induced lipid peroxidation to near control levels. The increased lipid peroxidation following chronic hyperglycemia was accompanied by a significant increase in the total lipids which can be attributed to increase in the levels of cholesterol, triglycerides and glycolipids. On the contrary phospholipid and ganglioside levels were decreased. Hyperglycemia-induced increase in cholesterol to phospholipid ratio reflected decrease in membrane fluidity. Fluorescence polarization (p) with DPH also confirmed decrease in synaptosomal membrane fluidity that influenced the activity of membrane bound enzymes. An inverse correlation was found between fluorescence polarization with the activities of Na(+),K(+)-ATPase (r(2)=0.416, P<0.05) and Ca(2+) ATPase (r(2)=0.604, P<0.05). NAC was found to significantly improve lipid composition, restore membrane fluidity and activity of membrane bound enzymes. Our results clearly suggest perturbations in lipid composition and membrane fluidity as a major factor in the development of diabetic encephalopathy. Furthermore, NAC administration ameliorated the effect of hyperglycemia on oxidative stress and alterations in lipid composition thereby restoring membrane fluidity and activity of membrane bound enzymes.

[Characteristics of thiamine triphosphatase from neural cells plasma membranes]

The kinetic parameters of the ThTP hydrolysis by synaptic plasma membranes isolated from rat brain were investigated. It was shown that the ThTPase reaction pH optimum was 7.4, the apparent K(m) was 52 microM and the apparent affinity constant for Mg2+ was 1.9 mM. The comparative analysis of the indicated parameters was done for the ThTPase activity of membrane bound (the data of present work and literature data) and cytosolic (literature data) proteins. The analysis allows us to suppose that thiamine-binding protein described earlier is the single ThTPase activity carrier in neural cells plasma membranes. It was shown that the active site of the enzyme that catalyzes the ThTP hydrolysis in neural cells plasma membranes is associated with the inside membrane surface.

Effect of Chronic Renal Failure with and without Secondary Hyperparathyroidism on the Activities of Synaptosomal Tyrosine Hydroxylase and Monoamine Oxidase

Norepinephrine (NE) content, release and uptake by brain synaptosomes are reduced in chronic renal failure (CRF), and this has been attributed to the state of secondary hyperparathyroidism. The decrease in NE content in CRF could not be explained by changes in NE uptake or release since in normal circumstances, NE content usually remains unchanged despite fluctuation in NE uptake and release. Since NE content is determined by its production and degradation, we examined the effect of CRF with and without excess parathyroid hormone (PTH) on the Michaelis-Menton constant (Km) and Vmax of tyrosine hydroxylase (TH), the rate-limiting enzyme for NE production, and monoamine oxidase (MAO), an enzyme involved in NE degradation of brain synaptosomes. Brain synaptosomes from rats with a 21-day CRF have a significantly (p less than 0.01) lower Vmax of TH (39.5 +/- 5.3 pmol tritiated H2O/mg protein/min) than that of normal rats (61. +/- 7.5 pmol tritiated H2O/mg protein/min) and a higher Km of MAO (59 +/- 2.9 nM tyramine) than normal animals (46 +/- 1.7 nM tyramine). Parathyroidectomy (PTX) in CRF rats normalized Vmax of TH (54 +/- 4.5 pmol tritiated H2O/mg protein) and Km of MAO (48.4 +/- 2.3 nM tyramine). Cytosolic calcium, [Ca2+]i, in brain synaptosomes is significantly (p less than 0.01) higher in rats with CRF (488 +/- 8.5 nM) than in normal (355 +/- 6.0 nM) or PTX-CRF (360 +/- 8.1 nM) rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of respiration in brain mitochondria and synaptosomes: restrictions of ADP diffusion in situ, roles of tubulin, and mitochondrial creatine kinase

The role of ubiquitous mitochondrial creatine kinase (uMtCK) reaction in regulation of mitochondrial respiration was studied in purified preparations of rat brain synaptosomes and mitochondria. In permeabilized synaptosomes, apparent Km for exogenous ADP, Km (ADP), in regulation of respiration in situ was rather high (110 +/- 11 microM) in comparison with isolated brain mitochondria (9 +/- 1 microM). This apparent Km for ADP observed in isolated mitochondria in vitro dramatically increased to 169 +/- 52 microM after their incubation with 1 muM of dimeric tubulin showing that in rat brain, particularly in synaptosomes, mitochondrial outer membrane permeability for ADP, and ATP may be restricted by tubulin binding to voltage dependent anion channel (VDAC). On the other hand, in synaptosomes apparent Km (ADP) decreased to 25 +/- 1 microM in the presence of 20 mM creatine. To fully understand this effect of creatine on kinetics of respiration regulation, complete kinetic analysis of uMtCK reaction in isolated brain mitochondria was carried out. This showed that oxidative phosphorylation specifically altered only the dissociation constants for MgATP, by decreasing that from ternary complex MtCK.Cr.MgATP (K (a)) from 0.13 +/- 0.02 to 0.018 +/- 0.007 mM and that from binary complex MtCK.MgATP (K (ia)) from 1.1 +/- 0.29 mM to 0.17 +/- 0.07 mM. Apparent decrease of dissociation constants for MgATP reflects effective cycling of ATP and ADP between uMtCK and adenine nucleotide translocase (ANT). These results emphasize important role and various pathophysiological implications of the phosphocreatine-creatine kinase system in energy transfer in brain cells, including synaptosomes.

Ischemic preconditioning targets the respiration of synaptic mitochondria via protein kinase C epsilon

In the brain, ischemic preconditioning (IPC) diminishes mitochondrial dysfunction after ischemia and confers neuroprotection. Activation of epsilon protein kinase C (epsilonPKC) has been proposed to be a key neuroprotective pathway during IPC. We tested the hypothesis that IPC increases the levels of epsilonPKC in synaptosomes from rat hippocampus, resulting in improved synaptic mitochondrial respiration. Preconditioning significantly increased the level of hippocampal synaptosomal epsilonPKC to 152% of sham-operated animals at 2 d of reperfusion, the time of peak neuroprotection. We tested the effect of epsilonPKC activation on hippocampal synaptic mitochondrial respiration 2 d after preconditioning. Treatment with the specific epsilonPKC activating peptide, tat-psiepsilonRACK (tat-psiepsilon-receptor for activated C kinase), increased the rate of oxygen consumption in the presence of substrates for complexes I, II, and IV to 157, 153, and 131% of control (tat peptide alone). In parallel, we found that epsilonPKC activation in synaptosomes from preconditioned animals resulted in altered levels of phosphorylated mitochondrial respiratory chain proteins: increased serine and tyrosine phosphorylation of 18 kDa subunit of complex I, decreased serine phosphorylation of FeS protein in complex III, increased threonine phosphorylation of COX IV (cytochrome oxidase IV), increased mitochondrial membrane potential, and decreased H2O2 production. In brief, ischemic preconditioning promoted significant increases in the level of synaptosomal epsilonPKC. Activation of epsilonPKC increased synaptosomal mitochondrial respiration and phosphorylation of mitochondrial respiratory chain proteins. We propose that, at 48 h of reperfusion after ischemic preconditioning, epsilonPKC is poised at synaptic mitochondria to respond to ischemia either by direct phosphorylation or activation of the epsilonPKC signaling pathway.

Chronic antidepressants induce redistribution and differential activation of alphaCaM kinase II between presynaptic compartments

Changes in synaptic plasticity are involved in pathophysiology of depression and in the mechanism of antidepressants. Ca(2+)/calmodulin (CaM) kinase II, a protein kinase involved in synaptic plasticity, has been previously shown to be a target of antidepressants. We previously found that antidepressants activate the kinase in hippocampal neuronal cell bodies by increasing phosphorylation at Thr(286), reduce the kinase phosphorylation in synaptic membranes, and in turn its phosphorylation-dependent interaction with syntaxin-1 and the release of glutamate from hippocampal synaptosomes. Here, we investigated the chronic effect of different antidepressants (fluoxetine, desipramine, and reboxetine) on the expression and function of the kinase in distinct subcellular compartments in order to dissect the different kinase pools affected. Acute treatments did not induce any change in the kinase. In total tissue extracts chronic drug treatments induced activation of the kinase; in hippocampus (HC), but not in prefrontal/frontal cortex, this was partially accounted for by increased Thr(286) phosphorylation, suggesting the involvement of different mechanisms of activation. In synaptosomes, all drugs reduced the kinase phosphorylation, particularly in HC where, upon fractionation of the synaptosomal particulate into synaptic vesicles and membranes, we found that the drugs induced a redistribution and differential activation of the kinase between membranes and vesicles. Furthermore, a large decrease in the level and phosphorylation of synapsin I located at synaptic membranes was consistent with the observed decrease of CaM kinase II. Overall, antidepressants induce a complex pattern of modifications in distinct subcellular compartments; at presynaptic level, these changes are in line with a dampening of glutamate release.

Biochemical characterization of ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP, E.C. 3.1.4.1) from rat heart left ventricle

In the present study we investigate the biochemical properties of the members of NPP family in synaptosomes prepared from rat heart left ventricles. Using p-nitrophenyl-5'-thymidine monophosphate (p-Nph-5'-TMP) as substrate for E-NPPs in rat cardiac synaptosomes, we observed an alkaline pH dependence, divalent cation dependence and the K ( M ) value corresponded to 91.42 +/- 13.97 microM and the maximal velocity (V ( max )) value calculated was 63.79 +/- 3.59 nmol p-nitrophenol released/min/mg of protein (mean +/- SD, n = 4). Levamisole (1 mM), was ineffective as inhibitor of p-Nph-5'-TMP hydrolysis in pH 8.9 (optimum pH for the enzyme characterized). Suramin (0.25 mM) strongly reduced the hydrolysis of p-Nph-5'-TMP by about 46%. Sodium azide (10 and 20 mM) and gadolinium chloride (0.3 and 0.5 mM), E-NTPases inhibitors, had no effects on p-Nph-5'-TMP hydrolysis. RT-PCR analysis of left ventricle demonstrated the expression of NPP2 and NPP3 enzymes, but excluded the presence of NPP1 member. By quantitative real-time PCR we identified the NPP3 as the enzyme with the highest expression in rat left ventricle. The demonstration of the presence of the E-NPP family in cardiac system, suggest that these enzymes could contribute with the fine-tuning control of the nucleotide levels at the nerve terminal endings of left ventricles that are involved in several cardiac pathologies.

The effect of paraoxon on GABA uptake in rat cerebellar synaptosomes

BACKGROUND

The compounds used to treat organophosphate (OP) poisoning are not able to fully alleviate long-lasting effects. They are mainly used to antagonize the cholinergic effects of OPs; however, non-cholinergic effects such as interference with different neurotransmitter systems, especially GABA release and uptake, are now attracting more attention.

MATERIAL/METHODS

Cerebellar synaptosomes were used to investigate any potential interaction between paraoxon and GABA uptake. The cerebella of 250- to 280-g Wistar rats were rapidly dissected out, homogenized, centrifuged, and incubated with 0.004 microM [(3)H]GABA in the presence of different doses of paraoxon for 15 minutes at 37 degrees C. At the end of the incubation period, the synaptosomes were layered in chambers of a superfusion system (UGO). To assay the amount of [(3)H]GABA uptake, radioactivity was measured using a beta-counter (Winspectrul).

RESULTS

Mean GABA uptake was 111, 95, 71, 73, and 75 percent of the control values in the presence of paraoxon concentrations of 0.01, 0.1, 1, 10, and 100 microM, respectively. Accordingly, GABA uptake was significantly reduced at doses 1, 10, and 100 microM of paraoxon (P<0.05).

CONCLUSIONS

Paraoxon may interfere with GABA uptake by cerebellar synaptosomes at micromolar concentrations or higher.

Maintenance of homeostasis for thyroid hormone in the adult rat brain: possible involvement of a nuclear-mediated phenomenon

During adult-onset peripheral hypothyroidism, the brain maintains normal levels of thyroid hormone for some time through a mechanism of 'central homeostasis'. Although onset, duration, and termination of such a homeostatic phenomenon have been recently evaluated in rat models, the mechanism behind remains unknown. During our investigation to understand the mechanism further, we injected the protein synthesis blockers actinomycin D and cycloheximide along with propylthiouracil to adult male rats during the days of onset (day 2) and termination (day 20) of the homeostatic mechanism. We evaluated synaptosomal T(3) level and neuronal Na(+)-K(+)-ATPase and acetylcholinesterase activities along with deiodinase II activity and cyclic adenosine monophosphate level in the cerebral cortex. The results indicated prevalence of unchanged or lower levels of synaptosomal T(3) on the 2nd and on the 20th day, respectively. Such a condition has been parallely supported by reflections in cerebrocortical deiodinase II activity and cyclic adenosine monophosphate levels. The activities of cerebrocortical synaptosomal Na(+)-K(+)-ATPase and acetylcholinesterase, which are the two important physiological parameters for neuronal function, have been found to be supportive of the involvement of a neuronal protein-mediated factor in the 'on' and 'off' reactions in central homeostasis during peripheral hypothyroidism. The results of our study indicate that the expression of 'central thyroid hormone homeostasis' is a genomic nuclear-mediated mechanism.

Honokiol, a Neuroprotectant against Mouse Cerebral Ischaemia, Mediated by Preserving Na+, K+-ATPase Activity and Mitochondrial Functions

Honokiol, a component of the herb Magnolia officinalis, exhibits antioxidant, anti-inflammatory and anxiolytic properties, increases seizure threshold, and promotes neurite outgrowth. Because stroke has become the second leading cause of death in industrialized countries, an effective neuroprotectant is urgently required. In this study, we attempted to elucidate in a mouse cerebral ischaemia model whether honokiol could be a neuroprotectant. Adult male Institute of Cancer Research (ICR) mice were subjected to middle cerebral artery occlusion for 45 min. Honokiol (10 microg/kg in 0.2 ml of saline) or control vehicle was intraperitoneally administered twice, 15 min. before and 60 min. after the induction of ischaemia. Cerebral ischaemia induced by this method was associated with an increase in synaptosomal production of reactive oxygen species, with decreases in synaptosomal mitochondrial membrane potential (DeltaPsim) and synaptosomal mitochondrial metabolic function, and with reductions in Na(+), K(+)-ATPase activities of tissues isolated from selected brain regions. Administration of honokiol resulted in significant reductions in brain infarct volume and in synaptosomal production of reactive oxygen species. The decreases in synaptosomal mitochondrial membrane potential, synaptosomal mitochondrial metabolic function and tissue Na(+), K(+)-ATPase activities observed in the ischaemic brains were also attenuated by honokiol treatments. It is concluded that honokiol can protect brain against ischaemic reperfusion injury and preserve mitochondrial function from oxidative stress. Regarding therapeutic application, further studies are needed to assess the efficacy and safety of honokiol in clinical situations.

The effect of aluminium on NTPDase and 5'-nucleotidase activities from rat synaptosomes and platelets

Aluminium (Al), a neurotoxic compound, has been investigated in a large number of studies both in vivo and in vitro. In this study, we investigated the effect in vivo of long-term exposure to Al on NTPDase (nucleoside triphosphate diphosphohydrolase) and 5'-nucleotidase activities in the synaptosomes (obtained from the cerebral cortex and hippocampus) and platelets of rats. Here, we investigated a possible role of platelets as peripheral markers in rats. Rats were loaded by gavage with AlCl(3) 50 mg/(kg day), 5 days per week, totalizing 60 administrations. The animals were divided into four groups: (1) control (C), (2) 50 mg/kg of citrate solution (Ci), (3) 50 mg/kg of Al plus citrate (Al+Ci) solution and (4) 50 mg/kg of Al (Al). ATP hydrolysis was increased in the synaptosomes from the cerebral cortex by 42.9% for Al+Ci and 39.39% for Al, when compared to their respective control (p<0.05). ADP hydrolysis was increased by 13.15% for both Al and Al+Ci, and AMP hydrolysis increased by 32.7% for Al and 27.25% for Al+Ci (p<0.05). In hippocampal synaptosomes, the hydrolysis of ATP, ADP and AMP, was increased by 58.5%, 28.5% and 25.92%, respectively, for Al (p<0.05) and 36.7%, 22.5% and 37.64% for Al+Ci, both when compared to their respective controls. ATP, ADP and AMP hydrolysis, in platelets, was increased by 172.3%, 188.52% and 92.1%, respectively in Al+Ci, and 317.9%, 342.8% and 177.9%, respectively, for Al, when compared to their respective controls (p<0.05). Together, these results indicate that Al increases NTPDase and 5'-nucleotidase activities, in synaptosomal fractions and platelets. Thus, we suggest that platelets could be sensitive peripheral markers of Al toxicity of the central nervous system.

Role of cannabinoid CB1 receptors and Gi/o protein activation in the modulation of synaptosomal Na+,K+-ATPase activity by WIN55,212-2 and delta(9)-THC

In the present study, we evaluated the effects of the synthetic cannabinoid receptor agonist (R)-(+)-[2,3-Dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN55,212-2) and the active component of Cannabis delta-9-tetrahydrocannabinol (triangle up(9)-THC) on Na(+),K(+)-ATPase activity in synaptosomal mice brain preparation. Additionally, the potential exogenous cannabinoids and endogenous opioid peptides interaction as well as the role of G(i/o) proteins in mediating Na(+),K(+)-ATPase activation were also explored. The ouabain-sensitive Na(+),K(+)-ATPase activity was measured in whole-brain pure intact synaptosomes (obtained by Percoll gradient method) of female CF-1 mice and was calculated as the difference between the total and the ouabain (1 mM)-insensitive Na(+),K(+)-ATPase activities. Incubation in vitro of the synaptosomes with WIN55,212-2 (0.1 pM-10 microM) or triangle up(9)-THC (0.1 pM-0.1 microM), in a concentration-dependent manner, stimulated ouabain-sensitive Na(+),K(+)-ATPase activity. WIN55,212-2 was less potent but more efficacious than triangle up(9)-THC. N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM-251) (10 nM), a CB(1) cannabinoid receptor selective antagonist, had not effect per se but antagonized the enhancement of Na(+),K(+)-ATPase activity induced by both, WIN55,212-2 and triangle up(9)-THC. AM-251 produced a significant reduction in the E(max) of cannabinoid-induced increase in Na(+),K(+)-ATPase activity, but did not significantly modify their EC(50). On the other hand, co-incubation with naloxone (1 microM), an opioid receptor antagonist, did not significantly modify the effect of WIN55,212-2 and completely failed to modify the effect of triangle up(9)-THC on synaptosomal Na(+),K(+)-ATPase. Finally, pre-incubation with 0.5 microg of pertussis toxin (G(i/o) protein blocker) completely abolished the enhancement of ouabain-sensitive Na(+),K(+)-ATPase activity induced by WIN55,212-2. A lower dose, 0.25 microg, decreased the E(max) of WIN55,212-2 by 70% but did not significantly affect its EC(50). These results suggest that WIN55212-2 and triangle up(9)-THC indirectly enhance Na(+),K(+)-ATPase activity in the brain by activating cannabinoid CB(1) receptors in a naloxone-insensitive manner. In addition, the effect of WIN55,212-2 on neuronal Na(+),K(+)-ATPase is apparently due to activation of G(i/o) proteins.

Subcellular compartmentalization of aromatase is sexually dimorphic in the adult zebra finch brain

The vertebrate brain is a source of estrogen (E) via the expression of aromatase (E-synthase). In the zebra finch (Taeniopygia guttata), despite documented dimorphisms in E-action, no differences are detectable in circulating E, or the neural levels of aromatase transcription, activity, or somal protein expression. Studies of aromatase expression at the light- and electron-microscope levels reveal greater numbers of fibers and presynaptic boutons in adult males relative to females. We assayed aromatase activity and content in synaptosomes and microsomes from the anterior [containing lMAN and Area X (males)] and posterior telencephalon (containing HVC and RA) of adult birds. In contrast to non-song birds and mammals, both cell fractions contain abundant aromatase measurable in terms of activity (enzyme assays) and content (Western blots) with minimal enrichment in microsomes. From brain homogenates of identical concentration, aromatase activity was higher in the synaptosomal relative to the microsomal fraction, in males relative to females, and in the posterior compared to anterior telencephalon. These effects were driven by high levels of synaptosomal aromatase in the male posterior telencephalon. These data suggest that males possess more aromatase per presynaptic bouton, or a greater number of aromatase-containing presynaptic boutons than females in the posterior telencephalon. Further, the present report reveals synaptic aromatization as a considerable source of E in the zebra finch brain, and supports the idea that telencephalic synapses in and around the adult male song production nuclei may be exposed to higher levels of E compared to the female brain.

Evidence of calcium- and SNARE-dependent release of CuZn superoxide dismutase from rat pituitary GH3 cells and synaptosomes in response to depolarization

The antioxidant enzyme CuZn superoxide dismutase (SOD1) is secreted by many cell lines. However, it is not clear whether SOD1 secretion is only constitutive or can be regulated in an activity-dependent fashion. Using rat pituitary GH(3) cells that express voltage-dependent calcium channels and are subjected to Ca(2+) oscillations, we found that treatment with high K(+)-induced SOD1 release that was significantly higher than the constitutive secretion. Evoked SOD1 release was correlated with depolarization-dependent calcium influx and was virtually abolished by removal of extracellular calcium with EGTA or by pre-incubation of GH(3) cells with Botulinum toxin A that cleaves the SNARE protein SNAP-25. Immunofluorescence experiments performed in GH(3) cells and rat brain synaptosomes showed that K(+)-depolarization induced a marked depletion of intracellular SOD1 immunoreactivity, an effect that was again abolished in the absence of extracellular calcium or after treatment with Botulinum toxin A. Subcellular fractionation analysis showed that SOD1 was present in large dense core vesicles. These data clearly show that, in addition to the constitutive SOD1 secretion, depolarization induces an additional rapid calcium-dependent SOD1 release in GH(3) cells and in rat brain synaptosomes. This likely occurs through exocytosis from SOD1-containing vesicles operated by the SNARE complex.

Antiepileptic drugs prevent changes induced by pilocarpine model of epilepsy in brain ecto-nucleotidases

Ecto-nucleotidases, one of the main mechanisms involved in the control of adenosine levels in the synaptic cleft, have shown increased activities after the pilocarpine model of epilepsy. Here we have investigated the effect of the antiepileptic drugs (AEDs) on ecto-nucleotidase activities from hippocampal and cerebral cortical synaptosomes of rats at seven days after the induction of the pilocarpine model. Expression of these enzymes were investigated as well. Our results have demonstrated that phenytoin (50 mg/kg) and carbamazepine (30 mg/kg) were able to prevent the increase in ecto-nucleotidase activities elicited by pilocarpine in brain synaptosomes. However, sodium valproate (at 100 mg/kg) was only able to avoid the increase on ATP and ADP hydrolysis in hippocampal synaptosomes. Increase on ATP hydrolysis in hippocampal synaptosomes was also prevented by sodium valproate at 286 mg/kg, which corresponds to ED50 for pilocarpine model. NTPDase1, NTPDase2, NTPDase3, and ecto-5'-nucleotidase expressions were not affected by pilocarpine in cerebral cortex. However, expressions of NTPDase2, NTPDase3, and ecto-5'-nucleotidase were increased by pilocarpine in hippocampus. Our results have indicated that previous treatment with AEDs was able to prevent the increase in hippocampal ecto-nucleotidases of pilocarpine-treated rats. These findings have shown that anticonvulsant drugs can modulate plastic events related to the increase of nucleotidase expression and activities in pilocarpine-treated rats.

NTPDase and 5'-nucleotidase activities of synaptosomes from hippocampus of rats subjected to hyperargininemia

ATP is an important excitatory neurotransmitter and adenosine acts as a neuromodulatory structure inhibiting neurotransmitters release in the central nervous system. Since the ecto-nucleotidase cascade that hydrolyzes ATP to adenosine is involved in the control of brain functions and previous studies realized in our laboratory have recently reported that acute administration of Arg decreases the NTPDase and 5'-nucleotidase activities of rat blood serum, in the present study we investigated the effect of arginine administration on NTPDase and 5'-nucleotidase activities by synaptosomes from hippocampus of rats. First, sixty-days-old rats were treated with a single or a triple intraperitoneal injection of arginine (0.8 g/Kg) or an equivalent volume of 0.9% saline solution (control) and were killed 1 h later. Second, rats received an intracerebroventricular injection of 1.5 mM arginine solution or saline (5 microL) and were killed 1 h later. We also tested the in vitro effect of arginine (0.1-1.5 mM) on nucleotide hydrolysis in synaptosomes from rat hippocampus. Results showed that intraperitoneal arginine administration did not alter nucleotide hydrolysis. On the other hand, arginine administered intracerebroventricularly reduced ATP (32%), ADP (30%) and AMP (21%) hydrolysis, respectively. In addition, arginine added to the incubation medium, provoked a decrease on ATP (19%), ADP (17%) and AMP (23%) hydrolysis, respectively. Furthermore, kinetic studies showed that the inhibitory effect of arginine was uncompetitive in relation to ATP, ADP and AMP. In conclusion, according to our results it seems reasonable to postulate that arginine alters the cascade involved in the extracellular degradation of ATP to adenosine.

Synapsin phosphorylation by SRC tyrosine kinase enhances SRC activity in synaptic vesicles

Synapsins are synaptic vesicle-associated phosphoproteins implicated in the regulation of neurotransmitter release. Synapsin I is the major binding protein for the SH3 domain of the kinase c-Src in synaptic vesicles. Its binding leads to stimulation of synaptic vesicle-associated c-Src activity. We investigated the mechanism and role of Src activation by synapsins on synaptic vesicles. We found that synapsin is tyrosine phosphorylated by c-Src in vitro and on intact synaptic vesicles independently of its phosphorylation state on serine. Mass spectrometry revealed a single major phosphorylation site at Tyr(301), which is highly conserved in all synapsin isoforms and orthologues. Synapsin tyrosine phosphorylation triggered its binding to the SH2 domains of Src or Fyn. However, synapsin selectively activated and was phosphorylated by Src, consistent with the specific enrichment of c-Src in synaptic vesicles over Fyn or n-Src. The activity of Src on synaptic vesicles was controlled by the amount of vesicle-associated synapsin, which is in turn dependent on synapsin serine phosphorylation. Synaptic vesicles depleted of synapsin in vitro or derived from synapsin null mice exhibited greatly reduced Src activity and tyrosine phosphorylation of other synaptic vesicle proteins. Disruption of the Src-synapsin interaction by internalization of either the Src SH3 or SH2 domains into synaptosomes decreased synapsin tyrosine phosphorylation and concomitantly increased neurotransmitter release in response to Ca(2+)-ionophores. We conclude that synapsin is an endogenous substrate and activator of synaptic vesicle-associated c-Src and that regulation of Src activity on synaptic vesicles participates in the regulation of neurotransmitter release by synapsin.

Habituation to an open field alters ecto-nucleotidase activities in rat hippocampal synaptosomes

ATP and adenosine may play a role in the mechanisms of synaptic plasticity and memory formation. Previous studies have shown that ecto-nucleotidase activities are altered during memory consolidation of an aversive task named step-down inhibitory avoidance. Here we investigate ecto-nucleotidase activities in hippocampal synaptosomes of rats submitted to training and test sessions of habituation to open field, which is one of the most elementary forms of learning. There were no significant alterations on ATP, ADP and AMP hydrolysis immediately after the training session. However, immediately after the test session (0min), there was a significant increase of ATP hydrolysis (61%), but not of ADP and AMP hydrolysis. Sixty minutes after the test session, a significant increase of NTPDase (75% and 60.5% for ATP and ADP hydrolysis, respectively) and ecto-5'-nucleotidase (40%) activities was observed. This study reveals the involvement of ecto-nucleotidase activities in different learning paradigms during memory processing.

Sertraline and clomipramine inhibit nucleotide catabolism in rat brain synaptosomes

The effects of sertraline, a selective serotonin reuptake inhibitor, and clomipramine, a tricyclic antidepressant, were tested on ecto-nucleotidases from synaptosomes of cerebral cortex and hippocampus of rats. Sertraline and clomipramine (100-500 microM) inhibited NTPDase, but not ecto-5'-nucleotidase activity in both cerebral cortex and hippocampus. In cortical synaptosomes, sertraline inhibited both ATP and ADP hydrolysis in the concentrations tested. The inhibitory effect varied from 21% to 83% for ATP hydrolysis and 48% to 75% for ADP hydrolysis. The inhibition promoted by sertraline in hippocampal synaptosomes varied from 38% to 89% for ATP hydrolysis and 45% to 77% for ADP hydrolysis. A significant inhibition of cortical NTPDase activity by clomipramine was observed in the all concentrations tested (35-72% and 36-87% for ATP and ADP hydrolysis, respectively). Similar effects were observed in hippocampus (29-91% and 48-83% for ATP and ADP hydrolysis, respectively). There was no inhibitory effect of sertraline and clomipramine on AMP hydrolysis in cerebral cortex and hippocampus. Our results have shown that classical antidepressants inhibit the extracellular catabolism of ATP. Therefore, it is possible to suggest that changes induced by antidepressants on bilayer membrane could affect NTPDase activities and consequently, modulating ATP and adenosine levels in the synaptic cleft.

Biochemical analysis of ecto-nucleotide pyrophosphatase phosphodiesterase activity in brain membranes indicates involvement of NPP1 isoenzyme in extracellular hydrolysis of diadenosine polyphosphates in central nervous system

Synaptosomes and plasma membranes obtained from rat brain display ectoenzymatic hydrolytic activity responsible for hydrolysis of the neurotransmitter/neuroregulatory nucleotides diadenosine polyphosphates. Intact synaptosomes and plasma and synaptic membranes isolated by sucrose-gradient ultracentrifugation from several brain regions (hypothalamus, hippocampus, temporal cortex, frontal cortex striatum and cerebellum) degraded the fluorogenic substrates diethenoadenosine polyphosphates up to ethenoadenosine as by-product. Purified ectoenzyme cleaved substrates always releasing the mononucleotide moieties ethenoadenosine 5'-monophosphate and the corresponding ethenoadenosine (n-1) 5'-phosphate. Ectoenzymatic hydrolysis reached maximal activity at pH 9.0 (pH range 6.5-9.0) and was activated by Ca(2+) and Mg(2+) ions, with maximal effects around 2.0 mM cation. EDTA drastically reduced activity and Zn(2+) was required for enzyme reactivation. Hydrolysis of substrates followed hyperbolic kinetics with K(m) values in the 3-10 microM range. Diadenosine polyphosphates and heparin behaved as competitive inhibitors in the enzymatic hydrolysis of diethenoadenosine polyphosphates and AMP, ATP, alpha,beta-methyleneADP, ADPbetaS ATPgammaS, beta,gamma-methyleneATP, suramin and diethyl pyrocarbonate were also inhibitors. Ectoenzymatic activity shared the typical characteristics of members of the ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) family and inhibition data suggest that NPP1 ectoenzyme is involved in the cleavage of extracellular diadenosine polyphosphates in brain. Synaptic membranes from cerebellum, hypothalamus and hippocampus presented the highest activities and no activity differences were observed between young and aged animals. However, plasma membranes showed a more homogeneous distribution of ectoenzymatic activity but a general increase was detected in aged animals. Enhancement of ectoenzymatic diadenosine polyphosphate cleaving activity found in plasma membranes from old animals could play a deleterious role in aged brain by limiting neuroprotective effects reported for extracellular diadenosine tetraphosphate.

Presynaptic plasma membrane Ca2+ ATPase isoform 2a regulates excitatory synaptic transmission in rat hippocampal CA3

Plasma membrane calcium ATPase isoforms (PMCAs) are expressed in a wide variety of tissues where cell-specific expression provides ample opportunity for functional diversity amongst these transporters. The PMCAs use energy derived from ATP to extrude submicromolar concentrations of intracellular Ca2+ ([Ca2+]i) out of the cell. Their high affinity for Ca2+ and the speed with which they remove [Ca2+]i depends upon splicing at their carboxy (C)-terminal site. Here we provide biochemical and functional evidence that a brain-specific, C-terminal truncated and therefore fast variant of PMCA2, PMCA2a, has a role at hippocampal CA3 synapses. PMCA2a was enriched in forebrain synaptosomes, and in hippocampal CA3 it colocalized with the presynaptic marker proteins synaptophysin and the vesicular glutamate transporter 1, but not with the postsynaptic density protein PSD-95. PMCA2a also did not colocalize with glutamic acid decarboxylase-65, a marker of GABA-ergic terminals, although it did localize to a small extent with parvalbumin-positive presumed inhibitory terminals. Pharmacological inhibition of PMCA increased the frequency but not the amplitude of mEPSCs with little effect on mIPSCs or paired-pulse depression of evoked IPSCs. However, inhibition of PMCA activity did enhance the amplitude and slowed the recovery of paired-pulse facilitation (PPF) of evoked EPSCs. These results indicated that fast PMCA2a-mediated clearance of [Ca2+]i from presynaptic excitatory terminals regulated excitatory synaptic transmission within hippocampal CA3.

Rat brain synaptic vesicles are devoid of Mg2+-ATPase activity and contain beta-amyloid precursor protein

Rat brain synaptic vesicles (SVs) isolated by gel filtration on Sephacryl S-500 had little Mg2+(H+)-ATPase activity, though it was identified by Western blots with antibodies against the H+-ATPase A-subunit and other vesicle proteins. In contrast, tyrosine hydroxylase and dopa decarboxylase activities in the SVs were substantial, suggesting that the absence of Mg2+(H+)-ATPase activity was not due to inactivation during isolation but rather to the nature of the SVs. The vesicle component reactive to H+-ATPase antibody was also identified in the synaptosomal cytosol, so the antibody for the A-subunit seemed unnecessary to detect H+-ATPase. The SVs contained beta-amyloid precursor protein of approximately 100 kDa. Based on these observations, SVs without Mg2+(H+)-ATPase seemed to play a role(s) in the delivery of cytoplasmic and plasma membrane proteins to nerve terminals as well as in neurotransmission.

In vivo and in vitro effects of hyperglycemia on Na+ -K+, Ca+2, Mg+2-dependent ATPases activity in brain synaptosomes of aging rats

Cerebral metabolism of glucose, one of the determinants of tissue ATP level, is crucial for the CNS function. The activity of P-type pumps: Na(+), K(+)-ATPase, Ca(+2)-ATPase and Mg(+2)-ATPase were examined in rat brain synaptosomes to determine if changes in the enzyme activity related to aging are potentially associated with alterations in glucose homeostasis. Male Wistar rats (newborn, 3- and 18-month-old) were sacrificed by decapitation and synaptic plasma membranes were isolated from brains. In vivo study demonstrated that 18-month-old rats were characterized by hyperglycemia, hyperinsulinemia and increased total antyoxidative status (TAS) level. These conditions had a different impact on activities of the ATPases tested in vivo: only the activity of Ca(+2)-ATPase decreased whereas that of Mg(+2)-ATPase increased significantly. In vitro experiments, prior incubation of isolated synaptosomes with glucose of concentrations corresponding to normoglycemia in vivo (4.5 - 6.5 mM), stimulated Ca(+2)-ATPase activity, whereas higher glucose concentrations (10.0 - 12.5 mM) inhibited significantly the enzyme activity. The most sensitive to hyperglycemia appeared Na(+), K(+)-ATPase in old rats synaptosomes with the progressive decline starting at 6.5 mM glucose. The activity of Mg(+2)-ATPase was not inhibited in vitro even at high glucose concentrations that may explain the increased in vivo, activity of this enzyme in old, hyperglycemic rats.

Kinetic Parameters and Lactate Dehydrogenase Isozyme Activities Support Possible Lactate Utilization by Neurons

Lactate is potentially a major energy source in brain, particularly following hypoxia/ischemia; however, the regulation of brain lactate metabolism is not well understood. Lactate dehydrogenase (LDH) isozymes in cytosol from primary cultures of neurons and astrocytes, and freshly isolated synaptic terminals (synaptosomes) from adult rat brain were separated by electrophoresis, visualized with an activity-based stain, and quantified. The activity and kinetics of LDH were determined in the same preparations. In synaptosomes, the forward reaction (pyruvate + NADH + H(+ )--> lactate + NAD(+)), which had a V (max) of 1,163 micromol/min/mg protein was 62% of the rate in astrocyte cytoplasm. In contrast, the reverse reaction (lactate + NAD(+ )--> pyruvate + NADH + H(+)), which had a V (max) of 268 micromol/min/mg protein was 237% of the rate in astrocytes. Although the relative distribution was different, all five isozymes of LDH were present in synaptosomes and primary cultures of cortical neurons and astrocytes from rat brain. LDH1 was 14.1% of the isozyme in synaptic terminals, but only 2.6% and 2.4% in neurons and astrocytes, respectively. LDH5 was considerably lower in synaptic terminals than in neurons and astrocytes, representing 20.4%, 37.3% and 34.8% of the isozyme in these preparations, respectively. The distribution of LDH isozymes in primary cultures of cortical neurons does not directly reflect the kinetics of LDH and the capacity for lactate oxidation. However, the kinetics of LDH in brain are consistent with the possible release of lactate by astrocytes and oxidative use of lactate for energy in synaptic terminals.

Maintenance of brain thyroid hormone level during peripheral hypothyroid condition in adult rat

Thyroid hormones are essential for normal functioning of adult mammalian brain. The present investigation deals with the understanding of the time course of thyroid hormone homeostasis in adult rat brain. Animals were rendered hypothyroid by PTU injections (2 mg/100 g bw) for 30 consecutive days. Serum and synaptosomal T3/T4 content, synaptosomal AChE and Na+-K+-ATPase activities were determined on alternate days. While serum T4 level initially increased on the second day compared to control, serum T3 declined in a triphasic pattern; the first phase lasting from the second day to the 6th day, the second phase ended on the 14th day and last phase continued till the 30th day. Cerebro-cortical synaptosomal T3 level increased on the 2nd day from the control, attained a peak on the 4th day, remained stable until the 18th day, and abruptly declined on the 20th day. Synaptosomal T4 content remained negligible or undetected throughout. Synaptosomal membrane Na+-K+-ATPase and AChE activity exhibited an inverse relationship during the experimental regime, being much more prominent on the 2nd, 18th and 20th day coinciding with the variations in brain T3 level. Thus, the study identifies the onset of central homeostasis between the first and second day, its continuation for about 16-18 days and its termination between the 18th and 20th day.

Involvement of Na(+), K(+)-ATPase and endogenous digitalis-like compounds in depressive disorders

BACKGROUND

Sodium and potassium-activated adenosine triphosphatase (Na(+), K(+)-ATPase) and endogenous digitalis-like compounds (DLC) in the brain have been implicated in the pathogenesis of mood disorders. This hypothesis was examined by the determination of Na(+), K(+)-ATPase/DLC system in parietal cortex of patients with different mood disorders and two animal models of depression.

METHODS

Na(+), K(+)-ATPase concentrations in human brain synaptosomal fractions, from patients with mood disorders, schizophrenia, and normal individuals, were determined by (3)H-ouabain binding assay. Alpha isoforms were quantified by Western blotting. Brain DLC were measured using sensitive enzyme linked immunosorbant assay (ELISA). The effects of ouabain and ouabain-antibodies on behavior were determined in two animal models of depression.

RESULTS

(3)H-ouabain binding in bipolar patients was significantly lower than in major depressed and schizophrenic patients. Na(+), K(+)-ATPase alpha isoforms in synaptosomal fractions were not different among the groups. DLC levels in the parietal cortex of bipolar patients were significantly higher than in normal individuals and depressed patients. Injection of lipopolysaccharide (intraperitoneally) to rats elicited depression-like symptoms, which were significantly attenuated by pre-injection of ouabain-antibodies. Injection of ouabain and ouabain-antibodies (intracerebroventricular) reduced depression-like symptoms in the forced swimming test in rats.

CONCLUSIONS

The results support the possibility that Na(+), K(+)-ATPase and endogenous DLC participate in the pathogenesis of depressive disorders.

Reduced NMDA receptor tyrosine phosphorylation in PTPalpha-deficient mouse synaptosomes is accompanied by inhibition of four src family kinases and Pyk2: an upstream role for PTPalpha in NMDA receptor regulation

Mice lacking protein tyrosine phosphatase alpha (PTPalpha) exhibited defects in NMDA receptor (NMDAR)-associated processes such as learning and memory, hippocampal neuron migration, and CA1 hippocampal long-term potentiation (LTP). In vivo molecular effectors linking PTPalpha and the NMDAR have not been reported. Thus the involvement of PTPalpha as an upstream regulator of NMDAR tyrosine phosphorylation was investigated in synaptosomes of wild-type and PTPalpha-null mice. Tyrosine phosphorylation of the NMDAR NR2A and NR2B subunits was reduced upon PTPalpha ablation, indicating a positive effect of this phosphatase on NMDAR phosphorylation via intermediate molecules. The NMDAR is a substrate of src family tyrosine kinases, and reduced activity of src, fyn, yes and lck, but not lyn, was apparent in the absence of PTPalpha. In addition, autophosphorylation of proline-rich tyrosine kinase 2 (Pyk2), a tyrosine kinase linked to NMDAR signaling, was also reduced in PTPalpha-deficient synaptosomes. Altered protein tyrosine phosphorylation was not accompanied by altered expression of the NMDAR or the above tyrosine kinases at any stage of PTPalpha-null mouse development examined. In a human embryonic kidney (HEK) 293 cell expression system, PTPalpha enhanced fyn-mediated NR2A and NR2B tyrosine phosphorylation by several-fold. Together, these findings provide evidence that aberrant NMDAR-associated functions in PTPalpha-null mice are due to impaired NMDAR tyrosine phosphorylation resulting from the reduced activity of probably more than one of the src family kinases src, fyn, yes and lck. Defective NMDAR activity in these mice may also be linked to the loss of PTPalpha as an upstream regulator of Pyk2.

Acetylcholinesterase Activity in Rats Experimentally Demyelinated with Ethidium Bromide and Treated with Interferon Beta

The ethidium bromide (EB) demyelinating model was associated with interferon beta (IFN-beta) to evaluate acetylcholinesterase (AChE) activity in the striatum (ST), hippocampus (HP), cerebral cortex (CC), cerebellum (CB), hypothalamus (HY), pons (PN) and synaptosomes from the CC. Rats were divided into four groups: I control (saline), II (IFN-beta), III (EB) and IV (EB and IFN-beta). After 7, 15 and 30 days rats (n = 6) were sacrificed, and the brain structures were removed for enzymatic assay. AChE activity was found to vary in all the brain structures in accordance with the day studied (7-15-30 days) (P < 0.05). In the group III, there was an inhibition of the AChE activity in the ST, CB, HY, HP and also in synaptosomes of the CC (P < 0.05). It was observed that IFN-beta per se was capable to significantly inhibit (P < 0.05) AChE activity in the ST, HP, HY and synaptosomes of the CC. Our results suggest that one of the mechanisms of action of IFN-beta is through the inhibition of AChE activity, and EB could be considered an inhibitor of AChE activity by interfering with cholinergic neurotransmission in the different brain regions.

Age-associated changes of insulin action on the hydrolysis of diacylglycerol generated from phosphatidic acid

Age-related changes in insulin action on diacylglycerol (DAG) degradation was studied in rat cerebral cortex synaptosomes. The generation of monoacylglycerol (MAG) and water soluble products (WSP, glycerol plus glycerol-3-phosphate) from DAG was studied in cerebral cortex (CC) synaptosomes from adult (4-month-old) and aged (28-month-old) rats. Additionally, the effect of porcine insulin and tyrosine phosphorylation was evaluated in the same group of animals. In this study we demonstrate that the age-related increase in WSP generation was accompanied by unmodified MAG levels. In the presence of diacylglycerol lipase (DAG lipase) inhibitor, RHC-80267, a lower inhibitory effect on MAG production was observed in CC synaptosomes from aged rats with respect to that in adult membranes. Under these experimental conditions, WSP formation was only diminished in aged membranes. Insulin stimulated MAG and WSP formation at long incubation times (30 min) in adult animals, while it had an inhibitory effect in aged animals. Insulin plus vanadate (as tyrosine-phosphatase inhibitor) inhibited MAG production at short incubation times whereas the same effect was observed in aged animals at long times of incubation. WSP formation was stimulated by insulin plus vanadate both in adult and aged animals at 30 min of incubation. Our results show that insulin differentially modulates MAG and WSP production from exogenous PA in CC synaptosomes from aged rats compared with adult rats.

[Mechanisms of diabetes-induced impairements of serotonin release from rat brain synaptosomes: effect of nicotinamide]

It has been previously shown that diabetes-associated central nervous system abnormalities are characterized by progressive alterations of neurotransmission. In particular, recent studies from our group have demonstrated that more early diabetes is accompanied by the increased spontaneous serotonin release from isolated synaptic endings; however the mechanism is still not clear. The current study was undertaken to estimate the relative importance of membrane potential and extracellular Ca2+ in the serotonin secretion process in diabetes. With the premise that increased phosphorylation of target proteins may be responsible for the increase in transmitter release we tested whether cAMP/PKA-mediated phosphorylations as well as mono-ADP-ribosylation of effector proteins were implicated in diabetes-associated brain failures. In addition, the effects of nicotinamide, a multiple-action compound, were examined. It was shown that diabetes caused a significant increase in spontaneous release of [2-(14)C]serotonin that was accompanied by synaptic membranes depolarization. Omission of Ca2+ from the incubation medium largely inhibited serotonin release only in untreated diabetes. Exposure of diabetic synaptosomes to cAMP-dependent protein kinase inhibitor H89, similar to Ca2+ -free medium, downregulated serotonin release. The level of constitutively mono-ADP-ribosylated proteins of diabetic synaptosomes was elevated vs control. Protein mono-ADP-ribosylation induced by cholera toxin (CTX), activator of Gs-protein-coupled adenylyl cyclase, resulted in excessive 1.2-fold enhancement over basal level but to the less extent in diabetes as compared with that of control. Nevertheless, CTX as well as forskolin exerted more strong stimulating effect on serotonin release from diabetic synaptosomes as compared to control. H89 counteracted CTX-related action on this variable strongly suggesting that impaired serotonin release is, at least, dependent on Gs-protein-mediated phosphorylation. Nicotinamide treatment virtually normalized both protein mono-ADP-ribosylation and serotonin release as well as synaptosomal response to all stimuli used. The data suggest that alterations in protein mono-ADP-ribosylation may be involved as a possible mechanism responsible for the impaired neurotransmission in diabetes and nicotinamide may efficiently protect against ADP-ribosylationmediated abnormalities in brain function.

Rab3 GTPase-activating protein regulates synaptic transmission and plasticity through the inactivation of Rab3

Rab3A small G protein is a member of the Rab family and is most abundant in the brain, where it is localized on synaptic vesicles. Evidence is accumulating that Rab3A plays a key role in neurotransmitter release and synaptic plasticity. Rab3A cycles between the GDP-bound inactive and GTP-bound active forms, and this change in activity is associated with the trafficking cycle of synaptic vesicles at nerve terminals. Rab3 GTPase-activating protein (GAP) stimulates the GTPase activity of Rab3A and is expected to determine the timing of the dissociation of Rab3A from synaptic vesicles, which may be coupled with synaptic vesicle exocytosis. Rab3 GAP consists of two subunits: the catalytic subunit p130 and the noncatalytic subunit p150. Recently, mutations in p130 were found to cause Warburg Micro syndrome with severe mental retardation. Here, we generated p130-deficient mice and found that the GTP-bound form of Rab3A accumulated in the brain. Loss of p130 in mice resulted in inhibition of Ca(2+)-dependent glutamate release from cerebrocortical synaptosomes and altered short-term plasticity in the hippocampal CA1 region. Thus, Rab3 GAP regulates synaptic transmission and plasticity by limiting the amount of the GTP-bound form of Rab3A.

Apyrase and 5'-nucleotidase activities in synaptosomes from the cerebral cortex of rats experimentally demyelinated with ethidium bromide and treated with interferon-beta

Apyrase and 5'-nucleotidase activities were analyzed in an ethidium bromide (EB) demyelinating model associated with interferon-beta (IFN-beta). The animals were divided in groups: I, control (saline); II, saline and IFN-beta; III, EB and IV, EB and IFN-beta. After 7, 15 and 30 days the animals (n = 5) were sacrificed and the cerebral cortex was removed for synaptosome preparation and enzymatic assays. Apyrase activity using ATP as substrate increased in groups II, III and IV (P < 0.001) after 7 days and in groups III and IV (P < 0.001) after 15 days. Using ADP as substrate, an activation of this enzyme was observed in group III (P < 0.05) after seven and 15 days. The 5'-nucleotidase activity increased in group III (P < 0.05) after 7 days and in groups II, III and IV (P < 0.001) after 15 days. After 30 days treatment, no significant alteration was observed in enzyme activities. Results showed that apyrase and 5'-nucleotidase activities are altered in demyelination events and that IFN-beta was able to regulate the adenine nucleotide hydrolysis.

Cellular and subcellular localization of PDE10A, a striatum-enriched phosphodiesterase

PDE10A is a recently identified phosphodiesterase that is highly expressed by the GABAergic medium spiny projection neurons of the mammalian striatum. Inhibition of PDE10A results in striatal activation and behavioral suppression, suggesting that PDE10A inhibitors represent a novel class of antipsychotic agents. In the present studies we further elucidate the localization of this enzyme in striatum of rat and cynomolgus monkey. We find by confocal microscopy that PDE10A-like immunoreactivity is excluded from each class of striatal interneuron. Thus, the enzyme is restricted to the medium spiny neurons. Subcellular fractionation indicates that PDE10A is primarily membrane bound. The protein is present in the synaptosomal fraction but is separated from the postsynaptic density upon solubilization with 0.4% Triton X-100. Immuno-electron microscopy of striatum confirms that PDE10A is most often associated with membranes in dendrites and spines. Immuno-gold particles are observed on the edge of the postsynaptic density but not within this structure. Our studies indicate that PDE10A is associated with post-synaptic membranes of the medium spiny neurons, suggesting that the specialized compartmentation of PDE10A enables the regulation of intracellular signaling from glutamatergic and dopaminergic inputs to these neurons.

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.

The CD38-independent ADP-ribosyl cyclase from mouse brain synaptosomes: a comparative study of neonate and adult brain

cADPR (cADP-ribose), a metabolite of NAD+, is known to modulate intracellular calcium levels and to be involved in calcium-dependent processes, including synaptic transmission, plasticity and neuronal excitability. However, the enzyme that is responsible for producing cADPR in the cytoplasm of neural cells, and particularly at the synaptic terminals of neurons, remains unknown. In the present study, we show that endogenous concentrations of cADPR are much higher in embryonic and neonate mouse brain compared with the adult tissue. We also demonstrate, by comparing wild-type and Cd38-/- tissues, that brain cADPR content is independent of the presence of CD38 (the best characterized mammalian ADP-ribosyl cyclase) not only in adult but also in developing tissues. We show that Cd38-/- synaptosome preparations contain high ADP-ribosyl cyclase activities, which are more important in neonates than in adults, in line with the levels of endogenous cyclic nucleotide. By using an HPLC method and adapting the cycling assay developed initially to study endogenous cADPR, we accurately examined the properties of the synaptosomal ADP-ribosyl cyclase. This intracellular enzyme has an estimated K(m) for NAD+ of 21 microM, a broad optimal pH at 6.0-7.0, and the concentration of free calcium has no major effect on its cADPR production. It binds NGD+ (nicotinamide-guanine dinucleotide), which inhibits its NAD+-metabolizing activities (K(i)=24 microM), despite its incapacity to cyclize this analogue. Interestingly, it is fully inhibited by low (micromolar) concentrations of zinc. We propose that this novel mammalian ADP-ribosyl cyclase regulates the production of cADPR and therefore calcium levels within brain synaptic terminals. In addition, this enzyme might be a potential target of neurotoxic Zn2+.

Differential regulation of proteasome activity in the nucleus and the synaptic terminals

Proteasome is a multi-subunit proteolytic complex that degrades proteins covalently linked to multiple molecules of ubiquitin. Earlier studies showed a role for the ubiquitin-proteasome pathway in several models of long-term memory and other forms of synaptic plasticity. In Aplysia, the ubiquitin-proteasome pathway has been shown to contribute to the induction of long-term facilitation. In other model systems, ubiquitin-proteasome-mediated proteolysis has also been shown to play a role in synapse development. Previous studies of synaptic plasticity focused on changes in components or the substrates of the ubiquitin-proteasome pathway in whole neurons. Modification of specific synapses would require precise spatial and temporal regulation of the components of the ubiquitin-proteasome pathway within the subcellular compartments of neurons during learning. As a first step towards testing the idea of local regulation of the ubiquitin-proteasome pathway in neurons, we investigated proteasome activity in nuclear and synaptosomal fractions. Here we show that proteasome activity in the synaptic terminals is higher compared to the activity in the nucleus in the Aplysia nervous system as well as in the mouse brain. Furthermore, the proteasome activity in the two neuronal compartments is differentially modulated by protein kinases. Differential regulation of proteasome activity in neuronal compartments such as the synaptic terminals is likely to be a key mechanism underlying synapse-specific plasticity.

[Comparative study of molecular mechanisms of natural and synthetic polycationic peptides action on the activity of the adenylyl cyclase signaling system]

The molecular mechanisms of action of natural and synthetic polycationic peptides, forming amphiphilic helices, on the heterotrimeric G-proteins and enzyme adenylyl cyclase (AC), components of hormone-sensitive AC system, were studied. It is shown that synthetic peptides C-epsilonAhx-WKK(C10)-KKK(C10)-KKKK(C10)-YKK(C10)-KK (peptide I) and (GRGDSGRKKRRQRRRPPQ)2-K-epsilonAhx-C(Acm)(peptide II) in dose-dependent manner stimulate the basal AC activity, inhibit forskolin-stimulated AC activity and decrease both stimulating and inhibiting AC effects of the hormones in the tissues (brain striatum, heart muscle) of rat and in smooth muscles of the mollusc Anodonta cygnea. AC effects of these peptides are decreased after membrane treatment by cholera and pertussis toxins and are inhibited in the presence of the peptides, corresponding to C-terminal regions 385-394 alphas- and 346-355 alphai2-subunits of G-proteins. These data give evidence that the peptides I and II act on the signaling pathways which are realized through Gs- and Gi-proteins. At the same time, natural polycationic peptide mastoparan acts on AC system through Gi-proteins and blocks hormonal signals mediated via Gi-proteins only. Consequently, the action of mastoparan on G-proteins is selective and differs from the action of the synthetic peptides. It is also shown that peptide II, with branched structure, directly interacts not only with G-proteins (less effective in comparison with peptide I with hydrophobic radicals and mastoparan), but also with enzyme AC, the catalytic component of AC system. On the basis of data obtained the following conclusions were made: 1) the formation of amphiphilic helices is not enough for selective activation of G-protein by polycationic peptides, and 2) the primary structure of the peptides, the distribution of positive charged amino acids and hydrophobic radicals in them are very important for selective interaction between polycationic peptides and G-proteins.