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M Samochocki

Publications and source records attributed to M Samochocki.

15 recordsLinked to original sources
PubMed1998

Aging and beta-amyloid peptides decrease cholinergic receptor-mediated calcium increase in brain cortex synaptoneurosomes.

In this study, the muscarinic cholinergic receptor (MAChR)-evoked inositol 1,4,5-trisphosphate (IP3)-mediated increase of cytosolic calcium concentration ([Ca]i) in synaptoneurosomes from brain cortex of adult and aged rats was investigated. In addition, the effect of two beta-amyloid (A beta) peptides, 1-28 and 25-35, on the resting and MAChR-induced increase of [Ca]i in brain cortex synaptoneurosomes of adult rats was evaluated. Release of IP3 was measured after prelabeling of synaptoneurosomal phosphoinositides with myo-[2-3H]inositol. Changes in [Ca]i were monitored by using fura-2 indicator. The effect of A beta peptides was evaluated following their preincubation with synaptoneurosomal protein for 1, 5, 30 and 60 min. It was observed that in brain cortex synaptoneurosomes from aged rats, Ca(2+)-dependent and MAChR-mediated IP3 production was not changed in comparison with that estimated in adult brain, over 60 min of incubation. Activation of MAChR in synaptoneurosomes from brain cortex of adult rats for 10 min increased [Ca]i by about 60% over its resting level (240 nM). This increase was completely blocked by muscarinic antagonists, atropine and pirenzepine, as well as by the antagonist of IP3 receptor, 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate (TMB-8). In aged brain, there was no detectable change in resting [Ca]i (165 nM) due to MAChR stimulation. The 25-35 A beta peptide caused a time-dependent significant increase of resting [Ca]i in synaptoneurosomes from brain cortex of adult rats, which was almost five-fold after 60 min. In the same conditions, the action of 1-28 A beta peptide was statistically insignificant up to 30 min, then a rapid increase of resting [Ca]i by two-fold was observed up to 60 min. Both A beta peptides decreased markedly the MAChR-dependent elevation of [Ca]i in respect to control (resting [Ca]i) in synaptoneurosomes from brain cortex of adult rats. These results indicate that beta-amyloid 1-28 and 25-35 peptides may be involved in alteration of muscarinic receptor-mediated signal transduction during brain aging.

Aging↗
PubMed1996

Nitric oxide responsible for NMDA receptor-evoked inhibition of arachidonic acid incorporation into lipids of brain membrane.

The activation of the glutamatergic NMDA receptor has no effect on arachidonic acid release from cortical synaptoneurosomal lipids prelabeled with [1-14C]arachidonic acid ([14C]AA). However, activation of NMDA receptor leads to the reduction of AA incorporation into rat brain cortex synaptoneurosomal membrane phosphatidylinositol (PI). The competitive NMDA receptor antagonist, 2-amino-5-phosphovaleric acid (APV), completely eliminates the effect of NMDA on this process. More precise analysis of the sequence of events leading to NMDA-induced decrease of AA incorporation indicates that this process is significantly blocked by voltage-gated sodium and calcium channels inhibitors, such as tetrodotoxin (TTX) and omega-conotoxin (CTX), respectively. Then the antagonist of inositol trisphosphate receptor, TMB-8, totally abolishes the effect of NMDA on AA incorporation into PI. The lowering of AA incorporation evoked by NMDA is significantly diminished by nitric oxide (NO) synthase inhibitor, NG-nitro-L- arginine (NNLA). Further studies were carried out with NO donor(s) to explain the mechanism of NO action in the inhibition of AA incorporation into PI. Our results suggest the following sequence of events: opening of voltage-dependent sodium and calcium channels, subsequent activation of PI-4,5-bisphosphate-specific phospholipase C (PLC), elevation of inositol trisphosphate (IP3)-sensitive calcium ions, stimulation of NO production and NO-mediated S-nitrosylation, or free radical effect on enzymes involved in AA incorporation. Our data suggest that NO-mediated events may be responsible for NMDA-evoked inhibition of AA incorporation into PI of synaptoneurosomal membrane.

2-Amino-5-phosphonovalerate↗
PubMed1996

Activation of serotonergic 5-HT1A receptor reduces Ca(2+)- and glutamatergic receptor-evoked arachidonic acid and No/cGMP release in adult hippocampus.

Stimulation of glutamatergic NMDA receptor in adult rat hippocampal synaptoneurosomes induces statistically significant Ca(2+)-dependent liberation of arachidonic acid (AA) and nitric oxide (NO)-activated cGMP synthesis. NMDA acting for 5 min at 100 microM markedly increases, by approx. 25%, Ca(2+)-mediated AA release from phospholipids of hippocampal synaptoneurosomes. Prolonged stimulation of NMDA receptor up to 10 min has smaller stimulatory effect and enhances AA release by about 6%. Moreover, NMDA activates NO-dependent cGMP production by approx. 5 times more than the Ca2+ itself. Release of both these second messengers is completely blocked by the competitive NMDA antagonist, APV (100 microM). The NMDA-mediated cGMP elevation completely depends on NO action, and is abolished by the specific inhibitor of NO synthase, NG-nitro-L-arginine. Moreover, serotonin at 10 microM in the presence of 10 microM pargyline, potently decreases both Ca(2+)- and NMDA receptor-mediated AA and cGMP release in hippocampal synaptoneurosomes. The agonist of 5-HT1A receptor, buspirone, in a way similar to serotonin itself, counteracts the Ca(2+)- and also NMDA receptor-evoked AA release and cGMP accumulation. An antagonist of 5-HT1A receptor, NAN-190, eliminates the effect of serotonin and buspirone on AA and NO/cGMP liberation. An antagonist of serotonergic 5-HT2 receptor, ketanserin, has no effect on the Ca2+ and serotonin action. These results indicate that serotonin, through 5-HT1A receptor, potently antagonizes the action of excitatory amino acid for AA release and NO/cGMP synthesis in the adult rat hippocampus. In conclusion, the interaction of serotonin with the glutamatergic system in the hippocampus may play an important role in the modulation of a signal transduction pathway, and by this molecular mechanism serotonin may exert a neuroprotective effect on hippocampal neurons.

2-Amino-5-phosphonovalerate↗
PubMed1995

The negative coupling between serotonin and muscarinic receptor(s) for arachidonic acid and inositol phosphates release in brain cortex synaptoneurosomes. Effect of aging.

In the present study we have investigated the relationship between serotonergic receptor(s) (5-HTR) and muscarinic cholinergic receptor (mAChR) activation, leading to the arachidonic acid (AA) release and inositol phosphates (IPs) formation in adult and aged brain cortex synaptoneurosomes. It was observed that serotonin (5-HT) almost completely inhibits carbachol-stimulated AA release in adult brain. This negative coupling between 5-HTR and mAChR probably depends on the direct stimulation of the acylation reaction coupled with 5-HT1AR. In the aged brain this type of interaction does not occur because aging eliminates carbachol and 5-HT effect. On the other hand, in aged brain, both 5-HT and carbachol more actively stimulate IPs accumulation than in adult brain. Serotonin inhibits carbachol-stimulated IPs release to the level observed during 5-HT2R activation. Our study indicates for the first time, the negative coupling between 5-HTR and mAChR for AA liberation in adult brain and a lack of this kind of receptors interaction in senescent brain. In adult brain, 5-HT1AR-stimulated AA incorporation is responsible for this coupling. Moreover, serotonin through the stimulation of 5-HT2R, suppresses mAChR-dependent IPs liberation in adult and aged brain similarly. The interactions between these two neurotransmitter receptors lead to the modification of lipid mediators formation and may have important implications in alteration of signal transduction in adult and in aged brain.

Aging↗
PubMed1994

Aging modulates calcium-dependent phosphatidylinositol degradation by cerebral cortex synaptic plasma membrane phospholipases.

The synaptic plasma membrane (SPM) and cytosol fractions from cerebral cortex of adult (4-mo-old) and aged (27-mo-old) rats were used as a source of phospholipase A2 (PLA2) and phospholipase C (PLC). The activity of PLC acting on [3H-inositol]phosphatidylinositol ([3H]PtdIns) was investigated in the presence of endogenous and 2 mM Ca2+. Arachidonic acid (AA) release was studied in the same conditions, using 1-stearoyl-[2-14C]arachidonyl-sn-glycerophosphoinositol ([14C]PtdIns) as a substrate. In the presence of endogenous Ca2+ (i.e., no added Ca2+) SPM-bound PLC and PLA2 or diacylglycerol (DAG) lipase of aged brain exert significantly higher activity in degradation of PtdIns as compared to their activities in adult brain. Moreover, these enzymes of aged brain are less or not further activated by 2 mM Ca2+, contrary to the enzymes isolated from adult brain. The activity of cytosolic enzymes involved in degradation [3H]PtdIns and [14C]PtdIns and their regulation by Ca2+ ions are not significantly changed in senescent cerebral cortex as compared to the adult. The intracellular calcium concentration ([Ca2+]i), measured with fura-2, is lower in aged brain compared to adult brain, which may suggest the modification in Ca2+ ion redistribution in aged brain and probably its higher concentration in membranes. These results indicate that aging modifies significantly the activity of membrane-bound, Ca(2+)-dependent phospholipase(s) degrading PtdIns, which may be connected with alteration of Ca2+ ion redistribution and may influence the formation and accumulation of very potent lipid messengers as diacylglycerol, lysophospholipid, and arachidonic acid, known to be involved in neurotransmission processes.

Aging↗
PubMed1994

Serotonin, a potent modulator of arachidonic acid turnover, interaction with glutamatergic receptor in brain cortex.

Brain cortex synaptoneurosomes actively incorporated [14C]arachidonic acid (AA) into lipids. Serotonin (5-HT), at a concentration range of 10 microM-1 mM, significantly stimulates the incorporation of AA mainly into phosphatidylinositol (PI) of brain cortex synaptoneurosomes. The stimulation rate of AA incorporation by 5-HT was the same in the presence and absence of lysophosphatidylinositol (LPI). However, in the absence of LPI some stimulation of AA uptake was also observed into phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid. Buspirone, an agonist of 5-HT1A receptor, has a similar effect on AA incorporation into membrane lipids as serotonin itself. Moreover, ketanserin, an antagonist of 5-HT2 receptor, also induces activation of AA incorporation into membrane lipids. On the other hand, glutamate, in a concentration dependent manner, significantly inhibits AA uptake into PI and also has some inhibitory action on AA uptake into the other lipids. Serotonin itself and the agonist of 5-HT1A receptor through the activation of AA turnover counteract glutamate-induced inhibition of AA uptake into lipids of brain cortex. Our results indicated that serotonin directly, through the specific receptors, or indirectly, through the interaction with glutamatergic receptors, modulates turnover and the level of arachidonic acid in the brain.

Animals↗
PubMed1994

Aging diminishes serotonin-stimulated arachidonic acid uptake and cholinergic receptor-activated arachidonic acid release in rat brain cortex membrane.

Synaptoneurosomal and synaptosomal fractions from the brain cortex of adult (4-month-old) and aged (27-month-old) rats were used for studies on the uptake and subsequent release of [14C]arachidonic acid ([14C]AA) from brain lipids. The incorporation of AA and the pattern of its uptake into lipids of the aged brain cortex synaptoneurosomes and synaptosomes were not significantly different when compared with those in the adult brain cortex fractions. Serotonin (5-HT), at 10 microM to 1 mM in the presence of pargyline and the agonist of the 5-HT1A receptor, buspirone, stimulated AA uptake into membrane lipids, mainly into phosphatidylinositol, by about 40% exclusively in adult brain synaptoneurosomes. Aging significantly diminished the effect of 5-HT on AA uptake. Synaptoneurosomal and synaptosomal fractions prelabeled with [14C]AA were used subsequently for investigation of voltage-dependent, muscarinic and 5-HT receptor-mediated AA release. Aging diminished markedly carbachol-stimulated Ca(2+)-dependent AA liberation from membrane lipids of synaptoneurosomes and synaptosomes. Moreover, aging decreased voltage-dependent and 5-HT2 receptor-mediated AA release. These results show that aging affects receptor-dependent AA uptake and pre- and postsynaptic receptor-mediated AA release. These modulations of AA incorporation and release in aged brain may be of pathophysiological significance, in view of the importance of these processes for signal transmission in the brain. The changes of receptor-dependent processes of deacylation and reacylation may be responsible for alteration in the function of neuronal cells and may affect learning and memory ability and brain plasticity during aging.

Aging↗
PubMed1994

Age-related changes of GABA-activated chloride channel properties in brain cortex synaptic plasma membrane: evidence for phospholipase involvement.

Brain aging decreases binding of tert-butylbicyclophosphorothionate (TBPS), a specific ligand for Cl- channels, but has no effect on Cl- influx. Detailed studies on the kinetics of TBPS dissociation allowed the characterization of Cl- channel properties. Aging lowers, exclusively in the presence of GABA agonist, muscimol, the half-life of the fast phase of TBPS dissociation, indicating an opening time of receptor-dependent Cl- channels shorter than that in adult brain. The half-life of the slow phase of TBPS dissociation is significantly lower in aged brain in the presence and absence of muscimol. These results suggest a sustained Cl- current, including also the other channel(s) not connected with GABAA receptor activation. The analysis of biphasic TBPS dissociation demonstrates a lowered number of binding sites resulted in the reduction of the number of Cl- channels in the "open" state. This may explain an observed decrease of TBPS binding in aged brain. One of the possible factors involved in modification of GABAA receptor behavior during aging may be arachidonic acid or diacylglycerol, known to be accumulated in aged brain. The action of these compounds on the Cl- channel, observed in this study, correlates well with the effect of aging.

Aging↗
PubMed1993

Modulatory action of arachidonic acid on GABAA/chloride channel receptor function in adult and aged brain cortex membranes.

Effect of arachidonic acid on binding parameters of two binding sites on the GABAA receptor and on GABA activated Cl- uptake was investigated in synaptic plasma membrane and in synaptoneurosomes from brain cortex of adult (4-months old) and aged (27-months old) rats. The ligands used were [3H]muscimol, a GABA agonist and [35S]-t-butylbicyclophosphorothionate ([35S]TBPS), a convulsant that binds to the site near the chloride channel. Arachidonic acid increases significantly GABAA agonist binding and concomitantly decreases [35S]TBPS binding in a concentration dependent manner. The analysis of binding parameters in adult brain showed a significant decrease by AA of KD value for low but not for high affinity of [3H]muscimol binding. Concomitantly, AA enhances Bmax values for high affinity binding and has no effect on Bmax value for low affinity binding in synaptic plasma membrane (SPM) from adult brain. In synaptic plasma membrane from aged brain AA increases low and high affinity binding of agonist to GABAA receptor, modified significantly KD value by about 30 and 66%, respectively. On the other hand, AA significantly decreases of [35S]TBPS binding to chloride channel recognition site. Scatchard's analysis indicates that this inhibition results from a decrease of total number of binding sites. Moreover, the affinity of [35S]TBPS binding was increased (KD = 37.0 nM for AA-treated membrane, as compared to 69.3 nM KD in control membrane). GABA-dependent chloride uptake into synaptoneurosomes is also inhibited by AA in a concentration dependent manner in adult brain. In aged brain synaptoneurosomes AA has similar inhibitory effect on GABA-activated chloride uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1992

Carbachol-stimulated release of arachidonic acid and eicosanoids from brain cortex synaptoneurosome lipids of adult and aged rats.

Synaptoneurosomes from the brain cortex of adult rats (4 months old) and aged rats (27 months old), prelabeled with [14C]arachidonic acid (AA), were used as the source of enzyme(s) and substrates to study the effect of a cholinergic agonist on the release of AA and eicosanoids. In synaptoneurosomes from adult brains, carbachol, the nonhydrolyzable analog of acetylcholine, increased AA release by 16% in the presence of 2 mM calcium. This agonist-mediated AA release occurred specifically from phosphatidylinositol (PI). Concomitantly, carbachol in the presence of 2 mM Ca2+ significantly activated the formation of 15-HETE and PGF2 alpha. This effect of carbachol on the level of eicosanoids was also observed in the presence of endogenous calcium. In synaptoneurosomes from aged brains, carbachol had no effect on the release of AA and eicosanoids. The results of studies involving inhibitors of phospholipase A2 (PLA2) and phospholipase C (PLC) suggested that PLA2 is almost completely responsible for the Ca(2+)-dependent, carbachol-mediated AA liberation. The distribution of labeled AA in the lipids after incubation of synaptoneurosomes in the presence of 2 Mm Ca2+ and carbachol indicated that in aged synaptoneurosomes, the muscarinic receptor-mediated degradation of phosphoinositides through phospholipase C is preserved, but the turnover of the phosphoinositide cycle is probably suppressed. These results indicate that aging significantly affects the population of cholinergic-muscarinic receptors coupled to PLA2.

Aging↗
PubMed1991

Ca(2+)-independent, Ca(2+)-dependent, and carbachol-mediated arachidonic acid release from rat brain cortex membrane.

Synaptoneurosomes obtained from the cortex of rat brain prelabeled with [14C]arachidonic acid [( 14C]AA) were used as a source of substrate and enzyme in studies on the regulation of AA release. A significant amount of AA is liberated in the presence of 2 mM EGTA, independently of Ca2+, primarily from phosphatidic acid and polyphosphoinositides (poly-PI). Quinacrine, an inhibitor of phospholipase A2 (PLA2), suppressed AA release by about 60% and neomycin, a putative inhibitor of phospholipase C (PLC), reduced AA release by about 30%. An additive effect was exhibited when both inhibitors were given together. Ca2+ activated AA release. The level of Ca2+ present in the synaptoneurosomal preparation (endogenous level) and 5 microM CaCl2 enhance AA liberation by approximately 25%, whereas 2 mM CaCl2 resulted in a 50% increase in AA release relative to EGTA. The source for Ca(2+)-dependent AA release is predominantly phosphatidylinositol (PI); however, a small pool may also be liberated from neutral lipids. Carbachol, an agonist of the cholinergic receptor, stimulated Ca(2+)-dependent AA release by about 17%. Bradykinin enhanced the effect of carbachol by about 10-15%. This agonist-mediated AA release occurs specifically from phosphoinositides (PI + poly-PI). Quinacrine almost completely suppresses calcium-and carbachol-mediated AA release. Neomycin inhibits this process by about 30% and totally suppresses the effect of bradykinin. Our results indicate that both phospholipases PLA2 and PLC with subsequent action of DAG lipase are responsible for Ca(2+)-independent AA release. Ca(2+)-dependent and carbachol-mediated AA liberation occurs mainly as the result of PLA2 action. A small pool of AA is probably also released by PLC, which seems to be exclusively responsible for the effect of bradykinin.

Animals↗
PubMed1990

Brain ischemia increased high affinity binding of [3H]muscimol into synaptic plasma membrane receptor.

The authors investigated the high affinity binding of [3H] muscimol to the receptor of synaptic plasma membranes (SPM) isolated from a normoxic and ischemic brain. Brain ischemia enhanced the [3H] muscimol binding to the receptor, located in native (Triton X-100 untreated) membranes. Scatchard's analysis showed that the total number of binding sites (BMAX) and the KD value increased by about 60%. The higher KD value persisted during 20 min of the reperfusion period. Concomitantly, ischemia stimulated the activity of phospholipase C and phospholipase A2, acting against phosphatidylinositol (PI). The degradation of PI and a transient accumulation of docosahexaenoic and arachidonic acids may be important factors involved in the modification of high affinity agonist binding to the GABAA receptor of SPM isolated from the brain submitted to ischemia.

Animals↗
PubMed1990

Regulation of arachidonic acid release by enzyme(s) of rat brain cortex.

Brain cortex membranes labeled with [14C]arachidonic acid were used as the source of substrate and enzyme for the assay of arachidonic acid (AA) liberation. A significant amount of AA was released Ca2(+)-independently, mainly from phosphatidic acid, polyphosphoinositides and phosphatidylserine. Quinacrine, inhibitor of phospholipase A2 (PLA2), suppressed AA release by 60% and neomycin, inhibitor of phospholipase C (PLC) by about 30%. Both inhibitors applied together have an additive effect. Physiological calcium level elevated AA liberation by 50%, whereas 2 mM calcium enhanced this process by a further 30%. Carbachol, exclusively in the presence of calcium, activated AA release selectively from phosphatidylinositol and diglycerides. We suggest that Ca2(+)-independent PLA2 and PLC play an important role in AA liberation, and that physiological increments of calcium may have serious implications.

Arachidonic Acid↗
PubMed1989

Dolichol alters GABA uptake and high affinity binding of agonist to rat brain synaptic plasma membranes.

The effects of dolichol on high affinity [3H]muscimol binding to synaptic plasma membrane (SPM) and [3H]GABA uptake into synaptosomes from rat brain were analyzed. Membranes were enriched with dolichol, by preincubation, in the presence of bovine serum albumin (BSA) as a vehicle (40-100 micrograms of dolichol/mg protein + 5% BSA). The rate of dolichol incorporation into the membrane was determined using [1-3H]dolichol C95, and it was in the range of 5-7 nmol/mg protein/h for synaptosomes and SPM, respectively. The uptake of [3H]GABA into synaptosomes enriched with dolichol decreased significantly by about 30%. Dolichol alone added into the incubation medium produced only a negligible effect. Specific binding of [3H]muscimol, which was higher than 90% of total binding, was significantly reduced to SPM enriched with dolichol as compared to controls. The Kd of the high affinity sites was significantly elevated by about 30% in SPM enriched with dolichol (10.8 +/- 0.3 nM vs 7.3 +/- 0.2 nM in control). This difference was more pronounced for SPM isolated from cerebellum (Kd increased by about 50%). The Bmax value was not changed. Dolichol alone did not alter the agonist binding. These results indicate for the first time that the higher level of dolichol in SPM might influence the GABAergic transmission system. An increase in dolichols in membranes may be an important factor in the decline of brain function during aging.

Animals↗