Biomedical subjects

J Strosznajder

Publications and source records attributed to J Strosznajder.

At least 37 records · Page 2Linked to original sources

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↗

PubMed1992

Uptake and subcellular distribution of intraventricularly injected [1-3H]dolichol in rat brain.

The uptake of C95[1-3H]dolichol in the form of liposomes into rat brain after the intracerebral and intraperitoneal injection was investigated. Efficient, time-dependent uptake of dolichol into the brain was observed exclusively after the intraventricular injection. Within 24 h after the injection about 10% of the applied dolichol was found in the brain and 1.5% in liver. The distribution of dolichol in various parts of rat brain decreased in the order: cerebellum greater than midbrain greater than grey matter and brain stem greater than white matter. Seven days after the injection total radioactivity in the brain decreased and concomitantly a significant increase was observed in blood circulating and liver of the rat. The highest activity was found in grey matter and it remained a few times higher in comparison with that in white matter. About 80% of the dolichol taken up by the brain membrane was recovered in the following subcellular fractions: crude nuclear fraction greater than microsomes greater than mitochondria greater than synaptosomes greater than myelin. These results demonstrate for the first time that dolichol is actively taken up by the brain membrane exclusively after intraventricular injection of dolichol-phosphatidylcholine in the form of liposomes; this method may be useful in studies on the role of dolichol in brain function.

Animals↗

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

Synaptic vesicle-bound phospholipase(s) acting on phosphatidylinositol exhibit(s) high susceptibility to brain ischemia.

The activity of phospholipase C acting against [3H]-inositol-phosphatidylinositol (PI) and the activity of arachidonic acid (AA) release from [1-14C]arachidonoyl-phosphatidylinositol by enzyme(s) located in synaptic vesicles (SV) isolated from normoxic and ischemic brains was investigated. Brain ischemia significantly activated phospholipase C (PhLC) by about 90% and AA release by about 50%. PhLC and AA release in SV isolated from brain submitted to ischemia were not further activated by 2 mM CaCl2 contrary to the enzymes from normoxic brain. The activation of PhLC and PhLA2 may produce conformational changes and rearrangement of the SV membranes leading to vesicle-membrane fusion and subsequently to massive neurotransmitter release known to occur during ischemia.

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

Prolonged ischemia differently affects phospholipase C acting against phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate in brain subsynaptosomal fraction.

The effect of 10 min ischemia on the activity of phospholipase C acting against [3H]inositol-phosphatidylinositol (PI) and [3H]inositol-phosphatidylinositol 4,5-bisphosphate (PIP2) in the brain subsynaptosomal fractions was investigated. In the presence of endogenous CaCl2, specific activity of phospholipase C acting on phosphatidylinositol was as follows: synaptic cytosol (SC) greater than synaptic vesicles (SV) greater than synaptic plasma membrane SPM). Brain ischemia activated phospholipase C acting on PI by about 60% and 40% in SV and SPM, respectively. The enzyme of synaptic cytosol was not affected by ischemic insult. Phospholipase C acting against PIP2 in the presence of endogenous calcium expressed the specific activity in the following order: SV greater than SPM greater than SC. After 10 min of brain ischemia, activity of phospholipase C acting on PIP2 was significantly suppressed in all subsynaptosomal fractions by about 50-60%. These results indicate that prolonged ischemia produced activation exclusively of phospholipase C acting against phosphatidylinositol.

Animals↗

PubMed1989

Stimulation of phosphoinositide degradation and phosphatidylinositol-4-phosphate phosphorylation by GTP exclusively in plasma membrane of rat brain.

The effect of GTP on the hydrolysis of [3H]phosphatidylinositol (PI), [3H]phosphatidylinositol-4-phosphate (PIP) and [3H]phosphatidylinositol-4,5-bisphosphate (PIP2) by phospholipase C of rat brain plasma membrane, microsomes and cytosol was determined. Moreover the regulation of PI and PIP phosphorylation by GTP in brain plasma membrane was investigated. In the presence of EGTA PIP2 was actively degraded, opposite to PI and PIP which require Ca2+ for their hydrolysis. Addition of calcium ions in each case caused stimulation of inositide phosphodiesterase(s). GTP independently of calcium ions activates by about 3 times phospholipase C acting on PIP and PIP2 exclusively in the plasma membrane. PI degradation was unaffected by GTP. In the presence of Ca2+ guanine nucleotides have synergistic stimulatory effect on plasma membrane bound phospholipase C acting on PIP2. PIP kinase of brain plasma membrane was stimulated by GTP by about 20-100% in the presence of exogenous and endogenous substrate respectively. PI kinase was negligible activated by about 20% exclusively in the presence of endogenous substrate. These results indicated that guanine nucleotide modulates the level of second messengers as diacylglycerol and IP3 through the activation of phospholipase C acting on PIP2 exclusively in brain plasma membrane. The stimulation of phospholipase C by GTP may occur directly or through the enhancement of substrate level PIP2 due to stimulation of PIP kinase.

Animals↗

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↗

PubMed1988

Effect of atropine and gammahydroxybutyrate on ischemically induced changes in the level of radioactivity in [3H]inositol phosphates in gerbil brain in vivo.

Brain ischemia in gerbils was induced by ligation of both common carotid arteries for 1 min or 10 min. Sham-operated animals served as controls. Intracerebral injection of [3H]inositol into gerbil brain 16 hr before ischemic insult resulted in equilibration of the label between inositol lipids and water-soluble inositol phosphate. A short ischemic period (1 min) resulted in a statistically significant increase in the radioactivity of inositol triphosphate (IP3) and inositol monophosphate (IP), by about 48% and 79%, respectively, with little change in that of the intermediate inositol biphosphate (IP2), which increased by about 16%. When the ischemic period was prolonged (10 min), an increase in the radioactivity of inositol monophosphate exclusively, by about 84%, was observed. The level of radioactivity in inositol phosphates IP2 and IP3 decreased by about 50%, probably as a consequence of phosphatase activation by the ischemic insult. The agonist of the cholinergic receptor, carbachol, injected intracerebrally (40 micrograms per animal) increased accumulation of radioactivity in all inositol phosphates. The level of radioactivity in IP3, IP2, and IP was elevated by about 40, 23, and 147%, respectively. The muscarinic cholinergic antagonist, atropine, injected intraperitoneally in doses of 100 mg/kg body wt. depressed phosphoinositide metabolism in control animals. The level of radioactivity in water-soluble inositol metabolites in the brain of animals pretreated with atropine was evidently about 32% lower than in untreated animals. Pretreatment with atropine decreased the radioactivity of all inositol phosphates in the brain of animals subjected to 1-min ischemia and the radioactivity of IP in the case of 10-min brain ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Modulation of calcium-dependent neutral protease activity by fatty acids and lysophospholipids.

The effect of fatty acids and lysophospholipids on calcium-activated neutral protease (CANP) was investigated. mu CANP, low calcium ion (microM concentration)-requiring CANP is more strongly inhibited by unsaturated fatty acids than is mCANP--the high calcium ion (mM concentration)-requiring form. Lysophospholipids in concentrations ranging from 10(-5) M to 10(-3) M inhibit mu CANP exclusively, whereas mCANP activity is unaffected or even slightly increased. Calpastatin decreases the activity of mCANP and, in the presence of polyunsaturated fatty acids such as docosahexaenoic acid, the inhibition is not increased. In the presence of lysophosphatidyl-ethanolamine, however, the inhibition of mCANP by calpastatin does not occur. The results indicate that fatty acids and lysocompounds liberated under different physiological and pathological conditions may modulate calcium-activated neutral protease.

Animals↗

PubMed1988

Lipid composition of myelin and protein--lipid complex in a neurological rabbit mutant.

The neurological mutant of the paralytic tremor "pt" rabbit is characterized by a reduced amount of myelin to 25-30% of control with no change in specific activity for 2',3'-cyclic nucleotide phosphodiesterase. The ratio of total lipids to protein was higher in "pt" rabbit myelin than in control by about 20%. Analysis of the lipid composition of "pt" rabbit myelin indicated a significantly lower level of galactolipids (by about 30%) and a higher level of gangliosides compared to control. The percentage composition of phospholipids in "pt" myelin was characterized by a lower proportion of acidic phospholipids (polyphosphoinositides, phosphatidic acid, phosphatidylserine). The protein-lipid complex in "pt" rabbit myelin was decreased by about 10-15% compared to control. The ratio by weight of protein to lipid in myelin was 0.24 and 0.20 in control and "pt" rabbit, respectively, but in protein-lipid complex isolated from myelin it was 1.73 in control and 0.72 in "pt" rabbit. Protein-lipid complex isolated from myelin of "pt" rabbit brain contained about 34% less protein and about 16% less acidic phospholipids but neutral phospholipids were increased by 24%. The lipid abnormalities in "pt" rabbit myelin and in the composition of protein-lipid complex may be responsible for the disturbances of myelin formation and compaction in "pt" rabbit.

Animals↗

PubMed1988

Guanine nucleotides activate cytosolic phospholipase C of ascites tumour cells stimulated by 1-oleoyl-2-acetyl-sn-glycerol.

The hydrolysis of [3H]phosphatidylinositol (PI) and [3H]phosphatidylinositol-4,5-bisphosphate (PIP2) by cytosolic inositide phosphodiesterase (phospholipase C) from Ehrlich ascites tumour cells was determined. Cytosolic fractions were prepared from tumour cells that had been cultivated for two days at low serum level (2%) in the presence of 1-oleoyl-2-acetyl-sn-glycerol (OAG). Cytosols from unstimulated cells (2% serum without OAG) were used for comparison. Phospholipase C acting on PI and PIP2 was significantly inhibited in the cytosol of OAG-stimulated cells. The suppressed enzyme was activated by Ca2+ and also by the guanine nucleotide GTP in a concentration-dependent manner independently of calcium ions. In the presence of Ca2+, GTP exerted a synergistic stimulatory effect. In contrast, GTP and GTP gamma S showed no effect on the phospholipase C activity of unstimulated cells. It is suggested that the suppressed PI- and PIP2-specific enzyme activity can be modulated by its susceptibility to Ca2+ ions and GTP probably via the GTP-binding protein.

Animals↗

PubMed1987

Phosphatidylinositol degradation in ischemic brain specifically activated by synaptosomal enzymes.

The effect of ischemia on phosphatidylinositol (PI) degrading enzymes in brain homogenate, cytosol and synaptosomes was investigated to evaluate the involvement of cholinergic receptor in PI hydrolysis during ischemia. The activity of phospholipase C in cytosol was not changed by ischemic insult. PI degradation in synaptosomes was significantly (60%) enhanced by ischemia. Atropine and gamma-butyrolactone abolished the ischemic effect on PI degradation, suggesting that the cholinergic receptor system mediates breakdown of PI during ischemia.

4-Butyrolactone↗

PubMed1987

Metabolic studies on dysmyelinating mutant "pt" rabbit brain in vitro.

"Paralytic tremor" (pt) rabbit mutant is characterized by a severe hypomyelination of the CNS, however, it is not defined if the defect in myelinogenesis is an "assembly" or "synthesis" type. In this study, we have compared the general metabolic and biosynthetic properties of the myelinating mutant brain with unaffected controls of the same age. In the brain slices of 4 wk old "pt" rabbits the incorporation of U-[14C]glucose, 6-[3H] galactose, and U-[14C] leucine into macromolecules (total lipids and proteins, galactolipids, and myelin basic protein) was substantially elevated. In isolated myelin fraction, the total reduction of the radioactivity was followed by the increased specific activity of all examined macromolecules. The myelin to homogenate specific activity ratio was similar in control and "pt" rabbits. Distribution of the label and myelin marker, cyclic nucleotide 3'-phosphodiesterase (CNP-ase) among the membranous fractions suggests the partial inhibition of myelin formation in "pt" rabbits on the step of premyelin, unilamellar membranes. 14CO2 yields derived from differently labeled glucose were used for the evaluation of the basal oxidative metabolism in "pt" brain slices. 14CO2 production from U-[14C] glucose was normal. The depolarization of the slices by 50 mM K+ stimulated glucose oxidation to a higher extent in "pt" than in control. Hexose monophosphate pathway (HMP), the route providing much of NADPH required for lipid biosynthesis, did not change significantly by mutation. The activity of glucose 6-phosphate dehydrogenase (Glc-6-P DH), an oligodendroglia enriched, HMP connected enzyme, was slightly lower in "pt" homogenates by 13-17%, whereas CNP-ase was lowered more than 30% in the same samples. All this data suggest that the capacity for the synthesis of myelin constituents is well preserved in the mutant brain and the impairment of myelogenesis is probably caused by increased elimination of already synthesized, myelin-related components.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗

PubMed1987

Effects of cerebral ischemia on [3H]inositol lipids and [3H]inositol phosphates of gerbil brain and subcellular fractions.

Intracerebral injection of [3H]inositol into gerbil brain resulted in labeling of phosphoinositides and inositol-phosphates in various subcellular membrane fractions. Phosphatidylinositol (PI) comprised greater than 90% of the radioactivity of inositol lipids. However, the level of labeled poly-PI (with respect to PI) was higher in synaptosomes than in other membrane fractions. Ischemia induced in gerbils by ligation of the common carotid arteries resulted in a 30% decrease in labeled poly-PI in brain homogenates and this decrease was largely attributed to the poly-PI in synaptosomes (50% decrease). Among the inositol phosphates, the ischemia induction resulted in a decrease in labeling of inositol triphosphate (63%) and inositol biphosphate (38%), but labeling of inositol phosphate (IP) was increased by 59%. The results suggested a rapid turnover of the inositol phosphates in the gerbil brain. In general, changes in inositol lipids and inositol phosphates due to ischemia were attenuated after pretreatment with lithium (3 meq/kg) injected intraperitoneally 5 h prior to ligation. Surprisingly, lithium treatment alone did not cause an increase in IP labeling in the gerbil brain.

Animals↗