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J Kardos

Publications and source records attributed to J Kardos.

At least 55 records · Page 3Linked to original sources
PubMed1989

Determination of selenium in foods by inductively-coupled plasma atomic emission spectrometry and hydride generation.

Within the framework of a survey launched by the Istituto Superiore di Sanità to assess the average daily intake of Se with food in the Italian population, a preliminary study was carried out to develop an analytical procedure for the quantification of the element in food products. The method implies the use of a hydride generation system in combination with inductively-coupled plasma atomic emission spectrometry (ICP-AES) and exploits the inherent advantages of this last also for the analysis of non-metals. The overall approach was tested in some Hungarian and Italian foods, adequately lending itself to routine and reliable Se assay.

Food Analysis↗
PubMed1988

Comparative studies on fresh and postmortem isolated synaptosomes: ATPase activities and ouabain binding.

In earlier studies we have established that rat cortical synaptosomes isolated after a 2-h postmortem storage period showed functional performance and morphological characteristics similar to those isolated immediately after decapitation. The present paper is an account of further functional studies involving the activity of Na-K- and Mg-dependent ATPase and the binding of ouabain in postmortem synaptosomes. These functions were found to survive without major alteration even in the 6-h postmortem fractions. On the other hand the 6-h postmortem fractions showed a very slow oxygen consumption unaffected by DNP and veratrine. In both control and postmortem synaptosomes the actual activity of Na-K-ATPase as calculated from the ouabain-sensitive component of oxygen consumption was consistently less than the potential activity of the enzyme revealed if determination was carried out on the basis of phosphate splitting.

Animals↗
PubMed1987

GABAA receptor-controlled 36Cl- influx in cultured rat cerebellar granule cells.

gamma-Aminobutyric acid (GABA)-mediated and bicuculline-sensitive 36Cl- influx and bicuculline-sensitive [3H] GABA binding were demonstrated in cultures of rat cerebellar granule cells. The addition of 10(-5) M GABA produced a two-fold increase in 36Cl-influx over the basal level and the maximal increase was observed after approximately 20 sec. Progressive occupation of GABAA receptor by [3H]-(1S-9R)-bicuculline methiodide decreased 36Cl- influx activated by 10 microM GABA. The above results suggest that primary cultures of rat cerebellar granule cells provide a new and reliable model for studying the GABA activated chloride fluxes.

Animals↗
PubMed1987

Potent inhibitory GABAB receptors in stimulated guinea-pig taenia coli.

gamma-Aminobutyric acid (GABA, half-maximal inhibitory concentration, IC50 = 9.9 microM) and (-)-baclofen (IC50 = 4.5 microM) but not 10(-4) M muscimol, exerted a presynaptic inhibitory effect on cholinergic transmission in field-stimulated guinea-pig taenia coli preparations, in vitro. The antagonism by 10(-5) M (1S, 9R)-bicuculline methiodide was not specific for GABA agonists. The results suggest that the GABA receptors involved were of type B.

Acetylcholine↗
PubMed1984

Cu2+ is the active principle of an endogenous substance from porcine cerebral cortex which antagonizes the anticonvulsant effect of diazepam.

A boiled extract of porcine cerebral cortex was fractionated on Sephadex G-75 and LH-20 followed by paper chromatography of the active fraction having inhibitory activity towards [3H]GABA binding to rat brain synaptic membranes. A ninhydrin-negative substance migrating more quickly than authentic GABA was identified as a copper-GABA complex. The complex inhibited specific [3H]GABA binding (IC50 approximately equal to 1 microM) and antagonized the anticonvulsant effect exerted by intraamygdaloid injection of diazepam. The effect of a synthetic copper-GABA complex was compared and found to be similar to the endogenous complex. Cu2+ alone has no affinity for the GABA recognition site but antagonizes the anticonvulsant effect of diazepam. Therefore, Cu2+ is suggested to be the pharmacologically active principle of the endogenous substance. Cu2+ does not seem to function via the recognition site of the GABA receptor.

Amygdala↗
PubMed1984

Inhibition of [3H]GABA binding to rat brain synaptic membranes by bicuculline related alkaloids.

The binding of 45 bicuculline related phthalideisoquinoline alkaloids to the GABAA receptor was studied using rat brain synaptic membranes prepared both in Tris-HCl and in Tyrode buffers. The IC50 values determined in Tyrode for phthalideisoquinolines are lower (by about one order of magnitude) than and correlate well (r2 = 0.95) with the IC50 data obtained by [3H]GABA displacement in Tris-HCl. Applying Tyrode, the activities of GABA agonists relative to Tris-HCl are decreased. It can be recognized that activities in receptor binding are dependent on the conformations phthalideisoquinolines prefer in solution. On the basis of systematic alterations in the phthalideisoquinoline molecule the main structural elements involved in the binding of phthalideisoquinoline alkaloids appear to be identical with those of GABA agonists, suggesting that the same binding conformation of the GABAA receptor may be implicated for both agonists and antagonists. The opposite shift in relative potencies of agonists and antagonists may be the consequence of an alteration in the "ionic status" rather than that in the conformation of the GABAA receptor.

Animals↗
PubMed1984

Differential localization of GABA-dependent and GABA-independent benzodiazepine binding sites within synapses of rat cerebral cortex.

Fractions containing non-junctional membranes (fraction 1) could be separated from those enriched in junctional complexes (fraction 2) by sucrose gradient centrifugation of osmotically disrupted rat cerebral cortex synaptosomes. [3H]flunitrazepam binding sites were found to be homogeneous characterized by Kd = 0.65 nM, Bmax = 13 pM for fraction 1; and Kd = 2 nM, Bmax = 45 pM for fraction 2. GABA-dependent benzodiazepine receptor sites were found to be localized to the junctional complex fraction, while non-junctional membranes showed GABA-independent receptor and acceptor binding sites.

Animals↗
PubMed1984

Pharmacodynamic investigation of (+/-)-salutaridine.

The alkaloid 5,6,8,14-tetradehydro-4-hydroxy-3, 6-dimethoxy-17-methyl-morphinan-7-one[+/-)-salutaridine) was found to possess 3H-gamma-aminobutyric acid (3H-GABA) displacing activity (IC50 less than 1 mumol/l) in rat brain synaptic membranes. The enhancement of specific 3H-diazepam binding by increasing concentration of (+/-)-salutaridine follows a maximum curve indicating (+/-)-salutaridine to be a partial agonist at the GABA/benzodiazepine receptor complex.

Animals↗
PubMed1981

Specific binding of racemic oxazepam esters to rat brain synaptosomes and the influence of bioactivation by esterases.

Six aliphatic esters of oxazepam were investigated for 3H-diazepam displacing activity and hydrolysis in rat in the brain P2-fraction treated with diisopropylfluorophosphate. The esters are prodrugs in relation to oxazepam. Increasing size of the 3-substituent and steric hindrance increased the value of IC50. Controversial reports on oxazepam hemisuccinate could be explained by its stereoselective hydrolysis in vivo.

Animals↗
PubMed1979

Investigation of the common mechanism of action of antibacterial compounds containing gamma-pyridone-beta-carboxylic acid structure by principal component.

On the basis of 576 in vitro antibacterial positive results of 99 compounds containing gamma-pyridone-beta-carboxylic acid structure conclusions have been drawn on the mechanism of action of the derivatives by principal component analysis. It has been found that the compounds exert their effect essentially by influencing two types of physiological processes or series of processes. The more important of the two "mechanisms", responsible for 50-95% of the activity of the compounds, is common for the compounds investigated, and is associated with the gamma-pyridone-beta-carboxylic acid structure.

Anti-Bacterial Agents↗