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Z Huszti

Publications and source records attributed to Z Huszti.

At least 19 recordsLinked to original sources
PubMed2001

Enhancing effect of zinc on astroglial and cerebral endothelial histamine uptake.

We have studied the effect of zinc ion on the uptake of histamine (HA) into cultured astroglial and cerebral endothelial cells and established that Zn(2+) enhances the uptake of the amine dose-dependently and in remarkable extents by increasing the V(max) to about 3-fold (from 3.25 +/- 0.42 to 8.50 +/- 0.97 pmol/mg protein/min in astroglial cells) without altering the K(M) (0.20 +/- 0.03 microM) significantly. The stimulatory effect of zinc ion showed strong sensitivity for VUF 8407, an inhibitory compound of astroglial and cerebral endothelial uptake of HA. In the presence of 20 microM VUF 8407 the zinc-enhanced uptake was reduced by about 50% in both cell types. Binding measurements revealed increased capacities of the zinc-exposed HA binding (B(max)= 0.41 +/- 0.05 increased to 1.21 +/- 0.16 pmol/mg protein in astroglial membranes and B(max) = 0.25 +/- 0.03 enhanced to 1.05 +/- 0.12 pmol/mg protein in cerebral endothelial membranes) but statistically unchanged affinity of the ligand for HA carrier (K(D) values calculated as 35.2 +/- 3.4 nM and 45.1 +/- 3.8 nM for astroglial bindings; whereas 25 +/- 2.1 nM and 30 +/- 2.6 nM for cerebral endothelial bindings of the amine). The compound VUF 8407 reduced the B(max) of zinc-exposed HA binding of astroglial membranes but did not modify the K(D) of the zinc-exposed membrane significantly. The ex vivo experiments confirmed our in vitro findings; an i.c.v. dose of 0.4 micromol/kg ZnSO(4,) 24 hr after the injection, enhanced the uptake of [(3)H]HA into dissociated hypothalamic and cerebellar cells to about 2- and 3-fold, respectively. Present data clearly showed that zinc exposures enhance the astroglial and the cerebral endothelial uptake of HA in vitro and it might be considered that zinc produces similar effects in vivo. Free zinc may participate in the regulation of the extraneuronal HA concentration and this metal ion (endogenous or exogenous) might be favored in the removal of the amine from the interstitial space especially in conditions with relatively high HA.

Animals↗
PubMed1998

Glial cells participate in histamine inactivation in vivo.

The ability of glial cells to take up histamine in vitro suggests that these cells may be involved in histamine inactivation. This prompted us to study the possible interactions between neuronal and glial processes which determine the histamine concentration in the synaptic cleft. In vitro experiments showed that the glial metabolic toxin, fluoroacetate (20 and 40 mmol/l) depressed histamine uptake into cultured astroglial cells and dissociated hypothalamic cells of rats. For in vivo experiments, the push-pull superfusion technique was used. In anaesthetized rat, the anterior hypothalamic area was superfused through the push-pull cannula with artificial cerebrospinal fluid (aCSF) or with aCSF which contained fluoroacetate and the release of endogenous histamine was determined in the superfusate. Hypothalamic superfusion with fluoroacetate (20 mmol/l) led to a pronounced increase in extracellular histamine. The effect of fluoroacetate was inhibited by 5 micromol/l tetrodotoxin. Superfusion with Ca++-free, Mg++-rich (12 mmol/l) aCSF inhibited the basal release rate of histamine. Under these conditions, 20 mmol/l fluoroacetate did not modify the level of the amine in the superfusate. These data demonstrate that depression of glial function enhances the concentration of histamine in the extracellular space by slowing down the uptake of the amine into the glial cells. Thus, under in vivo conditions, glial cells are directly involved in the continuous removal of neuronal histamine from the synaptic cleft.

Animals↗
PubMed1997

Mercury-stimulated histamine uptake and binding in cultured astroglial and cerebral endothelial cells.

The effects of mercuric compounds on histamine uptake and binding to uptake carrier in cultured rat astroglial and cerebral endothelial cells were investigated. Experimental results showed that mercuric compounds produced strong stimulation of glial and cerebroendothelial histamine uptake over a concentration range of 25-500 microM. The stimulated histamine uptake showed characteristics similar to those described for basal uptake in terms of sensitivity to inhibitory agents (e.g., impromidine) and the requirement of external Na+. Mercury-induced stimulation of histamine uptake could be abolished by sulfhydryl agents, dithiotreitol and cysteamine, indicating a complete reversal of, and not simply a protection from, the action of mercury. Basal and stimulated uptake of histamine represent bindings to uptake carrier with high and closely equal affinities but markedly higher capacities for stimulated uptake. In controls, the mean value of apparent KD (derived from saturation kinetics at equilibrium) was obtained as 26.7 +/- 3.9 nM for astroglial cells; and 100 microM mercuric chloride did not modify it significantly. In contrast, the apparent Bmax values differed markedly; found as 0.63 +/- 0.10 pmol/mg protein and 3.32 +/- 0.47 pmol/mg protein in the absence and the presence of 100 microM mercuric chloride respectively. For the cerebral endothelial cell line, RBE4, the apparent KD was calculated as 22.5 +/- 3.2 nM and was comparable to that obtained for astroglial cells in control and mercury-stimulated conditions. The apparent Bmax values were less, but markedly different in these conditions, obtained as 0.18 +/- 0.03 pmol/mg protein and 1.2 +/- 0.36 pmol/mg protein in the absence and the presence of mercuric ion respectively. In both cells, impromidine, the potent inhibitor of basal and stimulated histamine uptake, decreased the enhanced capacities of histamine binding (Bmax) (without affecting the dissociation constant, KD) in micromolar range, comparable to its inhibiting potency. Results confirmed that mercuric ion might enhance the binding capacity of histamine carrier and protein sulfhydryls might play a role in this effect. The observed stimulations by mercuric compounds suggest close similarities in the mechanism of histamine uptake and the structure of histamine carrier in astroglial and cerebral endothelial cells.

Animals↗
PubMed1995

Carrier-mediated uptake and release of histamine by cultured rat cerebral endothelial cells.

The present study demonstrates that histamine could be taken up by and released from endothelial cells of brain capillaries. Incubation of cultured endothelial cells, with low (0.01-0.50 microM) concentrations of [3H]histamine, resulted in a rapid uptake of the amine. The uptake was saturable, Na(+)-dependent and yielded an apparent Km 0.3 +/- 0.02 microM and a Vmax 4.6 +/- 0.04 pmol/mg protein per min. After a 10-min incubation in a histamine-free medium, about 65% of [3H]histamine was released from the cells. Na(+)-deprivation and high K+, as well as the treatment of the cells with ouabain affected the release, resulting in significantly higher rates of the efflux. The ability of cerebral endothelial cells to take up histamine from both luminal and abluminal sides but to release it mainly luminally, may function as an important mechanism to protect the neural tissue from the harmful effects of this endogenous mediator of inflammation.

Animals↗
PubMed1995

Effects of lead and mercury on histamine uptake by glial and endothelial cells.

The effects of lead and mercury on [3H]-histamine uptake by cultured astroglial and endothelial cells of rat brain were studied. Experimental data showed that both metal ions inhibited the uptake in both cell types of concentrations as low as 1-10 microM. The effects were consistent with non/competitive inhibitions. With either lead or mercury exposure, the inhibition of the uptake was greater in astroglial than in cerebral endothelial cells. Contrary to the above findings, 100 microM of mercuric chloride produced stimulation of histamine uptake and this stimulation was much more pronounced in cultured cerebral endothelial cells than in astroglial cells. Inhibition of [3H]-histamine uptake by lead acetate and mercuric chloride was considered to be association with a loss of the transmembrane Na+ and/or K+ gradient while stimulation of the uptake by high concentration of mercury might be related to a direct effect on histamine transporter. It is noteworthy, that cultured astroglial cells, derived from neonatal rat brain, are much more sensitive to the toxic effects of these heavy metal ions than cultured endothelial cells derived from the brain capillaries of the same species of animals.

Animals↗
PubMed1994

[3H]histamine uptake and release by astrocytes from rat brain: effects of sodium deprivation, high potassium, and potassium channel blockers.

Histamine transport has been characterized in cultured astroglial cells of rat brain. The kinetics of [3H]-histamine uptake yielded a Km of 0.19 +/- 0.03 microM and a Vmax of 3.12 +/- 0.75 pmol X mg protein-1 X min-1. Transport system revealed high affinity for histamine and an approximately ten times higher capacity than that shown in cultured glial cells of chick embryonic brain. Ouabain which interferes with utilization of ATP to generate ion gradients, and the replacement of Na+ with choline inhibited the initial rate of uptake showing a strong Na(+)-dependency and suggesting the presence of a tightly coupled sodium/histamine symporter. Dissipation of K(+)-gradient (in > out) by high K+ or by K(+)-channel blockers, BaCl2, (100 microM), quinine (100 microM) or Sparteine (20 microM) produced also remarkable inhibitions in the uptake of [3H]-histamine. Impromidine, a structural histamine-analogue could inhibit the uptake non-competitively in a range of concentrations of 1 to 10 microM with a Ki value of 2.8 microM, indicating the specificity of the uptake. [3H]histamine uptake measurements carried out by using a suspension of dissociated hypothalamic cells, of rat brain showed a strong gliotoxin-sensitivity and yielded a Km of 0.33 +/- 0.08 microM; and a Vmax of 2.65 +/- 0.35 pmoles x mg protein-1 x min-1. The uptake could be reversed by incubating the cells in histamine-free Krebs medium. The [3H]histamine efflux was sensitive to Na+ omission, ouabain treatment and high K+ or K+ channel blockers, resulting in marked elevations in the efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Possible regulation of hypothalamus and lung histidine decarboxylase activity by cAMP-dependent protein kinase.

Activity of crude histidine decarboxylases (HisDC) from the hypothalamus and the lungs, was markedly reduced by incubating with ATP.Mg, cAMP and cAMP-dependent protein kinase A, whereas activity of the crude glandular stomach enzyme changed only slightly under equal condition. The omission of one of these components failed to reduce HisDC activity by as much as the complete system. Addition of bovine heart (type II) or rat cerebellum protein kinase A (types I and II) inhibitor to the assay prevented enzyme inactivation; moreover, protein kinase A inhibitors permitted moderate activation under phosphorylating and control conditions. Cytosolic hypothalamus HisDC activity was elevated 2-2.2-fold by incubating the cytosol for 15 min in the presence of MnCl2, a known stimulator of phosphoprotein phosphatase; this was prevented when 20 mM NaF, a common inhibitor of phosphoprotein phosphatase, was added to the cytosol. The apparent Km of ATP.Mg-treated hypothalamus HisDC for histidine was elevated 5-10-fold compared to controls, whereas the Vmax was approximately the same. Under this condition, the Km was calculated as high as 0.5-2.2 mM (depending on phosphorylating conditions), while controls had a Km of 0.1-0.3 mM (depending on the initial phosphorylating states). Addition of rabbit muscle (type I), bovine heart (type II) or rat cerebellum (types I and II) inhibitor of protein kinase A, to the phosphorylating mixture, abolished the difference in Km between control and ATP.Mg-treated HisDC. Moreover, rat cerebellum protein kinase A inhibitors increased Vmax to above the control level; while 20 mM NaF (inhibitor of phosphoprotein phosphatase) decreased Vmax to approximately one half of that of the controls. These data indicate that HisDC activity in the hypothalamus and the lungs, but not in the stomach, is affected in oppositely by protein kinase A and phosphoprotein phosphatases.

Animals↗
PubMed1990

Uptake, metabolism, and release of [3H]-histamine by glial cells in primary cultures of chicken cerebral hemispheres.

Labelled histamine was taken up into cultured glial cells of chick embryonic brain by a system with high affinity for histamine and diffusion. The active uptake, occurring at low concentrations of the amine, was Na+ dependent and gave an apparent Km of 0.24 microM and a Vmax of 0.31 pmol x mg protein-1 x min-1. The uptake was completely blocked by desmethylimipramine (Ki = 2.5 microM) and partially by the histamine agonists and histamine-N-methyltransferase blockers 4-methylhistamine and 2-methylhistamine (I30 values obtained were 2 microM and 5 microM). Other psychoactive drugs were either ineffective (imipramine) or they showed moderate inhibitory effects (amitriptyline and cocaine). Ouabain (100 microM) inhibited uptake by approximately 50%. Diffusion occurred at high concentrations of the amine, was insensitive to extracellular Na+, and was proportional to histamine concentration up to 1 mM. [3H]-Histamine, taken up into the cells, was metabolized and/or released. The spontaneous efflux of the radioactivity measured after 10 min of exposure to [3H]-histamine (when most of it was still unmetabolized), was moderately Ca++ dependent, accelerated by both reduced concentrations of extracellular Na+ and enhanced concentrations of K+ and inhibited by desmethylimipramine. After prolonged (60 min) incubation, histamine metabolites detected in the cells presented 78% of the chromatogram radioactivity and consisted of N tau-methylhistamine and N tau-methylimidazole acetic acid. These results indicate that at low nM concentrations, histamine is taken up and metabolized by (and released from) glial cells by an Na(+)-dependent system, and the intracellular metabolism seems to serve an increased uptake of the amine.

Animals↗
PubMed1990

Histamine inactivation in the brain: aspects of N-methylation.

This report deals with molecular and anatomical site of histamine N-methylation assumed to be the exclusive route of HA inactivation. The methyl transfer from the -S-CH3 of S-adenosyl-L-methionine to the ring (tele)-nitrogen of histamine, appears as much more complex than a one-step transformation. It seems that -S-CH3 is transformed before being transferred to the nitrogen of the acceptor probably via methanol (formaldehyde) formation. For localizations of transmethylation of neuronal histamine we assume at least a two-compartment model in which glia participate to a significant extent. The uptake of neuronal HA into glial cells might be the first step of histamine inactivation.

Animals↗
PubMed1990

Inhibition of potassium-induced release of histamine from mast cells by tetraethylammonium and tetramethylammonium.

In accordance with our previous results, a marked release of histamine (HA) from rat peritoneal mast cells was initiated by 150 mM KCl in the absence of extracellular Ca2+. This release could be reduced by 20-60 mM tetraethylammonium (TEA) or tetramethylammonium (TMA), the non-selective K(+)-channel blockers, Ouabain, the general inhibitor of (Na+ + K+) ATP-ase, failed to produce any changes in this release. The action of TEA discriminated between the initiation of HA release evoked by different agents, producing a blockade of the K(+)-induced but not the 48/80-stimulated HA release. In total, these data suggest the presence of TEA/TMA-sensitive K(+)-channels in the mast cell membrane and their involvement in one of the possible pathways for the initiation of HA release.

Animals↗
PubMed1990

Contribution of glial cells to histamine inactivation.

DL-alpha-aminoadipic acid (DL-alpha AA), a selective gliotoxic agent produced significant reductions in histamine-N-methyl-transferase (HNMT) and monoamine oxidase-B (MAO-B) activities and an enhancement in histamine (HA) level in the hypothalamus of rats 2 and 4 h after single intracerebroventricular (i.c.v.) or subcutaneous (s.c.) injections of the compound. Histidine decarboxylase (HD) and monoamine oxidase-A (MAO-A) were unaffected after these treatments. Following a single i.c.v. injection of DL-alpha AA of 200 micrograms/rat, or a single s.c. injection of 5 mg/rat, marked diminutions in the astrocytic marker glutamine synthetase (GS) activity occurred suggesting marked glial damage in the hypothalamus. In total, these studies indicate an important role for glial cells in HA metabolism (inactivation).

2-Aminoadipic Acid↗
PubMed1988

The effect of a new antihistamine drug, Loderix (EGIS-2062), on stimulus-evoked histamine release from rat peritoneal mast cells.

The ability of a new, non-sedative antihistamine drug, Loderix (EGIS-2062), to inhibit stimulus-evoked histamine release from rat peritoneal mast cells has been investigated and compared with that of ketotifen (Zaditen). At low concentrations Loderix preincubated with the cells for 10 min prior to the addition of various stimulants (immune aggregates, ionophore A23187 and compound 48/80) produced a concentration-dependent inhibition of histamine release, while at high concentrations it induced the release of histamine. The IC50 values were calculated as 0.2, 15 and 50 microM by using immune aggregate, (rat IgG2 alpha + anti rat IgG) calcium ionophore and 48/80 as stimulants, respectively. At the IC50 level Loderix was more effective than Zaditen (100 times more effective when immune aggregate and 4 times when 48/80 were used for stimulation). Both drugs had a dual effect on mast cells. The morphological observations confirmed the pharmacological action of the drugs, showing also that the histamine release at high concentrations is due to their cytotoxic effect.

Animals↗
PubMed1987

Potassium-induced histamine release from mast cells and its inhibition by ketotifen.

Potassium chloride induced a dose-dependent release of histamine from rat peritoneal mast cells at concentrations from 5 to 150 mM in the absence of extracellular Ca2+. Potassium concentrations greater than 150 mM produced less histamine release. The release was energy-dependent and was complete within one minute. The histamine liberating effect of KCl could be inhibited by NaCl and by preincubation with ketotifen. The monovalent cations, Rb+ and Cs+ also evoked histamine release, whereas Na+ and Li+ were ineffective.

Animals↗
PubMed1987

Stimulation of hypothalamic histidine decarboxylase by calcium-calmodulin and protein kinase (cAMP-dependent) inhibitor.

Stimulatory effects of Ca2+-CaM and PKI on partially purified hypothalamic HD (10 fold purification) have been shown under conditions involving inhibition of the enzyme by cAMP-induced phosphorylation and under control conditions. A 1:1 (v/v) mixture of 0.1 mM CaCl2 and 10 units of CaM from human red blood cells reversed the inhibition of HD induced by cAMP-dependent protein phosphorylation activity to the control level. Verapamil (0.01 mM) could partially block the former effect without affecting the control level of enzyme activity. 0.01 mM TPA did not further increase the effect of Ca2+-CaM on HD, in the presence of 0.01 mM ATP, indicating that this stimulation does not require the action of Ca2+-dependent protein kinase. The control level of HD is not influenced by 0.1 mM CaCl2 or 0.02 mM EGTA but is raised by CaM in the presence of CaCl2 (0.1 mM). A highly purified protein kinase (cAMP-dependent) inhibitor (PKI) from bovine heart and a crude inhibitor from rat cerebellum could also reverse the inhibitory effect of cAMP-dependent protein kinase under phosphorylating conditions and enhanced HD activity above control levels. PKI and Ca2+-CaM, added together, produced single, not additive effects. We conclude that cAMP-induced phosphorylation is probable the main regulatory mechanism of histamine formation and this could be influenced by both Ca2+-CaM and PKI. Inhibition of cAMP-dependent protein kinase as well as stimulation of phosphoprotein phosphatase and Ca2+-CaM-dependent phosphodiesterase might be involved in the above actions.

Animals↗