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I Zimányi

Publications and source records attributed to I Zimányi.

13 recordsLinked to original sources
PubMed1993

Regulation of inositol 1,4,5-trisphosphate receptors in rat basophilic leukemia cells. I. Multiple conformational states of the receptor in a microsomal preparation.

A detailed characterization of the inositol 1,4,5-trisphosphate (IP3) receptor in rat basophilic leukemia (RBL) cells, a neoplastic mast cell line, has been possible through the growth of solid RBL cell tumors which provide a rich source of IP3 receptor. Equilibrium binding studies show a 1.6 +/- 0.1 pmol/mg of protein maximal binding capacity for [3H]IP3 at optimal Ca2+ (10 microM). The specificity of the RBL cell IP3 receptor towards phosphoinositides, ATP and heparin parallels those previously described with excitable and nonexcitable tissues. [3H]IP3 binding is slightly enhanced from < 1 nM to 10 microM Ca2+ and inhibited by > 10 microM Ca2+. Kinetic and equilibrium studies provide evidence for at least two classes or conformational states of binding sites with pico- and nanomolar affinities. At nM concentrations of IP3, neither binding to the IP3 receptor nor IP3-induced Ca2+ efflux from permeabilized cells demonstrates cooperativity. In contrast, at pM concentrations, IP3 binding kinetics deviate from simple mass action suggesting a complex interaction among binding sites for IP3 on the receptor-channel oligomer. The mechanisms that regulate [3H]IP3 binding in RBL cells are unique when compared to what has been reported in other cells.

Animals↗
PubMed1992

Discrimination of multiple binding sites for antagonists of the calcium release channel complex of skeletal and cardiac sarcoplasmic reticulum.

The mechanisms by which ruthenium red (RR), neomycin and FLA 365 ([2,6-dichloro-4-aminophenyl]isopropylamine) inhibit calcium channels of skeletal and cardiac sarcoplasmic reticulum (SR) are characterized. Neomycin and FLA 365 inhibit ryanodine-enhanced calcium release from skeletal SR vesicles in a dose-dependent manner. The apparent affinity of [3H]ryanodine is reduced in a dose-dependent manner by each inhibitor indicative of competitive mechanisms. Displacement studies with skeletal and cardiac SR demonstrate that the order of inhibitory potency is RR greater than neomycin greater than FLA 365 and RR greater than FLA 365 greater than neomycin, respectively. Neomycin is 100-fold less potent in cardiac SR and inhibition of [3H]ryanodine binding is biphasic in both tissues. Neomycin induces a greater proportion of [3H]ryanodine binding states recalcitrant to inhibition in cardiac SR. The ability of neomycin to increase the apparent affinity of [3H]ryanodine for its binding sites is potentiated by RR and attenuated by FLA 365. Kinetic binding studies reveal that increasing neomycin concentrations decreases the association of [3H]ryanodine as predicted for competitive inhibition. However, high (much greater than Kn) neomycin increases [3H]ryanodine binding affinity by slowing dissociation of the radioligand demonstrating that, like micromolar ryanodine, neomycin induces allosterism. Studies with combinations of antagonists demonstrate the existence of two non-overlapping inhibitor recognition sites within the ryanoid site, one polycationic inhibitor site and one FLA 365 inhibitor site. These results suggest that aminoglycoside-induced muscle paralysis may be mediated by direct block of pre- and postsynaptic calcium release channels of endoplasmic reticulum.

Animals↗
PubMed1992

Ryanodine induces persistent inactivation of the Ca2+ release channel from skeletal muscle sarcoplasmic reticulum.

Junctional sarcoplasmic reticulum (SR) membranes isolated from rabbit skeletal muscle were pretreated with 0.1-500 microM ryanodine under equilibrium conditions optimal for receptor binding, followed by the removal of bound alkaloid by several washes in Ca(2+)- and ryanodine-free buffer. Pretreatment with > 100 nM ryanodine results in a concentration-dependent decrease in the Bmax of the high affinity sites and a complete loss of measurable low affinity binding sites that persist for > 48 hr. Quantitative analysis of residual ryanodine using three different methods demonstrates that the inhibition is not the result of residual ryanodine bound to its receptor. Ca2+ transport measurements made with antipyrylazo III show that actively loaded ryanodine-pretreated SR exhibits a persistent insensitivity to ryanodine- and daunomycin-induced Ca2+ release that is not seen with washed control vesicles. Lipid bilayer membranes fused with SR vesicles exhibit rapidly fluctuating single-channel events with a conductance of 468 pS in asymmetric CsCl solutions. Ryanodine (10 microM) produces a unidirectional transition to a slowly fluctuating half-conductance state that is not reversed by perfusion of the bilayer with Ca(2+)-free buffer and subsequent addition of dithiothreitol. However, dithiothreitol added in the ryanodine pretreatment medium offers marked protection against ryanodine-induced loss of binding sites and allows complete restoration of native gating behavior of single channels in bilayer lipid membrane. Using three different experimental approaches, the data demonstrate that the alkaloid at micromolar concentration persistently alters SR Ca2+ release channel function, perhaps by uncoupling four negatively cooperative binding sites. The oxidation of critical receptor thiols is implicated in the process.

Animals↗
PubMed1991

Comparison of [3H]ryanodine receptors and Ca++ release from rat cardiac and rabbit skeletal muscle sarcoplasmic reticulum.

Sarcoplasmic reticulum (SR) vesicles prepared from rat ventricle muscle are isolated, and their [3H]ryanodine-binding and calcium transport properties are studied in detail under active loading conditions in the presence of pyrophosphate. Experiments are performed in tandem with rabbit skeletal SR under identical conditions to allow direct comparisons of the mechanisms by which activators and inhibitors influence the calcium release channel. Ca(++)-induced Ca++ release is demonstrated with both preparations and the cardiac channel is about 1.5-fold more sensitive to activation by Ca++, which is in excellent quantitative agreement with the ability of Ca++ to activate [3H]ryanodine-binding sites. The cardiac and skeletal receptors show major quantitative differences with respect to sensitivity to pharmacologic modulators, cations and pH. The inhibitors ruthenium red, Mg++ and neomycin are significantly more potent in inhibiting the skeletal receptor, whereas the activators daunorubicin and caffeine are significantly more potent towards the cardiac receptor. The ATP analog, beta,gamma-methyleneadenosine 5'-triphosphate, enhances the binding of [3H]ryanodine to the high-affinity site in skeletal SR by a factor of 4 but has a negligible effect on the cardiac receptor, although at suboptimal Ca++ for the binding of ryanodine, beta,gamma-methyleneadenosine 5'-triphosphate activates the cardiac receptor to a greater extent. High levels of salt (1 M NaCl) enhance the rate of [3H]ryanodine association with its binding sites in both preparations, although they selectively reduce the binding-site capacity in skeletal SR due to a failure to maintain a stable equilibrium. Although high- and low-affinity binding of [3H]ryanodine have a similar response to changing pH, the skeletal receptors are significantly more sensitive to pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Evidence for a common site of action of lidocaine and carbamazepine in voltage-dependent sodium channels.

The finding that the development of lidocaine-kindled seizures is blocked by carbamazepine suggests an interaction of carbamazepine with local anesthetic mechanisms. To study the site of interaction, the effects of lidocaine, carbamazepine and another anticonvulsant drug, phenytoin on scorpion venom-enhanced specific binding of [3H]batrachotoxinin A 20-alpha-benzoate to the sodium channel gating complex were examined in vitro in a rat brain hippocampus preparation. Lidocaine shifted the concentration inhibition curve of carbamazepine to the right and vice versa. Carbamazepine shifted the concentration inhibition curve of phenytoin to the right and vice versa. The experimentally determined apparent dissociation constants were in a good agreement with the dissociation constants calculated for a one-site model, suggesting that the interaction occurs because lidocaine shares a common binding site with carbamazepine and phenytoin in the voltage-dependent sodium channels.

Animals↗
PubMed1989

Effect of cocaine and cocaine congeners on veratridine-induced depolarization in mouse cerebrocortical synaptoneurosomes.

Structure-activity relationships were determined for cocaine congeners in counteracting the depolarization induced by the action of veratridine on voltage-dependent sodium channels of synaptoneurosomes from mouse brain cortex, and their potency was compared to those determined previously on Na+ uptake and batrachotoxinin binding. Cocaine, norcocaine, (+)-pseudococaine, (-)-pseudococaine, (+)-neopseudococaine, benzoyltropine, benzoylpseudotropine, ecgonine methylester, atropine, WIN-35,428, WIN-35,140, WIN-35,065-3, WIN-35,004, and procaine were tested for their potency in inhibiting depolarization as measured by the distribution of the lypophilic cation [3H]triphenylmethylphosphonium across the membrane. All of the tested compounds inhibited the veratridine-induced depolarization in a competitive manner. The structure-activity relationships were similar to those for inhibition of 22Na+ uptake in mouse brain homogenates, and the potency of these local anesthetics in inhibiting veratridine-induced uptake of [3H]triphenylmethylphosphonium correlated well with their potency in inhibiting [3H]batrachotoxinin A 20-alpha-benzoate binding in mouse brain synaptosomes.

Anesthetics, Local↗
PubMed1989

Long-term blockade of the dopamine uptake complex by metaphit, an isothiocyanate derivative of phencyclidine.

[3H]Mazindol was used to label the dopamine uptake complex in mouse striatum in vitro in the presence and absence of metaphit, an isothiocyanate derivative of phencyclidine. In some experiments, metaphit was present in the incubation fluid throughout the procedure; in other experiments it was eliminated by several washings and centrifugations. It was found that after removal of the metaphit by washing and centrifugation, the mazindol binding was not restored. Membranes that were pretreated with metaphit and washed had a lower density of mazindol binding sites than control membranes; the remaining mazindol sites had the same afinity for [3H]mazindol. These findings are in agreement with the previous studies on [3H]cocaine and [3H]methylphenidate binding. The following observations support that metaphit is irreversibly acting and not slowly dissociating from the mazindol recognition sites of the dopamine uptake carrier complex: 1) Metaphit did not change the off-rate of [3H]mazindol binding, arguing against an allosteric action at a distinct site. 2) The presence of cocaine protected the mazindol binding sites from the action of metaphit, supporting binding of metaphit and mazindol to the same site. 3) Nine hours after metaphit pretreatment and removal, the degree of inhibition of mazindol binding was the same as immediately after pretreatment, consonant with an irreversible effect of metaphit. 4) The potency of metaphit in inhibiting mazindol binding was greater under slightly alkaline conditions, consistent with acylation of the mazindol sites. Furthermore, it was found that intracerebroventricular application of metaphit did not result in a decrease in the binding of [3H]mazindol 5 hr after the administration.

Animals↗
PubMed1989

Comparison of characteristics of dopamine uptake and mazindol binding in mouse striatum.

Biochemical and pharmacological studies suggest that the binding of [3H]mazindol is functionally related to the dopamine uptake carrier complex in rodent striatum. In order to study further the relationship between the substrate recognition site for dopamine uptake and the high-affinity binding site for mazindol the uptake of [3H]dopamine and the binding of [3H]mazindol was studied in BALB/cBy mouse striatum in various buffers (Tris, HEPES, bicarbonate-phosphate). Kinetic analysis showed that the Kd of the binding of [3H]mazindol and the Km of the uptake of [3H]dopamine was changed by different sodium concentrations and/or by the presence of Tris, while the Bmax and the Vmax remained essentially the same. However, the shape of the Na+ dependency curves was not the same for mazindol binding and dopamine uptake in the various buffers. The inhibitory effect of other cations such as K+ and Tris was also different on binding and uptake under similar experimental circumstances. Dopamine did not slow down the dissociation of mazindol from its site and this effect was not sodium-sensitive. These complexities can be accommodated by a model that involves overlapping sites for mazindol and dopamine on the dopamine uptake carrier complex, and translocation-reorientation steps.

Animals↗
PubMed1988

The mode of action of ethanol on batrachotoxinin-A benzoate binding to sodium channels in mouse brain cortex.

Since ethanol has local anesthetic activity its effect was examined in vitro on the scorpion toxin-enhanced specific binding of [3H]batrachotoxinin A 20-alpha-benzoate ([3H]BTX-B) to the gating complex in sodium channel preparations from mouse brain cortex by equilibrium and kinetic experiments. Ethanol inhibited the specific binding of [3H]BTX-B in a vesicular preparation with an IC50 value of 310 mM and a Hill number of 1.0. Ethanol increased the equilibrium dissociation constant of batrachotoxin in a concentration dependent manner without changing the maximal binding capacity and decreased the half-time of the aconitine-induced dissociation of [3H]BTX-B. Thus, ethanol acts as an apparent competitive inhibitor, allosterically affecting the [3H]BTX-B binding, like other local anesthetics. Results of competition experiments in the presence of different concentrations of ethanol and fixed concentration of tetracaine (and vice versa) are consonant with an interaction of ethanol and tetracaine with the same binding sites. Experiment carried out at 32, 37 and 42 degrees C indicated that the effect of ethanol is not mimicked by increasing the temperature.

Animals↗
PubMed1985

Erythrocyte enzyme allotypes in the X-linked recessive disorders, Duchenne muscular dystrophy and haemophilia-A hemizygotes and heterozygotes.

The erythrocyte enzyme-systems acid phosphatase, phosphoglucomutase, glutamate pyruvate transaminase, adenosine desaminase, adenylate kinase, glyoxase, glucose-6-phosphate dehydrogenase and esterase-D-isoenzyme phenotypes were studied for their percentile distribution and were compared with their incidence in the diseases with X-linked recessive heredity, Duchenne muscular dystrophy (DMD) and haemophilia-A, in hemizygous male children and heterozygous mothers. Considering the frequency distribution of the above mentioned isoenzyme phenotypes of the enzyme-systems in DMD, the phenotypes proved to be homogeneous, only the X transmitted 6-phosphogluconate dehydrogenase (6-PGD) isoenzyme types were found to be genetic markers in DMD hemizygotes and heterozygotes. In these genotypes the 6-PGD A phenotype showed a decrease while the phenotypes 6-PGD AB and B were significantly increased. The adenylate kinase (AK) 2-1 isoenzyme phenotype was increased to 25% against the population frequency of 6.34%, while the AK 1-1 phenotype occurred in 75% against its population frequency of 93.59%, showing a significantly decreasing tendency in haemophilia-A hemizygotes and heterozygotes.

Acid Phosphatase↗