Biomedical subjects

T Kiss

Publications and source records attributed to T Kiss.

At least 55 records · Page 3Linked to original sources

PubMed2000

Ultrahigh-resolution photoemission spectroscopy of Ni borocarbides: direct observation of the superconducting gap and a change in gap anisotropy by impurity

We have performed ultrahigh-resolution photoemission spectroscopy of Y(Ni1-xPtx)2B2C ( x = 0.0 and 0.2) in order to study the changes in the density of states across the superconducting transition. Because of a drastic increase in energy resolution, we clearly observe the opening of superconducting gaps across T(c) in both compounds. Furthermore, we find a small but significant difference in the superconducting-state spectral shape. This can be explained in terms of reduction in gap anisotropy by introducing impurities and provides spectroscopic evidence for an anisotropic s-wave gap in YNi2B2C.

Journal Article↗

PubMed2000

Photoemission spectroscopy of the strong-coupling superconducting transitions in lead and niobium

We study the changes in the electronic structure associated with low- T(c) strong-coupling superconducting transitions in Pb and Nb using ultrahigh-resolution (2.3 meV) temperature-dependent (5.3-12.0 K) photoemission spectroscopy. We observe peaks in the density of states on entering the superconducting-phase accompanying gap formation and spectacular redistribution of spectral weight at low energy scales as a function of temperature. The well-known peak-dip feature of the high- T(c) cuprates is seen in Pb, making it a characteristic of strong-coupling superconductivity.

Journal Article↗

PubMed2000

[CT- and MRI-guided conformal interstitial and external beam radiotherapy of primary brain tumors: prospects in Hungary].

The technical improvements gained over the last decade in neuroradiology and radiotherapy have brought significant theoretical and experimental changes in the treatment of primary glial brain tumours. The follow-up of patients with CT, MRI and isotope diagnostic examinations proves that the relapses take place in the vicinity of the primary site in most cases. Consequently, the conventional large fields or whole brain irradiation techniques have been phased out and the conformal irradiation methods focused on the tumorous targets have gained ground. The exact neuroanatomic projection, the image based 3-dimensional treatment planning methods and the conformal irradiation techniques ensure that only the tumorous or the potentially infiltrated regions become irradiated with maximal protection of the normal brain tissues. The increased protection of the normal tissues makes a dose escalation possible, which may result in the augmentation of the therapeutic benefits. In Hungary both the interstitial and the external beam conformal radiotherapies of the CNS have become accessible in practice over the recent years. In possession of manifold treatment modalities (percutaneous fractionated conformal radiotherapy, stereotactic radiosurgery, high dose rate after-loading and low dose rate interstitial irradiation), it is found necessary to overview the indicative territories, advantages, limitations and possible complications of different interventions. The authors describe the possible routes of further improvements and ways of dose escalation. Nevertheless, it is emphasised that gliomas--with reduced radiosensitivity and high potential to infiltrate the adjacent brain tissues-represent the illness in the whole CNS. It implies that in the future it will probably be necessary to initiate systemic therapeutic modalities in the course of routine treatment strategies in addition to the focused and more effective radiotherapy regimens.

Brain Neoplasms↗

PubMed2000

Speciation of insulin-mimetic VO(IV)-containing drugs in blood serum.

The biospeciations of three potential insulin-mimetic VO(IV) compounds, VO(maltolate)2, VO(picolinate)2 and VO(6-Me-picolinate)2, in blood serum were assessed via modelling calculations, using the stability constants reported in the literature for the binary insulin-mimetic complexes and their ternary complexes formed with the most important low molecular mass binders in the serum: oxalic acid, lactic acid, citric acid and phosphate. The binding capabilities of two high molecular mass serum proteins, albumin and transferrin, were also taken into account.

Citric Acid↗

PubMed2000

Characterisation of the U83 and U84 small nucleolar RNAs: two novel 2'-O-ribose methylation guide RNAs that lack complementarities to ribosomal RNAs.

In eukaryotic cells, the site-specific 2'- O -ribose methylation of ribosomal RNAs (rRNAs) and the U6 spliceosomal small nuclear RNA (snRNA) is directed by small nucleolar RNAs (snoRNAs). The C and D box-containing 2'- O -methylation guide snoRNAs select the correct substrate nucleotide through formation of a long 10-21 bp interaction with the target rRNA and U6 snRNA sequences. Here, we report on the characterisation of two novel mammalian C/D box snoRNAs, called U83 and U84, that contain all the elements that are essential for accumulation and function of 2'- O -methylation guide snoRNAs. However, in contrast to all of the known 2'- O -methylation guide RNAs, the human, mouse and pig U83 and U84 snoRNAs feature no antisense elements complementary to rRNA or U6 snRNA sequences. The human U83 and U84 snoRNAs are not associated with maturing nucleolar pre-ribosomal particles, suggesting that they do not function in rRNA biogenesis. Since artificial substrate RNAs complementary to the evolutionarily conserved putative substrate recognition motifs of the U83 and U84 snoRNAs were correctly 2'- O -methylated in the nucleolus of mouse cells, we suggest that the new snoRNAs act as 2'- O -methylation guides for cellular RNAs other then rRNAs and the U6 snRNA.

Animals↗

PubMed2000

Ternary complex formation between VO(IV)-picolinic acid or VO(IV)-6-methylpicolinic acid and small blood serum bioligands.

In order to assess the role of the low molecular mass bioligands of blood serum in vanadium binding, a study was made of the interactions of the complexes formed in the VO(IV)-picolinic acid and VO(IV)-6-methylpicolinic acid systems with various low molecular mass constituents of blood serum, such as oxalate, lactate, citrate and phosphate. The speciation of VO(IV) in these ternary systems and also in the binary VO(IV)-picolinic acid and VO(IV)-6-methylpicolinic acid systems was studied by pH-potentiometry at 25 degrees C and at an ionic strength I = 0.2 M (KCl). The binding modes of the complexes formed were determined by spectral (electronic absorption and EPR) methods. Picolinic acid and 6-methylpicolinic acid were found to form mono and bis complexes through the pyridine nitrogen and carboxylate oxygen, but the presence of the methyl group in 6-methylpicolinic acid surprisingly decreases the stability of its complexes significantly. The results obtained on the ternary systems reveal that mixed ligand complex formation is favoured in these systems, especially with citrate, and must therefore be taken into account in the speciation description of VO(IV) in blood serum.

Citric Acid↗

PubMed2000

Mytilus inhibitory peptides (MIP) in the central and peripheral nervous system of the pulmonate gastropods, Lymnaea stagnalis and Helix pomatia: distribution and physiological actions.

The distribution and neuroanatomy of Mytilus inhibitory peptides (MIP)-containing neurons in the central nervous system and their innervation pattern in the peripheral nervous system of the pulmonate snail species, Lymnaea stagnalis and Helix pomatia, have been investigated immunocytochemically, by applying an antibody raised to GSPMFVamide. A significant number of immunoreactive neurons occurs in the central nervous system of both species (Lymnaea: ca 600-700, Helix: ca 400-500), but their distribution is different. In Lymnaea, labeled neurons are found in all central ganglia where a number of large and giant neurons, previously identified physiologically, reveal MIP immunoreactivity. In Helix, most of the immunolabeled neurons are small (12-30 microm) and concentrated in the buccal and cerebral ganglia; the parietal ganglia are free of labeled cells. In both species, the ganglionic neuropils, peripheral nerves, connectives, and commissures are richly supplied with immunolabeled fibers. The MIP-immunoreactive innervation pattern in the heart, intestine, buccal mass and radula, and foot is similar in both species, with labeled axonal bundles and terminal-like arborizations (buccal mass, foot) or a network of varicose fibers (heart, intestine). Intrinsic neurons are not present in these tissues. The application of GSPYFVamide inhibits the spontaneous contractions of the esophageal longitudinal musculature in Helix, indicating the bioactivity of the peptide. An outside-out patch-clamp technique has demonstrated that GSPYFVamide opens the K+ channels in central nerve cells of Helix. Injection of GSPYFVamide into the body cavity inhibits the feeding of starved Helix. A wide modulatory role of MIP at central and peripheral levels is suggested in Lymnaea and Helix, including the participation in intercellular signalling processes and remote neurohormonal-like control effects.

Animals↗

PubMed2000

The application of image fusion in stereotactic brachytherapy of brain tumours.

BACKGROUND: The visualization of any morphological volume (i.e. CT, MRI) together with an additional second morphological volume (i.e. CT, MRI) or functional data set, which may come from SPECT or PET, is a new method for treatment planning, verification and follow-up of interstitial irradiation. METHOD: The authors present their experience on interstitial irradiation of brain tumours with stereotactically implanted I-125 seeds supported by image fusion. The image fusion was performed by the BrainLab-Target 1.13 software on Alfa 430 (Digital) workstation before, during, and after interstitial irradiation of brain tumours with Iodine125 seeds. RESULTS AND INTERPRETATION: On the basis of 20 brachytherapeutic image fusion of stereotactic CT (slices with fiducials) with additional stereotactic CT, MRI, PET and SPECT images provides more accurate and precise target volume, more exact localization of catheters and isotope seeds (verification fusion), differentiation between the localization and amount of the necrotic and proliferating parts of the tumours and shows the volume changes in consequence of interstitial irradiation. The image fusion should help to improve the accuracy and minimize the perifocal morbidity of interstitial irradiation.

Adult↗

PubMed2000

Formation of a new class of oxylipins from N-acyl(ethanol)amines by the lipoxygenase pathway.

N-Acylethanolamines (NAEs) constitute a new class of plant lipids and are thought to play a role in plant defense strategies against pathogens. In plant defense systems, oxylipins generated by the lipoxygenase pathway are important actors. To date, it is not known whether plants also use endogeneous oxylipins derived from NAEs in their defense reactions. We tested whether members of the NAE class can be converted by enzymes constituting this pathway, such as (soybean) lipoxygenase-1, (alfalfa) hydroperoxide lyase and (flax seed) allene oxide synthase. We found that both alpha-N-linolenoylethanolamine and gamma-N-linolenoylethanolamine (18:3), as well as alpha-N-linolenoylamine and gamma-N-linolenoylamine were converted into their (13S)-hydroperoxide derivatives by lipoxygenase. Interestingly, only the hydroperoxides of alpha-N-linolenoyl(ethanol)amines and their linoleic acid analogs (18:2) were suitable substrates for hydroperoxide lyase. Hexanal and (3Z)-hexenal were identified as volatile products of the 18:2 and 18:3 fatty acid (ethanol)amides, respectively. 12-Oxo-N-(9Z)-dodecenoyl(ethanol)amine was the nonvolatile hydrolysis product. Kinetic studies with lipoxygenase and hydroperoxide lyase revealed that the fatty acid ethanolamides were converted as readily or even better than the corresponding free fatty acids. Allene oxide synthase utilized all substrates, but was most active on (13S)-hydroperoxy-alpha-N-linolenoylethanolamine and the (13S)-hydroperoxide of linoleic acid and its ethanolamine derivative. alpha-Ketols and gamma-ketols were characterized as products. In addition, cyclized products, i.e. 12-oxo-N-phytodienoylamines, derived from (13S)-hydroperoxy-alpha-N-linolenoylamines were found. The results presented here show that, in principle, hydroperoxide NAEs can be formed in plants and subsequently converted into novel phytooxylipins.

Ethanolamines↗

PubMed2000

Pre-ribosomal RNA is processed in permeabilised cells at the site of transcription.

The available data concerning the subnucleolar localisation of the individual steps of precursor-ribosomal RNA (pre-rRNA) processing are ambiguous. According to in situ hybridisation studies, the late steps of pre-rRNA processing have been located into the granular component of the nucleolus, but factors engaged in these events were found being enriched in the dense fibrillar component. In this study, by utilisation of permeabilised human cells, we demonstrate that the newly synthesised, bromouridine-labelled pre-rRNAs reside at, or near, the sites of transcription. We provide evidence that processing of pre-rRNA occurs in permeabilised mammalian cells and that the incorporated bromouridine residues do not interfere with pre-rRNA maturation. Our results suggest that the maturation process of ribosomal RNA in permeabilised cells takes place at, or nearby, the site of transcription and that the processing complex is assembled during or early after the rRNA transcription.

Bromouracil↗

PubMed2000

Processing of intron-encoded box C/D small nucleolar RNAs lacking a 5',3'-terminal stem structure.

The C and D box-containing (box C/D) small nucleolar RNAs (snoRNAs) function in the nucleolytic processing and 2'-O-methylation of precursor rRNA. In vertebrates, most box C/D snoRNAs are processed from debranched pre-mRNA introns by exonucleolytic activities. Elements directing accurate snoRNA excision are located within the snoRNA itself; they comprise the conserved C and D boxes and an adjoining 5',3'-terminal stem. Although the terminal stem has been demonstrated to be essential for snoRNA accumulation, many snoRNAs lack a terminal helix. To identify the cis-acting elements supporting the accumulation of intron-encoded box C/D snoRNAs devoid of a terminal stem, we have investigated the in vivo processing of the human U46 snoRNA and an artificial snoRNA from the human beta-globin pre-mRNA. We demonstrate that internal and/or external stem structures located within the snoRNA or in the intronic flanking sequences support the accumulation of mammalian box C/D snoRNAs lacking a canonical terminal stem. In the intronic precursor RNA, transiently formed external and/or stable internal base-pairing interactions fold the C and D boxes together and therefore facilitate the binding of snoRNP proteins. Since the external intronic stems are degraded during snoRNA processing, we propose that the C and D boxes alone can provide metabolic stability for the mature snoRNA.

Animals↗

PubMed2000

Mytilus inhibitory peptide (MIP) induces a Na+-activated K+-current in snail neurons.

Two microelectrode voltage-clamp and single-channel recordings were performed on D-cluster neurons of snail right parietal ganglion in order to study the properties of MIP-activated potassium current. It was found that the octapeptide member of the MIP-family, ASHIPRFVa elicits an outward current, which possesses all the properties characteristic for the hexapeptide(s) inward membrane response. The main component of the peptide elicited response is highly [K+]o dependent, however the response was attenuated in Na-free extracellular saline. The peptide elicited response was mimicked by raising the [Na+]i by pressure injection of Na+ into the cell. Single channel recordings indicated that MIP-induced outward K-current is Na-dependent. The probability to find a channel in open state increases with increasing intracellular Na+-concentration. Excised inside-out patches obtained from D-neurons contained I(K(Na)) channels could be activated by exposure of the cytoplasmic face of the patch membrane to 40 mM Na+, and 40 mM Li+, as well. The single channel current amplitude at -60 mV is 15 pA and the single channel conductance is 212 pS between -80 and 0 mV. It was concluded that MIP's activate a novel type of K+-current in the snail neurons. This current is the Na-activated K+-current. The single channel properties of the MIP activated channel is in concert with I(K(Na)) data obtained on different vertebrate and invertebrate preparations.

Amino Acid Sequence↗

PubMed2000

Morphometric analysis of dendritic tree of cerebellar Purkinje-cells.

Basic neural processes of sensorimotor adaptation can be observed by cellular-level studies on cerebellar cortex, both by electrophysiological and morphological means. In earlier studies we demonstrated double (sometimes triple or quadruple) rhythmic prespike activity patterns in dendritic microelectrode records taken from cerebellar Pc. By their active and passive interactions, the actual input pattern will turn into an arrhythmic output spiking, realizing a nonlinear and phase-sensitive integration. This curious complex spike-generating process can give rise to novel cerebellar functional models. The acting membrane dynamics rely not just upon the ionic current machinery but also upon the specific micromorphology of the dendritic tree, especially that of the branching areas. Although, statistical analyses on Pc dendrites generally followed the graph-theory, elaborated abstract parameters for complexity and hierarchy, and denied realistic geometry. Thus a novel specific morphometric study should be carried out, first applied to the main branching sites.

Animals↗

PubMed1999

Nucleolar localization signals of box H/ACA small nucleolar RNAs.

The two major families of small nucleolar RNAs (snoRNAs), Box C/D and Box H/ACA, are generated in the nucleoplasm and transported to the nucleolus where they function in rRNA processing and modification. We have investigated the sequences involved in the intranuclear transport of Box H/ACA snoRNAs by assaying the localization of injected fluorescent RNAs in Xenopus oocyte nuclear spreads. Our analysis of U17, U64 and U65 has revealed that disruption of either of the conserved sequence elements, Box H or Box ACA, eliminates nucleolar localization. In addition, the stem present at the base of the 3' hairpin is required for efficient nucleolar localization of U65. Fragments or rearrangements of U65 that consist of Box H and Box ACA flanking either the 5' or 3' hairpin are targeted to the nucleolus. The targeting is dependent on the presence of the Box sequences, but not on their orientation. Our results indicate that in each of the two major families of snoRNAs, a motif composed of the signature conserved sequences and an adjacent structural element that tethers the sequence elements directs the nucleolar localization of the RNAs. We demonstrate that telomerase RNA is also targeted to the nucleolus by a Box ACA-dependent mechanism.

Animals↗

PubMed1999

Ionic mechanism mediating Mytilus inhibitory peptides elicited membrane currents in identified Helix neurons.

Effects of seven, pressure applied MIP (Mytilus inhibitory peptides) had been studied on D-neurons of the CNS of Helix pomatia in voltage-clamp experiments. In physiological saline, the peptides produced a hyperpolarization usually coupled with the cessation of any spontaneous spiking activity. Clamped at the resting potential ( approximately -60 mV), peptide applications elicited an outward current, which increased its amplitude by shifting the holding potential towards depolarisation. The response was concentration-dependent and accompanied by an increased membrane conductance. Reversal potentials obtained at different [K+]o were plotted with a slope of 52 mV per ten-fold change in [K+]o showing that the peptide-elicited current was mainly due to the increased K+-conductance(s). The peptide-induced outward current could partially be blocked by Ba2+ (5 mM), CdCl2 (1 mM), TEACl (10 mM) or apamin (2.5x10(-5) M) or furosemide (10 mg/ml) and decreased either in Na+-free or Cl--free solutions. 4-Aminopyridine at 5 mM concentration completely blocked the peptide-induced current. In the presence of high [K+]o, the peptide(s) was still found to induce an outward current at membrane potentials beyond K+-reversal potential. This component was not present in Cl--free saline, suggesting that the current was due to the inward flow of Cl- ions. Our results show that the MIPs have at least two (three) independent actions, each associated with different voltage-, concentration-dependence and ionic mechanisms. It is suggested, that the peptide-induced currents are carried by K+, and Cl- ions. According to our present finding, the observed effects are mediated by the same receptor, activating different second messenger systems, inducing multiple conductance changes in the membrane of neurons of the snail ganglia.

Animals↗

PubMed1999

Elements essential for accumulation and function of small nucleolar RNAs directing site-specific pseudouridylation of ribosomal RNAs.

During site-specific pseudouridylation of eukaryotic rRNAs, selection of correct substrate uridines for isomerization into pseudouridine is directed by small nucleolar RNAs (snoRNAs). The pseudouridylation guide snoRNAs share a common 'hairpin-hinge- hairpin-tail' secondary structure and two conserved sequence motifs, the H and ACA boxes, located in the single-stranded hinge and tail regions, respectively. In the 5'- and/or 3'-terminal hairpin, an internal loop structure, the pseudouridylation pocket, selects the target uridine through formation of base-pairing interactions with rRNAs. Here, essential elements for accumulation and function of rRNA pseudouridylation guide snoRNAs have been analysed by expressing various mutant yeast snR5, snR36 and human U65 snoRNAs in yeast cells. We demonstrate that the H and ACA boxes that are required for formation of the correct 5' and 3' ends of the snoRNA, respectively, are also essential for the pseudouridylation reaction directed by both the 5'- and 3'-terminal pseudouridylation pockets. Similarly, RNA helices flanking the two pseudouridylation pockets are equally essential for pseudouridylation reactions mediated by either the 5' or 3' hairpin structure, indicating that the two hairpin domains function in a highly co-operative manner. Finally, we demonstrate that by manipulating the rRNA recognition motifs of pseudouridylation guide snoRNAs, novel pseudouridylation sites can be generated in yeast rRNAs.

Base Sequence↗

PubMed1999

Nucleolar factors direct the 2'-O-ribose methylation and pseudouridylation of U6 spliceosomal RNA.

The nucleolus has long been known as a functionally highly specialized subnuclear compartment where synthesis, posttranscriptional modification, and processing of cytoplasmic rRNAs take place. In this study, we demonstrate that the nucleolus contains all the trans-acting factors that are responsible for the accurate and efficient synthesis of the eight 2'-O-methylated nucleotides and three pseudouridine residues carried by the mammalian U6 spliceosomal small nuclear RNA. Factors mediating the formation of pseudouridine residues in the U3 small nucleolar RNA are also present and functionally active in the nucleolus. For selection of the correct target nucleotides in the U6 and U3 RNAs, the nucleolar 2'-O-methylation and pseudouridylation factors rely on short sequences located around the target nucleotide to be modified. This observation further underscores a recently proposed role for small nucleolar guide RNAs in the 2'-O-methylation of the U6 spliceosomal RNA (K. T. Tycowski, Z.-H. You, P. J. Graham, and J. A. Steitz, Mol. Cell 2:629-638, 1998). We demonstrate that a novel 2'-O-methylated nucleotide can be generated in the yeast U6 RNA by use of an artificial 2'-O-methylation small nucleolar guide RNA. We also show that a short fragment of the 5.8S rRNA, when expressed as part of the human U6 RNA, is faithfully 2'-O-methylated and pseudouridylated. These results are most consistent with a trafficking pathway in which the U6 spliceosomal RNA cycles through the nucleolus to undergo nucleolar RNA-directed modifications.

Base Sequence↗

PubMed1999

Effects of veratridine and its derivatives on the Na-conducting channels in Helix neurons.

Effects of veratrum alkaloids were studied on the Na-channels of the land snail Helix pomatia. It was found that veratridine and its analogues depolarize the membrane due to the increased Na-permeability. The inactivation was shifted right along the voltage axis and the recovery from the inactivation was faster after veratridine treatment. After alkaloid treatment the selectivity of the Na-channel decreased, however, the selectivity sequence was not altered. The activation curve was not shifted. Veratridine derivatives, which appeared to be more effective on insects, had almost no effect on the Na-current.

Action Potentials↗