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Biomedical subjects

A Ivanov

Publications and source records attributed to A Ivanov.

At least 19 recordsLinked to original sources
PubMed1999

Excitatory amino acids and synaptic transmission in embryonic rat brainstem motoneurons in organotypic culture.

We used brainstem motoneurons recorded in organotypic slice co-cultures maintained for more than 18 days in vitro, together with multibarrel ionophoretic applications of glutamate receptor agonists and bath applications of specific blocking agents, to study the responses of rat brainstem motoneurons to glutamate receptor activation, and the contribution of these receptors to synaptic transmission. Differentiated brainstem motoneurons in vitro are depolarized by glutamate, N-methyl-d-aspartate (NMDA) and dl-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) iontophoresis, and express NMDA, AMPA and also specific kainate receptors, as evidenced by (+/-)2-amino-5-phosphonovaleric acid (APV)- and (-)1-(4-aminophenyl)-3-methyl-carbamoyl-4-methyl-7, 8-methylenedioxy-3,4-dihydro-5H-2,3-benzo-diazepine [GYKI 53784 (LY303070)]-resistant depolarizations. Electrical stimulations applied to the dorsal part of the explant trigger excitatory synaptic potentials with latencies distributed in three regularly spaced groups. Excitatory postsynaptic potentials (EPSPs) in the earliest group have a similar latency and time course and correspond to monosynaptic activation. EPSPs in later groups have more scattered latencies and time courses and correspond to polysynaptic activation. Monosynaptic EPSPs are insensitive to the specific NMDA blocker APV, and are completely and reversibly suppressed by the non-competitive AMPA receptor antagonist GYKI 53784 (LY303070). Detailed analysis of the spontaneous excitatory synaptic activity shows that APV decreases the frequency of spontaneous EPSPs without modifying their shape or amplitude. We conclude that excitatory synapses on brainstem motoneurons in vitro are mainly activated through AMPA receptors (AMPA-Rs). NMDA receptors (NMDA-Rs) are present in the membrane, but are located either at extrasynaptic sites or silent synapses, and are not directly involved in synaptic transmission on motoneurons. On the contrary, NMDA receptors contribute to synaptic transmission within the premotor interneuronal network.

Animals↗
PubMed1998

Developing rat brainstem motoneurones in organotypic culture express calcium permeable AMPA-gated receptors.

Recent studies suggest that calcium permeable excitatory amino acid receptors may play an important role in many developmental processes including dendritic differentiation, synaptogenesis and activity dependent plasticity or excitotoxicity related disorders. In this work, we investigate the existence of calcium permeable AMPA receptors in embryonic rat motoneurones in organotypic slice culture, which display an early sensitivity to AMPA and Kainate. We used excitatory amino acids induced cobalt uptake and show that developing motoneurones express Ca2+ permeable AMPA receptors. We demonstrate, as already described for other neuronal types in acute slices of adult animals, that the cobalt loading of motoneurones is not suppressed by blockade of synaptic activity by TTX. It is not induced by NMDA stimulation and does not result from the activation of voltage dependent calcium channels. It is specifically suppressed by the non-competitive AMPA antagonist GYKI 53784 (LY303070) and enhanced by the AMPA-receptor desensitization blocker Aniracetam. We conclude that cobalt loading results from the specific activation of AMPA receptors. We further show that, when cobalt loading is induced by threshold doses of Glutamate agonists, cobalt-sulfide deposits are found specifically in primary dendrites, dendritic spines and localized spots on the somatic and peripheral dendritic membrane. We suggest that this particular pattern of staining, different from the Golgi-like staining obtained with excitotoxic doses, may offer new information regarding the membrane density and distribution of calcium permeable AMPA receptors.

Animals↗
PubMed1998

Are bacterial proteins part of the matrix of kidney stones?

An extracellular protein, produced from Pseudomonas fluorescens strain D with molecular mass of 41.5 kDa was partially purified. Its first 12 amino acid sequence shows strong similarity to a sequence reported to belong to a protein isolated from a urate-calcium oxalate stone (Binnette & Binnette, Scan Microsc1994; 2: 233-239). A possible involvement of bacterial proteins in stone matrix is discussed.

Amino Acid Sequence↗
PubMed1997

Structural analysis of the products of chymotryptic cleavage of the E1 form of Na,K-ATPase alpha-subunit: identification of the N-terminal fragments containing the transmembrane H1-H2 domain.

Chymotryptic cleavage of the Na,K-ATPase in NaCl medium abolishes ATPase activity and alters other functional parameters. The structure of this modified enzyme is uncertain since only one product of selective proteolysis, the 83-kDa fragment of the alpha-subunit (Ala267-C-terminus) has been identified previously. Here, we applied additional tryptic digestion followed by oxidative cross-linking to identify the products originating from the N-terminal part of the alpha-subunit. These fragments start at Ala72 or Thr74 and contain the transmembrane H1-H2 domain. Formation of cross-linked product between alpha-fragments containing H1-H2 and H7-H10 demonstrate that the structural integrity of the membrane moiety is preserved. We also determined that secondary cleavage of the 83-kDa fragment leads to the formation of C-terminal 48-kDa alpha-fragments with multiple N-termini at Ile582, Ser583, Met584 and Ile585.

Animals↗
PubMed1997

Ligand-sensitive interactions among the transmembrane helices of Na+/K+-ATPase.

An extensively trypsin-digested Na+/K+-ATPase, which retains the ability to bind Na+, K+, and ouabain, consists of four fragments of the alpha-subunit that contain all 10 transmembrane alpha domains, and the beta-subunit, a fraction of which is cleaved at Arg142-Gly143. In previous studies, we solubilized this preparation with a detergent and mapped the relative positions of several transmembrane helices of the subunits by chemical cross-linking. To determine if these detected helix-helix proximities were representative of those existing in the bilayer prior to solubilization, we have now done similar studies on the membrane-bound preparation of the same digested enzyme. After oxidative sulfhydryl cross-linking catalyzed by Cu2+-phenanthroline, two prominent products were identified by their mobilities and the analyses of their N termini. One was a dimer of a 11-kDa alpha-fragment containing the H1-H2 helices and a 22-kDa alpha-fragment containing the H7-H10 helices. This dimer seemed to be the same as that obtained in the solubilized preparation. The other product was a trimer of the above two alpha-fragments and that fraction of beta whose extracellular domain was cleaved at Arg142-Gly143. This product was different from a similar one of the solubilized preparation in that the latter contained the predominant fraction of beta without the extracellular cleavage. The cross-linking reactions of the membrane preparation, but not those of the solubilized one, were hindered specifically by Na+, K+, and ouabain. These findings indicate that (a) the H1-H2 transmembrane helices of alpha are adjacent to some of its H7-H10 helices both in solubilized and membrane-bound states, (b) the alignment of the residues of the single transmembrane helix of beta with the interacting H1-H2 and H7-H10 helices of alpha is altered by detergent solubilization and by structural changes in the extracellular domain of beta, and (c) the three-dimensional packing of the interacting transmembrane helices of alpha and beta are regulated by the specific ligands of the enzyme.

Amino Acid Sequence↗
PubMed1997

[The intraoperative determination of intestinal vitality with a fluorescent indicator].

Intestinal obstruction due to strangulation is induced in dogs under experimental conditions, with intestinal wall vitality assessment done on the ground of standard clinical criteria, using fluorescence dye and UV rays, as well as histological study. Sensitivity, specificity and prognostic value of each of the methods employed are determined. The fluorescence method advantages are recorded, and the prospects of its clinical implementation are estimated.

Animals↗
PubMed1997

[Volvulus of the small intestine].

Volvulus of the small intestine is a condition of bowel obstruction due to knotting and twisting of the small intestine. Two types of volvulus are described: 1) primary small intestinal volvulus where no predisposing factors exist, and 2) secondary volvulus where congenital or acquired conditions promote twisting of the small intestine. Over a 5-year period, 18 patients (eleven men and seven women) presenting volvulus of the small intestine are operated in the Emergency Surgery Clinic of the University Hospital "Queen Giovanna", representing 8.7 per cent of the total of 206 cases of small intestinal mechanical ileus (incarcerated herniations involving the small intestine are not included in the series). Primary volvulus is found in one patient. In those presenting secondary volvulus adhesions are the commonest underlying cause of small intestinal rotation--13 cases, next ranking primary tumor of the small intestine--one case, Meckel's diverticulum--one, carcinosis of peritoneum--one, and one patient with small intestine volvulation around colostomy. The most frequently encountered symptoms and laboratory examinations performed are analyzed. Intestinal necrosis is established in four instances (22 per cent). One patient dies of peritonitis and polyorganic insufficiency. Volvulus of the small intestine should be mandatorily considered in patients presenting mechanical ileus of the small intestine. Early operative intervention is a therapeutic approach contributing to preclude intestinal necrosis.

Adult↗
PubMed1996

Biotin-labeled antigen: a novel approach for detection of Puumala virus-specific IgM.

A novel enzyme-linked immunosorbent assay, BLA IgM-ELISA, based on baculovirus-expressed Puumala (PUU) virus nucleocapsid protein, was developed for rapid diagnosis of nephropathia epidemica. The recombinant antigen (bac-PUU-N) was purified to homogeneity by HPLC and conjugated to biotin. The biotin-streptavidin system, in combination with the mu-capture technique, rendered the BLA IgM-ELISA a sensitivity similar to or higher than that of PUU virus IgM mu-capture ELISA based on native antigen. The assay was shown to be highly specific when evaluated using a panel of 160 patient and control sera.

Antibodies, Viral↗
PubMed1996

Biophysical studies on the correction of uremic human serum albumin binding defects by in vitro charcoal adsorption treatment.

Spectrofluorimetry, flow microcalorimetry, and differential scanning microcalorimetry (DSMC) were used to study the conformation, binding function, and ligand loading of uremic albumin obtained from the blood plasma of 2 end-stage renal disease (ESRD) patients before and after charcoal plasma treatment at different pH values (3.0-9.0). The spectrofluorimetric patterns of conformational N-F transition at low pH (4.2-3.5) are practically identical for both samples of uremic human serum albumin (HSA) and control HSA from healthy donors. After the charcoal treatment at pH 3.0 and 4.0, the enthalpies of complexing on uremic HSA with bromsulfalein and sodium dodecylsulfate approach that of donor HSA. The binding affinity of uremic HSA for sodium octanoate, phenol red, and salicylic acid following low pH charcoal treatment even exceed those of donor HSA. At the same time the charcoal treatment of uremic plasma at neutral and alkaline pH does not notably improve the binding characteristics of isolated HSA. Adsorption at low pH values completely restores the tryptophan fluorescence spectrum position of uremic albumin and improves the thermodynamic characteristics of its melting process. Using DSMC data, it can nevertheless be concluded that some conformational changes or a certain amount of high-affinity bound endogenous ligands still remain after low pH uremic HSA purification. The latter conclusion requires additional improvements of adsorption treatment of uremic plasma.

Adsorption↗
PubMed1996

Ganglionic neuronal mechanisms involved in circulatory control system.

Intracellular tonic activity and responses to orthodromic stimuli were recorded from the neurones of rabbit superior cervical ganglion and compared with those recorded from the nerves containing pre- and postganglionic nerve fibres, with the use of a coherent recording technique. It was found that: (1) firing of each ganglion neurone is triggered by two presynaptic inputs, single and multiple, formed by a single preganglionic nerve fibre whose discharges evoke the postsynaptic spikes correlated with cardiac rhythm, and by a few converging preganglionic nerve fibres which evoke the postsynaptic spikes, either correlated with cardiac rhythm or irregular, only if two or more of them discharge together, correspondingly; (2) about 240 neurones of the ganglion, on the average, fire synchronously during their tonic activity, being driven by only three preganglionic nerve fibres; (3) only about 9% of a "neural unit", the number of the ganglion neurones receiving innervation from the same preganglionic nerve fibre, are discharged during their tonic activity through a single input, while the rest of neurones are either discharged through a multiple input (17%), or generate only the excitatory postsynaptic potentials subthreshold for spike generation (73%). The results obtained suggest that the ganglionic neuronal mechanisms responsible for vasomotor control involve much more complex ganglionic integrative processes than it has been commonly thought.

Animals↗
PubMed1996

Characterisation of a phospholipase C produced by Pseudomonas fluorescens.

Phospholipase C (phosphatidylcholine phosphohydrolase, EC 3.1.4.3) and lipase (EC 3.1.1.3) activities were detected in the supernatant fluid of Pseudomonas fluorescens strain D cultures. A combination of ultrafiltration and successive chromatography through columns of Sephadex G-75 and DEAE-cellulose was used to purify the phospholipase C over 700-fold from the culture medium, with 28.5% yield. The purified enzyme appeared as a single band after polyacrylamide gel electrophoresis. The apparent molecular mass of the phospholipase C was 36,000 daltons when estimated by gel permeation chromatography. The purified enzyme hydrolysed phosphatidylcholine more efficiently than phosphatidylethanolamine. The synthetic substrate p-nitrophenylphosphorylcholine, phosphatidylinositol or sphingomyelin were not hydrolysed. Hydrolysis of phosphatidylcholine was inhibited by EDTA (1mM) and stimulated by Zn2+, Mg2+ ions and detergents. These properties of the enzyme indicate that it is distinct from the previously reported Ps. fluorescens phospholipase C.

Chromatography, Gel↗
PubMed1996

Microorganisms as a tool of studying copper metal ions--induced changes in electrophysical cell properties.

Microorganisms are very sensitive to the effect of metal ions and a deficit or an excess of essential metal ions may induce some cell disturbances. The main objective of this research is to evaluate the effect of toxic metal ions. Doing that, the effects of metal ions on the electrophysical properties of the cell membrane, probed by electroorientational spectroscopic techniques and analysis of the electrophoretic mobility of cells have been chosen for investigation. The purpose of this work is to determine the optimal conditions of investigation of different kinds of microorganisms exposed to Cu. pH had a great influence on the electrophysical changes induced by Cu and this may be related to the speciation of the metal, according to its degree of hydroxylation. It will now be possible to compare the effects of toxic metal ions (Cd, Hg, Pb, etc..) or therapeutic metal ions (Pt, Ga, Ru, Ti, Sn, etc..) with those observed for Cu, in the conditions optimized by this study.

Bacteria↗
PubMed1996

[The level of lipid peroxidation products in the plasma of patients with acute pancreatitis].

Plasma malondialdehyde level is studied in patients presenting acute pancreatitis. In those subjected to nonoperative treatment no statistically significant variations in MDA level, by comparison with the reference values, are registered. In patients undergoing surgery, a statistically significant increase in MDA, exceeding the uppermost limit of the reference values, is documented. The inference is reached that values above the reference ones (3.2 nmol/ml plasma) are usually interpreted as pointing to necrosis development in the pancreas.

Acute Disease↗
PubMed1996

[The induction of lipid peroxidation in the serum of patients with acute peritonitis].

The level of lipid peroxidation products in the sera of patients with acute peritonitis and clinically healthy blood donors are studied. An increase in the level of TBA-reactive substances is documented in the acute peritonitis group--twice as high as compared to clinically healthy blood donors. Changes in the patients in toxic and terminal phases of peritonitis are rather significant. Following hemofiltration, the serum lipid peroxidation products are decreased in comparison with the pre-hemofiltration state.

Acute Disease↗
PubMed1996

[Transendoscopic drug denervation of the stomach in emergency surgical diseases of the gastrointestinal tract (a preliminary report)].

This is the first, preliminary report on the implementation of transendoscopic medicamentous denervation of the stomach as a therapeutic approach to acute surgical diseases of the gastrointestinal tract. Diminishing the vagus nerve influence after the method described contributes to a substantial improvement of the treatment results in acute pancreatitis patients by shortening the term of therapeutic fasting, avoiding nasogastric tube insertion, and making unnecessary H2-blockers application. TEMDS is indicated in all instances of acute pancreatitis, bleeding duodenal ulcer, bleeding ulcus pepticum jejuni following BII resection of the stomach.

Emergencies↗
PubMed1996

[Anaerobic surgical infection and septic shock].

In the period 1990 through 1995, one-hundred patients operated for acute abdomen or admitted on a routine basis, presenting evidence of anaerobic infection, undergo treatment in the clinic of emergency surgery. Septic shock develops in 10/100 patients (10 per cent). In six of the latter the outcome is fatal--three with infection caused by spore-forming anaerobes (gas gangrene of the inguinal region--of Fournier, and anterior abdominal wall--anus praeternaturalis--two), and three with infection caused by non-spore-forming anaerobes (mixed anaerobic-aerobic infection). Anaerobic surgical infection and septic shock specificity is discussed, with an algorithm of therapeutic approach, based on clinical experience had with 100 patients, being proposed in either of them. Special emphasis is laid on antibiotic prophylaxis against anaerobic surgical infection. Its implementation in the concrete clinical conditions in this country demands a clearcut hospital drug policy (adoption of the "Drug Formularies" system), and elaboration of a new economical approach to the choice of antibacterial agents (using some of the forms of pharmaco-economical analysis, practicable with a view to the Bulgarian health-care model).

Abdomen, Acute↗