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Biomedical subjects

M Wikström

Publications and source records attributed to M Wikström.

At least 91 records · Page 5Linked to original sources
PubMed1996

Myocardial cell death in reperfused and nonreperfused myocardial infarctions. MR imaging with dysprosioum-DTPA-BMA in the pig.

PURPOSE: To investigate whether Dy-DTPA-BMA-enhanced MR imagining would permit identification of myocardial cell death, myocardial infarction was induced in 12 domestic pigs. MATERIAL AND METHODS: In 6 pigs with irreversible cell damage, Dy-DTPA-BMA (1.0 mmol/kg b.w.) was administered i.v. 70 min after coronary occlusion. In 6 other pigs, the infarctions were reperfused 80 min after the occlusion, followed by injection of Dy-DTPA-BMA after 30 min of reperfusion. In 4 additional pigs, the hearts were reperfused after 2 min of occlusion. All 16 pigs were sacrificed 10 min after the injection of Dy-DTPA-BMA. The hearts were excised and imaged with MR. RESULTS: Reversibly injured myocardium could not be distinguished from adjacent nonischaemic myocardium after the administration of Dy-DTPA-BMA. Reperfused, infarcted myocardium demonstrated a high signal intensity in the proton-density- and T2-weighted sequences, despite a 5-fold higher Dy concentration compared with both nonreperfused infarcted and nonischaemic myocardium. CONCLUSION: This lack of susceptibility effect in infarcted myocardium, due to a homogeneous distribution of Dy, indicates the usefulness of Dy as a marker of tissue viability.

Animals↗
PubMed1996

Double-contrast MR imaging of reperfused porcine myocardial infarction. An experimental study using Gd-DTAA and Dy-DTPA-BMA.

PURPOSE: Myocardial infarctions were induced in 12 pigs to investigate whether a double-contrast method, combining a positive and a negative MR contrast agent, could improve the visualization of reperfused myocardial infarctions. MATERIAL AND METHODS: All 12 pigs were subjected to 80 min of occlusion followed by reperfusion. In the double-contrast group (6 pigs), Gd-DTPA-BMA (0.3 mmol/kg b.w.) and Dy-DTPA-BMA (1.0 mmol/kg b.w.) were administered i.v. after 30 min of reperfusion. In the remaining 6 pigs, a single injection of Gd-DTPA-BMA (0.3 mmol/kg b.w.) was given after 30 min of reperfusion. All pigs were sacrificed 10 min post-contrast injection, corresponding to a reperfusion time of 40 min. The hearts were excised and imaged with MR. The concentrations of GD and Dy were measured in infarcted and nonischaemic myocardium using ICP-AES. RESULTS AND CONCLUSION: Contrast media concentrations were more than 4-fold higher in infarcted compared with nonischaemic myocardium. The infarctions were best shown on T1-weighted images, and there were no differences between the double and single contrast groups. In the T2-weighted images, the infarctions were significantly better visualized in the double-contrast group, due to a Dy-induced signal intensity loss in nonischaemic myocardium.

Animals↗
PubMed1996

Treatment of periodontal disease based on microbiological diagnosis. Relation between microbiological and clinical parameters during 5 years.

The purpose of this study was to assess the clinical effect of treatment aimed to suppress Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis below detection level and Prevotella intermedia below 5% of the cultivable periodontal pocket flora. Sixteen patients and a total of 111 periodontal pockets with probing depth > or = 6 mm were included in the study. Twelve patients and a total of 77 sites completed the 5-year study. The results demonstrated clinical improvement of probing depth and gain of clinical attachment level of 3.4 mm and 1.2 mm, respectively. Treatment to eliminate indicator bacteria continued for 3 years before the aim was fulfilled. In order to eliminate A. actinomycetemcomitans from a majority of the sites, a combination of surgery and generalized tetracycline treatment was performed. A recolonization or regrowth of the indicator bacteria exceeding detection levels took place in several sites. The presence of A. actinomycetemcomitans. P. gingivalis, and P. intermedia, alone or in combination, correlated with attachment level change on the individual level. No such correlation was obtained by using presence of plaque, bleeding on probing, or three other bacteria (Campylobacter rectus, Eikenella corrodens, and Fusobacterium nucleatum) not used as treatment goal markers.

Adult↗
PubMed1996

Treatment of periodontal disease based on microbiological diagnosis. A 5-year follow-up on individual patterns.

Sixteen patients with advanced periodontitis (more than 3 sites with a probing depth > or = 6 mm) were treated with the aim of eliminating Actinobacillus actinomyce-temcomitans and Porphyromonas gingivalis and reducing Prevotella intermedia below 5% of the total viable count. The patients were followed clinically and microbiologically for over 5 years and showed a highly individual pattern with respect to presence of indicator bacteria, type of treatment needed to accomplish treatment goals, clinical response, and bacterial and disease recurrencies. The results of this study suggest that presence of the indicator bacteria in microbial samples taken after treatment may identify patients at risk for recurrent periodontitis.

Adult↗
PubMed1996

[Management of iatrogenic hemorrhage after mechanical vascular recanalization].

Nine patients with hemorrhage due to revascularization procedures underwent successful embolization (5), surgery (2), covered stent implantation (1), or long-lasting ballon dilatation (1). Bleeding was the result of Fogarty thrombectomy (3), ring stripper revascularization (1), balloon dilatation (3), or perforation of the artery with the guide wire (1). In all cases, bleeding was stopped successfully without sequelae for the patients. In spite of the preceeding hemorrhage, local fibrinolysis with 1,000,000 units of urokinase was performed on the same day in 3 patients without any complications being observed.

Adult↗
PubMed1995

Identification of a "peroxy" intermediate in cytochrome bo3 of Escherichia coli.

The respiratory heme-copper oxidases catalyze the reduction of dioxygen to water and link this chemistry to proton translocation. The main subgroups of the enzyme family are the cytochrome c oxidases and the quinol oxidases. For the cytochrome c oxidases, several key intermediates have been described in the oxygen reaction. Two of these (suggested to be "peroxy" and "ferryl" species) are also produced in the reaction of the oxidized enzyme with hydrogen peroxide. However, only a single product (a "ferryl" species) has been reported for the reaction of hydrogen peroxide with the quinol oxidase cytochrome bo3 from Escherichia coli. The same "ferryl" species has also been reported to be produced when two-electron reduced cytochrome bo3 reacts with oxygen, whereas this reaction leads to the "peroxy" intermediate in the cytochrome c oxidases. Consequently, the oxygen reaction has been considered to be different in the two enzyme subgroups. Here we show that both the peroxide reaction and the reaction of the two-electron reduced enzyme with oxygen actually result in primary formation of a hitherto unreported "peroxy" species in cytochrome bo3. This intermediate subsequently relaxes into the "ferryl" species which has been described previously. We conclude that the oxygen reaction is similar in the cytochrome c and quinol oxidases.

Cytochrome b Group↗
PubMed1995

Perturbation of the CuA site in cytochrome-c oxidase of Paracoccus denitrificans by replacement of Met227 with isoleucine.

Subunit II of cytochrome-c oxidase contains a redox centre, CuA, with unusual spectroscopic properties; this site consists of two copper atoms and acts as the entry point for electrons from cytochrome c. We have constructed a site-directed mutant of cytochrome-c oxidase from Paracoccus denitrificans in which the CuA site has been disturbed by replacement of Met227 with isoleucine. The purified, fully assembled enzyme complex has been investigated with various techniques including metal analysis, EPR and visible spectroscopies, steady-state and fast kinetics. The stoichiometry of the metals in the enzyme remains unchanged but a clear perturbation of the CuA site can be observed in the EPR and near-infrared optical spectra. It is concluded that in the mutant CuA is still binuclear but that the two nuclei are no longer equivalent, converting the delocalized [Cu(1.5)....Cu(1.5)] centre of the wild type into a localized [Cu(I)....Cu(II)] system. Changes in the overall kinetics of the mutant are correlated with a diminished electron transfer rate between CuA and heme alpha.

Copper↗
PubMed1995

The GA module, a mobile albumin-binding bacterial domain, adopts a three-helix-bundle structure.

We present the first study of the secondary structure and global fold of an albumin-binding domain. Our data show that the GA module from protein PAB, an albumin-binding protein from the anaerobic bacterial species Peptostreptococcus magnus, is composed of a left-handed three-helix bundle. The helical regions were identified by sequential and medium range NOEs, values of NH-C alpha H coupling constants, chemical shift indices, and the presence of slowly exchanging amide protons, as determined by NMR spectroscopy. In addition, circular dichroism studies show that the module is remarkably stable with respect to both pH and temperature.

Albumins↗
PubMed1995

Structure and stability of protein H and the M1 protein from Streptococcus pyogenes. Implications for other surface proteins of gram-positive bacteria.

M proteins and other members of the M protein family, expressed on the surface of Streptococcus pyogenes, bind host proteins such as immunoglobulins, albumin, and fibrinogen. Protein H and the M1 protein are expressed by adjacent genes and both belong to the M protein family. In this work, the structure and stability of these two proteins have been investigated. As judged from sequence analysis and circular dichroism spectroscopy, the proteins are almost entirely in an alpha-helix conformation. The amino acids are arranged in a seven-residue (heptad) repeat pattern along the greater part of the proteins. These observations support the previously accepted model of M proteins as coiled-coil dimers. However, it was also found that the structures of both proteins were thermally unstable; i.e., the content of helix conformation was greatly reduced at 37 degrees C as compared to 25 degrees C or below. Together with previous findings that these proteins appear as monomers at 37 degrees C and dimers at low temperatures, the results suggest that the coiled-coil dimers are unfolded at 37 degrees C. The heptad patterns of protein H and the M1 protein showed a nonoptimal distribution of residues expected for a coiled-coil conformation. This is a possible explanation for the low thermal stability of the proteins. It was also demonstrated that the proteins were stabilized in the presence of the ligands IgG and/or albumin. Protein H and M1 protein show a high degree of sequence similarity in their C-terminal regions, and a fragment from this region displayed a high content of helix conformation, whereas fragments from the nonsimilar N-terminal parts did not adopt any stable folded structure. Thus, the C-terminal parts, which are conserved within the M protein family, may constitute a framework for the formation of the parallel helical coiled-coil structure, and we propose that the less stable N-terminal part may also participate in antiparallel interaction with M proteins on adjacent bacteria. The results suggest that temperature fluctuations in the environment could change the properties of bacterial surface proteins, thereby affecting the molecular interactions between the bacterium and its host.

Amino Acid Sequence↗
PubMed1995

Raman detection of a peroxy intermediate in the hydroquinone-oxidizing cytochrome aa3 of Bacillus subtilis.

When the mixed valence, carbon monoxide-bound form of the hydroquinone-oxidizing cytochrome aa3-600 of Bacillus subtilis is illuminated in the presence of O2, it forms a species that corresponds to 'Compound C', first described for the mitochondrial cytochrome c oxidase by Chance, Saronio and Leigh (J. Biol. Chem. 250 (1975) 9226-9237). Resonance Raman spectra of the this species show a mode at 366 cm-1 that shifts to 342 cm-1 when the experiment is repeated with 18O2. The appearance of this mode is insensitive to deuteration exchange within the limits of resolution. High- (1200-1700 cm-1) and low-frequency (200-500 cm-1) data, allow us to assign the 366 cm-1 mode to the Fe(3+)-O stretching vibration of a peroxide adduct where the iron is either low or intermediate spin. This is to our knowledge the first time an 18O2-sensitive iron-oxygen stretching mode has been reported for 'Compound C', providing strong support for the notion that this species is a peroxide adduct. The observed 366 cm-1 v(Fe(3+)-O(-)-O-) frequency is 8 cm-1 higher than that previously found for a transient peroxy intermediate in the reaction between the fully reduced mitochondrial enzyme and O2. Our observation indicates that, while similar, the metastable peroxyheme a3 species reported here differs in the fine details of geometry, protonation state, and/or hydrogen bond status.

Bacillus subtilis↗
PubMed1995

Structure of CuB in the binuclear heme-copper center of the cytochrome aa3-type quinol oxidase from Bacillus subtilis: an ENDOR and EXAFS study.

We have studied the structure of the CuB site in the binuclear heme-copper center of the fully oxidized form of the quinol-oxidizing cytochrome aa3-600 from Bacillus subtilis by EXAFS and ENDOR spectroscopy. This enzyme is member of the large superfamily of heme-copper respiratory oxidases, which catalyze the reduction of dioxygen to water and link it to translocation of protons across the bacterial or mitochondrial membrane. The EXAFS of the CuB site strongly suggests tetragonal coordination by two or three histidines with one or two O/N donor ligands. There are some indications that a Cl- ion might fractionally occupy substitution-labile sites, although the majority of enzyme molecules did not contain any heavy (second row) scatters, indicative of a Cl- (or S) bridge between the heme iron and CuB [cf. Powers, L., et al. (1994) Biochim. Biophys. Acta 1183, 504-512]. Proton ENDOR spectroscopy of the CuB site in 1H2O and 2H2O media showed evidence of an oxygenous copper ligand with an exchangeable proton. 14N ENDOR revealed three inequivalent nitrogenous ligands with hyperfine coupling constants consistent with histidines. Together, these results strongly suggest that the fully oxidized enzyme has a low-symmetry, tetragonal CuB site with three histidine nitrogens and one oxygen as ligands, the latter with an exchangeable proton(s). The identity and assignment of these ligands are discussed.

Bacillus subtilis↗
PubMed1995

Mapping of the immunoglobulin light chain-binding site of protein L.

Protein L is a cell surface protein expressed by some strains of the anaerobic bacterial species Peptostreptococcus magnus. The molecule binds specifically and with high affinity to immunoglobulins (Ig) of a wide range of animal species. The Ig-binding activity is mediated through five highly homologous domains, each 72 to 76 amino acid residues long, which interact with framework regions in the variable domain of Ig light chains. The interaction does not interfere with the antigen binding capacity of the antibody. The fold of the Ig light chain-binding domains of Protein L is comprised of an alpha-helix packed against a four stranded beta-sheet and is similar to the fold of the IgG heavy chain-binding domains of streptococcal protein G, despite the fact that the two proteins show no significant sequence homology. In the present work, heteronuclear NMR spectroscopy has been utilized to define the interaction between the N-terminal Ig-binding domain of Protein L and the variable domain of a human Ig kappa light chain. The Ig-binding region of the Protein L domain involves most of the residues in the second beta-strand, the C-terminal residues of the alpha-helix and the loop connecting the alpha-helix with the third beta-strand. The Ig light chain-binding surface of Protein L thus resembles the surface of Protein G which binds to the C gamma 1 domain of IgG, but is different from the portion of Protein G involved in the contact with the C gamma 2-C gamma 3 interface region. The data suggest that the global fold shared by the Ig-binding domains of Proteins L and G provide bacteria with a flexible template for the evolution of surface structures capable of interacting with different conserved parts of Ig molecules of the infected host.

Bacterial Proteins↗
PubMed1995

Control of electron delivery to the oxygen reduction site of cytochrome c oxidase: a role for protons.

We have studied the reaction of oxidized "pulsed" cytochrome c oxidase with reduced cytochrome c and with ruthenium(II) hexaammine using stopped-flow mixing. The rate of reduction of Fea3 (the oxygen-binding heme) is not a linear function of the population of reduced Fea (the low-spin heme), as would be expected if electron transfer between these sites is rate-limiting. Instead, the rate can be increased significantly by increasing the driving force of the reductant (lowering of Eh) even after Fea is almost completely reduced. Reduction of Fea3 becomes slower as the pH is raised, and consumption of protons can be seen simultaneously with electron entry into Fea3. Both the reduction of Fea3 and the proton uptake are biphasic. To explain these findings, we propose a model in which (1) intramolecular heme-heme electron transfer is fast, and has an essentially constant rate; (2) when reduction begins, the midpoint potentials of Fea3 and CuB are initially low, and only a small fraction of these centers become reduced; and (3) this reduced population is then stabilized by the uptake of protons. Thus, net reduction of Fea3 and CuB is controlled by the amount of the low-potential population which becomes reduced together with the rate of proton uptake by this reduced low-potential species. Important consequences of this mechanism for the function of the enzyme and for the respiratory chain as a whole are discussed.

Animals↗
PubMed1995

The action of 5-HT on calcium-dependent potassium channels and on the spinal locomotor network in lamprey is mediated by 5-HT1A-like receptors.

5-HT has a powerful modulatory action on the firing properties of single neurons as well as on locomotor activity. In lamprey, 5-HT increases the neuronal firing frequency in spinal neurons by reducing the conductance in Ca(2+)-dependent K+ channels (KCa) underlying the slow afterhyperpolarization (sAHP), and it also lowers the burst frequency of the spinal locomotor network. To elucidate which type of 5-HT receptor mediates these effects, different specific receptor agonists and antagonists were applied during intracellular current clamp recordings and during NMDA-induced fictive locomotion in the lamprey spinal cord in vitro preparation. The 5-HT1A receptor agonist 8-OH-DPAT ((+/-)-8-hydroxy-dipropylaminotetralin hydrobromide), the 5-HT1 receptor agonist 5-CT (5-carboxyamidotryptamine maleate) and the 5-HT2 receptor agonist alpha-CH3-5-HT (alpha-methylserotonin maleate) all reproduced the actions of 5-HT at both the cellular and the network levels. The effects of all agonists were completely or partially blocked by the 5-HT1A and 5-HT2 receptor antagonist spiperone (spiroperidol hydrochloride) while selective 5-HT2 receptor antagonists were ineffective. The selective 5-HT1A receptor antagonist S(-)-UH301 (S(-)-5-fluoro-8-hydroxy-dipropylaminotetralin hydrochloride) also counteracted the effect of 5-HT on the sAHP. 5-HT3 and 5-HT4 receptor agonists and antagonists were without effects. The intracellular coupling mechanism was not sensitive to pertussis toxin nor to the cAMP dependent protein kinase blocker (Rp)-cAMPS.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1995

A novel antiporter activity catalyzing sodium and potassium transport from right-side-out vesicles of E. coli.

Downhill sodium efflux from right-side-out E. coli membrane vesicles was found to be stimulated by negative electric potential, as has been reported earlier [Bassilana et al., Biochemistry 23 (1984) 1015-1022], and in agreement with the concept of electrogenic Na+/nH+ antiporters with n > 1. However, sodium efflux was much more accelerated by positive electric potential, indicating the operation of another sodium transport system. delta pH (alkaline inside), created by a pH shift from 8.5 to 6.8 in the medium was found to drive sodium efflux against its concentration gradient, but only when the vesicles had been loaded with both Na+ and K+. Efflux of K+ against the concentration gradient was also observed under these conditions. When the vesicles were loaded separately with sodium tricine or potassium tricine, no K+ efflux and insignificant Na+ efflux were observed. We propose that there are at least two different mechanisms responsible for Na+ efflux in E. coli vesicles. One is the Na+/nH+ antiporter previously described, and the other is a novel Na+,K+/mH+ antiporter.

Antiporters↗
PubMed1995

Proton transfer in cytochrome bo3 ubiquinol oxidase of Escherichia coli: second-site mutations in subunit I that restore proton pumping in the mutant Asp135-->Asn.

The ubiquinol oxidase, cytochrome bo3, of Escherichia coli is a member of the respiratory heme-copper oxidase family and conserves energy from the reduction of dioxygen to water by translocation of protons across the bacterial membrane. Mutation of an aspartic acid residue (Asp135) to asparagine in subunit I of this enzyme was previously found to impair proton translocation [Thomas et al. (1993) Biochemistry 32, 10923-10928]. This residue is located in an interhelical "loop" between transmembranous helices II and III, which contains six well-conserved residues (Asn124, Pro128, Gly132, Asp135, Pro139, and Asn142). Site-directed mutagenesis was performed to study the function of this entire domain. Nonconservative mutations of Asn124 and Asn142 also resulted in a loss of proton translocation, whereas their conservative substitution to glutamine had no effect. Mutations in eight other positions within this domain did not affect proton translocation. Introduction of an acidic group at positions 139 or 142, but not at eight other tested positions, restored proton pumping in the Asp135-->Asn mutated protein. These results suggest that the C-terminal part of the domain may be alpha-helical and that the entire "loop" plays an important structural and functional role as part of an input channel of the proton translocation machinery.

Amino Acid Sequence↗
PubMed1995

Control of lamprey locomotor neurons by colocalized monoamine transmitters.

Neurons in the central nervous system (CNS) often store more than one neurotransmitter, but as yet the functional significance of this type of coexistence is poorly understood. 5-Hydroxytryptamine (5-HT) modulates calcium-dependent K+ channels (KCa) responsible for the postspike afterhyperpolarization in different regions of the CNS. In lamprey, 5-HT neurons control apamine-sensitive KCa channels in spinal locomotor network interneurons, thereby in addition regulating the duration of locomotor bursts. We report here that these spinal 5-HT neurons also contain dopamine. Like 5-HT, dopamine causes a reduction of the afterhyperpolarization, but in this case it is due to a reduction of calcium entry during the action potential, which results in a reduced activation of KCa. 5-HT and dopamine are both released from these midline neurons, and both reduce the afterhyperpolarization through two distinctly different, but complementary cellular mechanisms. The net effect of dopamine (10-100 microM) on the locomotor network is similar to that of 5-HT, and the effects of dopamine and 5-HT are additive at the network level.

Action Potentials↗