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Biomedical subjects

D Kunz

Publications and source records attributed to D Kunz.

At least 91 records · Page 5Linked to original sources
PubMed1992

Structural diversity in the extracellular faces of peptidergic G-protein-coupled receptors. Molecular cloning of the mouse C5a anaphylatoxin receptor.

The mouse C5a receptor gene was isolated using the human C5a receptor cDNA probe recently described (Gerard, N. P., and C. Gerard. 1991. Nature 349:614). By analogy with the human gene, the mouse homolog contains two exons with the 5' untranslated region and initiating methionine codon present in exon 1 and the remainder of the molecule in exon 2. Generation of an expressible cDNA for the mouse C5a receptor was accomplished using the polymerase chain reaction and a sense oligodeoxynucleotide primer which included an initiation codon just 5' to the sequence encoding the N-linked glycosylation site. When transfected into human 293 kidney epithelial cells the cloned cDNA directs expression of a binding site for human C5a anaphylatoxin with a binding constant of 2.5 +/- 0.3 nM; the human C5a receptor expressed under identical conditions has a Kd of 1.7 +/- 0.2 nM. Overall, the deduced amino acid sequences of the receptors are 65% identical given the analogous gene structures. Alignment of the sequences as seven transmembrane segment receptors reveals that the greatest structural diversity (approximately 70%) exists in the putative extracellular domains. In contrast, species differences among other members of this family of seven membrane-spanning receptors is generally only 10 to 20%, even for receptors whose ligands are relatively small and not expected to interact with sites on the extracellular surfaces. A high degree of structural identify is observed for the C5a receptors in the transmembrane segments and in all but one of the loops predicted to exist in the cytoplasm. Inasmuch as critical structures responsible for high affinity binding of the 74 amino acid polypeptide to both C5a receptors involve features conserved between species, these data provide the starting point for mutagenesis studies to determine the nature of the binding and activation sites for the chemotactic receptors. Additionally, these data provide a reagent for immunologic and molecular genetic studies on the role of C5a receptors in inflammatory models.

Amino Acid Sequence↗
PubMed1992

The human leukocyte platelet-activating factor receptor. cDNA cloning, cell surface expression, and construction of a novel epitope-bearing analog.

A human myeloid transcript of approximately 4 kilobases was cloned as a cDNA from an expression library based on homology with the guinea pig cDNA recently described by Honda et al. (Honda, Z-I., Nakamura, M., Miki, I., Minami, M., Watanabe, T., Seyama, Y., Okado, H., Tok, H., Ito, K., Miyamato, T., and Shimizu, T. (1991) Nature 349, 342-346) as a receptor for platelet-activating factor (PAF). The cloned DNA confers high affinity binding sites for platelet-activating factor when transfected into COS-7 cells and has binding and desensitization properties similar to the human leukocyte receptor. Southern analysis using this cDNA indicates that the PAF receptor gene is present as a single copy in the human genome. The deduced protein sequence predicts seven hydrophobic regions for the PAF receptor, characteristic of the rhodopsin gene family, and is 83% identical to the deduced protein sequence of the corresponding guinea pig molecule. A modified human PAF receptor cDNA was constructed by inserting an additional 30 nucleotides after the 5'-ATG, encoding the amino acid sequence MDYKDDDDKEF, which is specifically recognized by a monoclonal antibody. The modified cDNA encodes a functional PAF receptor and is detected by antibody on the membrane of transfected COS-7 cells. The use of this construct supports the structural model for the rhodopsin-like superfamily of receptors which places the NH2-terminal sequence on the extracellular side of the membrane, and should additionally be useful for affinity purification of the receptor protein.

Amino Acid Sequence↗
PubMed1992

Cervical stability after foraminotomy. A biomechanical in vitro analysis.

Laminectomy or facetectomy of the cervical spine, or both, may be needed for decompression of the spinal cord or of the nerve-roots. Acute stability of the cervical spine was tested after laminectomy and progressive staged foraminotomies in an in vitro model. Twelve cervical spines from human cadavera were used in the experiment. Biomechanical testing included the application of an axial load, the application of a flexion and extension moment, and the application of a torsional moment. Each specimen was tested intact, after laminectomy of the fifth cervical vertebra, and after progressive foraminotomy of the sixth cervical root. Foraminotomy was performed by resection of 25, 50, 75, and 100 per cent of the facet joint and capsule. Torsional stiffness decreased dramatically when more than 50 per cent of the facet had been resected. Statistically equivalent subsets were the intact specimen, laminectomy, 25 per cent facetectomy, and 50 per cent facetectomy in one subset, and 75 and 100 per cent facetectomy in the least-stiff subset. Flexion-moment testing showed that the posterior strain did not differ among three groups: the intact specimens, those that had been treated with laminectomy, and those that had been treated with a 25 per cent facetectomy. The 50 per cent facetectomy resulted in a 2.5 per cent increase in posterior strain, and the 75 or 100 per cent facetectomy, in a 25 per cent increase in posterior strain compared with the intact specimen. Segmental hypermobility of the cervical spine results if a foraminotomy involves resection of more than 50 per cent of the facet.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

[The demonstration of calcifications in magnetic resonance tomography (MRT). The effect of different parameters on the MRT imaging of cerebral calcifications].

The effect of various factors on the demonstration of calcified lesions was studied in 131 areas of calcification which had been demonstrated by CT. By means of MRI (SE 400/30 or GE315/14, 90 degrees and SE 1600/30 + 70; 0.5T) 117 of the 131 calcified lesions (89%) produced a signal difference. Of these 117 lesions, 80 (61%) were recognised as calcification by MRI. Large areas of calcification (more than 5 mm) and high density calcification (more than 100 Hu) were recognised significantly more often than small or low density calcifications. T2-weighted images demonstrated calcification more often than other sequences. With conventional pulse sequences, calcified lesions were frequently recognised as abnormalities on MRI, but their recognition as calcified lesions is unreliable.

Brain↗
PubMed1991

Membrane-bound peptidases of lymphocytes: functional implications.

The paper is aimed towards the role of the membrane ecto-enzymes aminopeptidase N (CD13, AP-N) and dipeptidyl peptidase IV (CD26, DP IV) in the immune system. Both peptidases have been identified on T lymphocytes, AP-N also on monocytes and non-T cells. Using enzyme inhibitors and antibodies it has been shown by different groups that DP IV plays a key role in T cell activation and growth. Inhibition studies of our laboratory, using bestatin, actinonin and probestin, also demonstrated an essential role of AP-N in regulation of T cell growth. Moreover, the action of cytokines/lymphokines having DP IV susceptible bonds, as IL-1, IL-2 and IL-6, on lymphocyte proliferation, was found to be suppressed by specific inhibitors of DP IV as well as AP-N. These results are in favour of our hypothesis that DP IV and AP-N, possibly both in a concerted action, are involved in cytokine/lymphokine mediated signalling between immune cells.

Amino Acid Sequence↗
PubMed1990

[Aminopeptidase activity in populations of human blood mononuclear cells].

The aminopeptidase N (AP N, EC 3.4.11.2) is an ectoenzyme of the plasma membrane, playing presumably an important role in the regulation of immunological processes. The specific activities of Ala-pNA and Leu-pNA cleavage (per cell) are distributed in monocytes T- and non-T-lymphocytes in a proportion of 1:0.2:0.25 and 1:0.17:0.18, respectively. The capacities of Ala-pNA and Leu-pNA hydrolysis in the total fraction T- and non-T-cells are distributed as 1:0.8 and 1:0.7, respectively. The main part of Ala-pNA cleavage was shown to be caused by AP N on the basis of the KM-value (0.5 mmol/l), the activation by CO2+ ions and the pH optimum (7.0-7.5). The Leu-pNA cleavage is dependent on CO2+ and DTT and distinct from the classical cytosolic leucyl aminopeptidase.

Aminopeptidases↗
PubMed1989

Identification of the promoter sequences involved in the interleukin-6 dependent expression of the rat alpha 2-macroglobulin gene.

The 5'-region of the rat alpha 2-macroglobulin gene has been characterized. A 5.6 kb Sal I - Xba I fragment containing the first 4 exons of the alpha 2-macroglobulin gene and 1.3 kb of its 5'-flanking region was sequenced. The putative transcriptional start site was determined by RNase protection and primer extension analysis. TATA- and CAAT-box equivalent sequences were found. A potential glucocorticoid receptor binding site was located on the antisense strand. DNA sequences containing the 5'-flanking region of the rat alpha 2-macroglobulin gene were linked to the gene coding for the bacterial chloramphenicol acetyltransferase and introduced into Hep G2 cells. In these transfected Hep G2 cells CAT activity could be induced by recombinant human interleukin-6. Deletion analyses have shown that the sequences between -852 and -777 as well as between -404 and -165 relative to the cap site, contain regulatory elements involved in the interleukin-6 dependent induction of the alpha 2-macroglobulin gene.

Amino Acid Sequence↗
PubMed1989

Spatial resolution of transcranial pulsed Doppler technique in vitro evaluation of the sensitivity distribution of the sample volume.

The spatial resolution of pulsed Doppler sonography is determined by the size of the sample volume. It is known that the axial length is dependent upon the duration of the range gate interval and the lateral extension upon the beam width. In addition, the working size is also a function of the sensitivity distribution within the sample volume. All of these parameters determine the working size of the sample volume. Especially for the transcranial Doppler evaluation of the basal cerebral arteries, the site and the working size of the sample volume are essential diagnostic criteria. To measure the working size of the sample volume a flow rig with a thin tube target has been developed and used. The highest sensitivity (100% level) was registered only in a relatively small area and only if the center of the sample volume hit the target. At the 10% level the size of the sample volume increased 5 to 10 times in the lateral and axial dimension in comparison with the 90% level. Therefore, the Doppler signal from a strong reflector distant from the center of the sample volume may mask the signal of a weak reflector located within the center. This lack of spatial resolution due to sensitivity effects may result in clinical misinterpretation. The manufacturers should be urged to supply more precise information relative to the sample volume size.

Blood Flow Velocity↗
PubMed1988

Spectroscopy and imaging with a 4 tesla whole-body MR system.

Magnetic resonance (MR) spectroscopy and imaging experiments on humans were performed with a whole-body MR system at a static field of 4 tesla. Spectroscopic studies focussed on 1H, 13C, and 31P. Imaging of humans turned out to be possible, although below the optimum at this field. This holds especially for body imaging, since RF penetration effects and dielectric resonances influence the RF field homogeneity. Excellent volume selective proton spectra of the human cerebrum and cerebellum were obtained using the stimulated echo method. Natural abundance carbon spectra of the human calf were acquired both undecoupled and with narrowband decoupling, resolving the various triglyceride resonances. Broadband decoupling, however, would have violated SAR guidelines. Liver glycogen was detected on natural abundance 13C spectra.

Female↗
PubMed1988

Regulation of alpha 2-macroglobulin gene expression by interleukin-6 (BSF-2/HSF).

In rat hepatocyte primary cultures recombinant human interleukin-6 (rhIL-6) induced alpha 2-macroglobulin (alpha 2M) synthesis 54-fold. Half-maximal induction was achieved at a rhIL-6 concentration of 30 pM. RhIL-1 beta led only to a 2-fold increase in alpha 2M synthesis, but strongly impaired the action of IL-6. Intraperitoneal injection of rhIL-6 into male rats resulted in a 19.7-fold increase of alpha 2M mRNA already after 4h. In contrast, alpha 2M mRNA levels (50-fold increase) were reached between 16 and 24 h after intramuscular injection of turpentine. Whereas turpentine-induced inflammation resulted in an increased alpha 2M synthesis in male and female rats, rhIL-6 injection had no effect in female rats. The increases after rhIL-6 administration in mRNA concentrations were followed by corresponding changes in alpha 2M levels in serum. By Northern analysis it was demonstrated that LPS-stimulated human monocytes synthesize IL-6 mRNA. The 5'-end of the rat alpha 2M gene has been isolated and the first 3 exons and 166 base pairs of the 5'-flanking region were identified by a combination of oligonucleotide hybridization and DNA sequencing. The transcriptional start site was determined by RNase protection as well as by primer extension experiments. 5'-CATAAAG-3' and 5'-TCAAAA-3' were found as TATA- and CAAT-box equivalent sequences, respectively. Furthermore, a potential glucocorticoid binding site (5'-TGTTCT-3') was localized on the antisense strand of the alpha 2M gene.

Animals↗
PubMed1987

Frequency-modulated radiofrequency pulses in spin-echo and stimulated-echo experiments.

Frequency-modulated rf pulses based on a linear frequency sweep are studied experimentally in spin-echo and stimulated-echo sequences. It turns out that these FM pulses generate a quadratic phase perpendicular to the selected slice and that the quadratic phases of the FM pulses in a spin-echo or stimulated-echo sequence may compensate each other if sweep velocity and gradients are suitably chosen. For a complete rephasing, a formula is given and supported by measured slice profiles. Slice profiles of excellent rectangularity are obtained. Finally, it is shown that with this technique images can be obtained using pulses of increased bandwidth and reduced peak power compared with the AM situation.

Fourier Analysis↗
PubMed1986

Use of frequency-modulated radiofrequency pulses in MR imaging experiments.

With increasing field strength for whole-body MR scanners there is a need for rf pulses of higher bandwidth to perform selective excitation or inversion. AM pulses will have to become shorter thus leading to an enormous requirement for the peak power of the power amplifier. To reduce these requirements the use of frequency modulation is investigated. The effect of pulses based on a linear frequency sweep on the spin system is analyzed by calculation and computer simulation. It turns out that the nonlinear phases induced by those pulses may compensate each other, that therefore spin-echo experiments as usual in MR imaging may be performed, and that the required peak power may be reduced by up to a factor of 50.

Magnetic Resonance Spectroscopy↗
PubMed1986

MR imaging using stimulated echoes (STEAM).

The introduction of STEAM (stimulated echo acquisition mode) magnetic resonance (MR) sequences provides access to a variety of MR parameters. T1-weighted and calculated T1 proton MR images of the head of healthy volunteers and a patient with an astrocytoma are presented. MR examinations were performed with a 2.0-T whole-body system. The STEAM T1 method can be used to characterize multiexponential relaxation behavior, to evaluate T1 relaxation times, and to improve the T1 contrast within MR images. Both the measuring time and the spatial resolution are the same as for a conventional image.

Astrocytoma↗
PubMed1985

Molecular cloning of cDNA sequences for rat alpha 2-macroglobulin and measurement of its transcription during experimental inflammation.

Poly(A)+ RNA enriched in alpha 2-macroglobulin (alpha 2M) mRNA isolated from livers of rats 18 h after injection of turpentine was used for the synthesis of double-stranded cDNA. The double-stranded cDNA was inserted into the PstI site of the plasmid pBR322 by oligo(dG)-oligo(dC)-tailing technique. Clones containing sequences complementary to alpha 2M mRNA were selected by differential colony hybridization using 32P-labeled poly(A)+ RNA and [32P]cDNA from livers of control and turpentine-treated rats and subsequent hybrid-selected translation. The isolated p alpha 2M1 clone had an insert of 657 base pairs. DNA sequence analysis revealed a homology of about 80% to human alpha 2M. Northern analysis showed that the alpha 2M mRNA from rat liver is about 5600 bases in length. The alpha 2M cDNA was used to measure the in vitro transcription of the alpha 2M gene in isolated nuclei. A 4-fold increase in alpha 2M gene activity was found 14 h after turpentine administration. We conclude that alpha 2M transcription is induced during inflammation.

Amino Acid Sequence↗