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K Kühn

Publications and source records attributed to K Kühn.

At least 91 records · Page 5Linked to original sources
PubMed1987

Construction of a model for the aggregation and cross-linking region (7S domain) of type IV collagen based upon an evaluation of the primary structure of the alpha 1 and alpha 2 chains in this region.

The amino acid sequence of the 212-residues-long N-terminal aggregation and cross-linking region of the alpha 2(IV) chain of human basement membrane collagen is presented. Comparing this with the primary structure of alpha 1(IV)7S [Glanville et al. (1985) Eur. J. Biochem. 152, 213-219] revealed a high degree of similar subdivisions in three functional regions. These are the 21-residue-long N-terminal non-triple-helical regions (NH1) containing cysteine and lysine residues which are putative cross-linking sites, a 117-residue-long triple-helical region (TH1) responsible for the aggregation of four molecules to form the 7S domain and which also possess cross-linking sites, and finally a 10-residue-long non-triple-helical region (NH2) which introduces the first of many flexible areas into the triple helical body of the molecule [Hofmann et al. (1984) J. Mol. Biol. 172, 325-343]. Computer calculations of interaction scores between parallel and antiparallelly aligned triple-helical regions (TH1) of the 7S domain allowed the prediction of a detailed model for the structure of the 7S complex which agreed well with models based primarily on electron micrographs of rotary shadowed type IV collagen tetramers. The results indicated that the assembly of the 7S domain is directed by hydrophobic interactions and is self-limiting to a tetramer. The most favourable chain configuration is alpha 2-alpha 1-alpha 1.

Amino Acid Sequence↗
PubMed1987

Cyclosporin A inhibits PGE2 release from vascular smooth muscle cells.

The influence of the fungoid undecapeptide cyclosporin A (CyA) on PGE2 release from cultured rat aortic smooth muscle cells was investigated in this study. We found that CyA time and concentration dependently (ED50:500 ng/ml) inhibited PGE2 release from the cells. CyA attenuated both basal and PGE2 release evoked by angiotensin II (10(-10)-10(-6) M), arginine vasopressin (10(-10)-10(-6) M) and ionomycin (10(-9)-10(-6) M). CyA (1 microgram/ml) did not affect the conversion of exogenous arachidonic acid (1 microM) into PGE2. The inhibitory effect of CyA was neutralized by high concentrations of the calcium ionophore ionomycin (greater than 3 X 10(-6) M). Taken together our results indicate that CyA inhibits both basal and vasoconstrictor evoked PGE2 release from vascular smooth muscle by impairing the availability of free arachidonic acid rather than by inhibiting the conversion of arachidonic acid into PGE2.

Angiotensin II↗
PubMed1987

Characterization of binding properties of the myelin-associated glycoprotein to extracellular matrix constituents.

The myelin-associated glycoprotein (MAG) can be obtained from adult mouse brain from detergent-lysates of a crude membrane fraction as a 96-100 kd form (detergent solubilized MAG), and from 100,000 g supernatants of homogenates as a 90-96 kd form (soluble MAG). The soluble form distributes into the Triton X-114-poor aqueous phase, while detergent-solubilized MAG predominantly enters the Triton X-114-rich phase. Both molecular forms bind to heparin in hypo- and isotonic buffers. Soluble MAG binds to several collagens (type G, I, II, III, IV, V, VI, IX) with a kd of 5.7 X 10(-8) M for collagen type IX and 2.0 X 10(-7) for collagen type IV. Binding of 125I-labeled MAG to collagen G can be completely inhibited by unlabeled MAG and collagen G, but not by heat-denatured collagen. MAG does not bind to itself, laminin, fibronectin, or the neural cell adhesion molecules L1 and N-CAM. Binding of MAG to collagen G is most effectively blocked by a high molecular weight dextran sulfate, heparan sulfate and heparin, with chondroitin sulfate and a low molecular weight dextran sulfate being less potent blockers. These findings are in agreement with previous observations on the localization of MAG in basal lamina and interstitial collagens of the sciatic nerve in situ.

Animals↗
PubMed1986

The C-terminus of type I collagen is a major binding site for heparin.

The binding of collagens and fragments of type I collagen to heparin was studied by gel electrophoresis and affinity chromatography. Samples bound in 150 mM NaCl/10 mM Hepes (pH 6.5) were eluted with 2 M NaCl, 6 M urea, or a linear gradient of 0.15-1.0 M NaCl. The triple-helical conformation was shown to be essential for binding. The vertebrate collagenase-generated C-terminal fragment, TCB, was shown to have greater binding affinity for heparin than the N-terminal TCA fragment. Both type II collagen and the NC1 domain of type IV collagen bound to heparin, whereas pepsin-solubilized tetrameric type IV failed to bind.

Amino Acid Sequence↗
PubMed1986

Structure of mouse type IV collagen. Amino-acid sequence of the C-terminal 511-residue-long triple-helical segment of the alpha 2(IV) chain and its comparison with the alpha 1(IV) chain.

The sequence of 511 residues from the C-terminal portion of the triple helix of mouse alpha 2(IV) chain was determined by using the pepsin fragment P2 of collagen IV and two cDNA clones selected from an Engelbreth-Holm-Swarm (EHS) tumor library. The sequence contains nine interruptions of the triplet repeat Gly-Xaa-Yaa ranging in size from single insertions or deletions up to stretches of eleven amino acid residues. Five of these interruptions match those present in the homologous segment of the alpha 1(IV) chain but are otherwise different in length and/or sequence. A low homology was found for the triplet regions of the alpha 1(IV) and alpha 2(IV) chain which constitute more than 90% of the sequence. The data indicate a remote evolutionary relationship of the triple-helical sequences of the two constituent chains of basement membrane collagen.

Amino Acid Sequence↗
PubMed1986

Effective hydraulic permeability of the glomerular capillary wall in rats after uninephrectomy.

The effective hydraulic permeability (k) of glomerular capillaries was studied in 2-month-old Wistar rats 4 weeks after uninephrectomy in comparison to age-matched control rats. Isolated kidneys were perfused with a cell-free solution containing 5% albumin. In this preparation the rise of colloid osmotic pressure along the glomerular capillaries can be neglected because the filtration fraction is low (3%) due to high perfusion rates at normal filtration rates. Single nephron filtration rates (SNGFR) and effective filtration pressures were estimated by micropuncture to calculate the ultrafiltration coefficient (Kf). Glomerular capillary surface area was measured morphometrically to obtain k (k = Kf/S). We found that the effective hydraulic permeability in uninephrectomized rats was higher than in rats of comparable age (26.0 vs 18.0 nl/mm Hg X s X cm2). This can contribute to the adaptive rise in SNGFR after uninephrectomy.

Animals↗
PubMed1986

Single nephron hyperfiltration and proteinuria in a newly selected rat strain with superficial glomeruli.

Alterations in glomerular permeability were studied in female MWF/Ztm rats, newly selected from the Munich Wistar rats with a high number of superficial glomeruli. This strain is characterized by a diminished number of functioning nephrons, an elevated arterial blood pressure and a high proteinuria averaging 24 mg/24 h. Samples of Bowman capsular space (BCS) obtained by free-flow renal micropuncture techniques with pressure control were analyzed for albumin and high-molecular-weight (HMW) proteins by ultramicrodisc electrophoresis. The measured mean albumin and HMW protein concentration in BCS were 1.72 g/l and 0.66 g/l, respectively. The glomerular filtration rate (GFR) averaged 0.74 ml/min/g kidney weight and the single nephron GFR (SNGFR) 48 nl/min. Ultrastructural studies revealed focal bleb-like alterations of the podocytes as has been observed in hyperfiltration states. We suggest that the reduced number of functioning nephrons in the kidneys of these rats could induce glomerular hyperfiltration and permselectivity changes, which cause a high glomerular protein leakage.

Animals↗
PubMed1986

Age-dependent glomerulosclerosis and proteinuria occurring in rats of the Milan normotensive strain and not in rats of the Milan hypertensive strain.

The development of an age-dependent glomerulosclerosis and proteinuria was investigated in two strains of rats in a model of moderate hypertension comparing rats of the Milan Hypertensive Strain (MHS) with rats of the Milan Normotensive Strain (MNS). Serum creatinine, urinary protein excretion, renal morphology (light- and electronmicroscopy) and morphometry of the media thickness of the intrarenal arteries and of the thickness of the glomerular basement membrane were studied in 2- to 16-month-old MHS and MNS rats. Serum creatinine did not differ between MNS and MHS rats in any age group. MNS rats developed a significant proteinuria which coincided with a glomerulosclerosis in about 22% of the glomeruli at 13 to 16 months. In contrast, urinary protein excretion in MHS rats remained stable during the entire observation period; glomerulosclerosis occurred only in 3% of the glomeruli at 13 to 16 months. As a consequence of hypertension media thickness of intrarenal arteries of MHS rats significantly exceeded that of MNS rats, in the interlobular arteries already at 2 months and in the arcuate arteries at 13 to 16 months. In contrast, thickness of the glomerular basement membrane of MHS rats never exceeded that of MNS rats. From these data we conclude, that glomeruli of MHS rats may be protected against the development of an age-dependent glomerulosclerosis and proteinuria. Further support for this conclusion may also be derived from recent experiments showing that the tubuloglomerular feedback sensitivity is significantly higher in MHS than in MNS rats (41).

Aging↗
PubMed1985

Amino acid sequence of the N-terminal aggregation and cross-linking region (7S domain) of the alpha 1 (IV) chain of human basement membrane collagen.

The amino acid sequence of the 216-residue-long N-terminal aggregation and cross-linking 7S domain of the alpha 1 (IV) chain of human placental basement membrane collagen is presented. The N terminus of the alpha 1 (IV) chain starts with a non-triple-helical region, which is at least 15 residues long and contains four cysteine and two lysine residues as putative cross-linking sites. This segment is followed by a 120-residue-long triple helical region, which contains the unusual occurrence of a cysteine residue in the Xaa position of a Gly-Xaa-Yaa triplet. Since individual molecules in the 7S domain are associated in an antiparallel manner, this cysteine probably aligns with one of the four cysteines in the amino-terminal end of an adjacent molecule, forming an intermolecular disulfide bridge. The length of the overlap of two adjacent molecules is estimated to be about 110 residues. The triple helix adjacent to the overlap zone is interrupted by a 10-residue-long non-helical area, which is probably responsible for the flexible region of the molecules in the neighbourhood of the overlap zone observed in the electron microscope. The mode of aggregation of the 7S domain, the formation of intermolecular cross-links as well as the relatively high stability of this region against proteolytic attack are discussed in the light of the elucidated amino acid sequence.

Amino Acid Sequence↗
PubMed1985

[Drug treatment of chronic glomerulonephritis: pro].

This paper sets out the arguments for drug treatment of chronic glomerulonephritides (GN). Although the pathogenesis and mechanism of progression of chronic GN remained to be clarified, on the basis of controlled studies performed to date, there is a strong case to be made for an aggressive treatment approach to this disease spectrum. For instance, in patients with idiopathic membranous glomerulonephritis a six months treatment with chlorambucil (0.2 mg/KG/day) or prednisone (0.6 mg/KG/day) each given once a day over a period of three months has recently been shown to improve the outcome of the renal functional parameters after three years follow up. In another controlled trial a daily dose of 225 mg dipyridamole and 975 mg aspirin given over 12 months in patients with membrano-proliferative GN type I has been reported to normalize the increased platelet consumption rate and to stabilize the glomerular filtration rate. A third trial has demonstrated that the combined use of cyclophosphamide (100 mg/day) and prednisone (30 mg/day) over several months was superior to the use of prednisone alone (40 mg/day) in improving the long-term prognosis of diffuse-proliferative lupus nephritis (type IV, WHO). In some entities, however, as in IgA-nephritis there is still no evidence for a specific treatment improving the course of the chronic glomerular disease. Other therapeutic problems have to be solved: thus, in patients with minimal change nephropathy with a steroid dependent nephrotic syndrome the benefit of cyclophosphamide (given over three months) or of cyclosporin A is still being investigated. Furthermore, there is some evidence that progression of chronic GN, particularly that of glomerular sclerosing, can be prevented by a low protein diet. The role of eicosanoides and their inhibitors in this context has not yet been fully investigated. The different drug trials and new therapeutic concepts indicate a rapid development of chronic GN treatment. Therefore, a failure to treat actively is difficult to understand.

Chlorambucil↗
PubMed1985

Structural studies of human basement-membrane collagen with the use of a monoclonal antibody.

A monoclonal antibody monospecific for human type IV collagen was used as a structural probe to examine aspects of the macromolecular organization of basement-membrane collagen. Electron-microscopic observation of rotary-shadowed antigen-antibody complexes demonstrated a unique binding site for the antibody 55 +/- 6 nm distant from the 7S cross-linking region of tetrameric type IV collagen. This observation allowed a series of studies that showed: (1) the localization of an intramolecular disulphide bridge within the helical domain of the molecule, (2) the alignment of major peptic-digest fragments of the alpha 1 (IV) chain, and (3) confirmation of the postulated antiparallel arrangement of individual molecules within type IV collagen tetramers.

Antibodies, Monoclonal↗
PubMed1985

Amino acid sequence of the non-collagenous globular domain (NC1) of the alpha 1(IV) chain of basement membrane collagen as derived from complementary DNA.

NC1, the C-terminal non-collagenous globular domain of collagen IV, represents one of the two end regions responsible for the assembly and cross-linking of the extracellular network of basement membrane collagen. Several cDNA clones for the NC1 domain of the alpha 1(IV) collagen chain of mouse have been isolated by using synthetic oligonucleotides as screening probes for mouse libraries. The oligonucleotides were synthesized according to known stretches of the corresponding protein sequence. Sequencing of the overlapping cDNA clones allowed the complete amino acid sequence of the NC1 domain to be deduced as well as the C-terminal 165 amino acid residues of the triple helix. It consists of 229 amino acid residues which comprise two homologous regions with a high content of cysteine. These DNA and protein sequences are compared to the corresponding sequences of other collagens and discussed with respect to their structural and biological significance.

Amino Acid Sequence↗
PubMed1985

Cationic dyes reveal proteoglycans on the surface of epithelial and endothelial kidney cells.

The glomerular epithelial cells of the rat kidney fixed by vascular perfusion with an aldehyde solution containing either safranine O or alcian blue (and 0.3 M MgCl2) display filaments which are located close to the outer surface of the plasma membrane. These filaments are similar to those revealed by the same methods in the laminae rarae of the glomerular basement membrane. Alcian blue (and MgCl2) further demonstrates the presence of anionic sites inside the endothelial cell pores of the glomerular and peritubular capillaries, on the luminal surface of endothelial cells of large renal vessels and along the basolateral surface of the epithelial cells of the Bowman capsule and of the proximal convoluted tubule.

Alcian Blue↗
PubMed1985

Structure and biochemistry of collagen.

The structure and immunochemistry of the interstitial collagens (types I, II, and III), and the structure of basement membrane collagen (type IV) and filamentous collagen (type VI) are described, together with the implications of the different types of collagen.

Animals↗