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K Klaushofer

Publications and source records attributed to K Klaushofer.

12 recordsLinked to original sources
PubMed1992

Mineral crystals in calcified tissues: a comparative study by SAXS.

The shape, the typical orientation, and the average size of mineral crystals in different types of mineralized tissues were investigated by means of small-angle x-ray scattering (SAXS). To rule out eventual artifacts due to sample preparation, four different standard preparation techniques were used and a comparison showed that the SAXS results were identical for all four methods. In mineralized turkey leg tendon, a frequently used model system for bone, the crystals were found to be typically plate-like with a thickness of the order of 2 nm. This stands in contrast to the case of bone (calvaria, femur, and iliac crest) from mouse, rat, and dog, where mainly needle-like crystals were found. The thickness of these crystals ranged from 3 to 4 nm but was remarkably constant for different bones of a given animal. The preferred orientation of the needle-like crystals was along the main axis of the femur and within the surface of the calvaria (for mouse, rat, and dog). The mineral plates in turkey leg tendon were located inside the hole zone and oriented along the fibril axis. Finally, no periodic arrangement of the crystals inside the hole zone of the collagen could be found.

Animals↗
PubMed1991

On the role of cyclic AMP as a mediator of bone resorption: gamma-interferon completely inhibits cholera toxin- and forskolin-induced but only partially inhibits parathyroid hormone-stimulated 45Ca release from mouse calvarial bones.

The effects of gamma-interferon (gamma-IFN) on bone resorption and cyclic AMP formation stimulated by parathyroid hormone (PTH), forskolin, and cholera toxin have been studied in cultured neonatal mouse calvarial bones. Bone resorption was assessed by the release of 45Ca from prelabeled mouse calvarial bone fragments. Cyclic AMP formation was quantified by analyzing the amount of the nucleotide in calvarial bone tissue. gamma-IFN completely blocked the 45Ca release response to forskolin and cholera toxin in 96 h cultures. In contrast, the 45Ca release response to PTH was only partially inhibited, an effect that was seen over a wide range of PTH concentrations. The inhibitory effect of gamma-IFN was dose dependent, with a threshold for action at 10 U/ml. Forskolin-stimulated 45Ca release could only be inhibited when gamma-IFN was added simultaneously with forskolin; gamma-IFN added to bones prestimulated with forskolin had no effect. The inhibitory effect of gamma-IFN on PTH-stimulated 45Ca release was seen first after a time lag of 48 h. In contrast calcitonin caused an inhibition after only 3 h. PTH and cholera toxin stimulation of radioactive calcium release was also inhibited by gamma-IFN in bones treated with indomethacin. gamma-IFN inhibited forskolin-induced 45Ca release in bones treated with the mitotic inhibitor hydroxyurea. No effect of gamma-IFN on cyclic AMP formation induced by PTH, cholera toxin, or forskolin could be seen. These data show that gamma-IFN inhibits forskolin- and cholera toxin-induced bone resorption by a mechanism unrelated to prostaglandin production or mitotic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Inhibitory effects of gamma-interferon on bradykinin-induced bone resorption and prostaglandin formation in cultured mouse calvarial bones.

The effects of mouse recombinant gamma-interferon (gamma-IFN) and indomethacin on bone resorption stimulated by bradykinin, Lys-bradykinin, Met-Lys-bradykinin, des-Arg9-bradykinin and prostaglandin E2 (PGE2) have been studied using cultures of neonatal calvarial bones and analyzing the release of 45Ca from prelabelled bones as a parameter of bone resorption. In addition, the effects of gamma-IFN and indomethacin on formation of PGE2 in bone cultures stimulated by bradykinin was analyzed. Indomethacin (1 mumol/l) totally abolished bradykinin (1 mumol/l) induced 45Ca release. The inhibitory effect of indomethacin could be fully reversed by addition of PGE2 (1 mumol/l). gamma-IFN (1000 U/ml) almost totally inhibited 45Ca release stimulated by bradykinin (1 mumol/l), but the inhibitory effect could only be partially overcome by PGE2. gamma-IFN and indomethacin also inhibited the stimulatory effects of Lys-bradykinin, Met-Lys-bradykinin and des-Arg9-bradykinin (1 mumol/l) on 45Ca release. The stimulatory effects of PGE2 (1 mumol/l) on radioactive calcium mobilization was partially inhibited by gamma-IFN (1000 U/ml), whereas indomethacin (1 mumol/l) was without effect. The inhibitory effect of gamma-IFN on 45Ca release stimulated by bradykinin and PGE2 was dose-dependent with threshold for action at 3-30 U/ml. Comparative dose-response curves showed that gamma-IFN was most potent as inhibitor of bradykinin induced 45Ca release. Bradykinin (1 mumol/l) significantly stimulated PGE2 formation by a mechanism that was completely inhibited by indomethacin (1 mumol/l). gamma-IFN (1000 U/ml) partially inhibited the stimulatory effect of bradykinin on PGE2 formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Nucleation and growth of mineral crystals in bone studied by small-angle X-ray scattering.

The mechanism of calcification in bone and related tissues is a matter of current interest. The mean size and the arrangement of the mineral crystals are important parameters difficult to obtain by electron microscopy. Furthermore, most studies have been carried out on poorly calcified model systems or chemically treated samples. In the work presented here, native bone was studied as a function of age by a quantitative small-angle X-ray scattering method (SAXS). Bone samples (calvariae and ulnae) from rats and mice were investigated. Measurements were performed on native bone immediately after dissection for samples up to 1 mm thick. The size, shape, and predominant orientation of the mineral crystals in bone were obtained for embryonal, young, and adult animals. The results indicate that the mineral nucleates as thin layers of calcium phosphate within the hole zone of the collagen fibrils. The mineral nuclei subsequently grow in thickness to about 3 nm, which corresponds to maximum space available in these holes.

Animals↗
PubMed1991

[DEXA (dual-energy x-ray absorptiometry) and DPA (dual photon absorptiometry) in densitometry of the femoral neck: correlation of the measurements of three commercially available instruments].

The bone mineral density measurements of three different instruments at the femoral head were compared using 12 cadaver specimens. Two of these instruments were operated by x-rays (dual energy x-ray absorptiometry = DEXA), whereas one system was based on a gadolinium source (dual photon absorptiometry = DPA). Although excellent correlation between the measurements was obtained (r greater than 0,9), the measurements of one of the DEXA-instruments were significantly higher than the measurements of the two other systems. We conclude that a comparison of bone mineral density measurements obtained on different densitometry instruments may pose problems. Follow-up examinations should be done on one single densitometry unit.

Absorptiometry, Photon↗
PubMed1979

A double-labelling radioassay for the determination of 5'-nucleotidase activity.

For the determination of 5'-ribonucleotide phosphohydrolase (EC 3.1.3.5;5'-Nase) in rat liver, a radiochemical double-labelling assay was developed. [14C]-labelled AMP which is hydrolyzed to [14C]-adenosine by 5'-Nase activity is added to crude liver homogenates. After 30 min, the process is stopped and [2-3H]-adenosine added to estimate the loss of [14C]-adenosine during separation by ion exchange column chromatography. The enzymatic reaction was found to be linear in correlation with the enzyme content and the incubation time. The specificity of the reaction was evaluated by addition of beta-glycerophosphate which acts as a competitive inhibitor to eliminate the catalytic effect of non-specific phosphatases, and addition of alpha, beta-methylene adenosine 5'-diphosphate, a specific inhibitor of 5'-Nase; both cause an almost complete suppression of enzyme activity.

Adenosine↗
PubMed1979

Freeze substituted tissue in 5'-nucleotidase histochemistry. Comparative histochemical and biochemical investigations.

The suitability of freeze-substitution in n-butanol and paraffin embedding of tissues for the histochemical demonstration of 5'-nucleotidase was investigated and compared with commonly used preparation techniques, such as fresh frozen sections and cryostate sections of cold formalin and glutaraldehyde-fixed rat liver. The influences of each step of the preparation techniques on the enzyme activity were controlled by a quantitative radiochemical assay. Freeze substitution was revealed to be superior to the commonly used preparation techniques with respect to: 1) high sensitivity and specificity of the histochemical 5'-nucleotidase reaction (this is based on the fact that incubation media with very low lead concentrations (0,6 mM/1) can be used); 2) excellent morphological appearance of the tissues showing cytological details of enzyme localization; 3) unlimited storage of the tissue materials and ease of sectioning.

Animals↗
PubMed1977

'VA', a new type of erythrocyte polyagglutination characterized by depressed H receptors and associated with hemolytic anemia. II. Observations by immunofluorescence, electron microscopy, cell electrophoresis and Biochemistry.

With help of immunoflorescence, best with anti-AHP from Helix pomatia, a stippled structure could be demonstrated on the patient"s red blood cells. Thus an "A-like" receptor could be detected on the erythrocyte membrane of this group O patient. The reactive antigen was proved not to be a crypt antigen exposed by the action of neuraminidase. The same stippled fluorescence with antiAhp was observed on the red blood cells of a patient suffering from hemolytic anemia induced by influnza A2 virus. In this case this virus was shown not to be responsible for polyagglutination. No virus or microorganism could be isolated from the patient"s blood. Also by immunofluorescence the weak expression of the H antigen could be demonstrated with an extract of Evonymus europaeus. Electron microscopy of erythrocytes was normal. The neuraminic acid content and the electrophoretic mobility were found to be decreased to a minor degree. No distinct cell populations could be observed.

ABO Blood-Group System↗
PubMed1975

[Light and electron microscopic localization of enzymes: 5'-nucleotidase (author's transl)].

5'-nucleotidase (EC 3.1.3.5), an important enzyme in the metabolism of nucleotides, is generally accepted as a plasma membrane marker. The enzyme selectively splits phosphoric acid from 5' mononucleotides. Several methods are available for the histochemical localization of enzymes (antigenic properties of the enzyme protein, enzyme properties and activity and labelled specific inhibitors). Only the method based on enzyme properties has been used up to now in the case of 5'-nucleotidase. Free phosphoric acid liberated during the dephosphorylation of substrates such as AMP or IMP is rendered visible at the sites of 5' nucleotidase activity in the tissue by precipitation as lead or calcium phosphate. An improvement in the light microscopic technique is achieved by the use of freezedried tissue embedded in glycol methacrylate, whereby the histochemical reaction can be performed on semi-thin sections. Since lead phosphate is electron dense, these precipitates can easily be detected in the electron microscope too. Wide species and organ differences are found with respect to the distribution of 5'-nucleotidase activity. The well-known localization of the enzyme on the outer cell surface according to biochemical studies is confirmed by electron microscopic findings. A purely catabolic function of 5'-nucleotidase, as propounded in the literature, seems dubious since high 5'-nucleotidase activity was demonstrated in rapidly proliferating tissue too.

Animals↗
PubMed1975

Studies on 5'-nucleotidase histochemistry. III. 5'-Nucleotidase activity in smooth muscle cells of the rat's gastrointestinal tube.

The distribution pattern of histochemically detectable 5'-nucleotidase (5'-Nase) activity is described in smooth muscle cells of the rat's gastrointestinal tube (esophagus, stomach, small intestine, large intestine). Both, light and electron microscopic methods are used. Faint positive 5'-Nase activity is observed on smooth muscle cells of the lamina muscularis mucosae in the thoracal esophagus whereas it is completely absent from smooth muscle cells of the abdominal esophagus and the stomach. In the small and large intestine strong positive 5'-Nase reaction is found on smooth muscle cells of the lamina muscularis mucosae and the innermost part of the lamina muscularis externa. In the circular and longitudinal layer of the lamina muscularis externa a slight increase in 5'-Nase activity is observed from the proximal to the distal segments. The reaction product is restricted to the outer cell surface of smooth muscle cells. In the small intestine the strong enzymatic activity in the innermost part of the muscularis externa is found to be localized at small and dense muscle cells (sd-cells). Common morphological and histochemical characteristics of sd-cells and smooth muscle cells of the lamina muscularis mucosae are emphasized. Hypothetical functions e.g. uptake of precursors of nucleosidephosphates, possible functional connection to a high glycogen content, correlation between 5'-Nase activity and proliferation capacity and local vasodilatory effect are discussed.

Adenosine Diphosphate↗