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Biomedical subjects

R Bischoff

Publications and source records attributed to R Bischoff.

At least 91 records · Page 5Linked to original sources
PubMed1984

The pericellular boundary layer modulates acetylcholine receptor stability in cultured myotubes.

Degradation of acetylcholine receptors in cultured chicken myotubes was measured by release into the medium of radioactivity from 125I-labeled alpha-bungarotoxin. Disturbance of the pericellular boundary layer by stirring of the culture medium shortened the half-life of receptor in the membrane from 24 to 12 h. The effect could not be explained by dissociation of toxin-receptor complexes or by conditioning of the bulk phase of the medium. The rates of synthesis and degradation of total cell protein and the degradation of lactoperoxidase-iodinated surface protein were not affected by medium stirring. The loss of glucosamine-labeled material from the cells was enhanced by stirring, however, and this resulted entirely from the increased shedding of high molecular weight glycosubstances from the cells. Cells in stirred cultures contained lower levels of surface coat material stainable with colloidal thorium. These results indicate that glycosubstances of the pericellular matrix protect ACh receptors from degradation.

Animals↗
PubMed1983

tRNA separation by high-performance liquid chromatography using an aggregate of ODS-Hypersil and trioctylmethylammonium chloride.

High-performance liquid chromatography on a reversed-phase support treated with a tetraalkylammonium salt was used to separate tRNAs from baker's yeast. While resolution by this column appears to result from both anion-exchange and reversed-phase chromatography, it is the hydrophobic interactions which govern the separation of one tRNA from another. Chromatography of bulk tRNA resulted in a number of fractions with different amino acid acceptor activities and little cross-contamination. In some cases the column resolved several single nucleotide modifications of tRNAPhe. Using a 250 x 6.2 mm column it has been possible to chromatograph a minimum of 100 A260 units of tRNA without serious loss in resolution. tRNAs isolated from this column as the last step of a purification procedure have very high amino acid acceptor activities.

Chromatography, High Pressure Liquid↗
PubMed1983

Electrophysiology of Duchenne dystrophy myotubes in tissue culture.

Single myotubes from cultures of 6 patients with Duchenne muscular dystrophy and 6 patients whose biopsy specimens lacked histological abnormality were studied with intracellular physiological recording. Average resting membrane potentials were 47.8 +/- 2.3 mV and 47.0 +/- 1.5 mV for the control and Duchenne cultures, respectively. Action potentials elicited at a standard resting potential of -80 mV were 97.3 +/- 4.0 mV and 98.6 +/- 8.2 mV for the two groups. Maximum rate of rise of action potentials was 154.2 +/- 25.2 V/sec for control and 143.1 +/- 37.1 V/sec for Duchenne myotubes. Action potentials mediated by an influx of calcium ions were seen only when the myotubes from both groups were bathed in high concentrations of calcium and 4-aminopyridine (20 mM and 1 mM, respectively). Thus, the plasma membrane of Duchenne dystrophy myotubes does not have active electrical properties that differ from those in controls. Previous reports of low resting membrane potentials in biopsies studied acutely may reflect secondary changes in degenerating fibers.

Action Potentials↗
PubMed1979

[Ten years experience with laparoscopy in the state women's clinic of Nurenberg].

During the period from 1968--1977 2400 laparoscopies were performed. Of these 10.7% were for diagnostic purposes only, in 3.6% of the cases laparoscopy was combined with biopsie and in 85.7% with tubal sterilization. Deaths or serious bleedings did not occur, laparotomies were not necessary. Total insignificant complications amounted to 1.6% (1.3% small bleedings which did not necessitate an operation and in 0.3% clinical signs of peritonitis, these disappeared after 3 to 15 days). In 0.7% laparoscopy was interrupted because of poor vision. Nine of 2055 women became pregnant after sterilization (4.5 pregnancies/1000 sterilizations). In 2 cases the ligamentum rotundum was coagulated, in 7 cases recanalization was histologically confirmed. Until Oct. 1975 coagulation was unipolar, afterwords bipolar. In 45.3% the patients had undergone an operation before, like Ceasarian section, gallbladder operation, appendectomy or umbilical hernia operation. Patients with longitudinal incision, with preceding peritonitis or ileus were excluded from laparoscopy. Laparoscopy was performed by all assistents during their last year of clinical instruction. Their first 30 laparoscopies were done under control, every assistent performed about 100 laparoscopies.

Female↗
PubMed1979

Immunofluorescent and histochemical localization of AMP deaminase in skeletal muscle.

Fluorescent antibody staining experiments with both isolated myofibrils and muscle fibers grown in culture show that AMP deaminase is bound to the myofibril in the A band. The strongest staining occurs at each end of the A band. The approximate width of the fluorescent stripes and their relation to the A band remains constant as a function of sarcomere length. Removal of enzyme from the myofibrils leads to loss of staining, and readdition of purified enzyme restores the original staining pattern. A histoenzymatic method for the detection of AMP deaminase activity in cultured fibers gives comparable localization. The results are consistent with the previous observation (Ashby, B. and C. Frieden. 1977.J. Biol. Chem. 252:1869--1872) that AMP deaminase forms a tight complex in solution with subfragment-2 (S-2) of myosin or with heavy meromyosin (HMM).

AMP Deaminase↗
PubMed1978

Expression of lactate dehydrogenase isozyme 5 (LDH-5) in cultured mouse blastocysts in the absence of implantation and outgrowth.

Extensive extraction studies with Triton X-100 revealed only LDH-1 (B4) but no trace of LDH-5 (A4) in one-cell and two-cell mouse and rat embryos. The LDH isozyme pattern of preimplantation mouse embryos changes from the maternally inherited B subunit isozyme (LDH-1) to a pattern dominated by LDH-5 when mouse blastocysts are cultured under conditions that prevent hatching but allow trophoblast giant cell transformation. During differentiation of mouse blastocysts in vitro, implantation is therefore not essential for the appearance of the A subunit form of LDH (LDH-5) coded for by the embryonic genome. Mechanisms controlling the expression of LDH-5 in mouse blastocysts during in vivo development are discussed.

Animals↗
PubMed1975

Regeneration of single skeletal muscle fibers in vitro.

A culture system utilizing single skeletal muscle fibers from adult rats was developed to study the origin and behavior of mononucleated myoblasts during muscle regeneration. The single fibers are removed manually from the leg and thigh muscles at 300-400 gm rats and maintained in vitro embedded in a fibrin clot overlain with culture medium. Regenerative events were monitored by continuous observations of the cultured fibers. During the first few hours in vitro the fibers undergo degenerative changes including the formation of myofibrillar contraction clots and pyknosis of myonuclei. The endomysial tube (basement lamina) remains intact along the entire length of the fiber and forms transparent chambers bridging the contraction clots. Single fibers are free of endomysial cells and display no cellular outgrowth in cultures, except at the cut ends. In contrast, a rich outgrowth of endomysial connective tissue cells is found with bundles consisting of two or more fibers. Isolated mononucleated cells, presumed to be muscle satellite cells, are present within the endomysial tube of single fibers at the onset of the culture period. There is no evidence that myonuclei contribute to the formation of mononucleated cells. The satellite cells enlarge and begin to proliferate during the second day in vitro to form clones of presumptive myoblasts within the endomysial tube. The early clones have a cell doubling time of about 22 hours and exhibit mitotic synchrony. After 5-7 days in vitro the satellite cell progeny begin to fuse to form multinucleated myotubes within the endomysial tube of the original fiber. The myotubes display spontaneous contractile activity and may extend throughout the length of the endomysial tube.

Animals↗
PubMed1973

Plasma membranes from cultured muscle cells: isolation procedure and separation of putative plasma-membrane marker enzymes.

Partially purified plasma membranes were obtained from chick-embryo muscle cells grown in tissue culture. The purification procedure involved homogenization in buffered isotonic sucrose followed by differential and sucrose density gradient centrifugations. The activities of five plasma-membrane markers, as well as microsomal and mitochondrial markers, were followed throughout the purification. When cultures were labeled with [(125)I]alpha-bungarotoxin, which binds to the surface of cultured muscle cells, the distributions of bound alpha-bungarotoxin and Na(+),K(+)-ATPase (EC 3.6.1.3) activity were nearly identical. The activities of these two plasma-membrane markers were maximal in the upper two fractions of the sucrose density gradient and were purified 5- to 7-fold with respect to total particulate protein. These fractions contained 20-30% of the Na(+),K(+)-ATPase activity and bound alpha-bungarotoxin, 4% of the microsomal marker TPNH-dependent cytochrome c reductase, 0.2% of the mitochondrial marker succinate-dependent cytochrome c reductase, 2.7% of the cellular RNA, and 0.02% of the DNA. The activity of the commonly used plasma-membrane marker, 5'-nucleotidase (EC 3.1.3.5), was low in the upper two sucrose gradient fractions and was maximal in a more dense fraction. The distributions of the other two plasma-membrane markers, leucyl beta-naphthylamidase and phosphodiesterase I, were intermediate between Na(+),K(+)-ATPase and 5'-nucleotidase. The distributions of all markers were similar in preparations from cultures containing mononucleated myogenic cells, multinucleated myotubes, fibroblasts, or all three cell types. Modification of the procedure to include homogenization in the absence of sucrose resulted in a 3.4-fold purification of the membranes containing 5'-nucleotidase, which were shifted to a lower density.

Adenosine Triphosphatases↗
PubMed1970

Inhibition of myoblast fusion after one round of DNA synthesis in 5-bromodeoxyuridine.

The thymidine analogue 5-bromodeoxyuridine (BUdR) has a differential effect on the synthesis of tissue-specific products and molecules required for growth and division. Proliferating myogenic cells cultured in BUdR fail to fuse and fail to initiate the synthesis of contractile protein filaments. Conversely, BUdR has but a minor effect on cell viability and reproductive integrity. Low concentrations of BUdR result in an enhancement of cell number relative to the controls; higher concentrations are cytotoxic. Suppression of myogenesis is reversible after at least 10 cell generations of growth in the analogue. Cells that do not synthesize DNA, such as postmitotic myoblasts and myotubes, are not affected by BUdR. Incorporation of BUdR for one round of DNA synthesis was accomplished by first incubating myogenic cells, prior to fusion, in 5-fluorodeoxyuridine (FUdR) to block DNA synthesis and collect cells in the presynthetic phase. The cells were then allowed to synthesize either normal DNA or BU-DNA for one S period by circumventing the FUdR block with BUdR or BUdR plus thymidine (TdR). The cultures were continued in FUdR to prevent dilution of the incorporated analogue by further division. After 3 days, the cultures from the FUdR-BUdR series showed the typical BUdR effect; the cells were excessively flattened and few multinucleated myotubes formed. Cells in the control cultures were of normal morphology, and multinucleated myotubes were present. These results were confirmed in another experiment in which BUdR-(3)H was added to 2-day cultures in which myotubes were forming. Fusion of thymidine-(3)H-labeled cells begins at 8 hr after the preceding S phase. In contrast, cells which incorporate BUdR-(3)H for one S period do not fuse with normal myotubes.

Animals↗
PubMed1969

Mitosis and the processes of differentiation of myogenic cells in vitro.

The relation between the mitotic cycle and myoblast fusion has been studied in chick skeletal muscle in vitro. The duration of the cell cycle phases was the same in both early and late cultures. By tracing a cohort of pulse-labeled cells, it was found that myoblast fusion does not occur in S, G(2), or M. Cell surface alterations required for fusion are dependent upon the position of the cell in the division cycle. In early cultures, fusion takes place only after a minimum delay of 5 hr from the time the cell has entered G(1). The mitosis preceding fusion may condition the cell for the abrupt shift in synthetic activity that occurs in the subsequent G(1). In older cultures fusion of labeled cells is diminished. Two factors account for the cessation of fusion in older cultures. First, the number of myogenic stem cells declines, but these cells do not disappear as the cultures mature. Their persistence was demonstrated by labeling dividing mononucleated cells in older cultures and challenging them with nascent myotubes. Some of these labeled cells were incorporated into the forming myotubes. Second, a block to fusion develops during myotube maturation. Well developed myotubes challenged with labeled competent myogenic cells failed to incorporate the labeled nuclei.

Animals↗
PubMed1969

Formation of arrowhead complexes with heavy meromyosin in a variety of cell types.

Heavy meromyosin (HMM) forms characteristic arrowhead complexes with actin filaments in situ. These complexes are readily visualized in sectioned muscle. Following HMM treatment similar complexes appear in sectioned fibroblasts, chondrogenic cells, nerve cells, and several types of epithelial cells. Thin filaments freshly isolated from chondrogenic cells also bind HMM and form arrowhead structures in negatively stained preparations. HMM-filament complexes are prominent in the cortex of a variety of normal metaphase and Colcemid-arrested metaphase cells. There is no detectable binding of HMM with other cellular components such as microtubules, 100-A filaments, tonofilaments, membranes, nuclei, or collagen fibrils. The significance of HMM-filament binding is discussed in view of the finding that arrowhead complexes form in types of cells not usually thought to contain actin filaments.

Animals↗