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Biomedical subjects

S Rapoport

Publications and source records attributed to S Rapoport.

At least 91 records · Page 5Linked to original sources
PubMed1977

PH-dependent changes of 2,3-bisphosphoglycerate in human red cells during transitional and steady states in vitro.

A systematic study of the pH-dependent changes in the range 6.6--7.4 of 2,3-bisphosphoglycerate and the adenine nucleotides was performed in the presence and absence of glucose during transitional and steady states. 1. The results indicatethat 2,3-gisphosphoglycerate phosphatase breaks down 2,3-bisphosphoglycerate nearly independent of pH at a rate of 480 mumol 2,3-bisphosphoglycerate x1 cells-1xh-1.2,3-Bisphosphoglycerate mutase is practically completely inhibited below pH value increases in long-term experiments with lower 2,3-bisphosphoglycerate levels. The formation of pyruvate corresponds to the breakdown of 2,3-bisphosphoglycerate afterconsumption of an unknown reducing substance.

Adenosine Diphosphate↗
PubMed1977

Properties of vestibular neurones projecting to neck segments of the cat spinal cord.

1. Vestibular neurones projecting to the upper cervical grey matter (vestibulocollic neurones) were identified by localized microstimulation in the C3 segment of the cat spinal cord.2. The neurones were found in the lateral (Deiters'), medial and descending nuclei bilaterally and projected to the spinal cord in the lateral and medial vestibulospinal tracts (LVST and MVST). Ipsilateral axons of Deiters' neurones were mostly in the LVST, axons of medial and descending neurones in the MVST; a few Deiters' neurones had axons in the MVST; some descending neurones had axons in the LVST. Most axons of contralateral neurones were in the MVST.3. The axons of 62% of ipsilateral vestibulocollic Deiters' neurones not only gave off a collateral to C3, but also extended as far as the cervical enlargement (;branching'); some of these neurones projected as far as the upper thoracic cord, almost none to the lumbar cord. Ipsilateral descending nucleus neurones branch in the same fashion, but there is no branching in the relatively small medial nucleus population.4. A large majority of vestibulocollic neurones receive monosynaptic excitation from the ipsilateral labyrinth and a number are inhibited by stimulation of the contralateral labyrinth (commissural inhibition). It is possible that commissural inhibition acts on a broad population of vestibular neurones involved in the control of eye, head and trunk movement.5. Vestibulocollic neurones do not make up a homogeneous population acting only on the neck. Instead it is likely that subpopulations, for example branching and non-branching neurones, have different functions.

Animals↗
PubMed1977

Synaptic actions of individual vestibular neurones on cat neck motoneurones.

1. Unitary synaptic potentials evoked by the activity of single vestibulocollic neurones were recorded by means of spike-triggered signal averaging in neck extensor motoneurones of decerebrate cats. Properties of the vestibulocollic neurones which produced the potentials were examined.2. Vestibulocollic neurones were first identified as projecting to the C3 grey matter by antidromic microstimulation within the C3 extensor motoneurone pool. The spontaneous or glutamate-driven activity of the vestibulocollic neurones was then used to trigger the averaging computer. In this way ten inhibitory and two excitatory neurones were identified (20% of neurones tested).3. Action potentials in local branches of vestibulocollic neurones were usually recorded in the vicinity of motoneurones. Mean orthodromic conduction time from the foot of the extracellular spike, recorded in the vestibular nuclei, that triggered the averager was 0.72 msec. Mean synaptic delay was 0.4 msec.4. I.p.s.p.s had a mean time to peak of 0.81 msec and were readily reversed by injection of hyperpolarizing current. These data, together with the shape indices of i.p.s.p.s indicate that they are generated proximally on motoneurones.5. All vestibulocollic neurones making synapses with motoneurones were monosynaptically driven by stimulation of the ipsilateral vestibular nerve. Four out of seven tested were inhibited by stimulation of the contralateral vestibular nerve (commissural inhibition).6. Two excitatory neurones were located in Deiters' nucleus or on the Deiters'-descending border. Inhibitory neurones were found relatively medially in the vestibular complex in the medial, descending and Deiters' nuclei.7. Vestibulocollic neurones acting on motoneurones were tested for axon branching to more caudal levels of the spinal cord with electrodes placed at C5-7. Both of the excitatory and two out of nine inhibitory neurones branched.

Action Potentials↗
PubMed1977

[Chacterization of human reticulocytes: respiration, Pasteur effect, and electron microscopic findings on mitochondria].

On 5 blood samples of newborns, whose reticulocytes had been enriched by density gradient centrifugation, and on 25 blood samples of different reticulocytoses of man were determined: the extent of intra- and extramitochondrial respiration, coupling of the electron transfer with the oxidative phosphorylation and the electronmicroscopic appearance, and the number of mitochondria. The reticulocytes occurring in the flowing human blood are in general relatively stiff and are characterized by the following properties:--low respiration--low capacity of the respiratory chain enzymes--weakened Pasteur effect --varying proportion of intramitochondrial respiration and total respiration--decoupling of a major part of the intramitochondrial respiration--low number of mitochondria--qualitative changes of mitochondria. However, there are situations of erythropoiesis where immature reticulocytes are discharged in man (similar to the socalled "stress reticulocytes" of rabbits). On the other hand, it could be shown that the reticulocytes of rabbits are mature in the normal state.

Animals↗
PubMed1977

Degradation of mitochondria by cytosolic factors in reticulocytes.

The degradation process of mitochondria in rabbit reticulocytes proceeds predominately directly in the cytosol rather than in secondary lysosomes as judged by electronmicroscopy. At least five cytosolic protein factors are present in reticulocytes, which could be related to the degradation of mitochondria: the two inhibitory proteins of the respiratory chain RF and RC and three enzymes which cause a lysis of mitochondria in vitro (lipoxygenase, proteinase, phospholipase A). The properties of these factors are the subject of this paper. A hypothetic scheme of the degradation of mitochondria in reticulocytes is proposed. The degradation of mitochondria in reticulocytes is viewed as a complex interplay of various cytosolic factors and the functional state of the mitochondrial membranes. The lipoxygenase damages the membranes and triggers the penetration of the respiratory inhibitors. In this manner, a catastrophic cycle is initiated which leads to the complete breakdown of the mitochondria.

5-Aminolevulinate Synthetase↗
PubMed1977

[Electron transport particles from beef-heart mitochondria as a test system for inhibitors of the respiratory chain].

Respiratory inhibitors exert a potentially biocidic action on all aerobic organisms. Therefore the systematic search for them and the elucidation of their mechanism of action is of great importance. The non-phosphorylating electron transfer particles (ETP) according to Crane et al. are a suitable test object for this aim. A standardized preparation of ETP from beef heart is described and characterized enzymatically. The ETP show a variety of advantages in comparison with other systems; their field of application is broad. Owing to the absence of bypasses of the respiration, particles from animals are more suitable than those from plants for the search for fungicides and herbicides which inhibit the respiratory chain. With relatively little expense, the two standard assay systems proposed (NADH oxidase and succinate-cytochrome c oxidoreductase) pick up with certainty all inhibitors of the main pathway of the respiratory chain; they are useful for screening studies. The system proposed is also suitable for the analysis of the exact site and the mechanism of action of respiratory inhibitors. Furthermore, ETP can be used to obtain parameters of the hydrophobicity of drugs as well as for toxicological studies.

Animals↗
PubMed1977

Some properties of the lipoxygenase from rabbit reticulocytes.

A lipoxygenase was enriched from the stoma-free supernatant of rabbit reticulocytes. The enzyme causes drastic deterioration of mitochondrial membranes. The release of matrix enzymes is paralleled by formation of products of lipid peroxidation. The enzyme reacts with isolated phospholipds and free cis-unsaturated fatty acids. Some properties were determined: molecular weight, isoelectric point, temperature and pH-dependence and Km value for linoleic acid. The enzyme is inhibited by reaction products and a variety of inhibitors, especially antioxidants and chelating agents.

Animals↗
PubMed1977

[Nitrogen-economy and synthesis of serine and glycine in reticulocytes].

Amino acids constitute the main substrate of the reticulocyte. The amino acid pool of reticulocytes represents a characteristic selection. The composition of the amino acid pool is dependent on maturation. From the preferential oxidation of short-chain amino acids one would expect a ratio about of 5:1 between the oxygen consumption and ammonia formation. If one corrects for NH3-formation by the deamination of nucleotides the ratio between the oxygen consumption and NH3-formation is about an order of magnitude higher than the theoretical ratio. The small liberation of NH3 in energy production from amino acids results from the re-utilization of their alpha-NH2-group for the synthesis of serine and glycine, while the C-skeleton stems from glucose. Serine is formed via OH-pyruvate and OH-pyruvate. Serine and glycine serve preferentially for synthesis of hemoglobin. In reticulocytes there exists a compartmentation of glycine which accounts for differences between serine and glycine in isotopic experiments. From the time dependent change of the specific activities of pulse-labelled serine and glycine one may calculate that the serine synthesis amounts to 15--30% of the glucose utilization.

Glutamates↗
PubMed1977

[Purification and characterization of the respiratory inhibitor RF from rabbit reticulocytes].

In the stroma-free hemolysate of rabbit reticulocytes there exists a respiratory inhibitor (RF) of protein nature. It could be purified by the following procedure: (NH4)2SO4-precipitation leads to DEAE-Sephadex A-50-chromatography leads to isoelectric focusing leads to gelfiltration on Sephadex G-200. In addition to the activity the identity of the inhibitor could be proved immunologically at all steps of the purification. A molecular weight of about 80,000 was determined by gelelectrophoresis in the SDS-mercaptoethanol-system. The protein has an IP of 5.55--5.65 and consists of one polypeptide chain. This could be shown both by SDS-gelelectrophoresis and by estimation of only one N-terminal amino acid residue (glycine). Only after oxidation with performic acid the amino acid analysis of the protein gives reproducible values. The sum of weight-% is about 80 (without Tyr). The polarity of the protein with 41 mol-% agrees with the polarity of soluble globular proteins investigated by other authors. Acid hydrolysis without preceeding performic acid oxidation gives a sum of amino acid residues of only 35--45 weight-%, the glycoprotein nature of the inhibitor could be shown by staining the SDS-gels with Schiff's reagents and by carbohydrate determination with anthrone reagent.

Animals↗
PubMed1977

Creatine during bleeding anemia of rabbits.

In bleeding induced anemia of rabbits an increase of creatine in the red cells occurred, which in some cases amounted to more than 5-times the normal concentration. In all but one case plasma creatine rose as well. Reticulocytosis, increased O2-consumption of the red cells and an increased level of erythropoietin indicated active erythropoiesis and a shift towards a younger cell population. Whether the rise of red cell creatine is solely due to a higher proportion of young cells remains an open question.

Anemia↗
PubMed1976

A comparison of the influence of potassium and ammonium ions on the phosphofructokinases from rabbit muscle and rat erythrocytes.

Phosphofructokinases from rat erythrocytes and rabbit muscle have been compared in their kinetic behavior with respect to monovalent cation activation and ATP inhibition. Both ammonium and potassium ions affect the muscle enzyme in a two-fold manner: they act both as activators and effectors. On the other hand only ammonium exerts the two-fold effects on the erythrocyte enzyme, while the potassium ions activate without affecting cooperativity. The lower ATP inhibition of muscle phosphofructokinase may be partially explained by the action of potassium ions on the cooperative behavior of the enzyme. The differences between the phosphofructokinases from erythrocytes and muscle in the potassium type-II activation and ATP inhibition represent an organ specifity. Furthermore, the inhibition constants for 2, 3-bisphosphoglycerate differ by 10-fold between the two enzymes.

Adenosine Triphosphate↗
PubMed1976

The blood-ocular barriers under osmotic stress. Studies on the freeze-dried eye.

Regional differences in the response of primate blood-ocular barriers to severe osmotic stress were measured. Marker dyes were localized by fluorescence microscopy in tissues that had been freeze-dried to prevent diffusion. Under severe osmotic stress, the form and the function of the ciliary process are grossly compromised while the iris is spared. Breakdown of the retinal pigment epithelial barrier is widespread, while the retinal blood vessels in large areas retain normal permeability characteristics. The pigment epithelial barrier mechanism is substantially more susceptible to osmotic stress in the region surrounding the optic disc than in the equatorial area.

Animals↗
PubMed1976

[Heinz body formation and abnormal methemoglobin reduction. Expressions of damage to erythrocytes in chronic kidney failure].

Erythrocytes of patients dialyzed due to chronic renal failure were investigated. An inhibition of the NADH-dependent methaemoglobin reductase, an insufficient methaemoglobin reduction by the NADPH-system, and Heinz-bodies as denaturation products, were found. The damage of erythrocytes was enhanced by incubation in both patient's plasma and dialysis medium. In erythrocytes of normal persons the damaging effect of incubation in plasma of chronic renal failure patients could also be demonstrated. The factors eliciting the oxidative injury are discussed. Factors that could further decrease the reduction capacity of red cells should be omitted.

Adult↗
PubMed1976

Maturation dependence of fluoride-sensitive adenylate cyclase in red blood cells.

Adenylate cyclase activity stimulated by fluoride was studied in membranes from different red cell populations produced by bleeding anemia in rabbits. The cells were fractionated by density gradient centrifugation in dextrane. The highest adenylate cyclase activity was found in the reticulocyte fractions with low density and the highest RNA-content. No activity was found in the mature erythrocytes. It is apparent that the adenylate cyclase in the red blood cells can serve as a useful indicator of the maturation process.

Adenylyl Cyclases↗