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  • Life and Medical Sciences  (6)
  • Species specificity  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Role of transferrin in iron uptake by the brain: a comparative study (1991)
    Springer
    Journal of comparative physiology 161 (1991), S. 521-524 
    Details
    ISSN: 1432-136X
    Keywords: Transferrin receptors ; Iron transport ; Brain capillaries ; Species specificity ; Blood brain barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The role of specific transferrin (Tf) and Tf receptor interaction on brain capillary endothelial cells in iron transport from the plasma to the brain was investigated by using Tf from several species of animals labeled with 59Fe and 125I, and 15-day and adult rats. The rate of iron transfer was much greater in the 15-day rats. It was greatest with Tf from the mammals, rat, rabbit and human, but much lower with chicken ovotransferrin and quokka (a marsupial), toad, lizard, crocodile, and fish Tf. The uptake of Tf by the brain showed a similar pattern, except for a very high uptake of ovotransferrin (ovo Tf). Iron uptake by the femurs (a source of bone marrow) was also high with Tf from the mammalian species and low with the other types of Tf, but showed little change with aging of the animals. It is concluded that iron transport into the brain is dependent on the function of Tf receptors, probably on capillary endothelial cells, and that these receptors show the same type of species specificity as the receptors on immature erythroid cells. Also, the decrease in iron uptake by the brain as rats age from 15 days to adulthood is specific for the brain and is not a general effect of the aging process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00257907
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of changes in the ionic environment of reticulocytes on the uptake of transferrin-bound iron (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 105 (1980), S. 489-502 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Rabbit reticulocytes were incubated with rabbit transferrin labelled with 59Fe and 125I in media in which the NaCl was replaced by other electrolytes or sucrose. Iron and transferrin uptake by the cells was affected by changes in the pH, ionic strength, ionic composition, and the osmolarity of the medium. Uptake was maximal at pH 7.4. A reduction in ionic strength produced by replacing NaCl with sucrose inhibited the uptake in a concentration-dependant manner, greatest inhibition occurring at lowest salt concentration. Similar results were obtained when KCl, LiCl, RbCl, Na2SO4, or K2SO4 were used instead of NaCl. Low ionic strength was found to inhibit the endocytotic uptake of transferrin labelled with colloidal gold, but had only a small effect on transferrin binding to cell membrane receptors. It was concluded that low ionic strength inhibits iron uptake primarily by blocking the endocytosis of transferrin. Three salts, NH4Cl, CaCl2, and MgCl2, produced different results from the above. NH4Cl inhibited iron uptake at all concentrations used. This action was due to an effect on the release of iron from transferrin, which appeared to be taken up by the cells in a normal manner. When the ionic strength of the sucrose medium was increased by adding low concentrations of CaCl2, iron uptake was greater than with equivalent concentrations of NaCl. However, with CaCl2 concentrations above 10 mM, iron uptake was inhibited, due to inhibition of transferrin uptake, possibly by blocking endocytosis. By contrast, MgCl2 stimulated iron uptake at all concentrations used. The results are discussed in terms of the possible effects of ionic strength, pH, and ionic composition of the extracellular fluid on the three main steps involved in iron uptake by immature erythroid cells: transferrin-receptor interaction, endocytosis, and iron release from transferrin.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041050313
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  • 3
    Electronic Resource
    Electronic Resource
    Intravesicular pH and iron uptake by immature erythroid cells (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 120 (1984), S. 225-232 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The intravesicular pH of intact rabbit reticulocytes was measured by two methods; one based on the intracellular:extracellular distribution of DMO (5, 5, dimethyl + oxazolidin-2,4-dione), methylamine, and chloroquine and the other by quantitative fluorescence microscopy of cell-bound transferrin. The latter method was also applied to nucleated erythroid cells from the fetal rat liver. A pH value of approximately 5.4 was obtained with both methods and in both types of cells. Treatment of the cells with lysosomotrophic agents, metabolic inhibitors, and ionophores elevated the intravesicular pH and inhibited iron uptake from transferrin. When varying concentrations of NH4Cl were used, a close correlation was observed between the inhibition of iron uptake and elevation of the intravesicular pH. At pH 5.4 iron release from rabbit iron-bicarbonate transferrin in vitro was much more rapid than from iron-oxalate transferrin. The bicarbonate complex donates its iron to rabbit reticulocytes approximately twice as quickly as the oxalate complex. It is concluded that the acidic conditions within the vesicles provide the mechanism for iron release from the transferrin molecule after its endocytosis and that the low vesicular pH is dependent on cellular metabolism.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041200217
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  • 4
    Electronic Resource
    Electronic Resource
    Uptake of transferrin and iron by cultured rat placental cells (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 122 (1985), S. 405-409 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: This paper describes a method for the culture of rat placental cells. The method involved separation of the basal layer from the labyrinth and sequential digestion of the cells. The cells were demonstrated not to be fibroblasts and are described in terms of their appearance under the light and electron microscopes. Transferrin and iron uptake by the cells was examined and compared with results achieved using other methods of study. The results showed that transferrin bound to receptors on the cell surface and that the transferrin, once bound, was taken into the cell. Only this internalized transferrin was capable of donating iron to the cells. The iron was accumulated within the cells and did not appear to be released to the incubation medium. The apparent dissociation constant (Ka) for transferrin was found to be 6.96 × 106 M-1, a value similar to that described by earlier workers. The placental cells had 3.4 × 1011 binding sites/μg DNA, equivalent to approximately 1 × 106 sites/cell. From these data, and from the rate of accumulation of iron by the cells, the receptor turnover time was estimated as being between 5 and 10 min.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041220310
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  • 5
    Electronic Resource
    Electronic Resource
    Transferrin receptor numbers and transferrin and iron uptake in cultured chick muscle cells at different stages of development (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 131 (1987), S. 342-353 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The mechanism of iron uptake and the changes which occur during cellular development of muscle cells were investigated using primary cultures of chick embryo breast muscle. Replicating presumptive myoblasts were examined in exponential growth and after growth had plateaued. These were compared to the terminally differentiated cell type, the myotube. All cells, regardless of the state of growth or differentiation, had specific receptors for transferrin. Presumptive myoblasts in exponential growth had more transferrin receptors (3.78 ± 0.24 × 1010 receptors/μg DNA) than when division had ceased (1.70 ± 0.14 × 1010 receptors/μg DNA), while myotubes had 3.80 ± 0.26 × 1010 receptors/μg DNA. Iron uptake occurred by receptor-mediated endocytosis of transferrin. While iron was accumulated by the cells, apotransferrin was released in an undegraded form. There was a close correlation between the molar rates of endocytosis of transferrin and iron. Maximum rates of iron uptake were significantly higher in myotubes than in presumptive myoblasts in either exponential growth or after growth had plateaued. There were two rates of exocytosis of transferrin, implying the existence of two intracellular pathways for transferrin. These experiments demonstrate that iron uptake by muscle cells in culture occurs by receptor-mediated endocytosis of transferrin and that transferrin receptor numbers and the kinetics of transferrin and iron uptake vary with development of the cells.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041310306
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  • 6
    Electronic Resource
    Electronic Resource
    Transferrin endocytosis and iron uptake in developing myogenic cells in culture: Effects of microtubular and metabolic inhibitors, sulphydryl reagents and lysosomotrophic agents (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 137 (1988), S. 483-489 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The experiments described in this study were designed to investigate receptor-mediated endocytosis of transferrin and its role in iron uptake by cultured chick presumptive myoblasts (dividing and non-dividing) and myotubes. The effects of a variety of inhibitors on the internalization of transferrin and iron were investigated and three main effects were found: (i) sulphydryl reagents and microtubular inhibitors reduced the rate of transferrin and iron internalization to similar degrees, (ii) metabolic inhibitors reduced the rate of iron uptake more than that of transferrin endocytosis, and (iii) lysosomotrophic agents almost completely abolished iron accumulation by the cells without any effect on the rate of transferrin internalization. The results suggest that metabolic energy is required not only for the endocytosis of transferrin but also for subsequent steps in the iron uptake process, and that iron release from transferrin occurs in acidified endosomes. Overall, these experiments show that all or virtually all of the iron taken up by developing muscle cells from transferrin occurs as a consequence of receptor-mediated endocytosis of the protein.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041370313
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  • 7
    Electronic Resource
    Electronic Resource
    Studies on the mechanism of interaction between rabbit transferrin and reticulocytes (1971)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 77 (1971), S. 377-384 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The two stages in the uptake of transferrin by rabbit reticulo-cytes were investigated using radioiodine-labeled rabbit transferrin and albumin. The first stage of rapid, temperature-insensitive uptake of transferrin was similar to albumin uptake: uptake of both proteins increased linearly with increasing protein concentration of the incubation medium up to at least 60 mg/ml, was maximal at low ionic strength and pH, and increased in the presence of basic polyamino acids. Transferrin uptake was in part dependent on the reticulocyte concentration of the blood, but albumin uptake was independent of reticulocyte concentration.The second slower, temperature-sensitive stage of transferrin uptake was linearly related to reticulocyte concentration, and was not found with albumin, α1-macroglobulin or γ-globulin. Transferrin uptake was optimal at physiological pH and ionic strength and was unaffected by basic polyamino acids. When the transferrin concentration was raised, uptake increased to reach a maximum at a concentration of 15 mg/ml.It was concluded that the first stage of transferrin uptake was in part or wholly due to non-specific adsorption of transferrin to erythrocytes, while the second stage of uptake was specific for transferrin and reticulocytes and depended upon normal function of the cells.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040770312
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