Paterson S, Morgan E H
J Cell Physiol. 1980 Dec;105(3):489-502. doi: 10.1002/jcp.1041050313.
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.
将兔网织红细胞与用(^{59}Fe)和(^{125}I)标记的兔转铁蛋白在氯化钠被其他电解质或蔗糖替代的培养基中孵育。细胞对铁和转铁蛋白的摄取受培养基的pH、离子强度、离子组成和渗透压变化的影响。在pH 7.4时摄取量最大。用蔗糖替代氯化钠导致离子强度降低，以浓度依赖的方式抑制摄取，在最低盐浓度时抑制作用最大。当用氯化钾、氯化锂、氯化铷、硫酸钠或硫酸钾替代氯化钠时，得到了类似的结果。发现低离子强度抑制用胶体金标记的转铁蛋白的胞吞摄取，但对转铁蛋白与细胞膜受体的结合只有很小的影响。得出的结论是，低离子强度主要通过阻断转铁蛋白的内吞作用来抑制铁的摄取。三种盐，氯化铵、氯化钙和氯化镁，产生了与上述不同的结果。氯化铵在所有使用的浓度下都抑制铁的摄取。这种作用是由于对转铁蛋白中铁释放的影响，铁似乎以正常方式被细胞摄取。当通过添加低浓度的氯化钙提高蔗糖培养基的离子强度时，铁的摄取比用等浓度的氯化钠时更大。然而，当氯化钙浓度高于10 mM时，铁的摄取受到抑制，这是由于转铁蛋白摄取受到抑制，可能是通过阻断内吞作用。相比之下，氯化镁在所有使用的浓度下都刺激铁的摄取。根据细胞外液的离子强度、pH和离子组成对未成熟红细胞摄取铁所涉及的三个主要步骤（转铁蛋白-受体相互作用、内吞作用和转铁蛋白中铁的释放）的可能影响，对结果进行了讨论。
