Transferrin receptor numbers and transferrin and iron uptake in cultured chick muscle cells at different stages of development

Abstract

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 X 10(10) receptors/micrograms DNA) than when division had ceased (1.70 +/- 0.14 X 10(10) receptors/micrograms DNA), while myotubes had 3.80 +/- 0.26 X 10(10) receptors/micrograms 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.

Glucose Modulation Induces Lysosome Formation and Increases Lysosomotropic Drug Sequestration via the P-Glycoprotein Drug Transporter

“…2B) between all glucose treatments. Notably, the initial transferrin uptake was found to be linear over 5 min, as has previously been shown (23,61). Collectively, our transferrin uptake studies indicate that glucose variation-induced stress does not stimulate transferrin receptormediated endocytosis.…”

Transferrin endocytosis and iron uptake in developing myogenic cells in culture: Effects of microtubular and metabolic inhibitors, sulphydryl reagents and lysosomotrophic agents

“…A previous investigation (Sorokin et al, 1987) provided evidence for receptor-mediated endocytosis of transferrin in cultured chicken myogenic cells. This study extends these findings using inhibitors which interfere with several aspects of the endocytotic process.…”

“…Cell growth and cell viability were assessed daily by phase-contrast microscopy, cell counts and DNA synthesis (Sorokin et al, 1987).…”

“…However, the internalized transferrin values were significantly higher than control values for all three myogenic cultures studied (P < 0.001) only in the case of 0.4 mM chloroquine. The internalization of iron proceeds linearly with time at 37°C in control cells (Sorokin et al, 1987). Assuming a similar linear increase in internalized 5YFe in the presence of inhibitors, the amount of iron accumuIated in the cells after the 60 min incubation with labeled TfFez in the presence of inhibitors is an indication of the effect of the inhibitors on the rate of iron internalization.…”

“…A previous investigation (Sorokin et al, 1987) established that specific binding sites for transferrin occur on cultured cells representing the two major stages in myogenic cell development, the differentiating presumptive myoblast and the terminally differentiated myotube, and that only transferrin bound to these specific binding sites was internalized by the cells. The rate of internalization of diferric transferrin (Tf-Fez) was also found to be sufficient to account for iron accumulation by the cells, suggesting that internalization and not simply binding of Tf-Fez to transferrin binding sites on the cell surface is necessary for iron uptake.…”